JP2002329308A - Magnetic recording medium and method of manufacturing for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetic recording medium which is extremely improved in the surface characteristics of a magnetic layer and is enhanced in the level- down characteristic of a recording regenerative signal and electromagnetic conversion characteristics by improving the dispersibility of the magnetic powder in a magnetic coating material. SOLUTION: The magnetic coating material prepared by adding a dispersant and a binder to the magnetic powder, etc., and kneading the mixture, further adding the dispersant to the resultant magnetic kneaded mixture and subjecting the mixture to dispersion treatment is used. This magnetic recording medium 10 is obtained by applying the magnetic coating material described above onto one main surface of a nonmagnetic base 11, thereby forming the magnetic layer 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium and a method for manufacturing the same, and more particularly, to a magnetic recording medium comprising a magnetic layer containing at least a magnetic powder and a binder formed on a non-magnetic support, The present invention relates to a magnetic recording medium having excellent level-down characteristics of recording / reproducing signals and electromagnetic conversion characteristics, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Recently, high-definition VTRs and digital V
With the high performance represented by the TR, the demand for improving the characteristics of the magnetic recording medium is increasing. Further, while high-density magnetic recording is progressing, a recording medium for forming a magnetic layer by applying a magnetic paint (magnetic paint mainly containing magnetic powder (for example, ferromagnetic powder)) on a non-magnetic support, In so-called coated magnetic recording media, for example, digital data storage and recording of digital signals for high-definition are performed,
Demands for high-density recording are increasing year by year.

In general, in a magnetic recording method of a coating type magnetic recording medium, a rotating drum having a plurality of magnetic heads mainly containing ferrite, amorphous, sendust or the like as a main component is used. The outer peripheral surface of the magnetic recording medium is slid with respect to the surface of the magnetic recording medium (the surface of the magnetic layer), and the relative speed between the magnetic head and the magnetic recording medium is increased to record more enormous information. Had been taken. In order to obtain a higher magnetic signal in performing high-density recording, a metal head made of amorphous or the like is used in particular.

As described above, when the magnetic head mainly composed of sendust, amorphous or the like and the magnetic layer surface of the magnetic recording medium formed of the magnetic powder and the binder slide continuously, the magnetic layer surface slightly Each time, the magnetic powder, binder, additives, etc. fall off. Among them, the dropped matter containing the magnetic powder is oxidized by oxygen in the air and adheres and accumulates on the surface of the magnetic head as an oxide or the like. As a result, the output obtained from the magnetic head is reduced, and a level-down phenomenon of the recording / reproducing signal occurs. In other words, spacing occurs due to oxides and the like accumulated on the magnetic head, so that a high output cannot be obtained in a magnetic recording medium (for example, a magnetic tape), and the performance of the magnetic head cannot be sufficiently brought out.

Therefore, it is necessary to increase the amount of abrasive contained in the magnetic layer or to roughen the surface of the magnetic layer to increase the polishing force on the surface of the magnetic recording medium (increase the frictional force between the recording medium and the magnetic head). Accordingly, there has been proposed a method of removing the accumulation of the magnetic head by sliding the surface of the magnetic recording medium.

[0006]

However, as described above, when the amount of the abrasive in the magnetic layer is increased, the amount of magnetic powder per unit area of the magnetic layer becomes relatively small. Magnetic Residual Magnetic Flux Density Br
And the output is reduced.

Further, if the magnetic layer contains a large amount of abrasive, the surface of the magnetic head is scraped off due to sliding between the magnetic recording medium and the magnetic head, and the life of the magnetic head is greatly shortened. Occurs. Further, if the surface of the magnetic recording medium is roughened, the amount of spacing between the magnetic recording medium and the magnetic head increases, which causes a problem that the output decreases and noise increases.

For this reason, while removing the accumulated substances as described above, the magnetic powder is highly filled to improve the electromagnetic conversion characteristics, and the surface of the magnetic recording medium is smoothed to suppress the spacing loss. Is required.

In recent years, there has been an increasing demand for making magnetic powder finer in order to cope with short-wavelength recording accompanying a thinner magnetic layer. However, for example, the specific surface area value (BE
When a fine magnetic powder having a T value of 50 to 80 m ² / g is used, it is difficult to uniformly and sufficiently disperse the magnetic powder in a binder, and thus the surface roughness (Ra) of the magnetic recording medium surface is reduced. ) Becomes worse.

Further, in response to a demand for a thinner magnetic layer, a magnetic recording medium having a thickness of, for example, 2 μm or less has been proposed. In the case of a magnetic recording medium having a thin magnetic layer as described above, the Since the magnetic layer is affected by the state of the surface of the non-magnetic support of the magnetic recording medium, the surface properties are further deteriorated, and it is difficult to secure a high C / N.

The present invention has been made on the basis of the above-mentioned problems, and by improving the dispersibility of magnetic powder in a magnetic paint, the surface properties of the magnetic layer can be improved even when fine magnetic powder is used. An object of the present invention is to provide a magnetic recording medium which is extremely good and has excellent level-down characteristics (output deterioration characteristics) of recording / reproducing signals and excellent electromagnetic conversion characteristics, and a method of manufacturing the same.

[0012]

According to a first aspect of the present invention, there is provided a magnetic recording medium comprising a magnetic layer formed on a non-magnetic support. The magnetic layer is made of a magnetic kneaded material obtained by kneading at least a magnetic powder (and a binder) and a dispersant, and is further made of a magnetic paint obtained by adding a dispersant to the magnetic kneaded material and performing a dispersion treatment. And

[0013] The invention according to claim 2 is characterized in that the dispersant is citric acid or succinic acid.

According to a third aspect of the present invention, there is provided a method for producing a magnetic recording medium in which a magnetic paint is applied on a non-magnetic support to form a magnetic layer, wherein at least a magnetic powder and a dispersant are kneaded. , A dispersing agent is further added to the magnetic kneaded material to perform a dispersion treatment, and a magnetic coating material is used.

The invention according to claim 4 is characterized in that citric acid or succinic acid is used as the dispersant.

The magnetic recording medium according to the present invention is a magnetic recording medium having a magnetic layer formed by applying a magnetic coating on a non-magnetic support, and the magnetic coating forming the magnetic layer comprises at least a magnetic coating. It shall be composed of powder, binder and dispersant.

The method for manufacturing a magnetic recording medium according to the present invention comprises:
After adding a dispersant to the magnetic powder and kneading the mixture (for example, kneading with a kneader), a process of adding a dispersant to the obtained magnetic kneaded material and performing a dispersion treatment (for example, dispersion treatment with a sand mill device) is performed. Have.

As in the method for producing a magnetic recording medium of the present invention, the dispersibility of a magnetic powder in a magnetic paint can be improved by adding a dispersant to the obtained magnetic kneaded material and subjecting it to a dispersion treatment. In addition, the surface property (smoothness) of the magnetic layer is improved.

According to the present invention, in order to obtain a magnetic recording medium with high density recording, even when extremely fine magnetic powder is used, the dispersibility of the magnetic powder in the binder is improved, Since the surface properties of the magnetic layer are improved, it is possible to improve the electromagnetic conversion characteristics of the magnetic recording medium and the level down characteristics (output deterioration characteristics) of the recording / reproducing signal, that is, to improve the durability.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific examples of a magnetic recording medium and a method of manufacturing the same according to an embodiment of the present invention will be described.

In the method of manufacturing a magnetic recording medium according to the present embodiment, a dispersing agent (and a binder) is added to magnetic powder (eg, magnetic powder and abrasive) and kneaded (for example, kneaded with a kneader). And a step of adding a dispersant to the obtained magnetic kneaded material and performing a dispersion treatment (for example, a dispersion treatment with a sand mill device). That is, while a magnetic paint obtained by adding a dispersant once is conventionally used, in the present embodiment, a magnetic paint obtained by adding a dispersant twice is used. Thereby, even when using a fine magnetic powder, the dispersibility of the magnetic powder can be improved,
For example, it is possible to cope with short wavelength recording accompanying thinning.

Then, the magnetic paint obtained through the above-described steps is applied onto one main surface of a non-magnetic support 11 as shown in a schematic sectional view of FIG. By forming the magnetic layer 12 containing the powder, the binder, and the dispersant, the intended magnetic recording medium 10 can be obtained.

As shown in the schematic sectional view of FIG. 2, the magnetic paint is applied on one main surface of the non-magnetic support 11 to form a magnetic layer 12. The magnetic recording medium 20 may be formed by forming the back coat layer 21 on the other main surface (the surface of the nonmagnetic support 11 opposite to the surface on which the magnetic layer 12 is formed). The back coat layer 21 is formed by applying a coating obtained by mixing and adjusting a non-magnetic pigment with a binder and an organic solvent, and any of the binder and the organic solvent of the back coat layer 21 are conventionally known. Can be used and is not particularly limited. Incidentally, the coating material for the back coat layer may contain a lubricant or a rust inhibitor, and the lubricant or the rust inhibitor may be applied to the surface of the back coat layer.

Further, for the purpose of improving the surface properties of the magnetic layer,
The magnetic recording medium 30 may be formed by forming an intermediate layer 31 between the nonmagnetic support 11 and the magnetic layer 12, as shown in the schematic sectional view of FIG. The intermediate layer 31 is formed by applying a paint comprising at least one of nonmagnetic powder, magnetic powder, or a mixture of nonmagnetic powder and magnetic powder and a binder onto one main surface of the nonmagnetic support 11. Formed by The magnetic layer 12 is formed by applying a magnetic paint on the intermediate layer 31.

(Dispersant used in magnetic layer) Examples of the dispersant used in the magnetic layer according to the present embodiment include fruit acid having a carboxyl group, fatty acid having 2 to 25 carbon atoms, and alkali metal or alkaline earth metal thereof. Gold-meal soaps composed of salts, fatty acid esters, fatty acid amides and amines, quaternary ammonium salts, phosphate esters, borate esters, and the like can be used. Further, specific examples of the above-mentioned fruit acid include malic acid, citric acid, succinic acid, tartaric acid, lactic acid and the like. Generally, citric acid is most utilized among the above dispersants.

(Non-magnetic support) Examples of the non-magnetic support in the present embodiment include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, and cellulose diacetate. For example, polymer materials such as celluloses, vinyl resins, polyimides, and polycarbonates, metals, glass, and ceramics can be used.

(Magnetic Powder) Examples of the magnetic powder in the present embodiment include metals such as Fe, Co, and Ni, and Fe—C
o, Fe-Ni, Fe-Al, Fe-Ni-Al, Fe
-Al-P, Fe-Ni-Si-Al, Fe-Ni-S
i-Al-Mn, Fe-Mn-Zn, Fe-Ni-Z
n, Co-Ni, Co-P, Fe-Co-Ni, Fe-
Co-Ni-Cr, Fe-Co-Ni-P, Fe-Co
-B, Fe-Co-Cr-B, Mn-Bi, Mn-A
1, an alloy such as Fe-Co-V, or a magnetic powder such as iron nitride and iron carbide can be used.

Each of the magnetic powders described above may be made of, for example, Al, Si, P,
Even if a light metal element such as B is contained in an appropriate amount, the effect of the present invention is not hindered. Also, γ-Fe
₂ O ₃ , Fe ₃ O ₄ , Belt compound of γ-Fe ₂ O ₃ and Fe ₃ O ₄ , γ-Fe ₂ O ₃ containing Co, Fe ₃ O ₄ containing Co, and Co γ-Fe ₂ O ₃ and Fe ₃ O ₄
Belt compound with Te, Sb, F in CrO ₂
An oxide containing at least one metal element such as e or B, or a hexagonal plate-like ferrite may be used. further,
M-type, W-type, Y-type, and Z-type barium ferrite, strontium ferrite, calcium ferrite, and lead ferrite may be used. For the purpose of controlling the coercive force of these magnetic powders, Co-Ti, Co-Ti −Zn,
Co-Ti-Nb, Co-Ti-Zn-Nb, Cu-Z
What added r, Ni-Ti, etc. may be used.

Each of the magnetic powders described above may be used alone or in combination with two or more of them.

(Binder Used in Magnetic Layer) Examples of the binder in the present embodiment include urethane resins, more specifically, polyester polyurethane resins such as adipate type and polycaprolactone type, depending on the polyol used.
Polyether polyurethane resins, other polycarbonates, acrylics, butadienes, and the like can be used. Among these binders, polyester polyurethane resin and polyether polyurethane resin are particularly preferable.

Examples of the tertiary amine contained in the above polyurethane resin include lipoprotective amines, aromatic amines, alkanolamines, alkoxyalkylamines and the like. For example, dimethylamine, diethylamine, diisopropylamine, diisobutyl Amine, methylethylamine, dioctylamine, N-methylaniline, N
-Methylbutylamine, N-methylphenylamine, 2
-Methoxyethylamine, di-2-methoxyethylamine and the like. When such a tertiary amine is introduced into the polyurethane resin, the tertiary amine may be introduced into either the main chain or the side chain of the polyurethane resin, and the content of the tertiary amine is from 0.01 mmol / g to 0.5
It is preferably within the range of mmol / g.

As the sulfonic acid metal salt introduced into the polyurethane resin, for example, sodium sulfite, sodium bisulfite, potassium bisulfite, sodium sulfanilate, sodium sulfamate, sodium taurine and the like can be used. The content of such a sulfonic acid metal salt is 0.01 mmol / g or more.
It is preferably in the range of 0.2 mmol / g.

As the binder, for example, a vinyl chloride resin may be used. Examples of the vinyl chloride resin include polyvinyl chloride resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer resin, and vinyl chloride-acetic acid. Vinyl-
And vinyl chloride copolymer resins such as a maleic acid copolymer resin and a vinyl chloride-vinyl acetate-maleic acid-vinyl alcohol copolymer resin. Examples of the metal sulfonic acid salt introduced into these vinyl chloride resins include sodium sulfite, sodium bisulfite, potassium bisulfite,
Sodium sulfanilate, sodium sulfamate, sodium taurine and the like may be used, and the content of the metal sulfonic acid salt is within the range of 0.01 mmol / g to 0.2 mmol / g in consideration of dispersibility. Preferably, there is. The above-mentioned vinyl chloride resin may contain an epoxy group or a hydroxyl group.

Examples of the binder include nitrocellulose resin, acrylate-acrylonitrile copolymer, methacrylate-styrene copolymer, phenoxy resin, polyvinyl fluoride, butadiene-acrylonitrile copolymer, butadiene. -Acrylonitrile-methacrylic acid copolymer, polyvinyl butyral, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde resin may be used.

Each of the above-mentioned binders may be used alone, or two or more of them may be used in combination.

(Additives Other than Binder) In the magnetic layer, the back coat layer and the intermediate layer in the present embodiment, a polyisocyanate may be added as a curing agent in addition to the binder. In the case of a magnetic layer formed on a non-magnetic support, additives such as a lubricant, an abrasive, and an antistatic agent may be added as necessary.

(Lubricant) Examples of the lubricant in the present embodiment include fluorine lubricants such as silicone oil, fatty acid-modified silicone, fluorine-containing silicon, polyolefin, polyglycol, alkyl phosphate and metal salt, and polyphenyl. Ethers, fluorinated alkyl ethers, alcohols having 12 to 24 carbon atoms (respectively, those containing unsaturation and branched ones are also possible), and carbon atoms having 12 to 24 carbon atoms
For example, 24 higher fatty acids and fatty acid esters (each of which may contain unbalanced or branched ones), alkyl carboxylic acid amine salts, and fluorinated alkyl carboxylic acid amines can be used.

The higher fatty acids and fatty acid esters include, for example, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, arachiic acid,
Use oleic acid, eicoic acid, elaidic acid, hebenic acid, linoleic acid, linoleic acid, octyl stearate, isooctyl stearate, octyl myristate, isooctyl myristate, butoxyethyl stearate, butyl stearate, heptyl stearate, etc. be able to.

Each of the above-mentioned lubricants may be used alone or in combination with two or more of them.
It may be added to the magnetic paint. Further, any one or two or more of the above lubricants may be applied to the surface of the formed magnetic layer.

(Abrasive) As the abrasive in the present embodiment, a known material having a Mohs hardness of 6 or more, for example, α-
Alumina, β-alumina, fused alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, diamond, silica, garnet, garnet, silicon nitride,
Materials mainly composed of boric acid nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium oxide, etc.
One or a combination of two or more of these materials can be used.

(Antistatic Agent) As the antistatic agent in the present embodiment, for example, carbon black, a natural surfactant, a nonionic surfactant, a cationic surfactant and the like can be used.

(Backcoat layer) As the nonmagnetic pigment used in the coating of the backcoat layer in the present embodiment, for example, carbon can be used. If necessary, the above-mentioned carbon and hematite, mica, silica gel, magnesium oxide, zinc sulfide, tungsten carbide,
Boron nitride, starch, zinc oxide, kaolin, talc, clay, lead sulfate, barium carbonate, calcium carbonate, magnesium carbonate, boehmite (γ-Al ₂ O ₃ .H ₂ O), alumina, tungsten sulfide, titanium oxide, poly A non-magnetic pigment may be used in combination with any one or more of tetrafluoroethylene powder, polyvinyl chloride powder, metal powder and the like.

Examples of the binder used for the coating of the back coat layer include acrylate-acrylonitrile copolymer, methacrylate-styrene copolymer,
Thermoplastic polyurethane resin, phenoxy resin, polyvinyl fluoride, butadiene-acrylonitrile copolymer, butadiene-acrylonitrile methacrylic acid copolymer,
Polyvinyl butyral, cellulose derivative, styrene butadiene copolymer, polyester resin, phenol resin, epoxy resin, thermosetting polyurethane resin, urea resin, melamine resin, alkyd resin, urea-formaldehyde resin, etc., and their respective binders. Any one of
Or a mixture of two or more.

The back coat layer using the above-mentioned binder may be one in which an isocyanate compound is used as a cross-linking agent to further improve durability or introduce an appropriate polar group.

(Intermediate Layer) The intermediate layer in the present embodiment
As the nonmagnetic powder to be used, for example, α-Fe _TwoO_ThreeEtc.
Non-magnetic iron oxide, goethite, rutile-type titanium oxide,
Tase type titanium oxide, tin oxide, tungsten oxide, oxidation
Silicon, zinc oxide, chromium oxide, cerium oxide, titanium oxide
-Bite, BN, α-alumina, β-alumina, γ-a
Lumina, calcium sulfate, barium sulfate, molybdenum disulfide
Den, magnesium carbonate, calcium carbonate, barium carbonate
Strontium carbonate, barium titanate, etc.
And any one of these non-magnetic powders may be used alone.
Or a mixture of two or more.

Depending on the purpose, the above-mentioned non-magnetic powder may be doped with an appropriate amount of impurities. For the purpose of improving dispersibility, imparting conductivity, adjusting color tone, etc.
Surface treatment with compounds such as i, Ti, Sn, Sb, and Zr is also possible. Further, if necessary, carbon black such as rubber furnace, pyrolytic carbon, color black, and acetylene black may be contained.
Furthermore, the intermediate layer has aluminum oxide (α, β, γ), chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride, titanium carbide, silicon carbide, titanium carbide, titanium oxide as nonmagnetic reinforcing particles. (Rutile, anatase) and the like.

(Solvent for Magnetic Layer and Intermediate Layer) Examples of the solvent used for the magnetic layer paint and the intermediate layer paint in the present embodiment include acetone, methyl ethyl ketone, and the like.
Ketone solvents such as methyl isobutyl ketone and cyclohexanone; alcohol solvents such as methanol, ethanol and propanol; ester solvents such as methyl acetate, ethyl acetate, butyl acetate, propyl acetate, ethyl lactate and ethylene glycol acetate; diethylene glycol Ether solvents such as dimethyl ether, 2-ethoxyethanol, tetrahydrofuran and dioxane; aromatic hydrocarbon solvents such as benzene, toluene and xylene; and halogens such as methylene chloride, ethylene chloride, carbon tetrachloride, chloroform and chlorobenzene. Hydrocarbonated solvents may be mentioned, and any one of these solvents may be used alone, or two or more of them may be used in combination.

[0048]

EXAMPLES Examples in which the present embodiment is applied to a magnetic tape as an example of a magnetic recording medium will be described below along with comparative examples.

[First Embodiment] In the first embodiment, each component of Fe-based metal ferromagnetic powder, polyvinyl chloride resin, polyester polyurethane resin, citric acid, heptyl stearate, methyl ethyl ketone, toluene, and cyclohexanone was prepared as follows. After kneading these components with a continuous kneader to obtain a magnetic kneaded product, 2 parts by weight of citric acid is further added to the magnetic kneaded material, and the mixture is dispersed using a sand mill. Polyurethane; trade name Coronate L) 4 parts by weight and myristic acid 2
Parts by weight were added to obtain a magnetic paint.

(Composition of Magnetic Kneaded Material) Fe-based metal ferromagnetic powder (average major axis length = 0.2 μm,
Needle ratio = 9, saturation magnetization = 130 Am^Two/ Kg, coercive force
= 135 kA / m) 100 parts by weight Polyvinyl chloride resin (degree of polymerization 150, polar functional group
5 × 10^-Fivemol / g
) 6 parts by weight ・ Polyester polyurethane resin (3 as polar functional group)
1 × 10 primary amine groups ^-Fourmol / g) 14 fold
Quantity part ・ Al_TwoO_Three(Primary particle size 0.09μ, dispersed in solvent
5 parts by weight, citric acid, 3 parts by weight, heptyl stearate, 1 part by weight, methyl ethyl ketone, 150 parts by weight, toluene, 150 parts by weight, cyclohexanone ... 100 parts by weight Carbon black, vinyl chloride-vinyl acetate-vinyl
Nyl alcohol copolymer, polyurethane resin, methyl ester
Lower each component of tilketone, toluene and cyclohexanone
Each component was separated using a sand mill.
After dispersing, polyisocyanate (Nippon Polyurethane Co., Ltd.)
By adding 4 parts by weight of trade name: Coronate L)
Thus, a paint for a back coat layer was obtained.

(Composition of paint for back coat layer) Carbon black (manufactured by CABOT; product name: BP-
1) 100 parts by weight vinyl chloride-vinyl acetate-vinyl alcohol copolymer (manufactured by UCC; brand name VINYLITE VAGH) 2
5 parts by weight ・ Polyurethane resin (Nippon Polyurethane Co .; trade name N
-2304) 25 parts by weight Methyl ethyl ketone 150 parts by weight Toluene 150 parts by weight Cyclohexanone 100 parts by weight Was applied at a thickness of 3.5 μm, dried after orientation, and calendered to form a magnetic layer. Further, the above-mentioned coating material for the back coat layer was applied to the other main surface of the polyethylene terephthalate film (surface opposite to the magnetic layer) at a thickness of 0.8 μm, dried, and dried. The sample S1 of the magnetic tape was manufactured by cutting to inch width.

[Second Embodiment] In the second embodiment, in the composition of the magnetic kneaded material shown in the first embodiment, the addition amount of the polyester polyurethane resin and the polyvinyl chloride resin as the binder was 6 parts by weight. , Used in place of 14 parts by weight,
After kneading each component of the magnetic kneaded material with a continuous kneader,
Further, 2 parts by weight of citric acid was added and dispersed using a sand mill, and 4 parts by weight of polyisocyanate (manufactured by Nippon Polyurethane Co .; trade name: Coronate L) and myristic acid 1 were added.
Parts by weight were added to obtain a magnetic paint. Then, a sample S2 of a magnetic tape was manufactured through the same steps as in the first example.

[Third Embodiment] In the third embodiment, in the composition of the magnetic kneaded material shown in the first embodiment, a Fe-based metal ferromagnetic powder to which 5% of Co is added is used.
The amounts of the polyester polyurethane resin and polyvinyl chloride resin as binders were changed to 6 parts by weight and 14 parts by weight, respectively, and succinic acid was used in place of citric acid, and each component of the magnetic kneaded product was continuously kneaded. After kneading, 2 parts by weight of succinic acid was further added, dispersed using a sand mill, and 4 parts by weight of polyisocyanate (manufactured by Nippon Polyurethane Co., Ltd .; trade name: Coronate L) and 1 part by weight of myristic acid were added. I got Then, a sample S3 of a magnetic tape was manufactured through the same steps as in the first example.

[First Comparative Example] The first comparative example is the first comparative example.
Using each component of the magnetic kneaded product having the same composition as in the example, each component of the magnetic kneaded product was kneaded with a continuous kneader, then dispersed using a sand mill, and further polyisocyanate (trade name: Coronate L, manufactured by Nippon Polyurethane Co., Ltd.) ) 4 parts by weight and 2 parts by weight of myristic acid were added to obtain a magnetic paint. Then, through a process similar to that of the first embodiment, a sample P1 of a magnetic tape was manufactured.

[Second Comparative Example] In the second comparative example, in the composition of the magnetic kneaded material shown in the first embodiment, the addition amounts of the polyester polyurethane resin and the polyvinyl chloride resin as binders were each 6 parts by weight. , Used in place of 14 parts by weight,
Each component of the magnetic kneaded product was kneaded with a continuous kneader, dispersed using a sand mill, and further added with 4 parts by weight of polyisocyanate (manufactured by Nippon Polyurethane Co., trade name: Coronate L) and 1 part by weight of myristic acid to obtain a magnetic mixture. Paint was obtained.
Then, through a process similar to that of the first embodiment, a sample P2 of the magnetic tape was manufactured.

[Third Comparative Example] In a third comparative example, in the composition of the magnetic kneaded product shown in the first embodiment, a Fe-based metal ferromagnetic powder to which 5% Co was added was used.
Using polyester polyurethane resin and polyvinyl chloride resin as binders in 6 parts by weight and 14 parts by weight, respectively,
Each component of the magnetic kneaded product was kneaded with a continuous kneader, dispersed using a sand mill, and further added with 4 parts by weight of polyisocyanate (manufactured by Nippon Polyurethane Co., trade name: Coronate L) and 1 part by weight of myristic acid to obtain a magnetic mixture. Paint was obtained.
Then, a sample P3 of a magnetic tape was manufactured through the same steps as in the first example.

Next, the first to third embodiments and the first
~ Samples S1 to S3, P1 of magnetic tape according to third comparative example
For P3 to P3, the level down characteristics were examined under the following conditions. Each of the samples S1 to S3, P1 to P3
Have a length of 120 minutes each. First, using a video cassette tape recorder (manufactured by Sony Corporation; trade name: DVW-A500), each of the above samples S1 to S3,
Each of P1 to P3 is run five times in the simultaneous recording / reproducing mode under the environment of a temperature of 40 ° C. and a relative humidity of 20%, and the difference between the output value of the first reproduction signal and the output value of the fifth reproduction signal is obtained. Was determined as the level down amount. Table 1 below shows the level down amounts thus obtained.

[0058]

[Table 1]

As is clear from the results shown in Table 1, each of the samples P1 to P3 has a level-down amount of 5 dB or more, and it can be read that there is a problem in practical characteristics. On the other hand, in the samples S1 to S3, the level down amount is 4 dB or less, which indicates that the characteristics are sufficient as practical characteristics. That is, in the magnetic tape according to the first to third embodiments, the level down amount is reduced.
It was confirmed that it was a good magnetic recording medium with excellent durability.

Next, by operating the video cassette tape recorder in the simultaneous recording / playback mode, a single frequency (2) is applied to each of the samples S1 to S3 and P1 to P3.
5.7 MHz), and the output of each sample was measured. Then, the difference between each output value and the output value of the standard tape was determined as a QF value, and the result is shown in Table 2 below.

[0061]

[Table 2]

As is evident from the results shown in Table 2, it can be seen that the samples P1 to P3 each have a QF value of 2 dB or less, while the samples S1 to S3 each have a QF value of 2 dB or more. That is, it was confirmed that the magnetic tapes according to the first to third examples were magnetic recording media having excellent electromagnetic conversion characteristics.

Next, a surface profile measuring device (Kosaka Laboratory Co., Ltd.)
The center line average roughness (surface roughness) Ra of each of the above samples S1 to S3 and P1 to P3 was measured using a Surfcoder (ET-30HK) manufactured by the company, and the results are shown in Table 3 below. Was.

[0064]

[Table 3]

As is clear from the results shown in Table 3, it can be seen that the surface roughness of the samples S1 to S3 is lower than those of the samples P1 to P3. That is, it was confirmed that the magnetic tapes according to the first to third examples were magnetic recording media having extremely good surface properties.

Although the present invention has been described in detail only with respect to the specific examples described above, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical idea of the present invention. It goes without saying that such variations and modifications belong to the scope of the claims.

For example, in this embodiment, a specific example in which citric acid and succinic acid are used as the dispersant has been described. However, similar effects can be obtained with a general dispersant in a magnetic recording medium. Is clear. In this example, the addition of the dispersant was performed twice, but the amount of each addition is not limited to the amount shown in the example, but may be adjusted according to the characteristics of the target magnetic recording medium. Can be adjusted.

[0068]

As described above, according to the present invention, a magnetic powder (for example, a fine magnetic powder) in a magnetic paint is obtained by using a magnetic paint obtained by adding a dispersant twice.
Becomes extremely good. Therefore, a magnetic recording medium having excellent surface properties of the magnetic layer and excellent electromagnetic conversion characteristics and level-down characteristics of a recording / reproducing signal can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a magnetic recording medium according to an embodiment.

FIG. 2 is a schematic sectional view of a magnetic recording medium having a back coat layer according to the embodiment.

FIG. 3 is a schematic sectional view of a magnetic recording medium having an intermediate layer according to the embodiment.

[Explanation of symbols]

 10, 20, 30: magnetic recording medium 11: non-magnetic support 12: magnetic layer 21: back coat layer 31: intermediate layer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hiroyuki Murakami 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation F-term (reference) 4J038 BA021 BA071 CA071 CB002 CD021 CD061 CD101 CD121 CE011 CE071 CF041 CG071 CG141 CG161 DA031 DA141 DA161 DB001 DD001 DG111 DG121 DG131 DG191 DL032 GA09 GA13 HA166 HA216 KA12 NA11 NA17 5D006 BA09 EA01 FA09 5D112 AA05 BB10 BB16 BB18

Claims (4)

[Claims] 1. A magnetic recording medium comprising a magnetic layer formed on a non-magnetic support, wherein the magnetic layer is a magnetic kneaded material obtained by kneading at least a magnetic powder and a dispersant. A magnetic recording medium comprising a magnetic paint which has been further dispersed by adding a dispersant thereto. 2. The magnetic recording medium according to claim 1, wherein the dispersant is citric acid or succinic acid. 3. A method for producing a magnetic recording medium, comprising forming a magnetic layer by coating a magnetic paint on a non-magnetic support, comprising: kneading at least a magnetic powder and a dispersant to obtain a magnetic kneaded material; A method for producing a magnetic recording medium, comprising using a magnetic coating material which has been subjected to a dispersion treatment by further adding a dispersant to the kneaded material. 4. The method according to claim 3, wherein citric acid or succinic acid is used as the dispersant.