JPH04330611A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium which does not generate head tapping, sticking of a magnetic tape, etc., and has high electromagnetic conversion characteristics even if the surface smoothness of a magnetic layer is enhanced as this layer is hard on the surface and is internally soft. CONSTITUTION:The Vickers hardness of the surface layer of the magnetic layer 2 on a nonmagnetic base 1 is 80 to 200 and the Vickers hardness of the inside layer of the above-mentioned magnetic layer is 40 to 150. Further, the Vickers hardness of the above-mentioned surface layer is of the value higher by >=10 than that of the above-mentioned inside layer.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to magnetic recording media such as magnetic disks, magnetic tapes, and magnetic sheets.

[0002] In recent years, there has been a demand for higher recording density in magnetic recording media, particularly in video magnetic recording media that require short wavelength recording. In order to obtain a medium capable of such high-density recording, it is necessary to improve the surface smoothness of the medium in order to prevent loss of RF output due to spacing between the medium and the head, as seen in Japanese Patent Application Laid-Open No. 2-177125. That's what I do.

However, if the surface smoothness of the medium is increased in order to improve the RF output, fatal problems such as poor running will occur when the medium is used for a long time under various environmental conditions (ie, temperature and humidity conditions). Conventionally, to solve this problem, lubricant was added to the magnetic layer, but
It was found that the following drawbacks could not be overcome.

That is, even when a lubricant is added to the magnetic layer, when the magnetic layer is pressed by the head or guide pin, the actual contact area increases, which causes an increase in the friction between the medium and the head or guide pin. Running becomes unstable, and sticking, edge bending, and magnetic head clogging are likely to occur.

[0005]

OBJECTS OF THE INVENTION An object of the present invention is to provide a magnetic recording medium with stable running properties and a smooth magnetic layer surface.

[0006]

Structure of the Invention and Its Effects The present invention provides a magnetic recording medium comprising a magnetic layer containing magnetic powder on a support, in which the surface layer of the magnetic layer has a Vickers hardness of 8.
0 to 200, the inner layer of the magnetic layer has a Vickers hardness of 40 to 150, and the surface layer has a Vickers hardness of 10 or more higher than that of the inner layer. Here, the surface layer is a layer in which when the triangular pyramidal needle for Vickers hardness measurement starts to be pushed in from the surface of the magnetic layer, a direct proportional relationship between the value of the load W and the value of the square of the indentation depth X continues. The inner layer refers to a region within the magnetic layer, and the inner layer is the area where W is formed again when the triangular pyramidal needle is further pushed through the surface layer.
This refers to the region in the magnetic layer where the value of X2 is directly proportional to the value of X2.

In order to improve the electromagnetic conversion characteristics of a magnetic recording medium, the present inventors have investigated running defects that occur when the surface smoothness of the magnetic layer is increased (in the case of magnetic tape, the adhesion between the head and the rotating cylinder is As a result of various studies on ways to prevent problems such as cracking of edges, clogging of magnetic heads, etc., we found that by keeping the hardness of the surface and inner layers of the magnetic layer within a specific range, these problems can be prevented. We have discovered that it is possible to prevent this from occurring.

For example, in magnetic tape, as the surface smoothness of the magnetic layer increases, especially under high temperature and high humidity conditions, sticking between the tape and the rotating cylinder becomes more likely to occur, and tape running becomes difficult. Becomes unstable. If this sticking becomes severe, the tape will eventually stop running.

Furthermore, as the surface smoothness of the magnetic layer of the magnetic tape increases, the contact area between the magnetic head, rotating cylinder, and guide pin increases. As a result, the coefficient of friction increases, which places a large load on the tape and causes the edges to break.Also, the magnetic head scrapes the surface of the tape magnetic layer, creating scratch lines on the tape side and scratches on the magnetic head side. Problems such as clogging occur.

On the other hand, if the hardness of the magnetic layer is increased in order to solve the above-mentioned problems, the contact of the magnetic tape against the head will become harder, which will amplify the minute vibrations that occur from various places during tape running, causing the tape to deteriorate. The phenomenon of hitting the magnetic head surface (head hitting) occurs. When this phenomenon occurs, the playback output becomes unstable and image quality abnormalities occur.

The magnetic tape according to the present invention has a hard surface layer;
Since the inner layer is soft, it is possible to eliminate all of the above-mentioned problems. In other words, the occurrence of sticking due to an increase in the surface smoothness of the magnetic layer, or the occurrence of edge bending, scratch lines, and head clogging due to an increase in the coefficient of friction, can be solved by increasing the hardness of the surface layer, and the head striking This problem was solved by lowering the hardness of the inner layer, which acts as a cushion and absorbs vibrations.

In the present invention, the above-mentioned Vickers hardness is defined as follows. That is, a diamond triangular pyramidal needle is pushed in by a piezoelectric actuator using the following indenter and under the following conditions. Indenter shape: 80 degree triangular indenter load
: 0.1mg ~ 0.15g Indentation speed: 1 ~ 25nm/sec Measurement environment
: 20~30℃/40~80%RH indentation depth
: Within 5μm from the surface

[0013] At this time, the load W
Letting the indentation depth at the time of indentation be X, and the hardness at depth ε be H(ε), the following equation holds true. W(X)=a∫H(ε)(X-ε)dε(a: constant) If it is a uniform material with no change in hardness, W(X)=1/2aHX2 Therefore, for the square of the indentation depth The graph of the load W(X) is a straight line, and H (Vickers hardness) can be determined from the slope.

When the magnetic layer according to the present invention is measured by the above method, the surface layer existing to a certain depth from the magnetic layer surface (X=0, ie, on the vertical axis) is subjected to the load W and the square of the indentation depth X are in the relationship of a straight line a. The thickness of the surface layer varies depending on the manufacturing conditions and cannot be generalized, but it is 0.
Preferably, the thickness is between 0.05 and 0.6 μm.

Next, when the indenter is further pushed through the surface layer, it eventually reaches the inner layer where W and X2 have a linear relationship again (straight line b in FIG. 3). There is an intermediate layer between the surface layer and the inner layer in which no linear relationship exists between W and X2, but this intermediate layer has a negligibly small thickness compared to the surface layer.

In the magnetic layer of the magnetic recording medium of the present invention, the Vickers hardness of the surface layer is 80 to 200, but 80
-150 is more preferable, and 90-120 is still more preferable. The inner layer has a Vickers hardness of 40 to 150, preferably 50 to 100, and more preferably 60 to 90. Further, the Vickers hardness of the surface layer needs to be 10 or more higher than that of the inner layer, preferably 15 to 50 higher, more preferably 20 to 40 higher.

[0017] Vickers hardness exceeds 200 at the surface layer;
Alternatively, if the hardness of the inner layer exceeds 150, the hardness of the magnetic layer becomes too high, causing head hitting, making the reproduction output unstable and causing image quality abnormalities. If the Vickers hardness of the surface layer is less than 80, the coefficient of friction on the surface of the magnetic layer increases, causing tape sticking, scratch lines, head clogging, etc. On the other hand, if the Vickers hardness of the inner layer is less than 40, the magnetic layer is weak, which tends to cause tape edge bending, increase in friction coefficient, head clogging, etc.

Furthermore, if the difference in hardness between the surface layer and the inner layer is less than 10, there will be no sufficient cushioning effect and head striking will occur, or the coefficient of friction will become high and running properties will become unstable.

To form the magnetic layer according to the present invention, various methods can be used to increase the density of the surface layer of the magnetic layer. It is preferable to use metal rolls for both the upper and lower rolls (steel calender) instead of the rolls. In order to achieve the purpose of the present invention, it is usually necessary to maintain the temperature at 50 to 140°C, the linear pressure at 50 to 400 kg/cm, and the C/S (coating speed) at 20 to 600 m/min in the above calendering step. preferable. Outside these numerical ranges, it may become difficult or impossible to specify the surface condition of the magnetic layer as in the present invention.

[0020] In addition to the above-mentioned steel calender, for example,
As a binder for the magnetic layer, which will be described later, there are two methods: a method of particularly strongly curing the surface layer using a moisture-curing type, an electron beam-curing type, or a photo-curing type resin, and a method of overcoating the magnetic layer with a hard resin such as acrylic resin. be.

As the magnetic powder that can be used in the present invention, commonly used ferromagnetic powders can be used, but ferromagnetic metal powders are particularly preferred. This ferromagnetic metal powder is a metal powder such as a simple substance such as Fe, Ni, or Co, or a metal powder mainly composed of Fe-Ni or Fe-Al-Ni, and Fe-based is preferable. These ferromagnetic metals are disclosed in paragraph number 0015 of JP-A-2-410458.

The above-mentioned ferromagnetic powder further has a particle size measured by X-ray of 200 Å or less, preferably 90 to 180 Å.
It is preferable to use one.

Particle size measurement using X-rays is carried out as follows. That is, using an X-ray analyzer and using the integral width of the (110) diffraction line of Fe, X-rays are measured using the Scherrer method using Si powder as a reference. Find the particle size.

In addition to the above, a more preferable structure of the ferromagnetic metal powder is that the content ratio of Fe atoms to Al atoms contained in the ferromagnetic metal powder is such that the atomic ratio is Fe:A.
l=100:1 to 100:20, and the content ratio of Fe atoms to Al atoms existing in a surface area of 100 Å or less in the analysis depth by ESCA of the ferromagnetic metal powder is Fe: It has a structure in which Al=30:70 to 70:30. Alternatively, Fe atoms, Ni atoms, Al atoms, and Si atoms are contained in the teachable metal powder, and further, at least one of Zn atoms and Mn atoms is contained in the ferromagnetic metal powder, and the content of Fr atoms is 90 atomic % or more, the content of Ni atoms is 1 atomic % or more and less than 10 atomic %,
The content of Al atoms is 0.1 atomic % or more and less than 5 atomic %, the content of Si atoms is 0.1 atomic % or more and less than 5 atomic %, the content of Zn atoms and/or the content of Mn atoms ( However, if it contains both Zn atoms and Mn atoms, the total amount) is 0.1 atomic % or more and less than 5 atomic %,
The depth of analysis by ESCA of the above ferromagnetic metal powder is 100.
The content ratio of Fe atoms, Ni atoms, Al atoms, Si atoms, Zn atoms and/or Mn atoms existing in the surface area of
n)=100:(4 or less):(10~60):(10~
70): ferromagnetic metal powder having a structure of (20 to 80).

Examples of magnetic powders that can be used in addition to the above-mentioned ferromagnetic metal powders include those shown in paragraph number 0014 of Japanese Patent Application No. 2-410458.

In the present invention, ferromagnetic powder having a specific surface area of 45 m 2 /g or more by the BET method is preferably used in response to higher recording density.

The specific surface area of the ferromagnetic powder in the present invention is expressed in square meters per unit gram, as measured by a specific surface area measurement method called the BET method. Regarding this specific surface area and its measurement method, see "Powder Measurement" (J.M. Dal).
Lavalle, Clydeorr Jr. (co-authored, translated by Benta et al.; published by Sangyo Toshosha).
Also, "Chemistry Handbook" Applied Edition, pages 1170-1171 (edited by the Chemical Society of Japan; published by Maruzen Co., Ltd. on April 30, 1960)
It is also stated. To measure the specific surface area, for example, heat the powder at around 105°C for 13 minutes while degassing it.
After removing the adsorbed material from the powder, the powder was introduced into the measuring device, the initial pressure of nitrogen was set to 0.5 kg/m2, and the nitrogen was heated at liquid nitrogen temperature (-105 °C) for 10 min.
Perform adsorption measurements in minutes. The measuring device is a counter soap (
(manufactured by Yuasa Ionics Co., Ltd.) was used.

[0028] The binder in the present invention is polyurethane,
polyester, vinyl chloride resin, etc., and these resins are preferably -SO3 M, -OSO3 M, -CO
Contains a repeating unit having at least one polar group selected from the group consisting of OM and -PO(OM')2 (where M' is a hydrogen atom or an alkali metal atom such as Na, K, or Li). and M is a hydrogen atom, Na, K,
It is an alkali metal atom such as Li or an alkyl group. )

[
The above polar group has the effect of improving the dispersion of the magnetic powder, and its content is from 0.1 to 8.0 mol% (more preferably from 0.5 to 6.0 mol%). When the content is less than 0.1 mol%, dispersibility decreases, and 8
．． When the amount is more than 0 mol%, the magnetic paint tends to gel. In addition, the weight average molecular weight is preferably 15,000 to 50
,000. The content of the binder in the magnetic layer is usually 10 to 40 parts by weight per 100 parts by weight of the ferromagnetic powder.
(preferably 15 to 30 parts by weight). In this case, the ratio of polyurethane and/or polyester to vinyl chloride resin is usually 90:10 to 10:90 (by weight).
Preferably it is within the range of 70:30 to 30:70).

In the present invention, when a vinyl chloride copolymer is used as a binder, a copolymer containing an OH group, such as a vinyl chloride-vinyl alcohol copolymer, and a polar group and a It can be synthesized by addition through reaction with a compound containing a chlorine atom. ClCH2 CH2 SO3 M, ClCH2 CH2 OSO3 M, ClCH2 PO(OM')2, ClCH2 COOM

Among these, ClCH2 CH2 SO
Taking 3Na as an example, it becomes as follows.

[0032] There is also a method of copolymerizing all of them using copolymerizable monomers. That is, a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced is injected into a reaction vessel such as an autoclave, and a general polymerization initiator such as BPO (benzoyl peroxide),
Polymerization can be carried out using a polymerization initiator such as a radical polymerization initiator such as AIBN (azobisisobutyronitrile), a redox polymerization initiator, an anionic polymerization initiator, or a cationic polymerization initiator. For example, specific examples of reactive monomers for introducing sulfonic acid or its salts include vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, p-
Examples include unsaturated hydrocarbon sulfonic acids such as styrene sulfonic acid and salts thereof. Furthermore, 2-acrylamide-
Sulfoalkyl esters of acrylic acid or methacrylic acid such as 2-methylpropanesulfonic acid, sulfoethyl (meth)acrylate, sulfopropyl (meth)acrylate, and salts thereof, or ethyl acrylate-2-sulfonate etc. can be mentioned.

[0033] Introduction of carboxylic acid or its salt (COO
When introducing M), (meth)acrylic acid, maleic acid, etc. may be used, and when phosphoric acid or a salt thereof is introduced, (meth)acrylic acid-2-phosphate ester may be used.

[0034] Furthermore, it is preferable that an epoxy group is introduced into the vinyl chloride copolymer. Introduction of epoxy groups improves the thermal stability of vinyl chloride copolymers. When introducing an epoxy group, the content of repeating units having an epoxy group in the copolymer is preferably 1 to 30.
mol% (more preferably 1 to 20 mol%). Glycidyl acrylate is preferably used as the monomer for introduction.

Regarding the introduction of polar groups into vinyl chloride copolymers, see JP-A-57-44227 and JP-A-57-44227.
No. 108052, No. 59-8127, No. 60-101
No. 161, No. 60-235814, No. 60-2383
No. 06, No. 60-238371, No. 62-12192
No. 3, No. 62-146432, No. 62-146433
There are descriptions in publications such as No., and these can also be used in the present invention.

Next, the synthesis of polyester and polyurethane resins among the binders according to the present invention will be described.

Polyesters are generally obtained by reacting polyols with polybasic acids. Using this known method,
A polyester (polyol) having a polar group can be synthesized using a polybasic acid having a polar group as a part of the polybasic acid.

Examples of polybasic acids include Japanese Patent Application No. 2-410
Those listed in paragraph number 0030 of Publication No. 458 can be used.

[0039] Polyesters having other polar groups introduced therein can also be synthesized by known methods.

[0040] Furthermore, for the synthesis of polyurethane resins, the reaction of polyol and polyisocyanate, which is a commonly used method, can be used. As the polyol component, generally used is a polyester polyol obtained by reacting a polyol with a polybasic acid. Therefore, by using the above polyester polyol having a polar group as a raw material, a polyurethane having a polar group can be synthesized. As an example of the polyisocyanate component, see paragraph number 0 of Japanese Patent Application No. 2-410458.
Those listed in 032 can be used.

As another method for synthesizing polyurethane, it can be synthesized by addition by reaction of polyurethane having an OH group with the following compound containing a polar group and a chlorine atom. ClCH2 CH2 SO3 M, ClCH2 CH2 OSO3 M, ClCH2 PO(OM')2, ClCH2 COOM

Regarding the introduction of polar groups into polyurethane, see Japanese Patent Publication No. 58-41565 and Japanese Patent Application Laid-open No. 57-9.
No. 2422, No. 57-92423, No. 59-81
There are descriptions in publications such as No. 27, No. 59-5423, No. 59-5424, and No. 62-121923, and these can be utilized in the present invention.

In addition to the above-mentioned resins, the following resins can be used as the binder in an amount of 20% by weight or less of the total binder.

[0044] As an example, Japanese Patent Application No. 2-410458
Paragraph No. 0036 of the publication is mentioned.

In order to improve the durability of the magnetic layer of the present invention, it is preferable to contain polyisocyanate. Examples of aromatic polyisocyanates that can be used include adducts of tolylein diisocyanate (TDI) and active hydrogen compounds. In addition, as the aliphatic polyisocyanate, hexamethylene diisocyanate (HM
There are also adducts of DI) and active hydrogen compounds. The weight average molecular weight of polyisocyanate is 100 to 3
,000 is preferred.

Other additives such as a dispersant, a lubricant, an abrasive, a matting agent, an antistatic agent, and a filler may be included as necessary.

As a dispersant, for example, Japanese Patent Application No. 2-4104
Those listed in paragraph number 0039 of Publication No. 58 are used. These dispersants are 0.5 to 5 for ferromagnetic powder.
It is preferable to add it within a range of % by weight.

As a lubricant, for example, Japanese Patent Application No. 2-410
Paragraph numbers 0040, 0041, 0042 of Publication No. 458
and 0043 are used.

[0049] As the abrasive, Japanese Patent Application No. 2-410458
The one shown in paragraph number 0044 of the publication is used.

As a matting agent, for example, JP-A-2-24
No. 9129, page 4, top right, line 10 to page 4, bottom left 4
The one shown in the row is used.

As the antistatic agent, for example, Japanese Patent Application No. 2-4
The material shown in paragraph number 0045 of Publication No. 10458 is used.

As the solvent to be added to the paint forming the magnetic layer, those described in paragraph number 0046 of Japanese Patent Application No. 2-410458 are used.

The magnetic paint used in the present invention is produced by kneading and dispersing ferromagnetic powder, binder, dispersant, lubricant, abrasive, antistatic agent, etc. in a solvent. Examples of kneading and dispersing machines used for kneading and dispersing magnetic paints include:
The material shown in paragraph number 0047 of Japanese Patent Application No. 2-410458 is used.

As the support for the above-mentioned magnetic recording medium, those shown in paragraph number 0048 of Japanese Patent Application No. 2-410458 are used.

As shown in FIG. 1, the magnetic recording medium of the present invention has a magnetic layer 2 on a non-magnetic support 1 such as polyethylene terephthalate, and if necessary, a magnetic layer 2 is provided on the opposite side of the magnetic layer. It has a structure in which a back coat layer (BC layer) 3 is provided. Further, an overcoat layer (OC layer) may be provided on the magnetic layer 2. Further, an undercoat layer (UC layer) may be provided between the magnetic layer and the support. Furthermore, the nonmagnetic support 1 may be subjected to a corona discharge treatment.

Next, an example of the above-mentioned medium manufacturing apparatus is shown in FIG. In this manufacturing apparatus, in manufacturing the medium shown in FIG. 1, the film support 1 fed out from the supply roll 32 is coated with the above-mentioned coating material for the magnetic layer 2 by the extrusion coater 10, and then coated with a coating material of, for example, 6500 Ga.
It is oriented by the front-stage orientation magnet 33 of the USS, and further introduced into a dryer 34 equipped with a rear-stage orientation magnet 35 of, for example, 6500 Gauss, where it is dried by blowing hot air from nozzles arranged above and below.

Next, the dried support 1 with each coated layer is
is led to a supercalender device 37 consisting of a combination of calender rolls 38, where it is calendered by metal rolls and then wound onto a winding roll 39. The magnetic paint may be supplied to the extrusion coater 10 through an in-line mixer (not shown). Note that arrow D in the figure indicates the direction of conveyance of the nonmagnetic base film.

[0058]

EXAMPLES The present invention will be explained below with reference to specific examples. The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention.

Examples 1 to 5, Comparative Examples 1 to 5 Ferromagnetic metal powder

100 parts by weight Fe-Al system, Fe
:Al=100 :5 (atomic ratio) - whole
Fe:Al=50:50
(Atomic ratio) - surface layer long axis: 0.16 μm, Hc
:1600Oe, BET specific surface area: 55m2/g,
Polyurethane containing sodium sulfonate group (Tg is shown in Table 1)
Reference) 10 parts by weight Vinyl chloride resin containing potassium sulfonate group
10 parts by weight (M manufactured by Nippon Zeon Co., Ltd.
R-110) α-alumina

8 parts by weight stearic acid

1 part by weight Butyl stearate

1 part by weight cyclohexanone
10
0 parts by weight methyl ethyl ketone

100 parts by weight toluene

10
0 parts by weight

[0060] The above composition was milled in a ball mill for 50 min.
The mixture was dispersed for a period of time, filtered through a 0.5 μm filter, and 5 parts by weight of a polyisocyanate compound (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to obtain a magnetic paint. This coating material was applied onto a non-magnetic support, then oriented (at 4000 Gauss) and dried, and calendered (calendering temperatures are shown in Table 1) to form a magnetic layer with a thickness of 2.5 μm. Thereafter, a back coat paint having the following composition was put into a ball mill, kneaded and dispersed for 70 hours, filtered through a 1 μm filter, and 20 parts by weight of a polyisocyanate compound (Coronate L manufactured by Nippon Polyurethane Co., Ltd.) was added to prepare the was applied to the opposite side of the magnetic layer to a thickness of 0.5 μm, and then coated to a thickness of 8 mm
An 8 mm videotape of each example was made by slitting the tape widthwise.

Coating liquid composition for back coat layer: Carbon black (A) (average particle size 30
nm) 70 parts by weight Carbon black (B) (average particle size 6
0nm) 30 parts by weight Nitrocellulose

30 parts by weight polyurethane resin
30 parts by weight
cyclohexanone

200 parts by weight methyl ethyl ketone

200 parts by weight toluene

200 parts by weight

Table 1 shows the details and evaluation results of each of the above examples. The method of performance evaluation is as follows.

(a) Average surface roughness (Ra) The Ra of the back coat layer was measured using a three-dimensional surface roughness meter (3F
K) (cutoff is 0.25 mm).

(b) Hit the head Using an 8mm video deck, record 50 minutes of 120-minute tape.
The tape is run repeatedly over the entire path length, and during this time it is observed whether any vibration occurs in the form of the tape hitting the magnetic head.

(c) Coefficient of dynamic friction (μK) Temperature 40°C
, Measure the tape tension at the inlet and outlet of the head cylinder at 20% humidity.

(d)
Using a video deck with a bent edge of 8mm, temperature 40℃, humidity 80%
A 120-minute tape was repeatedly run over its entire length for 100 passes, and it was observed whether or not the edges of the tape were bent.

[0067]

[0068]

As is clear from the above results, the magnetic tape of the present invention can suppress the occurrence of head knocking or edge bending while keeping the surface roughness of the magnetic layer the same as conventional products. It is possible to further increase the smoothness and improve the electromagnetic conversion characteristics.

[Brief explanation of drawings]

FIG. 1 is an example of a cross section of a multilayer coated magnetic recording medium.

FIG. 2 is an example of a magnetic recording medium manufacturing apparatus.

FIG. 3 is a graph showing the relationship between the load W on the magnetic layer and the indentation depth X during Vickers hardness measurement.

[Explanation of symbols]

1 Support 2 Magnetic layer 3 Back coat layer 10 Extrusion coater 13 Liquid pool 32 Supply roll 33 Pre-stage orientation magnet 34 Dryer 35　　　　Later orientation magnet 37 Super calendar device 38 Calendar roll 39 Take-up roll

Claims (1)

[Claims] 1. A magnetic recording medium comprising a magnetic layer containing magnetic powder on a support, wherein a surface layer of the magnetic layer has a Vickers hardness of 80 to 200, and an inner layer of the magnetic layer has a Vickers hardness of 80 to 200. 40-150
and further, a magnetic recording medium characterized in that the Vickers hardness of the surface layer is 10 or more higher than that of the inner layer (However, the surface layer refers to the surface of the magnetic layer when a triangular pyramidal needle for Vickers hardness measurement is used. The inner layer refers to a region in the magnetic layer where the direct proportional relationship between the value of the load W and the square of the indentation depth X continues when the indentation starts from When pushing the needle further, press W again.
(refers to the region in the magnetic layer where the value of X2 is directly proportional to the value of X2).