JPH09312014A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control denaturation of a solvent in a magnetic layer and to improve dispersibility by using both of a polyvalent carboxylic acid and a bisphenol-A epoxy oligomer as a dispersant which is an additive for a magnetic recording medium. SOLUTION: A polyvalent carboxylic acid and a bisphenol-A epoxy oligomer are both used as a dispersant to be added to a magnetic layer. In this method, one or more kinds selected from polycarboxylic acid compds. and anhydrides is used. When the polyvalent carboxylic acid compd. or its anhydride selected is mixed and dispersed with a ferromagnetic powder, a binder, an additive and a solvent to prepare a coating material, the polycarboxylic acid compd. or its anhydride suppresses denaturation of a ketone solvent such as cyclohexanone produced on the active points of the surface of the ferromagnetic powder. The amt. of the polyvalent carboxylic acid compd. or its anhydride is controlled to a predetermined pts.wt. to the magnetic powder used. As for the bisphenol-A epoxyollgomer, an oligomer having specified mol.wt. or lower is used.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a coating type magnetic recording medium. More specifically, it relates to a coating type magnetic recording medium having excellent running durability and electromagnetic conversion characteristics.

[0002]

2. Description of the Related Art In the field of magnetic recording, particularly in VTRs (video recorders) and the like, higher density recording is required to achieve high image quality. Along with this increase in density, iron or a metal material mainly containing iron has come to be used in place of the iron oxide-based material that has been conventionally used as magnetic powder for magnetic recording media. These iron or iron-based ferromagnetic metal particles include iron oxide, iron oxyhydroxide, Co, Ni, Cr, Mn, and C.
It is produced by reducing iron hydroxide, iron oxyhydroxide, or the like containing a metal other than iron such as u, Zn, and Ti with a reducing gas such as hydrogen gas. These ferromagnetic powders are
The magnetic properties are superior to those of the conventional iron oxide-based ferromagnetic powder.

However, since the magnetic metal fine particles have a high surface activity and are modified with the above metals other than iron, the acidity or basicity of the surface may become strong.
When a ketone-based solvent such as cyclohexanone is used as an organic solvent to form a paint together with a binder, it produces a modified product, which inhibits the binder from adsorbing to magnetic powder and deteriorates dispersibility, magnetostatic properties, and durability. There is a risk of causing it.

Such properties tend to become stronger as the magnetic powder is subdivided as the noise of the magnetic recording medium is reduced. For this reason, when the above magnetic metal particles are used as magnetic powder for a magnetic recording medium, they are mixed in a ball mill during the process of forming a coating material in combination with an organic solvent that produces a modified product such as resin or cyclohexanone. During the dispersion, or during the pretreatment of the magnetic powder and the resin during kneading, a modified product such as cyclohexanone is formed, which causes problems such as a decrease in dispersibility and deterioration of magnetostatic properties.

To solve this problem, the following method has been devised. (1) In order to suppress the generation of a modified compound such as an organic solvent on the surface of the ferromagnetic metal particles, the surface activity can be suppressed by attaching water to the surface of the ferromagnetic metal particles, or ( 2) A method of coating the surface of the ferromagnetic metal particles with a Si element having a low activity is useful. But,
In the methods (1) and (2), the adsorption amount of the resin may be decreased, and as a result, the dispersibility originally possessed by the resin and the dispersion stability may be deteriorated. , Not necessarily satisfactory. (3) There is also known a method of coating the surface of ferromagnetic metal particles with a low-molecular weight organic substance or oligomer to suppress contact with an organic solvent. The method (3) gives a highly dispersible magnetic coating, but the plasticization of the magnetic layer is more likely to occur as the number of low-molecular weight substances increases, and the efficiency of the calendering treatment as the surface treatment increases, resulting in a high-output magnetic coating. Although a recording medium can be obtained, it is considered that the plasticity of the magnetic layer is likely to occur and the durability is likely to be deteriorated.

As described above, when the magnetic powder having a high surface activity such as ferromagnetic metal particles is used, the dispersibility is improved by suppressing the transformation of the solvent such as cyclohexanone, and the running durability is further improved, In order to improve the dispersibility of (1), there are problems that have not been satisfied by the conventional methods.

[0007]

DISCLOSURE OF THE INVENTION The present invention has the above-mentioned conventional problems, that is, dispersibility due to suppression of modification of a solvent such as cyclohexanone when a magnetic powder having high surface activity such as ferromagnetic metal particles is used. It was invented in order to achieve further improvement of dispersion and further improvement of dispersibility without impairing running durability. It has excellent running durability and electromagnetic conversion characteristics, and is suitable for high density recording. The purpose is to provide a recording medium.

[0008]

The magnetic recording medium according to the present invention comprises a polyvalent carboxylic acid and a bisphenol A type epoxy oligomer in combination as a dispersant added to the magnetic layer. By using a polycarboxylic acid and a bisphenol A type epoxy oligomer together as a dispersant, it is possible to suppress the transformation of the solvent when magnetic powder with high surface activity is used, improve the dispersibility, and improve running durability and electromagnetic conversion characteristics. Can be improved.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As a result of intensive studies by the inventors of the present invention, the magnetic recording comprising a non-magnetic support and a magnetic layer in which a magnetic powder is dispersed in a binder is provided. In the medium, a polycarboxylic acid and a bisphenol A type epoxy oligomer are used together as a dispersant in the magnetic layer, and / or a magnetic powder and a binder are mixed, and kneading and dispersing steps are performed to form a coating material. By adding an isocyanate compound as a curing agent after conversion to
Alternatively, the amount of the bisphenol A-type epoxy oligomer used is 0.5 to 5 parts by weight based on the magnetic powder, and / or the amount of the polycarboxylic acid used is 0. It has been found that the amount of 5 to 5 parts by weight can improve the dispersibility and the magnetostatic property without impairing the running durability, and has completed the present invention.

That is, the magnetic recording medium according to the present invention is a magnetic recording medium comprising a non-magnetic support and a magnetic layer in which magnetic powder is dispersed in a binder. A carboxylic acid and a bisphenol A type epoxy oligomer are used in combination.

The present invention further comprises a composition in which an isocyanate compound is added as a curing agent after mixing magnetic powder and a binder, kneading and dispersing steps to form a coating material.

The present invention further relates to the bisphenol A used.
The content of the type epoxy oligomer is set to 0.5 to 5 parts by weight with respect to 100 parts by weight of the magnetic powder.

In the present invention, the amount of the polycarboxylic acid used is 0.5 to 5 parts by weight based on 100 parts by weight of the magnetic powder.

The present invention further relates to the bisphenol A used.
The molecular weight of the type epoxy oligomer is 5000 or less.

The polycarboxylic acid used in the present invention is further selected from succinic acid, glutaric acid, tartaric acid, apple acid, glutamic acid, citric acid, phthalic acid, pyromellitic acid, tetrahydrophthalic acid and anhydrides thereof. It is configured to use one or more kinds.

Examples will be described below.

The polyvalent carboxylic acid compound and its anhydride used in this example may have a plurality of carboxylic acids and may simultaneously have a plurality of hydroxyl groups. Examples include succinic acid, glutaric acid, tartaric acid, apple acid, glutamic acid, citric acid, phthalic acid, pyromellitic acid, tetrahydrophthalic acid, and the like, and anhydrides thereof, but not limited to these examples. Of course.

Then, one kind or two or more kinds selected from these polyvalent carboxylic acid compounds and their anhydrides can be used in combination. These polyvalent carboxylic acid compounds and their anhydrides are produced at the active points on the surface of the ferromagnetic powder when they are made into a paint through a mixing and dispersing process with the ferromagnetic powder and binders, additives, solvents and the like. Suppress the transformation of ketone solvents such as cyclohexanone.

The amount of the polyvalent carboxylic acid compound and its anhydride used is 0.5 to 5 with respect to the magnetic powder used.
A suitable amount is 1 part by weight, more preferably 1 to 3 parts by weight. The amount used depends on the surface area of the magnetic powder, but if it is less than 0.5 parts by weight, it acts on the active points of the ferromagnetic powder, and the suppressing effect is small. Although it is sufficient to suppress the point, the portion on which the binder resin acts becomes too small, and the dispersibility may decrease, so that there is no problem if used in an appropriate amount within the above range.

As the bisphenol A type epoxy oligomer, it is preferable to use one having a molecular weight of 5000 g / mol or less. When the molecular weight exceeds 5,000, dispersibility is poor,
It is also difficult to melt and not practical. As the bisphenol A type epoxy oligomer having a molecular weight of 5000 g / mol or less used in the present invention, the one shown in Chemical formula 1 is used.

[0021]

Embedded image (However, it is a repeating unit of n = 1, 2, 3, 4, 5, ..., And the viscosity may be adjusted by adding a diluent which is reactive in handling.)

The hydroxyl group and ester bond portion of this bisphenol A type epoxy oligomer act on the active sites of the ferromagnetic metal powder, and like the above-mentioned polyvalent carboxylic acid compound, inhibit the transformation of the ketone solvent such as cyclohexanone. . As described above, the property of easily acting on the surface active points of the metallic magnetic powder and 10,000 g / mo of the widely used binder resin
The molecular weight of the bisphenol A type epoxy oligomer is 5000 g compared with the molecular weight of 1 to 100000 g / mol.
Since it is as small as less than 1 mol / mol, it easily penetrates and adsorbs into the gaps of the agglomerate structure of the magnetic powder before the binder resin, acts as a dispersion aid, and the leveling of the paint during coating due to its low molecular weight. It has the property of facilitating

Further, it acts as a plasticizer in the surface treatment step to improve the surface property. However, when it simply acts as a plasticizer, the coating film tends to become brittle during driving during recording and reproduction, but the hydroxyl group of the bisphenol A type epoxy oligomer functions as a functional group reactive with the isocyanate compound. It reduces the brittleness of the film.

Further, epoxy groups are present at both ends of the bisphenol A type epoxy oligomer, and the epoxy groups have a higher reactivity with an amine formed by the reaction of an isocyanate compound with water and the like than a hydroxyl group, and thus have a crosslinking point. It is easy to act as.

The polycarboxylic acid modifies the active sites on the surface of the magnetic powder due to its strong adsorptive power, but when the adsorptive power is weaker than that of the polycarboxylic acid such as the bisphenol A type epoxy oligomer, the polycarboxylic acid is used. Without hindering acid adsorption
It is possible to act on the surface active points in the aggregate structure of the magnetic powder, and by using the polycarboxylic acid and the bisphenol A type epoxy oligomer in combination as described above, the dispersibility and the strength of the coating film are reduced. It is presumed that it will contribute to the improvement of the surface treatment efficiency.

The amount of the bisphenol A type epoxy oligomer used is suitably 0.5 to 5 parts by weight, more preferably, 100 parts by weight of the magnetic powder used.
1 to 3 parts by weight is suitable. This amount of use depends on the surface area of the magnetic powder, but if it is less than 0.5 parts by weight, it acts on the active points of the ferromagnetic powder, and the suppressing effect is small. This is because it is sufficient to suppress the active sites, but the portion on which the binder resin acts becomes too small, and the dispersibility may be reduced. If a proper amount is used within the above range, there will be no problem. There is no.

As the isocyanate compound, a plurality of isocyanate compounds, preferably three or more, are contained in one molecule in order to realize steric crosslinking with the binder resin and / or the bisphenol A type epoxy oligomer which is essential in the present invention. It is better to have an isocyanate group.

Hardeners that meet this condition are derived from tolylene diisocyanate (TDI), 4,4-diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), and the like. Examples thereof include polymers such as trimers, compounds having a structure in which they are reacted with a polyol compound such as 3,3,3, -trimethylolpropane (TMP), and the like. A specific example of the product name made by Nippon Polyurethane is HDI trimer, Coronate E.
Coronate HL, TMP for H, TMP and HDI compounds
And TDI compounds include Coronate L.

The amount of these isocyanate compounds is usually 10 to 30% by weight with respect to the binder so that the number of moles of isocyanate groups is equal to or more than the number of moles of hydroxyl groups contained in the binder resin. Need.

The magnetic recording medium to which the present invention is applied includes a so-called coating type magnetic recording medium in which a magnetic coating film is formed as a magnetic layer by first coating a magnetic coating on the surface of a non-magnetic support. . In the coating type magnetic recording medium, any conventionally known magnetic powder or the like can be used as the non-magnetic support or the magnetic coating film, and the magnetic powder is not limited in any way.

For example, as the magnetic powder, γ
-Fe ₂ O ₃ , Fe ₃ O ₄ , γ-Fe ₂ O ₃ and Fe ₃ O
_A beltride compound with ₄ , γ-Fe ₂ O ₃ containing Co,
Co-containing Fe ₃ O ₄ , a beltride compound of γ-Fe ₂ O ₃ and Fe ₃ O ₄ containing Co, one or more metal elements in CrO ₂ , such as Te, Sb, Fe,
Bi-containing oxides, Fe, Co, Ni and other metals, Fe-Co, Fe-Ni, Fe-Al, Fe-N
i-Al, Fe-Al-P, Fe-Ni-Si-Al,
Fe-Ni-Si-Al-Mn, Fe-Mn-Zn, F
e-Ni-Zn, Co-Ni, Co-P, Fe-Co-
Ni, Fe-Co-Ni-Cr, Fe-Co-Ni-
P, Fe-Co-B, Fe-Co-Cr-B, Mn-B
Examples include alloys such as i, Mn-Al, and Fe-Co-V, iron nitride, iron carbide, and the like. Of course, Al, Si added for the purpose of preventing sintering or maintaining the shape during reduction,
Even if a light metal element such as P or B is contained in an appropriate amount, the effect of the present invention is not hindered.

The resin binder usable in the present invention includes vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer. Coalesce, acrylic ester-vinylidene chloride copolymer, methacrylic acid ester-vinylidene chloride copolymer,
Methacrylate-vinyl chloride copolymer, methacrylate-ethylene copolymer, polyvinyl fluoride,
Vinylidene chloride-acrylonitrile copolymer, acrylonitrile-butadiene copolymer, polyvinyl butyral, cellulose derivative (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose), styrene butadiene copolymer, polyester There are thermoplastic resins such as resin and synthetic rubber. Further, the thermosetting resin as the conventionally known binder includes phenol resin, epoxy resin, silicone resin and the like.

The binder in the magnetic layer and the lower non-magnetic layer is 1 to 200 parts by weight, preferably 1 to 50 parts by weight, relative to 100 parts by weight of the magnetic powder and the lower non-magnetic layer.
Parts by weight. If the amount of the binder used is too large, the ratio of the magnetic powder in the magnetic layer is relatively reduced, resulting in a decrease in output.If it is too small, the mechanical strength of the magnetic layer and the lower non-magnetic layer is reduced, and The running durability of the medium is reduced.

In the present invention, if necessary, a lubricant,
Non-magnetic reinforcing particles, conductive particles and the like can be contained in the magnetic layer and the lower non-magnetic layer, and the compounding ratio and the like are set according to the case of an ordinary magnetic recording medium, and may be set according to the purpose. good.

As the above-mentioned lubricant, graphite, molybdenum disulfide, silicone oil, fatty acid having 10 to 22 carbon atoms, fatty acid ester consisting of this and alcohol having 2 to 26 carbon atoms, terpene compound, and these Oligomers.

The non-magnetic reinforcing particles include aluminum oxide, chromium oxide, silicon carbide, diamond, garnet, emery, boron nitride and the like. This particle is
20 parts by weight, preferably 10 parts by weight or less, relative to 100 parts by weight of magnetic powder, and the average particle size is 1.0 μm.
m or less, preferably 0.5 μm or less.

Examples of the conductive particles include carbon black, graphite and other metal particles.

Examples of the non-magnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyolefins such as polypropylene, celluloses such as cellulose triacetate and cellulose diacetate, vinyl resins, polyimides and polycarbonates. Examples thereof include a polymeric material represented by a class, a support formed of metal, glass, ceramics, or the like.

To form a magnetic layer on the above non-magnetic support, the magnetic layer forming material is coated and then dried. The solvent used for the coating is acetone, methyl ethyl ketone or methyl. Isobutyl ketone, ketone solvents such as hecyclohexanone, alcohol solvents such as methanol, ethanol, propanol, methyl acetate,
Ethyl acetate, butyl acetate, propyl acetate, ethyl lactate,
Ester solvents such as ethylene glycol acetate, diethylene glycol dimethyl ether, 2-ethoxyethanol, tetrahydrofuran, ether solvents such as dioxane, benzene, toluene, aromatic hydrocarbon solvents such as xylene, methylene chloride, ethylene chloride, carbon tetrachloride, A halogenated hydrocarbon solvent such as chloroform or chlorobenzene is used.

A roll mill, a ball mill, a sand mill, an agitator, a kneader, an extruder, a homogenizer, an ultrasonic disperser or the like is used for the dispersion / kneading for preparing the above-mentioned coating material. Furthermore, in order to apply the paint thus formed on a non-magnetic support, a gravure coater,
A knife coater, a wire bar coater, a doctor blade coater, a reverse roll coater, a dipping coater, an air knife coater, a die coater and the like are used. The upper magnetic layer may be coated by a prescription such as a die coater, and the coating method may be selected as desired within a range in which the object of the present invention can be achieved.

Specific examples of the present invention will be described below, but it goes without saying that the present invention is not limited to these examples.

Example 1 First, a commercially available bisphenol A type epoxy oligomer (made by Yuka Shell Epoxy) was prepared. The weight average molecular weight of this oligomer (in terms of polystyrene) was 380 g / mol, and it was measured by high performance liquid chromatography (Showa Denko). As the polycarboxylic acid, citric acid (manufactured by Wako Pure Chemical Industries, Ltd.) was prepared.

Next, magnetic powder for magnetic recording was prepared. The magnetic properties and powder properties are shown below. Saturation magnetization = 125 Am2 / Kg squareness ratio = 0.49 holding power = 119 kA / m specific surface = 53 m ² / g acicular ratio = 10, however, the magnetic properties vibrating sample magnetometer (manufactured by Toei Kogyo Co., Ltd.) so,
The specific surface area was measured by BET one point (manufactured by Tsushima Seisakusho).
The acicular ratio was randomly selected by observation with an equalizing electron microscope. 10
The average value of 0 points was adopted.

Using the above-mentioned citric acid, bisphenol A type epoxy oligomer, magnetic powder, binder resin and carbon, α-Al ₂ O ₃ as an additive, the following coating composition was used for the mixing, kneading and dispersing steps. After that, it became a paint.

[0045] [Coating Composition] ferromagnetic magnetic powder 100 parts by weight of the polyester polyurethane resin (-SO ₃ Na content) 10 parts by weight of the polyvinyl chloride resin (-OSO ₃ K content) 10 parts by weight of citric acid 2 parts by weight of bisphenol A type epoxy Oligomer (380 g / mol) 2 parts by weight α-Al ₂ O ₃ (average particle size 240 nm) 2 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight Cyclohexanone 50 parts by weight Heptyl stearate 1 part by weight Myristic acid 2 parts by weight

An isocyanate compound: Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) was added as a curing agent to the obtained magnetic paint, which was coated on a 14 μm PET (polyethylene terephthalate) film, oriented and dried. The obtained tape was subjected to calendering as a surface treatment step and cured in a curing oven at 60 ° C. for 24 hours to accelerate curing.

In the evaluation of the obtained coated tape, the dispersibility of the magnetic layer was evaluated as a glossiness with a gloss meter (manufactured by NIPPON COLOR CO., LTD.). The incident angle of the light beam was 45 degrees.
(According to JIS-8741). Magnetic properties were measured with a sample vibration magnetometer. The results are shown in Table 2.

As the durability of the obtained tape, the number of times until the base film was seen by sliding the tape surface with a cotton swab soaked with methyl ethyl ketone was evaluated as solvent resistance, and the results are shown in Table 2. Indicated. Here, the larger the number of slides, the better the crosslinkability, the less plasticization, and the better the durability.

(Examples 2 to 11), (Comparative Examples 1 to 6) As in Example 1, the factors shown in Table 1 were changed and Examples 2 to 2 were changed.
11, Comparative Examples 1 to 6 were produced, and the results are shown in Table 2.

[0050]

[Table 1]

[0051]

[Table 2]

First, comparing the presence or absence of addition of citric acid, which is a polyvalent carboxylic acid, and the bisphenol A type epoxy oligomer from Example 1 and Comparative Examples 1 to 7, the results of Table 2 show that no added Comparative Example 1, Comparative Example 2 in which citric acid or bisphenol A type epoxy oligomer was added from 5
The dispersibility (Gloss 45 °) and the magnetostatic properties were improved by 3, 6 and 7, and Example 1 and Comparative Example 4 in which citric acid and a bisphenol A type epoxy oligomer were used in combination
Then, it can be seen that they are greatly improved compared to the case where each of them is used alone.

Comparing the solvent resistances at this time, Example 1 and Comparative Example 5 using an isocyanate compound curing agent were compared.
It can be seen that in Comparative Examples 1 to 4 in which no curing agent is used, it is significantly lower than in Comparative Examples 6 and 7.

From these, citric acid and bisphenol A
It can be seen that the dispersibility and the magnetostatic properties are improved without impairing the solvent resistance when the type epoxy oligomers are used in combination rather than each, and the isocyanate compound curing agent is further used in combination.

Similarly, when the citric acid was changed to another polycarboxylic acid and the anhydride thereof was compared with Examples 2 to 6 and Comparative Examples 1 and 8 to 15, solvent resistance was the curing of the isocyanate compound. It was found that when the agent was used, the dispersibility was significantly improved, and the dispersibility was also improved, and it can be confirmed that the dispersibility is further improved in Examples 2 to 6 using the bisphenol A type epoxy oligomer.

Therefore, in the case of other polyvalent carboxylic acids as well as citric acid, bisphenol A type epoxy oligomers are used in combination without being used, respectively, and when a curing agent of an isocyanate compound is further used in combination, It can be seen that the dispersibility and magnetostatic properties are improved without impairing the solvent properties.

FIGS. 1 and 2 show the relationship between Gloss 45 ° and solvent resistance when the addition amounts of citric acid and bisphenol A type epoxy oligomer were changed respectively.

As is clear from the figure, in order to improve the dispersibility as compared with the case of using each of them without impairing the solvent resistance, the dispersibility and the static magnetic property should be set to 0.5 parts by weight or more and 5 parts by weight or less. It can be seen that the characteristics are improved.

Comparing the results of the weight average molecular weights of the bisphenol A type epoxy oligomers from Examples 1, 11, 12 and Comparative Example 18, the weight average molecular weight was 7,000 g / m 2.
It can be seen that, when ol is used, the solvent resistance is good, but the effect of improving the dispersibility is lost. Therefore, the weight average molecular weight is 50
It is suitable to use a bisphenol A type epoxy oligomer of not more than 00 g / mol, and it is understood that the dispersibility and magnetostatic properties are improved without impairing the solvent resistance.

[0060]

INDUSTRIAL APPLICABILITY According to the present invention, a polyvalent carboxylic acid is used to prevent the modification of a ketone solvent due to the surface activity of a metal powder, and a bisphenol A type epoxy oligomer reactive with a curing agent for an isocyanate compound is used. When used together as a dispersant, and further by using an isocyanate compound together therewith, it acts as a dispersant that acts on the surface of the magnetic powder, increases the calender surface treatment efficiency, and further has a crosslinking group. It is possible to realize an improved dispersibility of the magnetic recording medium without lowering the strength of the magnetic coating film. Therefore, according to the present invention, it is possible to manufacture a high dispersion coating type magnetic recording medium suitable for high density recording.

[Brief description of drawings]

FIG. 1 is a graph showing the amount of addition of citric acid in the case where citric acid and a bisphenol A type epoxy oligomer are used in combination.
It is a graph of ss 45 °.

FIG. 2 is a graph of Gloss 45 ° with respect to the addition amount of bisphenol A type epoxy oligomer when citric acid and bisphenol A type epoxy oligomer are used in combination.

Claims (6)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer mainly comprising magnetic powder and a binder, wherein a polyvalent carboxylic acid and a bisphenol A type epoxy are used as a dispersant in the magnetic layer. A magnetic recording medium characterized by using an oligomer together. 2. The content of the bisphenol A type epoxy oligomer is 0.5 to 100 parts by weight of the magnetic powder.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 5 parts by weight. 3. The magnetic recording medium according to claim 1, wherein the content of the polycarboxylic acid is 0.5 to 5 parts by weight with respect to 100 parts by weight of the magnetic powder. 4. The magnetic recording medium according to claim 1, wherein the bisphenol A type epoxy oligomer has a molecular weight of 5000 g / mol or less. 5. The polyvalent carboxylic acid is one or more selected from succinic acid, glutaric acid, tartaric acid, apple acid, glutamic acid, citric acid, phthalic acid, pyromellitic acid, tetrahydrophthalic acid and their anhydrides. The magnetic recording medium according to claim 1, which is used. 6. An isocyanate compound is added to the magnetic layer as a curing agent in the magnetic layer.
3. The magnetic recording medium according to claim 1.