JPH03173922A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To enhance the traveling property of the medium, a head cleaning effect and light shieldability by incorporating respectively prescribed abrasive into the uppermost layer and lower layers of magnetic layers and incorporating specific iron oxide into the lower layers. CONSTITUTION:The medium is formed by laminating the magnetic layers consisting of >=1 layers of the lower layer 2 and the uppermost layer 4 on a nonmagnetic substrate 1. The abrasive (e.g. alpha-alumina) particles and zirconia particles of >=6 Moh's hardness are incorporated into the layer 4 and substantially only the zirconia particles are incorporated into >=1 layers of the layers 2. In addition, the iron oxide consisting of a bivalent iron component (Fe<2+>) and a tervalent iron component (Fe<3+>) at the ratio thereof specified within the range of formula is incorporated into >=1 layers of the layers 2. Fe3O4 containing Co satisfying the above-mentioned formula, etc., are usable as the above-mentioned iron oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

Prior art - In JIQ, magnetic recording media such as magnetic tape are made of magnetic powder,
It is manufactured by applying a magnetic paint made of a binder resin or the like onto a support and drying it. Since conventional magnetic recording media have only one magnetic layer, it is necessary to cover a wide frequency band from low to high frequencies with one type of magnetic powder.

In particular, with the recent trend toward higher recording densities, magnetic powders with high Hc and high BET values are used because recording characteristics in high frequencies are improved and low noise is required.

However, since magnetic recording media are composed of a single type of magnetic powder (magnetic layer), high-H
c. Since it is necessary to use magnetic powder with a high BET value, the low-frequency characteristics may be insufficient.

On the other hand, in magnetic recording media for video, it is possible to increase the magnetic recording capacity, or to improve both the magnetic recording characteristics of the medium in the high frequency range and the low frequency range. A medium having multiple magnetic layers has been proposed in order to increase the
-98803, JP 59-172142, JP 32-2218, JP 51-64901, JP 56-12937, JP 58-56228, JP 63-146211 Publications, etc. 1゜According to these known techniques, relatively fine magnetic powder is used in the upper layer of the magnetic layer, and larger magnetic powder is used in the lower layer, the upper layer receives video output, and the lower layer receives chroma/audio output. It was designed to carry.

Generally, in magnetic recording media, an abrasive (eg, α-alumina) is added to the magnetic paint to improve the durability of the f'tl layer. In this case, the durability is further improved as the particle size of the abrasive is increased.

However, on the other hand, due to the large particle size of the abrasive,
The surface of the magnetic layer becomes rough, causing problems such as a decrease in output and an increase in noise, which deteriorates electromagnetic conversion characteristics.

On the other hand, as the magnetic substance (magnetic powder) contained in the magnetic layer, 2
The iron content (F e 2 + ) is 3.5 in terms of FeO.
~lO wt%, F e ''/F e '' is 0.04 ~
CO-containing 7-F containing 0.123 (4-12.3%)
e, ○.

is shown in Japanese Patent Application Laid-Open No. 61-61230. Also, JP-A-64-19524, JP-A-64-8632
No. 1, JP-A-64-13225, JP-A-63-300
No. 425 contains FeOx (however, 1.
33≦X≦1.50).

As magnetic powder, Fe'' is Fe2°/Fe''~0.
Compared to Co-T-Fez 03, which has a ratio of 001 to 0.1, Fe"
Co-containing iron oxide having a large content of 3 to 0.45 is called magnetite type (Fe:+04) and is composed of FeO and Fezes.

These magnetite-type Co-containing iron oxides generally have a black color and have good light-shielding properties (thus, the amount of carbon black added to the medium can be reduced), and electron exchange between Fe'' and Fe'' is possible. It has excellent properties such as being easy to use, reducing the surface resistivity of the magnetic layer, and exhibiting a value of coercive force (Hc) that is advantageous for chroma output and the like.

However, when a magnetite-type Co-containing iron oxide is used, the adsorption of fatty acids to the magnetic material increases because the proportion of Fed (Fe'') increases.

For this reason, it is difficult to control the fatty acids leached onto the surface of the medium, which increases the coefficient of friction and tends to cause poor runnability of the medium, particularly at high temperatures and under high temperatures. Also,
Magnetite type Co-containing iron oxide has low abrasive power, so if it is used in a magnetic layer, it will have poor durability, and the electromagnetic conversion characteristics will deteriorate due to defects such as staining the magnetic head.

The purpose of the present invention is to improve running performance, improve durability, and improve head cleaning while taking advantage of the features of magnetite type magnetic material in a magnetic recording medium having a magnetic layer consisting of multiple layers. effects, etc., and improve light-shielding properties.
The goal is to realize electromagnetic conversion characteristics.

20 Structure of the Invention That is, in the present invention, a magnetic layer formed by dispersing magnetic powder in a binder is formed by an uppermost layer and a lower layer consisting of at least one layer, and the uppermost layer is coated with an abrasive having a Mohs hardness of 6 or more. particles and zirconia particles, at least one layer of the lower layer contains substantially only zirconia particles as abrasive particles, and the magnetic material contained in at least IN of the lower layer is made of iron oxide. The ratio of the divalent iron component (Fe'') and the trivalent iron component (Fe'') in this iron oxide is 0.13≦Fe 2 + / Fe 2 + ≦0.45.
This relates to a magnetic recording medium. Here, the above-mentioned "substantially" means 100% of zirconia particles, and
It also means a case where a small amount (1.0% by weight or less) of other abrasive particles is also contained.

In the magnetic recording medium of the present invention, the magnetic layer is composed of a plurality of layers (the uppermost layer and at least one lower layer), and the magnetic powder contained in at least one of the lower layers is of the magnetite type according to the present invention, for example. CO-containing Fes
Os (F e”/F e”~0, 13~0.45
). Magnetic powders that can be used for the top layer or other lower layers other than those listed above include r-Fe, O, Co
Contains iron oxide magnetic powder such as y7Fe203 HFe, Ni, C
o, Fe-N1-C.

Alloy, Fe-Ni alloy, Fe-Aj! Alloy, Fe-Al
! , -Ni alloy, Fe-A/! -Co alloy, Fe-Mn
-Zn alloy, Fe-Ni-Zn alloy, FeAn-Ni-
Co alloy, Fe-An-Ni-Cr alloy, Fe-An-
Go-Cr alloy, Fe-C.

Ni-Cr alloy, Fe-Co-Ni-P alloy, Co-
Examples include various ferromagnetic powders such as metal magnetic powders mainly composed of Fe, Ni, Co, etc. such as Ni alloys.

The above magnetite type magnetic powder (fftl, 0.
By containing 13≦Fe2+/Fe''≦0.45) in the lower layer, the entire magnetic layer exhibits sufficient light-shielding properties, and furthermore, the surface resistivity is reduced). The amount of carbon black added can be reduced or eliminated.As a result, the amount of carbon black added to the magnetic layer can be reduced, resulting in improved electromagnetic characteristics. However, this is no longer necessary, and the back coat layer itself can be omitted.In addition, magnetite type iron oxide magnetic material has Hc which is advantageous for chroma output, etc., and is suitable as the lower layer magnetic powder. be.

On the other hand, in the present invention, if the magnetite type iron oxide magnetic material is contained not in the entire magnetic layer but only in the lower layer side, the surface properties of the layer (especially the top layer) using a magnetic material other than the magnetite type are improved. , it has good dispersibility and can maintain the electromagnetic conversion characteristics of the medium. In this case, if the surface of the nonmagnetic support on the magnetic layer side is made smooth,
The outermost surface of the magnetic layer also becomes relatively flat, making it possible to improve electromagnetic conversion characteristics.

Magnetite type iron oxide magnetic material has the property of adsorbing fatty acids to a large extent, but since the lower layer containing the magnetic material contains only zirconia (ZrO = particles) as abrasive particles, the amount of fatty acid adsorption is reduced. In other words, it is thought that zirconia interferes with the adsorption of fatty acids to the magnetite-type iron oxide magnetic material and facilitates the movement of fatty acids toward the surface of the magnetic layer.As a result, Since the coefficient of friction on the surface of the medium is reduced, the running properties of the medium are improved.The reason why only zirconia particles are included as an abrasive in the lower layer is that, in addition to the above, it is necessary to include other abrasive particles. Even if the amount of added acid is reduced, there is no problem in maintaining runnability because fatty acids are supplied from the bottom layer as mentioned above.
The amount of magnetic powder packed can be increased by the amount that can be added by reducing the amount added, which is also advantageous in terms of electromagnetic conversion characteristics.

In the present invention, hard particles with a Mohs hardness of 6 or more and zirconia particles are used together as abrasive particles in the uppermost layer of the magnetic layer. Even when a magnetite type iron oxide magnetic material is used, the durability of the top layer is increased. As a result, a head cleaning effect etc. can be obtained for the magnetic head. In particular, in a medium provided with a magnetic layer consisting of multiple layers as in the present invention, the top layer of the magnetic layer is extremely thin (usually 1.5 μm or less), so the durability of the top layer tends to decrease. The hard abrasive mentioned above provides sufficient durability of the top layer. The zirconia particles used together with the hard particles also act to contribute to the movement of fatty acids to the surface, as described above.

In the present invention, the ratio of Fe" in the magnetite type magnetic material is 0.20≦Fe"''/Fe3+≦0.4
1<, 0.25≦Fe2+/Fe3+≦0.38
is even more desirable. F of this magnetite type magnetic material
As a method of controlling the ratio of e"°, the ratio of Fe" is changed by controlling oxidation by changing the firing temperature and time in the step of generating oxides. .

Furthermore, in order to incorporate the above-mentioned zirconia particles into the magnetic layer, the zirconia particles can be added or contained in the coating material for forming each layer of the magnetic layer. The average particle size of the zirconia particles is 0.01 to 30 am.
(lower layer), 0.01-30 pm (top layer), 0.02-10 μm (lower layer), 0.0
5 to 15 am (uppermost N) is more preferred.

In addition, the amount added is 0.01 to 1 per 100 layers of magnetic powder.
Parts by weight (lower layer), 0.01-1 parts by weight (top layer), 0.05-0.8 parts by weight (lower layer), 0.05-1
0.8 N parts (top layer) is more preferable;
For example, α-alumina (Mohs hardness 9), nichrome trioxide (Mohs hardness 9), titanium dioxide (Mohs hardness 6.5),
), tin dioxide (Mohs hardness: 6.5), α-iron oxide, silicon dioxide (Mohs hardness: 7), silicon nitride, silicon carbide, zinc oxide, cerium oxide, magnesium oxide, boron nitride, and the like. Preferred abrasives are α-alumina, CrzO,. The average particle size of such abrasives is preferably 0.1 to 1.0 pm, and preferably 0.2 to 0.0 pm.
6 pm is more preferred. The amount added is magnetic powder 10
It is preferably 1 to 20 parts by weight, more preferably 3 to 10 parts by weight per 0 parts by weight.

The magnetic recording medium of the present invention uses relatively fine magnetic powder in the uppermost layer of the magnetic layer and larger magnetic powder (magnetite type) in the lower layer, so that the uppermost layer receives video output and the lower layer receives chroma and It can be designed to handle audio output.

Among the magnetic layers in the present invention, the thickness of the uppermost layer is 0.1
=1. It is more desirable that Oam is < 0.1 to 0.5 pm. The thickness of the lower layer below this top layer is 1.5 to 4.0
The thickness is preferably 1.5 to 3.0 μm, more preferably 1.5 to 3.0 μm.

In the present invention, it is desirable that the plurality of layers (the uppermost layer and the lower layer) constituting the magnetic layer are adjacent to each other. However, in addition to cases where there is substantially a clear boundary between each layer, there may also be a boundary area where magnetic powder from both layers coexist at a certain thickness; The removed upper or lower layer is each of the above layers. In particular, the media of the invention can be applied by wet simultaneous multilayer coating (net-on-coating) of each magnetic layer.
It is suitable for coating and forming using the net method. Of course, a wet-on-dry method may also be used in which the upper layer is applied after drying the lower layer.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
Non-magnetic support 1 made of polyethylene terephthalate cap
A first magnetic layer 2 and a second magnetic layer 4 are laminated thereon in this order. Further, although a bank coat layer 3 is provided on the support surface opposite to this laminated surface, this need not necessarily be provided. An overcoat layer may be provided on the second magnetic layer. In the example of FIG. 2, the upper layer is further divided into layers 5 and 6. The outermost magnetic layer 4.6 and the other magnetic N2.5 (and/or 2) are based on the present invention,
The former 4.6 is the top layer, and the latter 2.5 or 5 and 2 are the lower layers.

In the magnetic recording medium of FIGS. 1 and 2, the thickness of the first magnetic N2 is 1.5 to 4.0 μm (for example, 3.0 μm)
It is preferable that the film thickness of the second magnetic layer 4 or the second
, the total film thickness of the third magnetic M5.6 is 0.1 to 1.5 μ
m (for example, 0.75 μm).

The magnetic layer 2.4.5.6 contains the above-mentioned magnetic powder and abrasive particles, but each magnetic layer also contains a lubricant (for example, fatty acid (for example, stearic acid), fatty acid ester, etc.),
Antistatic agents (e.g. carbon black, graphite)
, a dispersant (for example, powdered lecithin), etc. may be added. Regarding fatty acids and/or fatty acid esters as lubricants, the fatty acids may be monobasic or dibasic.

Fatty acids having 6 to 30 carbon atoms, more preferably 12 to 22 carbon atoms, are preferred. Examples of fatty acids are as follows.

(1) Caproic acid (2) Caprylic acid (3) Capric acid (4) Lauric acid (5) Myristic acid (6) Pargotic acid (7) Stearic acid (8) Isostearic acid (9) Rilunic acid (10) Linoleic acid (11) Oleic acid (12) Elaidic acid (13) Behenic acid (14) Malonic acid (15) Succinic acid (16) Maleic acid (17) Glutaric acid (18) Adipic acid (19) Pimelic acid (20) Azelaic acid (21) Sebacic acid (22) 1,12-dodecanedicarboxylic acid (23
) Octane dicarboxylic acid Examples of the above fatty acid esters are as follows.

(1) Oleyl oleate (2) Oleyl stearate (3) Isocetyl stearate (4) Dioleyl maleate (5) Butyl stearate (6) Butyl balmite-1, (7) Butyl myristate (8) Octyl myristate (9) Octyl palmitate (10) Amyl stearate (11) Amyl palmitate (12) Isobutyl oleate (13) Stearyl stearate (14) Lauryl oleate (15) Octyl oleate (16) Isobutyl oleate (17) Ethyl oleate (1B) Isotridecyl oleate (19) 2-ethylhexyl stearate (20)
2-Ethylhexyl myristate (21) Ethyl stearate (22) 2-Ethylhexyl palmitate (23) Isopropylpal 2-I (24) Isopropyl myristate (25) Butyl laurate (26) Cetyl-2-ethyl Hexalate (27) Dioleyl adipate (28) Diethyl adipate (29) Diisobutyl adipate (30) Diisodecyl adipate When using the above fatty acids and fatty acid esters together, it is possible to use them alone while exerting their respective characteristics. can. In this case, the amount of fatty acid added is preferably 0.2 to 10 parts by weight, and even more preferably 0.5 to 8.0 parts by weight, per 100 parts by weight of fR lees flour. If the fatty acid content falls outside of this range, the dispersibility of the magnetic powder decreases, and the runnability of the medium tends to decrease, and if the fatty acid content exceeds this range, the fatty acid tends to seep out and the output decreases. The amount of fatty acid ester added is preferably 0.1 to 10 parts by weight per 100 parts of magnetic powder.
．． 2 to 8.5 parts by weight is even better. If the amount of ester is outside this range and the amount of ester decreases, the effect of improving running performance will be poor, and if the amount increases, the ester will easily seep out and the output will decrease.

In addition, in order to better achieve the above effects, the weight ratio of fatty acids and fatty acid esters should be adjusted to -
10/90 to 90/10 is preferred. Note that fatty acids also have a dispersing effect, and it is thought that by using fatty acids, the amount of other low molecular weight dispersants used can be reduced, and the Young's modulus of the magnetic recording medium can be improved by that amount.

In addition to the fatty acids and fatty acid esters mentioned above, other lubricants such as silicone oil (carboxylic acid modified or ester modified), graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, etc. , α-olefin oxide, etc.) may be added to the magnetic layer.

The binder that can be used for the magnetic layer 2.4.5.6 preferably has an average molecular weight of about 10,000 to 200,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, etc. , vinyl chloride-acrylonitrile copolymer, polyvinyl chloride, urethane resin, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate,
cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction Examples include resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

These binders are -3O,M, -COOM.

-PO(OM')z (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium; M' is an alkali metal such as hydrogen, lithium, potassium, or sodium, or a hydrocarbon residue); It is preferable that the resin contains In other words, due to the polar groups in the molecules, these resins have improved adhesion with magnetic powder, which further improves the dispersibility of magnetic powder and prevents agglomeration of magnetic powder, further improving coating liquid stability. This can improve the durability of the medium.

Such a binder, especially a vinyl chloride copolymer, can be obtained by copolymerizing a vinyl chloride monomer, a copolymerizable monomer containing an alkali salt of sulfonic acid or phosphoric acid, and other copolymerizable monomers as necessary. Can be done.

Since this copolymer is produced by vinyl synthesis, it is easy to produce a base, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

The metal of the above-mentioned salt of sulfonic acid or phosphoric acid is an alkali metal (especially sodium, potassium, lithium), and potassium is particularly preferred in terms of solubility, reactivity, yield, etc.

Further, when providing the bank coat layer 3, the above-described binder contains non-magnetic particles such as carbon blank or barium sulfate, and is applied to the back surface of the support.

Further, as the material of the support body 1, plasting such as polyethylene terephthalate and polypropylene, Af
Metals such as XZn, glass, BN.

Ceramics such as Si carbide, porcelain, and earthenware are used.

Next, FIG. 3 shows an example of the above-mentioned medium manufacturing apparatus.

In this manufacturing apparatus, in manufacturing the medium shown in FIG. 1, the film-like support 1 fed out from the supply roll 32 is coated with each of the above-mentioned magnetic N2.4 paints by an extrusion coater 10.11. After, for example 2000G
It is oriented by a front-stage orientation magnet 33 of Gauss, and further introduced into a dryer 34 equipped with a rear-stage orientation magnet 35 of, for example, 2000 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 led to a supercalender device 37 consisting of a combination of calender rolls 38, where it is calendered and then wound onto a winding roll 39.

Each paint may be fed to extrusion coater 10.11 through an in-line mixer (not shown). In addition, in the figure, the arrow indicates the conveyance direction of the nonmagnetic base film. Each extrusion coater 10.11 has a liquid reservoir 13.1.
4 is provided to wet-on the paint from each coater.
Layer using the wet method. To manufacture the media shown in Figure 2,
In FIG. 3, one more extrusion coater may be added.

E, Example The present invention will be explained in detail below.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention. In addition, in the following examples, all "parts" are parts by weight. Moreover, "actual" represents an example, and "ratio" represents a comparative example.

First, the compositions shown in Table 1 below were kneaded and dispersed using a kneader and a sand mill, respectively, to prepare magnetic paints for each type of footwear. next,
On a polyethylene terephthalate base film having a thickness of 14.5 μm, various lower layer magnetic paints and upper layer magnetic paints were sequentially applied using the apparatus shown in Figure 3, and after orientation and drying, calendering was performed.

Thereafter, a paint for the BC layer having the following composition was applied to the surface opposite to the magnetic layer to a dry thickness of 0.8 μm.

Carbon black (Raven1255)
40 parts barium sulfate (average particle size 300mm)
10 parts Ni-1-locellulose 25
Part N-2301 (manufactured by Nippon Polyurethane Co., Ltd.) 25 parts Coronate L () 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene 250 parts A wide magnetic film was thus obtained and wound up. This film was cut to a width of A inch to produce video tapes shown in Table 1 below.

In Table 1 below, each binder is as follows.

Polyvinyl chloride resin rMR110: PVC resin polyurethane rUR containing potassium sulfonate manufactured by Nippon Pion@
8300'': Sodium sulfonate-containing polyester polyurethane polyisocyanate manufactured by Toyobo Wa Co., Ltd. ``Coronate L'' manufactured by Nippon Polyurethane Co., Ltd.The following performance evaluations were carried out for each of the above tapes, and the results are shown in Table 2 below.

RF-output: A 100% white signal was recorded and reproduced, and the output level was measured.

A 100% chroma output color signal was recorded and reproduced, and the output level was measured.

Driving test: Full-length driving was repeated 50 times at 40°C and 180%. If the vehicle stops running, it will display the number of times.

RF Output Decrease: The RF output was measured using an 8M video deck, and after 100 playbacks, it showed a value that was lower than the original output (unit: dB).This value indicates the head cleaning effect.

Light transmittance: The transmittance of light with a wavelength of 900 nn+ was measured.

Surface resistivity: As shown in Figure 4, the cross section is a quarter of the radius of approximately 1 cm.
Two rod-shaped metal electrodes 22 forming a circle are connected with a gap d (12
, 7am) and tape 21 at right angles on top of these.
Place the magnetic surfaces of the tape in contact with each other and put weights w (16
0g), and using an insulation resistance tester,
A measuring voltage of ±50 V was applied to these electrodes to measure the resistance value, which was taken as the surface specific resistance. Measurements are made after the material has been left at a relative humidity of 30% for 24 hours.

(Left below) From this result, based on the present invention, it was found that Fe in the lower layer magnetic powder
It can be seen that by setting 2+/Fe3+ to 0.13 to 0.45 and selecting the abrasive for each layer, all of the electromagnetic conversion characteristics, running properties, light shielding properties, and surface resistivity are improved.

Next, as shown in Table 2 below, the magnetic layer is layered into layer 2 as shown in Figure 2.
．． 5.6 and three layers, the performance was evaluated in the same manner as above, and the results shown in Table 2 below were obtained. According to this, it can be seen that, as in the case of two layers, the configuration of the present invention provides sufficient performance.

(The following is a blank space) 1. Effects of the invention As described above, the present invention has the following characteristics: 0.13≦Fe2+/Fe
Since the magnetite type iron oxide magnetic powder of ≦0.45 is contained in at least one of the lower layers of the magnetic layer, the entire magnetic layer exhibits sufficient light-shielding properties and furthermore, the surface resistivity is reduced.) For this reason, the amount of carbon black added to the media constituent layer can be reduced or eliminated, improving electromagnetic conversion characteristics.The outermost surface of the magnetic layer also becomes relatively flat, which also improves electromagnetic properties. Conversion characteristics can be improved. Further, in the magnetite type iron oxide magnetic material, He is advantageous in terms of chroma output, etc., and is suitable as the lower layer magnetic powder.

Furthermore, in the lower layer containing magnetite type iron oxide magnetic material, zirconia (ZrO) is substantially used as abrasive particles.
2) Since only particles are contained, it is possible to reduce the amount of fatty acids adsorbed by the magnetic material, reduce the coefficient of friction on the surface of the medium, and improve the runnability of the medium. Moreover, since hard particles with a Mohs hardness of 6 or more and zirconia particles are used together as abrasive particles in the top layer of the magnetic layer, the hard particles improve the abrasive power of the top layer, increasing durability. As a result, a head cleaning effect etc. can be obtained for the magnetic head.

[Brief explanation of the drawing]

The drawings are for illustratively explaining the present invention, and FIGS. 1 and 2 are sectional views of two sides of a magnetic recording medium, FIG. 3 is a schematic diagram of a magnetic recording medium manufacturing apparatus, and FIG. is an explanatory diagram during surface resistivity measurement. In addition, in the reference numerals shown in the drawings, 1...Nonmagnetic support 2...Lower magnetic layer 3...Back coat layer 4. 6...-... Upper magnetic layer 5...
...This is an intermediate magnetic layer.

Claims (1)

[Claims] 1. A magnetic layer made by dispersing magnetic powder in a binder is formed by an uppermost layer and a lower layer consisting of at least one layer, and the uppermost layer contains abrasive particles with a Mohs hardness of 6 or more and zirconia particles, At least one layer of the lower layer contains substantially only zirconia particles as abrasive particles, and the magnetic substance contained in the at least one layer of the lower layer is made of iron oxide, and the divalent in the iron oxide is Iron component (F
The ratio between e^2^+) and trivalent iron component (Fe^3^+) is 0.13≦Fe^2^+/Fe^3^+≦0.45.
A magnetic recording medium.