JP2002288815A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium excellent in the electromagnetic characteristics, such as an output level and a C/N, excellent in running durability and being enhanced volume recording density. SOLUTION: This medium is a magnetic recording medium such that a magnetic layer 2 is formed by the coating on a non-magnetic support 1 without through a non-magnetic layer, and the magnetic layer 2 contains a pigment 5 having the bigger average particle size than the thickness of the magnetic layer 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium.

[0002]

2. Description of the Related Art As the development of digital recording systems has progressed and the demand for high recording density media has increased, higher output and higher C
/ N (carrier / noise ratio) has become important to develop a coating type magnetic recording medium. As one of the techniques for obtaining high output and high C / N, a lower layer which is a nonmagnetic layer mainly containing a nonmagnetic powder and a binder is provided, and the lower layer is an undried magnetic layer. The method of applying
It is proposed in Japanese Patent Publication No. 6-93297.

In addition, the shortest recording wavelength used in the conventional format often falls within the range of about 0.3 to 1.0 μm. It is expected to become. In order to obtain sufficient characteristics at these wavelengths, a magnetic layer that is thin and has no change in thickness is required. Heretofore, many attempts to form such a magnetic thin layer have included a method of applying a magnetic paint simultaneously with a non-magnetic paint on a non-magnetic support (Japanese Patent Application Laid-Open No. H08-08258).
No. 339531).

[0004]

However, in the above-described method of providing a lower layer made of a nonmagnetic layer and an upper layer made of a magnetic layer on a nonmagnetic support, the upper layer is formed when the lower layer is in an undried state. Since the interface between the upper layer (magnetic layer) and the lower layer (non-magnetic layer) is mixed immediately after coating, the unevenness is generated to some extent, and it is difficult to sufficiently smooth the interface between the upper layer and the lower layer. In addition, the thickness of the magnetic layer is not sufficiently uniform. When recording or reproducing at a wavelength four times or more the thickness of the magnetic layer, sufficient output and C / N characteristics could not be obtained due to this effect.

[0005] In order to keep the state of the interface favorable and to eliminate the fluctuation of the thickness of the magnetic layer, it is most preferable that the magnetic layer is a single layer and is prepared and coated so as to be a thin layer. Work favorably. However, the magnetic layer is a single layer,
In addition, if the thickness is adjusted to be small, there is a problem that the reliability of the magnetic coating film, that is, the running reliability of the magnetic recording medium cannot be sufficiently ensured, for example, the lubricant cannot be contained in a large amount.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and its object is to provide an output, C
/ N, etc., and excellent running durability,
An object of the present invention is to provide a magnetic recording medium with an improved volume recording density.

[0007]

That is, according to the present invention, a magnetic layer is formed on a nonmagnetic support by coating without interposing a nonmagnetic layer, and the magnetic layer has a thickness greater than the thickness of the magnetic layer. The present invention relates to a magnetic recording medium containing a pigment having a large average particle size.

Here, the “average particle size” means a size obtained by averaging the major axes of 100 pigments.

According to the present invention, since the magnetic layer is formed on the non-magnetic support by coating without interposing the non-magnetic layer, an interface between the non-magnetic support and the magnetic layer is formed. Is sufficiently smooth, the thickness of the magnetic layer is sufficiently uniform, and the output characteristics and the C / N characteristics are excellent.

[0010] Further, since the magnetic layer contains the pigment having an average particle diameter larger than the thickness of the magnetic layer, the pigment intervenes as a contact point during running, and the magnetic coating film is used for a drive or the like. No direct contact with the running system or magnetic head,
Stable running performance can be obtained.

[0011]

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

When the thickness of the magnetic layer is Tm and the average particle size of the pigment is Φp, the relationship of Tm <Φp ≦ 2Tm is preferably satisfied, and more preferably 1.2Tm ≦ Φt.
More preferably, p ≦ 2Tm. By setting the upper limit of the average particle diameter Φp of the pigment to twice the thickness Tm of the magnetic layer, the spacing between the magnetic head and the surface of the magnetic layer can be further optimized, and the output characteristics and C / N
The characteristics can be further improved. In this case, if the average particle diameter Φp of the pigment exceeds twice the thickness Tm of the magnetic layer, the space between the magnetic recording medium according to the present invention and the head becomes too large, so that the output characteristics and C / N characteristics may not be obtained.

The Mohs hardness of the pigment is preferably 6 or more. By setting the Mohs hardness to 6 or more, the head made of several kinds of metal materials can be uniformly polished.
Higher running reliability can be obtained. If the Mohs' hardness of the pigment is less than 6, the polishing head may be made of a plurality of materials having different hardnesses, so that a difference in abrasion between the materials may occur and a step may be generated. As a result, the output characteristics may be degraded.

As the pigment, alumina, chromium oxide, silicon oxide, titanium oxide, silicon carbide, calcium carbonate, α-iron oxide, kaolin, graphite, mica, titanium carbide,
Amorphous silica and the like can be mentioned.

Preferably, the thickness of the magnetic layer is 0.3 μm or less. In the magnetic recording medium according to the present invention, the magnetic layer is formed by coating on the non-magnetic support without interposing the non-magnetic layer, and as described above, the thickness of the magnetic layer is reduced to 0. The output and the C / N characteristics can be further improved by forming the thin film as thin as 0.3 μm or less.

Further, the magnetic layer is formed by coating on the non-magnetic support without interposing the non-magnetic layer,
Further, even when formed as a thin layer, since it contains the pigment having an average particle size larger than the thickness of the magnetic layer, the pigment intervenes as a contact point during running, and the magnetic coating film is used as a drive. Therefore, a more stable traveling property can be obtained without directly contacting the traveling system or the magnetic head.

In the present invention, as the ferromagnetic powder constituting the magnetic coating material, any conventionally known ferromagnetic powder can be used, and a magnetic oxide powder or a metal magnetic powder may be used. 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.

As the binder that can be used in the magnetic recording medium according to the present invention, any resin material that is usually used in this type of medium can be used, and the type thereof is not particularly limited. Representative 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 resins, epoxy resins, thermosetting polyurethane resins, urea resins, melamine resins, Arikido resins, urea - is formaldehyde resins. Such a binder includes, at least in part, a sulfonate (—SO ₃ M; M represents an alkali metal such as Na or K or an alkyl group), a sulfate (—SO ₃ M).
₄ M; M represents an alkali metal such as Na or K or an alkyl group), at least one of a carboxylic acid group, an amino acid group, an aminosulfonic acid group, a phosphone group, a phosphine group, and an amino group. Is desirable.

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. When preparing the magnetic paint, the components may be dispersed and kneaded by a roll mill, a ball mill, a sand mill, a kneader, an extruder, a homogenizer, an ultrasonic disperser, or the like. When applying the magnetic paint thus obtained on the non-magnetic support, a gravure coater, a knife coater, a blade coater,
A reverse roll coater, a die coater, or the like may be used.

On the surface of the non-magnetic support on which the magnetic layer is not provided (the back surface), a back coat layer is provided for the purpose of improving the running properties of the magnetic recording medium, preventing electrification 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, an abrasive, an antistatic agent and the like as additives 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 non-magnetic 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, an adhesive layer may be formed between the magnetic layer and the nonmagnetic support for the purpose of improving so-called adhesiveness.

The surface of the magnetic layer may be a surface normally formed as a magnetic recording medium, and when expressed in terms of roughness, it is preferable that SRa measured by an optical interference method falls within a range of 2 nm to 20 nm. .

FIG. 1 is a schematic enlarged sectional view of a magnetic recording medium according to the present invention.

As shown in FIG. 1, the magnetic recording medium according to the present invention has a magnetic layer 2 formed on a non-magnetic support 1 without coating a non-magnetic layer. On the side of the non-magnetic support 1 on which the magnetic layer 2 is not provided (the back side),
The back coat layer 3 may be formed. Further, as described above, a configuration in which an adhesive layer is formed between the magnetic layer 2 and the nonmagnetic support 1 for the purpose of improving so-called adhesiveness may be employed.

As shown in the enlarged schematic sectional view of part A, the magnetic layer 2 having the magnetic powder 4 contains a pigment 5 having an average particle size larger than the thickness of the magnetic layer 2.

The magnetic recording medium according to the present invention has a magnetic layer 2
Is formed on the non-magnetic support 1 by coating without the non-magnetic layer, so that the interface between the non-magnetic support 1 and the magnetic layer 2 is kept sufficiently smooth. The thickness is sufficiently uniform, and the output characteristics and C / N characteristics are excellent.

Further, since the magnetic layer 2 contains the pigment 5 having an average particle diameter larger than the thickness of the magnetic layer 2, the pigment 5 intervenes as a contact point during running, and the magnetic coating film A stable running property can be obtained without directly contacting the running system or the magnetic head.

[0033]

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 iron-cobalt alloy metal magnetic powder (major axis length: 0.08 μm, specific surface area: 55 m ² / g) Binder: 10% by weight of polyester polyurethane resin (average molecular weight = 21000) Part (manufactured by Toyobo Co., Ltd.) Polar group; sulfonic acid sodium salt containing 0.12 mmol / g Polyester main component; isophthalic acid-ethylene glycol urethanized isocyanate; diphenylmethane diisocyanate vinyl chloride copolymer 10 parts by weight (manufactured by Nippon Zeon Co., Ltd. Name: MR-110) Nitrilotriacetic acid 3 parts by weight Pigment: C (see Tables 1 and 2 below) Lubricant: 2 parts by weight butyl stearate 2 parts by weight stearic acid Solvent: 20 parts by weight methyl ethyl ketone 20 parts by weight toluene 20 parts by weight cyclohexanone 10 Parts by weight

The above materials are kneaded 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 coating material prepared as described above was added with 2 parts by weight of a polyisocyanate (a curing agent “Coronate L” manufactured by Nippon Polyurethane Co., Ltd.), stirred, and then dried on a nonmagnetic support to a thickness of 0%. .34 .mu.m.

As the non-magnetic support, a polyethylene naphthalate film having a thickness of 6.0 μm was used (the same applies to the following examples).

Then, the magnetic coating film in an undried state 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, a coating material for a back coat layer having the following composition was applied to the surface of the non-magnetic support opposite to the magnetic layer to form a back coat layer. [Coating composition for backcoat layer] Inorganic powder: carbon black-1 (average particle size = 0.02 μm) (manufactured by Cabot Corporation, trade name: BLACK PEALS L 95 parts by weight carbon black-2 (average particle size = 0.27 μm) 3 parts by weight titanium oxide (average particle size = 0.4 μm) 2 parts by weight Binder: polyester polyurethane (number average molecular weight = 24000) 50 parts by weight (manufactured by Toyobo Co., Ltd.) Product name: UR-8200) 30 parts by weight of nitrocellulose (Celnova BTH 1/2 manufactured by Asahi Kasei Kogyo Co., Ltd.) Curing agent: 10 parts by weight of polyisocyanate (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) Lubricant: 1 part by weight of stearic acid 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 A sample tape was prepared in the same manner as in Example 1 except that the coating was performed so that the thickness of the magnetic layer was 0.3 μm.

Example 3 A sample tape was prepared in the same manner as in Example 1 except that the coating was performed so that the thickness of the magnetic layer was 0.25 μm.

Example 4 A sample tape was prepared in the same manner as in Example 1 except that the coating was performed so that the thickness of the magnetic layer was 0.22 μm.

Example 5 A sample tape was prepared in the same manner as in Example 1 except that the coating was performed so that the thickness of the magnetic layer was 0.2 μm.

Example 6 A sample tape was prepared in the same manner as in Example 1, except that the coating was performed so that the thickness of the magnetic layer was 0.184 μm.

Example 7 A sample tape was prepared in the same manner as in Example 1, except that the coating was performed so that the thickness of the magnetic layer was 0.175 μm.

Example 8 A sample tape was prepared in the same manner as in Example 1, except that the coating was performed so that the thickness of the magnetic layer was 0.5 μm.

Example 9 A sample tape was prepared in the same manner as in Example 1, except that the coating was performed so that the thickness of the magnetic layer was 0.4 μm.

Example 10 A sample tape was prepared in the same manner as in Example 1 except that the coating was performed so that the thickness of the magnetic layer was 0.35 μm.

Example 11 A sample tape was prepared in the same manner as in Example 1, except that the coating was performed so that the thickness of the magnetic layer was 0.16 μm.

Example 12 A sample tape was prepared in the same manner as in Example 1, except that the coating was performed so that the thickness of the magnetic layer was 0.15 μm.

Example 13 Pigment A was used in place of Pigment C, and the thickness of the magnetic layer was 0.1%.
A sample tape was prepared in the same manner as in Example 1 except that the coating was performed so as to have a thickness of 15 μm.

Example 14 A sample tape was prepared in the same manner as in Example 13, except that Pigment B was used instead of Pigment A.

Example 15 A sample tape was prepared in the same manner as in Example 14, except that the coating was performed so that the thickness of the magnetic layer was 0.09 μm.

Example 16 A sample tape was prepared in the same manner as in Example 13, except that Pigment D was used instead of Pigment A.

Example 17 A non-magnetic layer paint having the following composition was applied on a non-magnetic support so as to have a thickness of 1.5 μm, and the same magnetic paint as in Example 13 having a thickness of 0.15 μm. A sample tape was prepared in the same manner as in Example 1 except that the sample tapes were simultaneously coated such that

Example 18 A non-magnetic layer paint having the following composition was applied to a non-magnetic support so as to have a thickness of 1.5 μm, and the same magnetic paint as in Example 13 having a thickness of 0.2 μm. A sample tape was prepared in the same manner as in Example 1 except that the sample tapes were simultaneously coated such that

<Lower layer coating composition> Inorganic powder: α-iron oxide (major axis length = 0.1 μm) 100 parts by weight Binder: polyester polyurethane resin (number average molecular weight = 24000) 50 parts by weight (trade name, manufactured by Toyobo Co., Ltd.) : UR-8200) 15 parts by weight of vinyl chloride copolymer (average degree of polymerization = 305) (trade name: MR-110, manufactured by Zeon Corporation) Lubricant: 2 parts by weight of stearic acid 2 parts by weight of butyl stearate Solvent: Methyl ethyl ketone 70 parts by weight toluene 70 parts by weight cyclohexanone 40 parts by weight

Various measurements shown below were performed on each of the sample tapes manufactured as described above.

The various measuring methods are as follows. -The thickness of the coating layer was measured using a TESA thickness gauge.
The measurement was performed with the layers stacked.・ Electromagnetic conversion characteristics (wavelength 0.3 μm signal output and C / N)
Used a drum tester. Wavelength of 0.
A frequency (1 / T) at which a signal of 3 μm can be written is recorded at an optimum recording current, and a reproduction output of 1 / T and a wavelength of 0.
3 μm output and the frequency at that time 1 / 1.125T, 1
C / N was measured from the average of the noise at /0.9T.・ Reliability is VTR DCR for Sony SONY DV
Using a -VX1000, recording and reproduction of the camera was repeated 100 times, and those in which a block error or abnormal reproduction occurred were evaluated as x, and those in which there was no abnormality in image quality or the like were evaluated as ○.

The results obtained by each of the above evaluation methods are summarized in Table 2 below. FIG. 2 shows the results of the output evaluation, the C / N evaluation, and the running reliability evaluation when the pigment C was used (Examples 1 to 12).

[0061]

[Table 1] * Examples of the organic filler as the pigment D in Table 1 include phthalocyanine pigments.

[Table 2]

As is clear from Table 2 and FIG. 2, each of the sample tapes according to Examples 1 to 7 has the magnetic layer formed by coating on the non-magnetic support without interposing the non-magnetic layer. Therefore, compared with the case where the nonmagnetic layer is provided, the interface between the nonmagnetic support and the magnetic layer is kept sufficiently smooth, the thickness of the magnetic layer is sufficiently uniform, and the output characteristics and C / C The N characteristics were excellent. Further, the magnetic layer contains a pigment having an average particle diameter larger than the thickness of the magnetic layer, and Tm <Φp (Tm is the thickness of the magnetic layer, Φp
Is the average particle diameter of the pigment), so that the pigment intervenes as a contact point during traveling and the magnetic coating film comes into direct contact with a traveling system such as a drive or a magnetic head, as compared with the case of Tm ≧ Φp. Therefore, a more stable running performance can be obtained, and an epoch-making result that no block error or abnormality at the time of reproduction is completely eliminated is obtained. Moreover, if the upper limit of the average particle size of the pigment is Φp ≦ 2Tm, Φp> 2T
As compared with the case of m, the spacing between the magnetic head and the surface of the magnetic layer can be further optimized, and both the output characteristics and the C / N characteristics are greatly improved.

The sample tapes according to Examples 8 to 10
Since the average particle size of the pigment was smaller than the thickness of the magnetic layer, the output characteristics and C / N characteristics were excellent, but the magnetic layer was in direct contact with a traveling system such as a drive or a magnetic head, Running reliability has deteriorated.

The sample tapes of Examples 11 and 12 had excellent running reliability because the average particle size of the pigment exceeded twice the thickness of the magnetic layer. Was too large, the output characteristics and C / N characteristics were sometimes reduced.

As apparent from Table 2, Examples 13, 14 and 15 in which the Mohs hardness of the pigment was 9 or 6 were obtained.
For the sample tape of Example 16, the sample tape of Example 16 is
Since the Mohs hardness of the pigment was less than 6, the output characteristics sometimes deteriorated due to uneven wear of the head material.

In the sample tapes of Examples 17 and 18, since the nonmagnetic layer was provided, the interface was disturbed.
C / N characteristics deteriorated.

In the above-described embodiment, the example in which the magnetic layer is provided directly on the nonmagnetic support has been described. However, the magnetic recording medium according to the present invention has a structure in which the magnetic layer is a single layer. The present invention is not limited to this, and a plurality of magnetic layers may be stacked. Further, an adhesive layer may be formed between the magnetic layer and the nonmagnetic support for the purpose of improving so-called adhesiveness.

[0068]

According to the present invention, since the magnetic layer is formed on the non-magnetic support by coating without interposing the non-magnetic layer, the non-magnetic support and the magnetic layer Interface is kept sufficiently smooth, the thickness of the magnetic layer is sufficiently uniform, and the output characteristics and C / N characteristics are excellent.

Further, since the magnetic layer contains the pigment having an average particle diameter larger than the thickness of the magnetic layer, the pigment intervenes as a contact point during running, and the magnetic coating film is used for a drive or the like. No direct contact with the running system or magnetic head,
Stable running performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic enlarged sectional view of a magnetic recording medium according to the present invention.

FIG. 2 is a graph summarizing output characteristics, C / N characteristics, and results of running reliability evaluation of each sample tape in the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Non-magnetic support, 2 ... Magnetic layer, 3 ... Back coat layer,
4: magnetic powder, 5: pigment

Claims (5)

[Claims] A magnetic layer is formed on a nonmagnetic support by coating without a nonmagnetic layer, and the magnetic layer contains a pigment having an average particle size larger than the thickness of the magnetic layer. A magnetic recording medium characterized by the above-mentioned. 2. The relationship of Tm <Φp ≦ 2Tm, and 1.2Tm ≦ Φp ≦ 2Tm, where Tm is the thickness of the magnetic layer and Φp is the average particle size of the pigment. 2. The magnetic recording medium described in 1. above. 3. The Mohs hardness of the pigment is 6 or more,
The magnetic recording medium according to claim 1. 4. The magnetic recording medium according to claim 1, wherein said magnetic layer has a thickness of 0.3 μm or less. 5. The magnetic layer has a surface average roughness SRa of 2 to 5.
2. The magnetic recording medium according to claim 1, which has a thickness of 20 nm.