JP2002304717A - Magnetic recording medium and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium and a method for manufacturing the medium having excellent electromagnetic transduction characteristics such as output characteristics and also having traveling reliability. SOLUTION: The medium has a magnetic layer and contains abrasive particles dispersed only in the surface area of the magnetic layer. The magnetic recording medium is manufactured by applying a coating material containing abrasive particles on the surface of the magnetic layer so as to disperse the abrasive particles only in the surface region of the magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a magnetic recording medium and a method for manufacturing the same.

[0002]

2. Description of the Related Art As digital recording systems have been developed on the premise that a magnetic recording medium of a vapor deposition type is used, compatible high output characteristics and high C / N (carrier / noise ratio) characteristics are obtained. The development of coated magnetic recording media has become an important theme in terms of productivity and production cost.

In such a coating type magnetic recording medium,
High output characteristics and high C / N equivalent to evaporation type magnetic recording media
In order to realize the characteristics, it is very important not only to smooth the surface of the medium but also to increase the filling ratio of the magnetic powder in the magnetic layer.

Further, a conventional coating type magnetic recording medium is
Usually, for the purpose of giving a self-cleaning effect, abrasive particles are contained in the magnetic coating film, and when this is not added, running reliability cannot be ensured.

[0005]

However, when abrasive particles are contained in a magnetic coating film as in the prior art, a predetermined number of abrasive particles are present on the surface of the magnetic layer. A considerable amount of abrasive particles must be added to the mixture. As a result, the packing ratio of the magnetic powder per unit volume in the magnetic layer is reduced, and it has been difficult to obtain high output characteristics and high C / N characteristics.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a magnetic recording medium having excellent electromagnetic conversion characteristics such as output characteristics and running reliability. It is to provide a manufacturing method thereof.

[0007]

That is, the present invention relates to a magnetic recording medium having a magnetic layer, wherein abrasive particles are distributed only in the surface area of the magnetic layer.

Further, the present invention relates to a method for manufacturing a magnetic recording medium, wherein a coating material containing abrasive particles is applied on a magnetic layer, and the abrasive particles are distributed only in a surface area of the magnetic layer.

According to the present invention, on the surface of the magnetic layer,
Since the coating containing the abrasive particles is applied to distribute the abrasive particles only in the surface area of the magnetic layer,
As in the prior art, a considerable amount of the abrasive particles of the magnetic powder was added to the magnetic layer in order to cause a predetermined number of the abrasive particles to exist on the surface of the magnetic layer. As compared with the above, the abrasive particles may be applied only in a necessary minimum amount in the surface area of the magnetic layer, and can be present at a uniform height. The magnetic recording medium that can be manufactured and obtained has excellent running reliability.

[0010] Further, since the abrasive particles are distributed only in the surface area of the magnetic layer, the abrasive particles need not be added to the magnetic paint forming the magnetic layer at all. It is possible to maintain a state where the filling rate of the magnetic powder is very high. For example, in the process of aligning the magnetic powder, the efficiency can be improved because there are no particles that hinder the alignment, and electromagnetic conversion characteristics such as high output characteristics can be obtained.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail based on embodiments.

Preferably, the abrasive particles are coated with a binder, and the abrasive particles are adhered on the surface of the magnetic layer, or at least a part of the abrasive particles are It is preferably embedded in the surface area of the magnetic layer. Thereby, the adhesion between the abrasive particles and the magnetic layer is improved, and the running reliability can be further improved.

The number of the abrasive particles present in the surface area of the magnetic layer is preferably 1 to 100/1 μm ² , and it is generally said that the number is less than 1/1 μm ² . The same thing as the insufficient amount of the abrasive particles may occur, and the running reliability may decrease. Also, 10
If it exceeds 0 particles / 1 μm ^2, the number of the abrasive particles becomes too large, and the electromagnetic conversion characteristics may be deteriorated.

As the non-magnetic inorganic powder as the abrasive particles, any conventionally known non-magnetic inorganic powder can be used.
For example, alumina (Mohs hardness 9), chromium oxide (9), silicon carbide (9), titanium oxide, silicon oxide (7), calcium carbonate (3), α-iron oxide (6) ), Kaolin (1-2.5), graphite (0.5-)
1), mica (2.8), titanium carbide, calcium phosphate (5), amorphous silica (7) and the like. Among these, it is more preferable to use one having a Mohs' hardness of 3 or more, and by setting it to 5 or more, a magnetic head made of several kinds of metal materials can be uniformly polished, and higher running reliability is obtained. be able to. In addition, one of the above nonmagnetic inorganic powders may be used alone, or two or more of them may be used in an appropriate combination.

The shape of the abrasive particles can be spherical, needle-like or plate-like, and is not particularly limited. In addition, in consideration of the smoothness when the paint containing the abrasive particles is applied, the particle size of the abrasive particles is a spherical shape having a major axis length of 0.35 μm or less if it is acicular. If so, the particle size is preferably 0.35 μm or less, and if it is plate-like, the diameter of the plate is preferably 0.35 μm or less, and the lower limit is preferably 0.02 μm. When the particle size is less than 0.02 μm, the dispersibility of the abrasive particles may decrease. When the particle size exceeds 0.35 μm, the space between the magnetic recording medium according to the present invention and the head becomes too large. In some cases, very high output characteristics cannot be obtained.

The magnetic layer mainly composed of a magnetic powder and a binder is coated on a non-magnetic support, and the magnetic layer contains the abrasive particles and the binder while the magnetic layer is in a dry state or a wet state. By applying a paint and then drying the paint, a magnetic recording medium according to the present invention can be manufactured. When the magnetic layer is in a dry state, when the paint containing the abrasive particles is applied, the abrasive particles can obtain a magnetic recording medium adhered on the surface of the magnetic layer, When the coating material is applied while the magnetic layer is in a wet state, it is possible to obtain a magnetic recording medium in which at least a part of the abrasive particles is embedded in a surface area of the magnetic layer.

The paint containing the abrasive particles includes:
In addition to the abrasive particles coated with the binder, a dispersant, a rust inhibitor and the like can be appropriately added, and these materials are the same as the respective compositions that can be contained in the magnetic paint described below. Can be used.

In order to apply the coating material containing the abrasive particles on the magnetic layer, the above-described constituent components of the coating material are dispersed in the binder, and depending on the type of the binder, etc. The coating material can be prepared by dispersing together with an organic solvent selected from ethers, esters, ketones, aromatic hydrocarbons, aliphatic hydrocarbons, and organic chlorine compound solvents. And when preparing the paint, a roll mill, a ball mill, a sand mill, a kneader,
The components may be dispersed and kneaded using an extruder, a homogenizer, an ultrasonic disperser or the like. When applying the coating material thus obtained on the magnetic layer, a gravure coater, knife coater, blade coater, reverse roll coater, die coater, or the like may be used.

In the method for manufacturing a magnetic recording medium according to the present invention, the paint containing the abrasive particles is applied on the surface of the magnetic layer, and the abrasive particles are applied only to the surface area of the magnetic layer. Since the abrasive particles are distributed, the abrasive particles only need to be applied in a necessary minimum amount in the surface area of the magnetic layer, and can be present at a uniform height. Can be manufactured,
The obtained magnetic recording medium according to the present invention is further excellent in running reliability.

Further, since the abrasive particles are distributed only in the surface area of the magnetic layer, the abrasive particles need not be added to the magnetic paint forming the magnetic layer at all. It is possible to maintain a state where the filling ratio of the magnetic powder is extremely high, and it is possible to obtain much higher electromagnetic conversion characteristics.

In the present invention, as the ferromagnetic powder constituting the magnetic paint, any conventionally known ferromagnetic powder can be used, and it may be an oxide magnetic powder or a metal magnetic powder. Examples of the oxide magnetic powder include γ-Fe ₂ O ₃ , Co-containing γ-Fe ₂ O ₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , Co-coated γ-Fe ₂ O ₃ , and Co-coated Fe ₃ O ₄ , CrO _{2 and the} like. Examples of the metal magnetic powder include Fe and C.
o, Ni, Fe-Co, Fe-Ni, Fe-Co-N
i, Co-Ni, Fe-Co-B, Fe-Co-Cr-
B, Mn-Bi, Mn-Al, Fe-Co-V and the like. Further, in order to improve these various characteristics, A
l, Si, Ti, Cr, Mn, Cu, Zn and other metal components and rare earth elements containing Y may be contained in appropriate amounts. Further, iron carbide such as Fe ₅ C ₂ , iron nitride and the like can also be used.
As the ferromagnetic powder, one of the above-mentioned materials may be selected, or two or more thereof may be used in combination.

A binder usable for the magnetic recording medium according to the present invention (this can be used as the binder among the constituents of the paint containing the abrasive particles in addition to the magnetic paint. Can be used, any of the resin materials usually used in this type of medium can be used, and the type thereof is not particularly limited. Typical examples of the binder resin include vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate-maleic acid copolymer, vinyl chloride-vinylidene chloride. Copolymer, vinyl chloride-acrylonitrile copolymer, acrylate-vinylidene chloride copolymer, methacrylate-vinylidene chloride copolymer, methacrylate-styrene copolymer, thermoplastic urethane resin, polyvinyl fluoride,
Vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, acrylonitrile-butadiene-methacrylic acid copolymer, polyvinyl butyral, polyvinyl acetal, cellulose derivative, styrene-butadiene copolymer, polyester resin, phenol resin, phenoxy resin, Epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, alkyd resins, urea-formaldehyde resins, and the like. Such binders include, at least in part, sulfonates (-SO
₃ M; M represents an alkali metal or alkyl group such as Na or K), sulfate (—SO ₄ M; M represents an alkali metal or alkyl group such as Na or K), carboxylic acid group, amino acid group , An aminosulfonic acid group, a phosphone group, a phosphine group, an amino group and the like are preferably introduced.

If necessary, a dispersant such as lecithin and an antistatic agent such as carbon black may be added to the magnetic paint. As the dispersant, antistatic agent, and rust inhibitor, any of conventionally known materials can be used, and there is no particular limitation. As the lubricant that can be used, any of conventionally known materials such as fatty acids and fatty acid esters can be used, and there is no particular limitation.

Further, a curable resin can be added to the magnetic paint in order to improve the durability. Specific examples include a thermosetting resin represented by a polyisocyanate compound and a polyepoxy compound, and an electron beam reactive curing resin. These can be used alone or in combination of two or more.

In order to form the magnetic layer on the non-magnetic support, the above-described constituents of the magnetic layer are dispersed in the binder, and ethers and esters are used depending on the type of the binder. The magnetic coating material can be prepared by dispersing together with an organic solvent selected from ketones, aromatic hydrocarbons, aliphatic hydrocarbons, and organic chlorine compound solvents. Then, when preparing the magnetic paint, by a roll mill, a ball mill, a sand mill, a kneader, an extruder, a homogenizer, an ultrasonic disperser, and the like.
What is necessary is just to disperse and knead the compounding components. When the magnetic paint thus obtained is applied onto the non-magnetic support, a gravure coater, knife coater, blade coater, reverse roll coater, die coater or the like may be used.

On the surface of the non-magnetic support on which the magnetic layer is not provided (rear surface), a back coat layer is provided for the purpose of improving the running properties of the magnetic recording medium, preventing charging and preventing transfer, and the like. Can be provided. The back coat layer is formed by, for example, dispersing solid particles such as an inorganic pigment in a binder (which may be basically the same binder as that which can be used for the magnetic layer), and the type of the binder. Is prepared by kneading together with an organic solvent selected according to the above, and applying this to the back surface of the non-magnetic support.

As the solid particles, any conventionally known materials can be used as long as they can impart an antistatic effect and a lubricating effect, and examples thereof include graphite, carbon black, and titanium oxide. These solid particles can be used alone or in combination of two or more.

As a material constituting the back coat layer, in addition to the solid particles and the binder, a dispersant as an additive, an abrasive, an antistatic agent and the like may be added. These additives are not particularly limited as long as they are materials generally used in this type of magnetic recording medium.

Examples of the nonmagnetic support include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate films, polyolefins, celluloses, vinyl resins, polyimides, polyamides and polycarbonates. Examples include a polymer support, a metal substrate made of an aluminum alloy, a titanium alloy, or the like, a glass substrate, an aramid film, and the like. The shape is not limited at all, and may be any shape such as a tape shape, a sheet shape, and a drum shape. Further, in order to control the surface properties, the non-magnetic support may be subjected to a surface treatment for forming fine irregularities.

It should be noted that the magnetic recording medium according to the present invention is not limited to the magnetic layer having a single layer, but may have a structure in which a plurality of magnetic layers are laminated. Further, a non-magnetic layer may be formed between the magnetic layer and the non-magnetic support, and an adhesive layer may be formed for the purpose of improving adhesiveness.

FIG. 1 shows that when the magnetic layer is in a wet state,
Fig. 3 shows an example of a method for producing a magnetic recording medium according to the present invention, in which the coating material containing the abrasive particles is applied.

First, the non-magnetic support 1 is coated with the magnetic powder and the magnetic layer 2 mainly composed of the binder, and the coating material containing the abrasive particles 3, the binder 4 and the solvent 5. Formed by As shown, the abrasive particles 3 are preferably coated with a binder 4.

Next, by performing a drying treatment, the solvent 5 of the paint is eliminated, the magnetic layer 2 is formed on the nonmagnetic support 1, and the abrasive particles 3 are distributed only in the surface area of the magnetic layer 2. And as shown, the abrasive particles 3
The magnetic recording medium according to the present invention, in which at least a part of the magnetic recording medium is buried in the surface area of the magnetic layer 2, can be manufactured.

Here, when the magnetic layer 2 is in a wet state, the above-mentioned paint containing the abrasive particles 3 can be applied, for example, by a wet-on-wet method. When this wet-on-wet method is applied, for example, as shown in FIG.
And a paint 7 containing abrasive particles 3 and two slits 10 and 11 for discharging the paints 6 and 7 toward the non-magnetic support 1. The two slits 10 toward the non-magnetic support 1 traveling in the direction of arrow A using the
From 11, the magnetic paint 6 and the paint 7 containing the abrasive particles 3 may be simultaneously discharged to form a coat of the paint 7 on the coat of the magnetic paint 6.

In the wet-on-wet method, the coating material 7 containing the abrasive particles 3 is applied on the wet coating film of the magnetic coating material 6. At least a part of the structure can be buried in the surface area of the magnetic layer 2, and in this case, the adhesion between the abrasive particles 3 and the magnetic layer 2 can be further improved, and the running reliability can be further improved. .

Further, at least a part of the abrasive particles 3 may not be buried in the surface area of the magnetic layer 2, but the whole of the abrasive particles 3 may be buried in the surface area of the magnetic layer 2. .

FIG. 3 shows that when the magnetic layer is in a dry state,
Fig. 3 shows an example of a method for producing a magnetic recording medium according to the present invention, in which the coating material containing the abrasive particles is applied.

First, a magnetic layer 2 mainly composed of the magnetic powder and the binder is formed on a non-magnetic support 1 by coating and dried. Thereafter, the paint containing the abrasive particles 3 coated with the binder 4 and the solvent 5 is applied onto the magnetic layer 2.

Next, by performing a drying treatment, the solvent 5 of the coating material is eliminated, the magnetic layer 2 is formed on the non-magnetic support 1, and the abrasive particles 3 are further deposited only on the surface area of the magnetic layer 2. A magnetic recording medium according to the invention can be produced in which the abrasive particles 3 are distributed and, as shown, are deposited on the surface of the magnetic layer.

The method for producing a magnetic recording medium according to the present invention comprises applying the above-mentioned paint containing abrasive particles 3 on the surface of the magnetic layer 2 so that the abrasive particles 3 are applied only to the surface area of the magnetic layer 2. Since the abrasive particles 3 are distributed, the abrasive particles 3 need only be applied in a necessary minimum amount in the surface area of the magnetic layer 2, and can be present at a uniform height. The magnetic recording medium according to the present invention, from which a medium can be manufactured and obtained, has further excellent running reliability.

Also, since the abrasive particles 3 are distributed only in the surface area of the magnetic layer 2, the abrasive particles 3 need not be added to the magnetic paint forming the magnetic layer 2 at all, and the magnetic layer 2
Can maintain a state in which the filling rate of the magnetic powder is extremely high, and can obtain much higher electromagnetic conversion characteristics.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

Example 1 First, a magnetic paint was prepared to have the following composition. [Magnetic paint composition] Fine ferromagnetic powder: 100 parts by weight of Fe-Co alloy (major axis length: 0.15 μm) Binder: 7 parts by weight of polyester-polyurethane (average molecular weight = 21000) Polar group: sodium sulfonate 0.12 mmol / G content Polyester main component; isophthalic acid-ethylene glycol urethanized isocyanate; diphenylmethane diisocyanate vinyl chloride copolymer (average degree of polymerization = 305) 8 parts by weight Polar group; potassium sulfate salt 0.08 mmol / g content Other major substitutions Group: Epoxy 0.8 mmol / g content Hydroxyl group 0.3 mmol / g content Nitrilotriacetic acid 3 parts by weight Lubricant: 1 part by weight of stearic acid 2 parts by weight of butyl stearate Solvent: 20 parts by weight of methyl ethyl ketone 20 parts by weight of toluene 10 parts by weight of cyclohexanone

The above materials are subjected to a kneading treatment with a continuous kneader, and further, methyl ethyl ketone, toluene,
After dilution with cyclohexanone, the mixture was dispersed in a sand mill to obtain a magnetic paint. The magnetic paint prepared as described above,
After adding 4 parts by weight of a polyisocyanate (a curing agent “Coronate L” manufactured by Nippon Polyurethane Co., Ltd.) and stirring, a polyethylene naphthalate film having a thickness of 6.0 μm as a non-magnetic support (Young's modulus in the tape running direction 6.0 GPa,
The film was applied on the film in such a manner that Young's modulus in the width direction was 10.0 GPa) so that the thickness after drying was 1.5 μm.

Next, a paint containing abrasive particles was prepared to have the following composition. [Coating composition for polishing layer] Inorganic powder: Alumina powder 100 parts by weight Alpha conversion = 85% Average particle size 0.08 μm Binder: Polyester polyurethane resin (number average molecular weight = 14000) 5 parts by weight Polar group: sodium sulfonate 0.08 mmol / g salt content Polyester main component; isophthalic acid, adipic acid-neopentyl glycol, ethylene glycol urethanized isocyanate; diphenylmethane diisocyanate Lubricant: 1 part by weight stearic acid 2 parts by weight butyl stearate Solvent: 70 parts by weight methyl ethyl ketone Toluene 70 parts by weight Cyclohexanone 40 parts by weight

The above-mentioned materials were dispersed in a sand mill to obtain the above-mentioned paint containing the above-mentioned abrasive particles.

After the abrasive coating is agitated, the abrasive coating is placed on the magnetic layer previously coated on the non-magnetic support while the magnetic coating is wet, and the surface of the dried magnetic layer is dried. It was applied so that the abrasive particles were present in an area equivalent to 1 particle / μm ² .

After the application of the paint containing the abrasive particles, the magnetic coating film was subjected to a magnetic field orientation treatment, dried appropriately, and wound up. Then, a calendering treatment was performed and a curing treatment was performed.

Thereafter, 20 parts by weight of a curing agent (Coronate L) was added to the coating material for the back coat having the following composition, and a thickness of 0.5 μm was formed on the nonmagnetic support surface opposite to the magnetic layer. To form a back coat layer. [Coating composition for back coat layer] Inorganic powder: carbon black-1 (average particle size = 0.02 μm) (manufactured by Cabot Corporation, trade name: BLACK PEARLS-L) DBP oil absorption = 105 cc / 100 g 95 parts by weight carbon black- 2 (Average particle size = 0.35 μm) (manufactured by COLUMBIAN, trade name: MT-C1) DBP oil absorption = 40 cc / 100 g 3 parts by weight Titanium oxide Average particle size = 0.4 μm 2 parts by weight Binder: polyester polyurethane ( 50 parts by weight Polar group; sodium salt of sulfonic acid 0.08 mmol / g Polyester main component; isophthalic acid, adipic acid-neopentyl glycol, ethylene glycol urethanized isocyanate; diphenylmethane diisocyanate nitrocellulose (Asahi Chemical Industry Co., Ltd.) Cellnova BTH 1/2) 30 parts by weight Hard Agent: polyisocyanate (Nippon Polyurethane Co., Coronate L) 10 parts by weight Lubricant: Stearic acid 1 part by weight butyl stearate 2 parts by weight Solvent: Methyl ethyl ketone 500 parts by weight Toluene 500 parts by weight

Thereafter, a sample tape was prepared by cutting to a width of 6.35 mm.

Example 2 The number of the abrasive particles was 50 particles / μm on the surface area of the magnetic layer.
^A sample tape was prepared in the same manner as in Example 1 except that the coating was carried out so that ² equivalents were present.

Example 3 The procedure of Example 1 was repeated, except that after the magnetic coating film was dried, the abrasive particles were applied so as to be present in an amount of 100 particles / μm ² on the surface area of the magnetic layer. A sample tape was prepared.

[0053] Example 4 The abrasive particles, 0.5 or the surface area of the magnetic layer / mu
A sample tape was prepared in the same manner as in Example 1 except that m ² was present in an amount equivalent to m ² .

[0054] Example 5 The abrasive particles, 120 / mu on the surface of the magnetic layer
A sample tape was prepared in the same manner as in Example 1 except that a corresponding amount of m ² was present.

Example 6 A sample tape was prepared in the same manner as in Example 1 except that the abrasive particles having an average particle size of 0.02 μm were used.

Example 7 A sample tape was prepared in the same manner as in Example 1 except that the abrasive particles having an average particle diameter of 0.35 μm were used.

Example 8 A magnetic paint was prepared to have the following composition. [Magnetic paint composition] Fine ferromagnetic powder: 100 parts by weight of Fe-Co alloy (major axis length: 0.15 μm) Binder: 8 parts by weight of polyester-polyurethane (average molecular weight = 21000) Polar group: sodium sulfonate 0.12 mmol / G content Polyester main component; isophthalic acid-ethylene glycol urethanized isocyanate; diphenylmethane diisocyanate vinyl chloride copolymer (average degree of polymerization = 305) 10 parts by weight Polar group; potassium sulfate salt 0.08 mmol / g content Other major substitutions Group: Epoxy 0.8 mmol / g content Hydroxyl group 0.3 mmol / g content Nitrilotriacetic acid 3 parts by weight Abrasive: Alumina powder 8 parts by weight Alpha conversion = 85% Average particle size 0.08 μm Lubricant: Stearic acid 1 part by weight Butyl stearate 2 parts by weight Solvent: methyl ethyl ketone 0 parts by weight Toluene 20 parts by weight Cyclohexanone 10 parts by weight

A sample tape was prepared in the same manner as in Example 1 except that a magnetic paint comprising the above-mentioned components was applied onto the non-magnetic support, and the paint containing the abrasive particles was not applied. Was prepared. The abrasive particles were prepared so as to be present in an amount of ² particles / μm ² on the surface of the magnetic layer.

Various measurements shown below were performed on each sample tape produced as described above.

The various measuring methods are as follows.・ The electromagnetic conversion characteristic (0.5μm wavelength signal output) is SON
A 1 / 2T signal was recorded on the tape to be measured using a Y DV DVR DCR-VX1000, and the reproduction output was measured.・ Driving reliability is VCR DCR-VX for Sony DV.
After running the tape to be measured 100 times continuously in an environment of 22 ° C. and 50% humidity using a 1000, the amount of RF output deterioration was measured. The one that ran without any abnormality was marked with “○”. The amount of abrasive particles present on the surface of the magnetic layer was observed using an AFM (atomic force microscope).

The results obtained by each of the above evaluation methods are summarized in Table 2 below.

[0062]

[Table 1]

As is clear from Table 1, each of the sample tapes of Examples 1 to 5 was prepared by applying the above-mentioned paint containing the above-mentioned abrasive particles on the above-mentioned magnetic layer, and applying the above-mentioned abrasive particles to the above-mentioned magnetic layer. The magnetic layer was distributed only on the surface area, and the abrasive particles were not internally added in the magnetic paint.Thus, compared with the case where the abrasive particles were contained in the magnetic paint, the magnetic layer was formed of magnetic powder. The filling rate was improved, high output characteristics could be obtained, and running reliability was excellent. Further, the number of the abrasive particles existing in the surface area of the magnetic layer is 1 to 100 / particle.
It can be seen that when the thickness is 1 μm ² , more stable running characteristics and higher output characteristics can be obtained as compared with the case outside the above range. Further, the abrasive particles have a particle size of 0.02 to 0.3.
It can be seen that when the thickness is 5 μm, a magnetic recording medium that can exhibit more excellent effects can be obtained.

In Example 6, the number of the abrasive particles existing in the surface area of the magnetic layer was 0.5 / 1 μm ² and 1/1.
Since it was less than μm ² , the magnetic layer was in direct contact with a traveling system such as a drive or a magnetic head, and traveling reliability was sometimes deteriorated.

In Example 7, the number of the abrasive particles existing in the surface area of the magnetic layer was 1200.5 / 1 μm ² ,
Since it exceeded 00 pieces / 1 μm ² , the output characteristics sometimes deteriorated.

In Example 8, the abrasive particles were added to the magnetic paint such that the abrasive particles existed at a rate of 2 particles / 1 μm ² on the surface of the magnetic layer. Although excellent, the filling rate of the magnetic powder in the magnetic layer was reduced, and the output characteristics were reduced.

[0067]

According to the present invention, the paint containing the abrasive particles is applied on the surface of the magnetic layer,
Since the abrasive particles are distributed only in the surface area of the magnetic layer, the abrasive particles may be applied only in a necessary minimum amount in the surface area of the magnetic layer, and at a uniform height. The magnetic recording medium can be efficiently produced, and the obtained magnetic recording medium has excellent running reliability.

Also, since the abrasive particles are distributed only in the surface area of the magnetic layer, the abrasive particles need not be added to the magnetic paint forming the magnetic layer at all, and the magnetic layer is It is possible to maintain a state where the filling rate of the magnetic powder is very high. For example, in the process of aligning the magnetic powder, the efficiency can be improved because there are no particles that hinder the alignment, and electromagnetic conversion characteristics such as high output characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method of manufacturing a magnetic recording medium according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a multilayer coating apparatus used for manufacturing a magnetic recording medium.

FIG. 3 is a diagram illustrating a method of manufacturing a magnetic recording medium according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support, 2 ... Magnetic layer, 3 ... Abrasive particles, 4 ...
Binder, 5 solvent, 6 magnetic paint, 7 paint containing abrasive particles, 8, 9 paint pool, 10, 11 slit, 12 die coater

Claims (15)

[Claims] 1. A magnetic recording medium having a magnetic layer, wherein abrasive particles are distributed only in a surface area of the magnetic layer. 2. The magnetic recording medium according to claim 1, wherein the abrasive particles are coated with a binder. 3. The magnetic recording medium according to claim 2, wherein the abrasive particles are attached on a surface of the magnetic layer. 4. The magnetic recording medium according to claim 2, wherein at least a part of the abrasive particles is embedded in a surface area of the magnetic layer. 5. The number of the abrasive particles is 1 to 100 /
^{2. The} magnetic recording medium according to claim 1, which is 1 μm ² . 6. The abrasive particles having a particle size of 0.02 to 0.5.
2. The magnetic recording medium according to claim 1, which has a thickness of 35 μm. 7. The magnetic recording medium according to claim 1, wherein the Mohs hardness of the abrasive particles is 3 or more. 8. A method for producing a magnetic recording medium, wherein a coating material containing abrasive particles is applied on a magnetic layer, and the abrasive particles are distributed only in a surface area of the magnetic layer. 9. The method according to claim 1, wherein the magnetic layer mainly composed of a magnetic powder and a binder is formed by coating on a non-magnetic support, and the abrasive particles and the binder are formed while the magnetic layer is in a dry state or a wet state. The method for manufacturing a magnetic recording medium according to claim 8, wherein the paint containing is applied, and thereafter, the paint is dried. 10. The method for manufacturing a magnetic recording medium according to claim 8, wherein the abrasive particles are coated with the binder. 11. The method for manufacturing a magnetic recording medium according to claim 10, wherein the abrasive particles are attached on a surface of the magnetic layer. 12. The method of manufacturing a magnetic recording medium according to claim 10, wherein at least a part of the abrasive particles is embedded in a surface area of the magnetic layer. 13. The method of manufacturing a magnetic recording medium according to claim 8, wherein the number of the abrasive particles is 1 to 100/1 μm ² . 14. The abrasive particles having a particle size of 0.02 to 0.02.
The method for manufacturing a magnetic recording medium according to claim 8, wherein the thickness is 0.35 µm. 15. The method for producing a magnetic recording medium according to claim 8, wherein the abrasive particles having a Mohs hardness of 3 or more are used.