JP2667286B2 - Magnetic recording medium and method of manufacturing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a magnetic recording medium such as a magnetic tape and a magnetic sheet used for audio and video equipment or a computer, and a method of manufacturing the same.

[Background of the Invention]

Magnetic recording media are widely used as recording tapes, video tapes, computer tapes, floppy disks, and the like. The magnetic recording medium is basically formed by laminating a magnetic layer in which ferromagnetic powder is dispersed in a binder (binder) on a non-magnetic support.

Basically, a magnetic recording medium is required to be at a high level in various characteristics such as electromagnetic conversion characteristics, running durability and running performance. In particular, with the recent increase in recording density of video tape recorders, video tapes are required to have high electromagnetic output characteristics, such as high video output and excellent original image reproduction capability. ing.

Ferromagnetic metal powders have been used as one method for improving the electromagnetic conversion characteristics of an electromagnetic recording medium.

However, on the other hand, γ-iron oxide, cobalt-coated γ-iron oxide,
Since the dispersibility tends to decrease in the order of the ferromagnetic metal fine powder, improvement of the ferromagnetic powder may adversely affect the dispersion state of the ferromagnetic powder in the magnetic layer. This is because the excellent properties of the powder are not sufficiently exhibited.

In order to improve the dispersion state of the ferromagnetic powder, there is a method in which kneading and dispersion are performed for a long time when preparing a magnetic coating material. However, a considerable shearing force acts on the ferromagnetic powder during the kneading and dispersing. The characteristics may be impaired, and it takes a long time to manufacture the magnetic recording medium, which causes a problem in working efficiency.

Ferromagnetic powder surface that provides dispersibility and magnetic material dispersion stability as a result of ferromagnetic powder surface stabilization in order to obtain a magnetic recording medium with excellent electromagnetic conversion characteristics and running durability using ferromagnetic metal powder Various treatment agents have been studied. Phosphate ester type (JP-A-63-23962) silane coupling agent (JP-A-63-4417), fatty acid (JP-A-53-15802,
Japanese Patent Application Laid-Open Nos. 53-116114 and 60-157722) Among them, fatty acids usually contained as a lubricant in a magnetic layer of a magnetic recording medium have a dispersing action on ferromagnetic powder. Therefore, it is possible to improve the dispersion state of the ferromagnetic powder by adjusting the amount used, but generally, when a fatty acid is used as a dispersant, it is usually more than when the fatty acid is blended in the magnetic layer as a lubricant. Unless used in a large amount, a sufficient effect cannot be obtained. On the other hand, fatty acids are known to act as a plasticizer for the binder when used in excess, and the problem that when the fatty acid acts as a dispersant for the ferromagnetic powder, the binder is inevitably plasticized. is there. On the other hand, by improving the dispersion state, the surface of the tape becomes smooth, and the friction coefficient increases. For example, it was possible to improve the dispersed state by using a large amount of a silane coupling agent, but the running durability was insufficient. It is also known to use a ferromagnetic powder having a stearic acid adsorbing group defined (JP-A-1-199316).

If the stearic acid adsorption amount is low, the demagnetization is large and there is a problem of storage stability.When using a ferromagnetic metal powder having a stearic acid adsorption amount of 5.0 × 10 ⁻⁶ mol / m ² or more, it is preferable to add an appropriate amount of fatty acid. It was difficult to obtain a high running durability. The ferromagnetic metal powder having a high stearic acid adsorption amount is, for example, a ferromagnetic metal powder gradually oxidized in a gas phase, and is likely to be lower in cost and has excellent storage stability (demagnetization). It is.

In other words, ferromagnetic powder with a high stearic acid adsorption amount adsorbs fatty acid added as a lubricant in the magnetic coating solution, so that the floating of the fatty acid on the magnetic layer surface decreases, the lubrication function decreases, and the friction coefficient decreases. Rose.

[Object of the invention]

An object of the present invention is to provide a magnetic recording medium having particularly good electromagnetic conversion characteristics and running durability.

More specifically, the present invention improves the dispersion state of the ferromagnetic powder in the magnetic layer so that the characteristics of the used ferromagnetic powder are sufficiently exhibited, thereby improving the electromagnetic conversion characteristics, and further improving the running durability. It is an object of the present invention to provide a magnetic recording medium which is kept.

[Configuration of the invention]

That is, the object of the present invention is to provide a magnetic recording medium having a non-magnetic support and a magnetic layer formed by dispersing a ferromagnetic powder provided on the support in a binder, wherein the ferromagnetic powder has a per unit surface area. Stearic acid adsorption of 5.0 × 10
By ^-6 mol / m ² or more is a ferromagnetic metal powder, a ferromagnetic metal powder surface-treated with at least one acid dissociation constant (pKa) of 4.0 or less of an organic acid compound, wherein the binder is a polar group _{as: -SO 3 M, -OSO 3 M} , -CO 2 M, -OPO 3 M 2, -P
O ₃ M ₂ (where M represents a hydrogen, an alkali metal or an ammonium salt) contains a polymer having at least one selected from the group consisting of: a saturated fatty acid and 0.3 to 5 parts by weight per 100 parts by weight of the ferromagnetic metal powder. This can be achieved by a magnetic recording medium characterized by having a magnetic layer including a portion. The above object of the present invention by adding a pKa relative to the ferromagnetic metal powder stearate adsorption amount per unit surface area is 5.0 × 10 ^-6 mol / m ² or more and 4.0 or less of an organic acid compound, surface-treated Thereafter, kneading and dispersing, and then adding and dispersing a polar group-containing binder to obtain a magnetic coating material, and applying the magnetic coating material on a non-magnetic support, can be achieved by a method for producing a magnetic recording medium. . That is, since the present invention uses an organic acid compound having a smaller acid dissociation constant (pKa) than a fatty acid, the amount of stearic acid adsorbed per unit area is large, that is, the demagnetization is small, the storage stability is high, and the cost is low. By using a combination of ferromagnetic metal powders gradually oxidized in the gas phase, the organic acid compound appropriately blocks the adsorption point of the ferromagnetic metal powder, and the organic acid compound does not substitute with a fatty acid. In addition, the adsorption point of the remaining ferromagnetic metal powder is adsorbed by the magnetic group of the polar group-containing binder, and the dispersibility is improved, and
N improves. On the other hand, the fatty acid is not adsorbed on the ferromagnetic metal powder due to the presence of the organic acid compound, and sufficiently exerts a function as a lubricant on the surface of the magnetic layer, and the μ value decreases. Further, since all of the organic acid compound is firmly adsorbed to the ferromagnetic metal powder, the plasticity of the magnetic layer is not increased, and the running property can be improved and the occurrence of tape damage can be prevented. As described above, the present invention uses an organic combination of a ferromagnetic metal powder with low demagnetization and good storage stability, an organic acid compound, a polar group-containing binder, and a fatty acid.
All items of C / N, μ value, runnability, tape flaw, and demagnetization were improved at the same time.

To explain these points in more detail, the magnetic recording medium of the present invention is characterized in that the compound acts as a dispersant on the ferromagnetic metal powder by using a strong organic acid having an acid dissociation constant (pKa) of 4.0 or less. The magnetic recording medium has an improved dispersion state of the ferromagnetic metal powder in the magnetic layer. Specifically, pK
After the surface treatment of the ferromagnetic metal with an organic acid of a ≦ 4.0, the ferromagnetic metal powder is dispersed well by dispersing the ferromagnetic metal powder in the polar group-containing resin, and the surface of the magnetic layer becomes smooth. The maximum magnetic flux density (Bm) and squareness ratio (SQ) increase. Therefore, the magnetic recording medium of the present invention exhibits good electromagnetic conversion characteristics. In addition, the surface treatment of the ferromagnetic metal powder with an organic acid having a pKa <4.0 or less eliminates fatty acid adsorption points (basic points) on the surface of the ferromagnetic powder, resulting in an increase in the amount of fatty acids floating on the surface of the magnetic layer and friction. The coefficient is low and shows excellent running durability. In particular, the present invention is effective for ferromagnetic metal powders having a high stearic acid adsorption amount, that is, many fatty acid adsorption points. On the surface of the ferromagnetic metal powder, there are a basic point (fatty acid adsorption point) and an acidic point, but the fatty acid is adsorbed to the basic point remaining after the binder is adsorbed when the treatment is not performed with an organic acid. . For this reason, the ratio of the fatty acid which floats on the surface of the magnetic layer and contributes to lubrication decreases. Therefore, the dispersion was moderate, but the running durability was poor. When the surface treatment is performed with an organic acid compound having a pKa> 4.0, the lipophilicity of the surface of the ferromagnetic metal powder is increased, and the affinity with the binder is improved, so that the dispersibility is improved. However, since the binding force between the polar group in the organic acid compound and the ferromagnetic metal powder is weak, exchange occurs with the fatty acid (the pKa of the fatty acid is 4.2 or more) in the magnetic layer, and as a result,
The floating amount of the fatty acid on the surface of the magnetic layer decreases, and sufficient running durability cannot be obtained.

In the case of the present invention, a suitable amount of the organic acid compound is adsorbed on the surface of the ferromagnetic metal powder, and the polar group-containing binder is adsorbed on the remaining adsorption points. Since the organic acid compound having a small pKa is a strong acid, it has a strong binding force with the ferromagnetic metal powder and does not exchange with the fatty acid in the magnetic layer, and the ratio of the floating of the fatty acid on the surface of the magnetic layer increases. As a result, a good magnetic recording medium having improved dispersibility and a low coefficient of friction can be obtained. At this time, the amount of the saturated fatty acid added as a lubricant to the magnetic coating liquid is suitably from 0.3 to 5 parts by weight based on 100 parts by weight of the ferromagnetic metal powder. On the other hand, if it is too high, it induces plasticization of the binder, and good durability cannot be obtained.

The magnetic recording medium of the present invention basically has a configuration in which a nonmagnetic support and a magnetic layer made of ferromagnetic powder (ferromagnetic material) dispersed in a binder are provided on the support. .

The ferromagnetic metal powder used in the present invention is obtained by providing a gradual oxide film on the surface of an acicular powder of an alloy containing iron as a main component.

This ferromagnetic metal powder has a pH of 8-12 or a stearic acid adsorption amount of 5.0 × 10 ^-6 mol / m ² or more.
In particular, a ferromagnetic metal powder containing iron, nickel, aluminum, and silicon, having a specific surface area of 45 m ² / g or more, a pH of 9-11, and a stearic acid adsorption amount of 6 × 10 ⁻⁶ mol / m ² or more It is particularly effective when a ferromagnetic metal powder of 7 × 10 ⁻⁶ mol / m ² or more is used.

The stearic acid adsorption amount of the ferromagnetic metal powder was measured by the following method.

5 g of the ferromagnetic metal powder was added to a 100 ml Erlenmeyer flask containing a methyl ethyl ketone solution containing 2% by weight of stearic acid, the flask was sealed, and the mixture was stirred with a magnetic stirrer for 25 hours. Separated, and the stearic acid concentration C (wt%) in the supernatant was measured using gas chromatography.

The stearic acid adsorption amount per unit area of the ferromagnetic metal powder was determined by the following equation.

However, SSA: ferromagnetic metal powder specific surface area (m ² / g) MW: stearic acid molecular weight (284) The magnetic recording medium of the present invention comprises an organic acid compound having a pKa ≦ 4.0 added to a binder comprising a polar group-containing resin component. And a magnetic layer in which the above-mentioned ferromagnetic metal powder surface-treated is dispersed.

As the organic acid compound used here, for example, there is a compound having a chemical structure shown in the following table.

Above all, when the ferromagnetic metal powder is surface-treated with the organic acid compound marked with ●, there is a good effect of dispersion and a reduction of μ value.

Such an organic acid compound has a property of adsorbing or binding to a fatty acid adsorption point (basic point) on the surface of the ferromagnetic metal powder. Therefore, since the surface of the ferromagnetic metal powder is coated with an organic substance, the affinity of the ferromagnetic metal powder for the binder component is improved, and it is speculated that the dispersion state of the ferromagnetic metal powder is improved. Is done. At this time, it is considered that the polar group in the binder is bonded to the remaining basic point of the ferromagnetic metal powder not coated with the organic acid compound.

Since the organic acid compound used in the present invention has a lower pKa value (higher acidity) than the fatty acid added as a lubricant, once it is bonded to the fatty acid adsorption site on the surface of the ferromagnetic metal powder, it is added later. No exchange occurs with the fatty acids used. As a result, it is presumed that a fatty acid added as a lubricant, for example, stearic acid, has an increased floating rate on the surface of the magnetic layer and has excellent running durability.

That is, stearic acid is not adsorbed on the ferromagnetic metal powder, but comes out on the surface of the magnetic layer and performs its original function as a lubricant.

In the magnetic layer, the above-mentioned organic acid compound is a ferromagnetic metal powder 10
It is contained in a content within the range of 0.03 to 10 parts by weight with respect to 0 parts by weight. In particular, by setting the content in the range of 0.3 to 5.0 parts by weight, the dispersion state of the ferromagnetic metal powder is improved, for example, the gloss Bm and SQ of the magnetic layer surface are increased. Further, by setting the content in the range of 0.5 to 3.0 parts by weight, the electromagnetic conversion characteristics are remarkably improved, the friction coefficient is reduced, and the running durability is excellent.

As a method of adding the organic acid compound, the ferromagnetic metal is dissolved or dispersed in a low-boiling organic solvent, and the ferromagnetic metal powder is put into the solution, mixed, and then the organic solvent is removed and the pre-treated ferromagnetic metal is removed. A method for preparing a magnetic recording medium using the ferromagnetic metal powder by adjusting the powder, and when adjusting the magnetic paint, dissolving or dispersing the organic acid compound, preferably in a part of a solvent for adjusting the magnetic paint. A method of kneading and dispersing the mixture in a state of being mixed can be used.

The polymer used as a binder for forming the magnetic layer of the present invention is a vinyl chloride / vinyl acetate copolymer resin (eg, vinyl chloride / vinyl acetate copolymer, vinyl chloride /
Vinyl acetate / vinyl alcohol copolymer, vinyl chloride /
Vinyl acetate / maleic acid copolymer), vinyl chloride / vinylidene chloride copolymer, acrylic resin (eg, vinyl chloride / acrylonitrile copolymer, vinylidene chloride / acrylonitrile copolymer, (meth) acrylate / acrylonitrile copolymer Polymer, (meth) acrylate / vinylidene chloride copolymer, (meth) acrylate / styrene copolymer, butadiene / acrylonitrile copolymer), polyurethane resin, polyester resin, polyvinyl fluoride, polyamide resin, As a polar group in polyvinyl butyrate and styrene / bradiene copolymer,
_{-SO 3 M, -OSO 3 M,} -CO 2 M, -OPO 3 M 2, -PO 3 M 2 ( however, M is. Representing H, an alkali metal or ammonium), at least one selected from the group consisting of Is selected from the polymers into which is introduced. Preferably, a polymer in which a polar group is introduced into a vinyl chloride / vinyl acetate copolymer resin.

The polar layer contains 10 ^-6 per gram of polymer in the polymer.
Preferably, it is contained in the range of 10 to ³ equivalents.

Compound having three or more isocyanate groups in one molecule, trimer and tetramer of diisocyanate) or a polymer thereof, polyisocyanate prepolymer and resin having active hydrogen (eg, polyester polyol, polyether polyol, acrylic acid copolymer) And a resin obtained by a combination thereof with a reaction product with a copolymer, a maleic acid copolymer, a 2-hydroxyethyl methacrylate copolymer, and a p-hydroxystyrene copolymer. The amount of the binder used is generally 10 to 100 parts by weight, based on 100 parts by weight of the ferromagnetic powder,
Preferably, 15 to 50 parts by weight are used.

Further, the fatty acid contained in the magnetic layer of the magnetic recording medium of the present invention is preferably a fatty acid having 14 to 22 carbon atoms, and may further contain a fatty acid amide if desired. In the magnetic layer, the fatty acid or fatty acid amide acts as a lubricant.

In this case, the content of the fatty acid or fatty acid amide is
Usually, the magnetic recording medium of the present invention, based on 100 parts by weight of the ferromagnetic metal powder, contains a ferromagnetic powder, a binder, and the above-mentioned additives used as desired, such as toluene, butyl acetate, and ethyl acetate, which are commonly used. A magnetic paint is prepared by dispersing in an organic solvent such as methylethylmethone and cyclohexanone and tetrahydrofuran, and the magnetic paint is applied on a nonmagnetic support so that the dry thickness of the magnetic layer is usually 0.1 to 10 μm. A magnetic field orientation treatment, a drying process, a surface smoothing treatment, a curing treatment, and the like are carried out, and then a usual method of cutting can be used.

In the present invention, it is preferable that an organic acid compound is added to the ferromagnetic metal powder to perform a surface treatment.

The surface treatment step of the ferromagnetic powder is a step of pulverizing while mixing the ferromagnetic powder and the organic acid compound.

In this surface treatment step, the same kneading apparatus used in the next kneading and dispersing step is used. Examples of the kneading apparatus include a roll mill, a kneader (batch type), a pressure kneader, a continuous kneading mixer and the like as described in "Kneading Technology" (by Kenji Hashimoto, published by the Industrial Technology Center). The mixing and pulverizing step is generally performed by the following method. That is, 100 parts by weight of the ferromagnetic powder is preferably purged with an inert gas such as nitrogen gas, argon gas, or neon gas, and supplied to a kneading apparatus such as a roll mill, a kneader, or a continuous kneading mixer in an atmosphere having an oxygen concentration of 4% or less. It is carried out by charging, subsequently adding 0.03 to 10 parts by weight of an organic acid compound, and mixing and pulverizing for 0.1 to 1 hour.

The kneading, dispersing, organic solvent used in the application of the present invention, acetone, methyl ethyl ketone in any ratio,
Ketones such as methyl isobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran; alcohols such as methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol and methyl cyclohexanol; methyl acetate, ethyl acetate;
Ester systems such as butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, and glycol monoethyl ether; ether systems such as diethyl ether, tetrahydrofuran, glycol dimethyl ether, glycol monoethyl ether, and dioxane; Hensen, toluene, xylene, cresol, and chlor Tar-based (aromatic hydrocarbons) such as benzene and styrene; methylene chloride, ethylene chloride, carbon tetrachloride, chloroform,
Chlorinated hydrocarbons such as ethylene chlorohydrin and dichlorobenzene, N, N-dimethylformaldehyde, hexane and the like can be used.

The method of kneading is not particularly limited, and the order of addition of each component can be appropriately set. For the preparation of the magnetic paint (a back layer paint if a back layer is provided if necessary), a usual kneading machine, for example, a two-roll mill, a three-roll mill, a ball mill, a pebble mill, a tron mill, a sand grinder (Zegvari) Szegvari) attritor , High-speed impeller, disperser, high-speed stone mill, high-speed impact mill, disper, kneader, high-speed mixer, ribbon blender, co-kneader, intensive mixer, tumbler, blender, disperser, homogenizer,
A single screw extruder, a twin screw extruder, an ultrasonic disperser, or the like can be used. For details on the technology related to kneading and dispersion, see "Paint Flow and Pigment Dispersion" by TCPATTON (TCC Patton).
(Paint Flow and Pigment Dispersion) 1964 Published by John Wiley & Sons (John Wiley and Sons) and Shinichi Tanaka, "Industrial Materials" 25
Vol. 37 (1977) and the references cited in the book. It is also described in specifications such as U.S. Patent Nos. 2,581,414 and 2,855,156. Also in the present invention, the magnetic coating material and the back layer coating material can be prepared by kneading and dispersing according to the method described in the above-mentioned book or the cited document of the book.

The formation of the magnetic layer is performed by dissolving in an organic solvent any combination of the above compositions and the like, and coating and drying the coating solution on a support. When used as a tape, the thickness of the support is 2.5 to 1
It is preferably about 00 microns, preferably about 3 to 70 microns. 0.5 ~ 10m for disc or card
m, and in the case of a drum, it can be used in a cylindrical shape. Materials include polyesters such as polyethylene terephthalate and polyethylene naphthalate; polyolefins such as polypropylene; cellulose derivatives such as cellulose triacetate and cellulose diacetate; vinyl resins such as polyvinyl chloride; and plastics such as polycarbonate, polyamide and polysulfone. Metals such as aluminum and copper, and ceramics such as glass can also be used. Prior to coating, these supports are subjected to corona discharge treatment, plasma treatment, undercoat treatment, heat treatment, dust removal treatment,
Metal deposition treatment and alkali treatment may be performed. Regarding these supports, for example, West German Patent 3338854A, JP
No. 116926, U.S. Pat. No. 4,388,368; Yukio Mitsuishi, "Textiles and Industry", vol. 31, p. 50-55, 1975.

As a method of applying the magnetic layer and the back layer on the support, air doctor coating, blade coating,
Air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, kiss coat, cast coat, spray coat, etc. can be used, other methods are also possible, and these specific explanations are published by Asakura store 「Coating Engineering」 253
Pp. 277 (published in 1963).

According to such a method, the magnetic layer applied on the support is subjected to a treatment for orienting the ferromagnetic powder in the layer as needed, if necessary, and then the formed magnetic layer is dried. The transport speed of the support at this time is usually 10 m / min to 900 m
/ Min and the drying temperature is controlled between 20 ° C and 130 ° C. If necessary, the magnetic recording medium of the present invention is manufactured by performing a surface smoothing process or cutting into a desired shape.
These are described, for example, in Japanese Patent Publication No.
No. 28368, U.S. Pat. No. 3,473,960, and the like. The method disclosed in Japanese Examined Patent Publication No. 41-13181 is considered to be a basic and important technique in this field.

The ferromagnetic fine powder or non-magnetic powder, binder, additive, solvent and support (which may have an undercoat layer, a back layer, and a back undercoat) used for the present invention, or a method for producing a magnetic recording medium are as follows. It is described in JP-B-56-26890.

(Effect of the Invention) Surface treatment of ferromagnetic metal powder having a high stearic acid adsorption amount using a strong organic acid having a lower pKa than that of a fatty acid, and adsorbing the remaining adsorption points with the polar group of the polar group-containing binder. Improves dispersibility and improves C / N. On the other hand, the fatty acid is not adsorbed on the ferromagnetic metal powder due to the presence of the organic acid compound, and exhibits a sufficient function as a lubricant because it exists on the surface of the magnetic layer, and the μ value is reduced.

Further, since the organic acid compound is firmly adsorbed on the ferromagnetic metal powder, the magnetic layer is not plasticized, so that the running property can be improved and the occurrence of scratches on the tape can be prevented.

(Example) An example of the present invention and a comparative example will be described. A magnetic tape was prepared using the following composition as a basic composition. However,
The properties of the ferromagnetic metal powder, the types of the organic acid compound, the binder resin, the fatty acid, and the fatty acid ester and the mixing ratio thereof are shown in Table 1.

After the above-mentioned organic acid compound and the above-mentioned ferromagnetic metal powder were kneaded and dispersed for 1 hour using a ball mill, the remainder of the composition component was added thereto, and further kneaded and dispersed for 48 hours. After kneading and dispersing, 8 parts by weight of an isocyanate compound (manufactured by Bayer Corp., Desmodur L) was added thereto, and the mixture was further kneaded and dispersed for 1 hour, and then filtered using a filter having an average pore diameter of 1 μm to prepare a magnetic paint. . The thickness of the obtained magnetic paint is adjusted so that the thickness of the dried magnetic layer becomes 4.0 μm.
It was applied to the surface of a 0 μm polyethylene terephthalate support using a reverse roll.

The non-magnetic support coated with the magnetic paint is subjected to a magnetic field orientation treatment with a 3,000 gauss magnet in a state where the magnetic paint is not dried, and further dried and then subjected to a super calender treatment.
An 8 mm video tape was manufactured by slitting to an 8 mm width.

Coefficient of friction The obtained video tape and stainless steel pole are brought into contact with each other with a tension (T1) of 50 g (wrap angle 180 °), and under these conditions, the video tape is required to run at a speed of 3.3 cm / s. The tension (T2) was measured. Based on this measurement,
The friction coefficient μ of the video tape was determined by the following formula.

μ = 1 / π · 1n (T2 / T1) The friction coefficient test was conducted under the conditions of 20 ° C and 70% RH.

 The results are shown in FIG.

C / N ratio Using a commercially available 8mm video tape recorder (Fujix-8), record a 5MHz signal, and measure the noise generated within the range of 5 ± 1MHz when this signal is reproduced. The ratio of the reproduced signals was measured. The measurement is NV-870H
The measurement was performed using a D-type output level measuring device (manufactured by Matsushita Electric Industrial Co., Ltd.). The values shown are the values when the C / N ratio of the magnetic recording medium obtained in Comparative Example 1 is 0 dB.

 FIG. 1 shows the evaluation results.

Tape running scratches Using a commercially available 8 mm video tape recorder (Fujix-8), running scratches into the magnetic layer when running 500-minute play-REW (play-rewind) repeatedly for 1 minute were visually observed. The judgment of running scratches is as shown in the table below.

Storability was evaluated by the rate of change in residual magnetic flux density (Bm) when the sample was left in a thermostat at 60 ° C and 90% for 1 week.

The preservability (%) is better as the value is smaller, and worse as the value is larger.

FIGS. 1 to 4 show the results of measurements of the tape scratches, .mu. Values, C / N, and storability values of the magnetic recording media obtained under the conditions shown in Table 1 after running the VTR1P (pass). The μ value on the vertical axis in FIG. 2 is the μ value after 100 passes.

The sample corresponding to the present invention in FIGS.
No.2, No.3, No.7, No.8, No.9, No.10, No.12, No.13
It is. It can be seen that these samples are all well-balanced in terms of tape scratches, μ value, C / N and storage stability after running the VTR1P. Samples No. 1 and No. 17 not using an organic acid compound, Samples No. 4, No. 5, and No. 1 in which the pKa of the organic acid compound was out of the range of the present invention.
5, sample No.6 which does not have polar group in the binder, sample No.11, No.14, N where the fatty acid addition amount is out of range
o.15, Samples No.16 and No.17 using ferromagnetic metal powder with too low stearic acid adsorption amount, tape scratches,
The results are inadequate and unbalanced in terms of μ-value, C / N and preservation.

[Brief description of the drawings]

FIG. 1 to FIG. 4 show the tape scratches (durability), μ value (runnability), and C / N (electromagnetic conversion characteristics) storage after running the VTR1P (pass) corresponding to the samples of the examples and comparative examples. It is a figure which shows the effect of sex.

Claims (2)

(57) [Claims] 1. A magnetic recording medium comprising a nonmagnetic support and a magnetic layer comprising a ferromagnetic powder provided on the support dispersed in a binder, wherein the ferromagnetic powder comprises stearic acid per unit surface area. Is a ferromagnetic metal powder having an adsorption amount of 5.0 × 10 ⁻⁶ mol / m ² or more, and a surface treatment with at least one organic acid compound having an acid dissociation constant (pKa) of 4.0 or less. , wherein the binder is a polar _{group: -SO 3 M, -OSO 3 M} , -CO 2 M, -OPO 3 M 2, -PO 3 M 2 ( where M
Represents a hydrogen, alkali metal or ammonium salt. A magnetic recording medium comprising a polymer having at least one selected from the group consisting of: and a magnetic layer containing 0.3 to 5 parts by weight of a saturated fatty acid per 100 parts by weight of the ferromagnetic metal powder. 2. A stearic acid adsorption amount per unit surface area of 5.
PKa for ferromagnetic metal powder of 0 × 10 ⁻⁶ mol / m ² or more
After adding an organic acid compound of 4.0 or less and performing a surface treatment,
A method for producing a magnetic recording medium, comprising kneading and dispersing, and then adding and dispersing a polar group-containing binder to obtain a magnetic paint, and applying the magnetic paint on a nonmagnetic support.