JPH04330623A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium which has high electromagnetic conversion characteristics and is decreased in drop-outs and output drop after a traveling durability test. CONSTITUTION:This magnetic recording medium is provided with at least two layers of magnetic layers 2, 4 contg. magnetic powder in superposition on a base 1. The coercive force of the magnetic layer 4 of the outermost layer is >=1700Oe and <=22000e and the saturation magnetic flux density thereof is >=3000 gauss and <=4500 gauss. The magnetic powder to be incorporated into at least one layer of the magnetic layers exclusive of the above-mentioned outermost layer is iron oxide magnetic powder having <=350Angstrom measured value of grain sizes by X-rays.

Description

Description: [0001] The present invention relates to magnetic recording media such as magnetic disks, magnetic tapes, and magnetic sheets. BACKGROUND OF THE INVENTION In recent years, magnetic recording media have become increasingly high-performance, and it has been desired to develop magnetic disks, magnetic tapes, etc. that have high electromagnetic conversion characteristics that enable high-density recording. In order to improve the electromagnetic conversion characteristics of magnetic recording media, conventional methods have been to use magnetic powder with a large saturation magnetization, improve the dispersibility of magnetic powder, and improve the magnetic layer by multilayering or squareness ratio, coercive force, Various attempts have been made to improve the saturation magnetic flux density, etc., and to adjust the surface smoothness. However, regarding the coercive force and saturation magnetic flux density of the magnetic layer, for example, if a magnetic tape with high coercive force is created in order to improve the characteristics in the short wavelength region, the output in this region will be improved; There was a problem in that the output in the long wavelength region was rather significantly reduced. In this case, in order to improve the output in the long wavelength region, it is necessary to increase the saturation magnetic flux density, but there is a contradiction in that doing so also reduces the output in the short wavelength region. Regarding the smoothness of the surface of the magnetic layer, for example, Japanese Patent Application Laid-Open No. 168124/1983 describes the surface condition of the magnetic layer of a magnetic recording medium by the center line average roughness Ra [JI
SB0601 (1976)] and the maximum height Rmax of surface irregularities, and thereby improving electromagnetic conversion characteristics as well as running performance. However, in the technology described in this publication, Although running performance was improved to some extent, electromagnetic conversion characteristics such as RF output could not be significantly improved. By the way, JP-A-2-110823 discloses a structure of a magnetic layer in which the magnetic powder in the upper layer is a ferromagnetic metal magnetic powder and the lower layer is a cobalt-containing iron oxide magnetic powder. However, in the technique disclosed in this publication, it is said that any ferromagnetic metal powder may be used, and therefore the desired RF output in the short wavelength range cannot be obtained. That is, the coercive force of the upper layer,
No consideration is given to setting the saturation magnetic flux density and surface roughness within a certain range to enhance the effect of the ferromagnetic metal powder. OBJECTS OF THE INVENTION The object of the present invention is to provide a magnetic material with high electromagnetic conversion characteristics, low dropout, and low running speed by specifying the coercive force, saturation magnetic flux density, and particle size of magnetic powder in the multilayer magnetic layer. An object of the present invention is to provide a magnetic recording medium with excellent durability. Structure of the invention and its effects: The present invention provides a support that includes:
In a magnetic recording medium in which at least two magnetic layers containing magnetic powder are stacked, the outermost magnetic layer has a coercive force of 1700 Oe or more and 2200 Oe or less, and a saturation magnetic flux density of 3000 Gauss or more and 4500 Gauss or less. The present invention relates to a magnetic recording medium, wherein the magnetic powder contained in at least one of the magnetic layers other than the outermost layer is iron oxide magnetic powder having a particle size measured by X-rays of 350 Å or less. The present invention also provides a magnetic recording medium in which at least two magnetic layers containing magnetic powder are stacked on a support, and the outermost magnetic layer has a coercive force of 1700.
Oe or more and 2200 Oe or less, and the saturation magnetic flux density is 3000 Gauss or more and 4500 Gauss or less, and the magnetic powder contained in the outermost layer has a particle size measured by X-rays of 200 Gauss or more.
ferromagnetic metal powder with an average major axis length of 0.25 μm or less, and further, the magnetic powder contained in at least one layer of the magnetic layer other than the outermost layer has a particle diameter of 350 μm or less.
The present invention relates to a magnetic recording medium characterized by being made of iron oxide magnetic powder having a particle diameter of Å or less. Furthermore, the present invention provides a magnetic recording medium in which at least two magnetic layers containing magnetic powder are stacked on a support, and the outermost magnetic layer has a coercive force of 1700.
Oe or more and 2200 Oe or less, and the saturation magnetic flux density is 3
000 Gauss or more and 4500 Gauss or less, and the surface roughness R10Z is 5 nm or more and 20 nm or less, and furthermore, the magnetic powder contained in at least one layer of the magnetic layer other than the outermost layer has a particle size measured by X-ray of 350 Å. A magnetic recording medium characterized by being the following iron oxide magnetic powder (however,
R10Z means ±2 from the center point of the magnetic recording medium in the width direction.
When a reference length is cut perpendicularly in the longitudinal direction in the range of mm, among the straight lines that are parallel to the horizontal line that cuts the outer surface contour curve on the cut plane, the line that passes through the 10th lowest summit from the highest and the 10th from the deepest. The line that passes through the shallowest valley bottom is selected, and the distance between these two lines is measured in the direction of the vertical magnification of the surface contour curve. ). The magnetic recording medium of the present invention has a multilayered magnetic layer, and the coercive force and saturation magnetic flux density of the outermost layer (hereinafter sometimes referred to as the upper layer), as well as the type of magnetic powder, For at least one magnetic layer other than the outermost layer (hereinafter referred to as the lower layer), the particle size and type of magnetic powder are specified. By specifying this, we have achieved high electromagnetic conversion characteristics, reduced dropouts, and improved running durability. [0012] Magnetic powders that can be used for the outermost magnetic layer are, for example, the general ones shown in JP-A No. 2-173931, page 3, line 11 in the lower left column to line 7 in the lower right column. Among these, ferromagnetic metal powder is particularly preferred. This ferromagnetic metal powder is composed of Fe, Ni, Co, etc., as well as Fe-Al series, Fe-Ni series, and Fe-Al series containing these as main components.
-Al--Ni based metal powders, among which Fe-based ones are preferred. Regarding these ferromagnetic metals, patent application No. 2-
It is disclosed in paragraph number 0015 of Publication No. 410458. The ferromagnetic metal powder preferably used in the outermost layer has a particle size measured by X-rays ((110
) Using the integral width of the diffraction line, determine the crystallite size=particle diameter by the Scherrer method using Si powder as a reference. ) is 200 Å
In order to adjust the surface roughness of the magnetic layer, particles with an average major axis length of 0.25 μm or less are preferable, and more preferably particles with an X-ray particle diameter of 140 to 180 Å and an average major axis length of 0.13 to 0.
．． Preferably, the thickness is 17 μm. Furthermore, the structure of the ferromagnetic metal powder is such that the content ratio of Fe atoms to Al atoms contained in the ferromagnetic metal powder is such that the atomic ratio is Fe:Al=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:Al=30 in terms of atomic ratio. :70 to 70:30. Alternatively, Fe atoms, Ni atoms, Al atoms, and Si atoms are contained in the ferromagnetic metal powder, and further, at least one of Zn atoms and Mn atoms is contained in the ferromagnetic metal powder, and the content of Fe atoms is 90 atom% or more, Ni atom content of 1 atom% or more but less than 10 atom%, Al atom content of 0.1 atom% or more but less than 5 atom%, Si atom content of 0.1 atom% or more, less than 5 at%, the content of Zn atoms and/or the content of Mn atoms (however, if it contains both Zn atoms and Mn atoms, this total amount) is 0
．． Fe atoms, Ni atoms, Al atoms, Si atoms, Zn atoms, and/or Mn atoms that are present in a surface area of 1 atomic % or more and less than 5 atomic % and that are present in a surface area of 100 Å or less according to the ESCA analysis depth of the ferromagnetic metal powder. The content ratio is atomic ratio Fe:Ni:Al:Si (Zn and or Mn) = 100
:(4 or less):(10-60):(10-70):(
Examples include ferromagnetic metal powder having a structure of 20 to 80). In the present invention, a ferromagnetic metal powder having a specific surface area of 45 m 2 /g or more by the BET method is preferably used in accordance with the need for higher density recording. The specific surface area of the ferromagnetic metal powder in the present invention is measured by a specific surface area measurement method called the BET method, and is expressed as a surface area per unit gram in square meters. This specific surface area and its measurement method are described in "Powder Measurement" (J.M. Dallavalle, Clyde).
co-authored by orr Jr., translated by Benta and others; published by Sangyo Toshosha)
It is described in detail in ``Chemistry Handbook'' Applied Edition, p.
1170 to 1171 (edited by the Chemical Society of Japan; published by Maruzen Co., Ltd. on April 30, 1960). The specific surface area can be measured, for example, by heating the powder at around 105°C at 13°C.
The powder is degassed while being heated for a minute to remove the substances adsorbed on the powder, and then introduced into the measuring device, the initial pressure of nitrogen is set to 0.5 kg/m2, and the temperature of liquid nitrogen ( -105 °C) for 10 minutes. The measuring device used was a counter soap (manufactured by Yuasa Ionics Co., Ltd.). The magnetic powder that can be used for at least one magnetic layer other than the outermost layer of the present invention has a particle size measured by X-rays of 350 Å or less, more preferably 150 to 200 Å.
iron oxide magnetic powder. When the particle size exceeds 350 Å,
This is not preferable because it has a negative effect on the surface roughness of the outermost magnetic layer. The iron oxide magnetic powder is FeOx (x is 1.
33 to 1.50), and preferably contains or is coated with a metal such as Co. Specifically, for example, those shown in paragraph number 0014 of Japanese Patent Application No. 2-410458 can be used. As the binder for the magnetic layer that can be used in the present invention, for example, those shown in JP-A-2-154320, page 3, upper right column, line 2 to page 4, lower right column, line 16, are listed. Can be mentioned. In addition, the magnetic layer may contain a dispersant,
Additives such as lubricants, abrasives, antistatic agents, and fillers may also be included. As a dispersant, for example, JP-A-2-249
129 Publication, page 4, upper left column, lines 3 to 11, or
From line 10 in the lower right column of page 4 of Publication No. 2-192017
An example of this is shown in the 20th line of the upper left column of the fifth page. [0021] As the lubricant, for example, JP-A-2-199
Listed are those shown in the 8th page, lower left column, line 1 to the 9th page, lower left column, line 8 of Publication No. 616, or the 5th page, upper right column, line 2 to 15th line of the lower right column of Publication No. 2-192017. It will be done. [0022] As the abrasive, for example, JP-A-1-277
322 Publication, page 7, upper left column, line 15 to upper right column, line 2, or Publication No. 2-192017, page 6, upper right column 2
Examples include those shown in the second row of the lower left column. [0023] As the antistatic agent, for example, JP-A-2-2
No. 85519, page 3, lower right column, line 16 to page 4, upper left column, line 9, or No. 2-192017, line 5
Examples include those shown in the 19th line of the lower right column of the page to the 2nd line of the upper right column of the 6th page. [0024] Examples of the solvent to be added to the magnetic paint for forming the magnetic layer include those described in Japanese Patent Application Laid-open No. 1-159828.
Lines 1 to 16 of the upper right column of page 8 of the publication, or lines 2-
Publication No. 192017, page 6, lower left column, line 13 - upper right column 2
Examples include those shown in the row. The magnetic paint used in the present invention is produced by kneading and dispersing ferromagnetic powder, a binder, a dispersant, a lubricant, an abrasive, an antistatic agent, etc. in a solvent. Examples of kneading and dispersing machines used for kneading and dispersing magnetic paints include:
Two-roll mill, three-roll mill, ball mill, tron mill, pebble mill, convol mill, sand mill, sand grinder, Szegveri attritor, high impeller dispersion machine, high speed impact mill, high speed stone mill, disper, high speed mixer, homogenizer, ultrasonic dispersion machine , open kneader, continuous kneader, pressure kneader, planetary kneader, etc. As a support for the above-mentioned magnetic recording medium, for example, the lower right column 6 of the second page of JP-A-2-260112 is used.
Line ~ 3rd page, upper left column, 11th line, or 2-19201
Examples include those shown in the 7th page of Publication No. 7, line 17 in the upper left column to line 5 in the upper right column. As shown in FIG. 1, the magnetic recording medium of the present invention, such as a magnetic tape, has magnetic layers 2 and 4 containing magnetic powder on one side of a support 1, and an overcoat layer if necessary. (not shown) are stacked in this order. The upper magnetic layer 4 has adjusted coercive force and saturation magnetic flux density. On the other hand, the lower layer 2 may be one layer as shown in FIG. 1, but may also be two or more layers, and contains iron oxide magnetic powder. If necessary, a back coat layer 3 may be provided on the surface opposite to the magnetic layer, and an undercoat layer (not shown) may be further provided between the lower layer 2 and the support 1. It may be. Further, the support 1 may be subjected to a corona discharge treatment. [0030] The multilayer structure of the magnetic layer of the present invention
Although it is preferable to form the coating by on-wet multilayer coating (that is, applying the paint for the outermost magnetic layer while the paint for the lower magnetic layer is not yet dry), it is of course possible to form the coating by wet multilayer coating.
It may be formed by an on-dry method (ie, applying the outermost layer after drying the lower layer) or by other methods. The thickness of the magnetic layer is 0.01 to 1.0 in the outermost layer.
The thickness is preferably .mu.m, more preferably 0.1 to 0.5 .mu.m. Further, the thickness of the lower layer is preferably 0.5 to 2.5 μm, more preferably 1.0 to 2.0 μm. Next, an example of the above-mentioned medium manufacturing apparatus is shown in FIG. In this manufacturing apparatus, when manufacturing the medium shown in FIG. , for example 65
Oriented by the front stage orientation magnet 33 of 00Gauss,
Furthermore, for example, a rear orientation magnet 35 of 6500 Gauss
The material is introduced into a dryer 34 equipped with a dryer 34, 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 and then wound onto a winding roll 39. Thereafter, if necessary, magnetic layers 2 and 4 are applied to other surfaces of the support 1 in the same manner as described above, dried, and calendered (not shown). A magnetic recording medium is manufactured by slitting the thus obtained magnetic film or punching it into a disk shape. In the above method, each paint is extruded through an in-line mixer (not shown) and passed through a coater 10,
11. In addition, in the figure, arrow D indicates the conveyance direction of the nonmagnetic base film. Extrusion coater 1
0 and 11 are provided with liquid reservoirs 13 and 14, respectively, and the paint from each coater is layered in a wet-on-wet manner. Examples of coating methods for forming the magnetic layer on the nonmagnetic support include air doctor coating, air knife coating, blade coating, squeeze coating,
Examples include impregnation coating, transfer coating, reverse roll coating, kiss coating, gravure coating, cast coating, and spray coating. In multilayer coating using this wet-on-wet method, since the upper magnetic layer is applied while the lower layer remains wet, the surface of the lower layer (that is, the interface with the upper layer) becomes smooth and the upper layer The surface properties of the material are improved, and the adhesion between the upper and lower layers is also improved. As a result, it satisfies the performance requirements of a magnetic recording medium, which requires high output and low noise, especially for high-density recording. Additionally, the wet-on-wet multilayer coating method reduces dropouts and improves reliability. [0036] Unless there is substantially a clear boundary between the upper and lower layers formed by the wet-on-wet multilayer coating method, the components of both layers may be mixed at a certain thickness. Although a boundary area may exist, any case in which the upper and lower layers excluding such boundary area are the magnetic layers is included within the scope of the present invention. The outermost magnetic layer of the magnetic recording medium produced by the above method has a coercive force of 1700 to 2200 O.
e, the saturation magnetic flux density is 3000 to 4500 Gauss, preferably the coercive force is 1700 to 2000 Oe, the saturation magnetic flux density is 3500 to 4500 Gauss, and the more preferable coercive force is 1750 to 1900 Oe, the saturation magnetic flux density is 3500 to 3500 Gauss. It is 4000 Gauss. If the coercive force is less than 1700 Oe, good RF output cannot be obtained in the short wavelength range because it is easily demagnetized, and 2
If it exceeds 200 Oe, the ability of the magnetic head to write to the medium decreases, making it impossible to obtain RF output in the short wavelength range. In addition, when the saturation magnetic flux density is less than 3000 Gauss,
As the filling rate of the magnetic powder decreases, the RF output decreases in the entire band, and when it exceeds 4500 Gauss, the magnetic powder aggregates during media preparation, so the decrease in the RF output becomes particularly noticeable in the short wavelength range. . That is, if both the coercive force and the saturation magnetic flux density are outside the above ranges, the effects of the present invention will not be exhibited. In order to adjust the coercive force of the magnetic layer within the range of the present invention, there is a method of controlling the dispersibility of the magnetic paint, the conditions of magnetic field orientation, the calendering conditions, the shape of the magnetic powder, etc. Further, methods for adjusting the saturation magnetic flux density of the magnetic layer within the range of the present invention include controlling the dispersibility of the magnetic paint, magnetic field orientation conditions, calendering conditions, and the like. In the present invention, the surface roughness R1 of the magnetic layer
It is preferable that 0Z is 10 to 18 nm, and 12 to 1
More preferably, the thickness is 5 nm. The surface roughness R10Z according to the present invention refers to the surface roughness of the magnetic recording medium at ±2
mm (indicated by R in the figure), when cutting vertically by the standard length in the longitudinal direction, the 10th lowest peak from the highest among the straight lines parallel to the horizontal line that cuts the outer surface contour curve at that cut plane. Select the line that passes through the bottom of the valley and the line that passes through the 10th shallowest valley bottom from the deepest one, and connect these two straight lines (l1 and l2
) is the value measured in the direction of the vertical magnification of the surface contour curve. [0043] To measure the above R10Z, a Talystep roughness meter (manufactured by Rank Taylor Hobson) was used, and the measurement conditions were as follows:
μm, stylus pressure 2mg, cut-off filter 0.
The measurement frequency was 33 Hz, the measurement speed was 2.5 μm/sec, and the reference length was 0.5 mm. In addition, in the roughness curve, irregularities of 0.002 μm or more are cut. In order to control the above R10Z to 20 nm or less, the surface smoothness of the magnetic layer may be controlled by setting calender conditions in the above manufacturing process, for example. That is, in this surface smoothing treatment,
Factors controlled as calendar conditions are temperature, linear pressure, C
/S (coating speed), etc. Further, other factors include the size and amount of particles added to the magnetic layer. [0045] In order to achieve the object of the present invention, the above temperature is usually set at 50 to 140°C, and the above line pressure is set at 50 to 400 k.
g/cm, and the above C/S is preferably maintained at 20 to 600 m/min. Outside these numerical ranges,
It may become difficult or impossible to determine the surface roughness of the magnetic layer as described above. [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 9, Comparative Examples 1 to 6 Paint A was prepared by kneading and dispersing the following upper layer compositions. Paint A Magnetic powder

100 parts by weight Sodium sulfonate group-containing polyurethane
10 parts by weight (manufactured by Toyobo Co., Ltd.)
UR-8300) Vinyl chloride resin containing potassium sulfonate group
10 parts by weight (MR-110 manufactured by Nippon Zeon Co., Ltd.
) α-Alumina

8 parts by weight stearic acid

1
Weight part Butyl stearate

1 part by weight cyclohexanone

100 parts by weight
Methyl ethyl ketone

100 parts by weight toluene

100 parts by weight [
Next, a lower layer coating composition having the same composition as the upper layer coating composition except that the magnetic powder in the upper layer coating composition was replaced with Co-containing iron oxide (FeOx: x=1.4) was kneaded.
Paint B was prepared by dispersing. [0049] Each of the above compositions was milled in a ball mill for 5 minutes.
The mixture was dispersed for 0 hours, 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 magnetic paints A and B. These paints are coated in multiple layers on a support, and then oriented (
4000 Gauss) and calendered at 80°C, lower layer 2.2 μm, upper layer 0.3 μm, total 2.5
A μm thick magnetic layer was formed. 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 prepared by adding 20 parts by weight of a polyisocyanate compound (Coronate L manufactured by Nippon Polyurethane Co., Ltd.). 0.5 on the opposite side of the magnetic layer
The film was applied to a thickness of μm and further slit to a width of 8 mm to prepare an 8 mm videotape. Composition of coating liquid for back coat layer: Carbon black (A) (average particle size 30 nm)
70 parts by weight
Carbon black (B) (average particle size 60nm)
30 parts by weight
nitrocellulose

30 parts by weight polyurethane resin

30 parts by weight cyclohexanone
20
0 parts by weight methyl ethyl ketone

200 parts by weight toluene

20
0 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) RF output and chroma output Measured using a noise meter 925C manufactured by Shibasoku and an 8 mm video movie V900 (manufactured by Sony Corporation). (b) Dropout Dropout counter VD-5M manufactured by Victor Japan
was used, and an output that was longer than 15 μsec and was lower than the output of the Rf envelope by 10 dB or more was regarded as one dropout, and the entire length was measured, and the average value per minute was determined. (c) Output decrease (RF after running durability test)
Output drop) Record and play the tape 100 times at a temperature of 40°C and a humidity of 20%, and display the output difference in dB between the RF output for the first time and the RF output after 100 times. [0055]
Table-1A Example
1 2 3
4 5 6 ──────────
──────────────────────
<Upper layer><Magneticpowder> Type
(1) (1) (1) (1)
(1) (1) Particle size (Å)
150 130 210
190 150 200
Average major axis length (μm) 0.18 0.16 0.
25 0.28 0.18 0.18
Coercive force (Oe) 1750 2
100 1950 1680 1750 18
30 <Magnetic layer> Coercive force (Oe) 18
00 2200 2000 1700 180
0 1900 Saturation magnetic density (Gau
ss) 3000 3150 4500 335
0 3030 3350 Surface roughness R10Z (nm) 19 11 2
3 21 20 19 <
Lower layer> Magnetic powder particle size (Å) 300
250 340 280 350
180 RF output (dB)
3.0 4.5 2.5 2.0
2.0 3.0 Chroma output (dB)
3.0 3.0 2.5
2.0 3.5 3.0 Dropout 30 15 3
5 40 10 18 Output drop (dB) -0.5 0
．． 0 -0.6 -0.7 -0.3 -0.
*Magnetic powder type (1) Fe-Al based ferromagnetic metal powder Fe:Al=10
0:5 (atomic ratio) - Total Fe:Al = 50:50 (atomic ratio) - Surface layer BET
Value 57m2/g (2) Fe-Ni system Fe
:Ni=100 :5-Overall BET value 53m2/g (3) Fe-Ni-Co system Fe:Ni
:Co=100 :5:5-Overall BET value 57m2/g 0057
Table-1C Comparative example
1 2 3 4
5 6──────────────────
──────────────〈Upper layer〉〈Magnetic powder〉 Type (1)
(1) (1) (1) (1)
- Particle size (Å) 160
170 140 250 150
- Average major axis length (μm) 0.19 0
．． 23 0.21 0.30 0.18 -
Coercive force (Oe) 1600 215
0 1700 1730 1750 - <
Magnetic layer>
−
Coercive force (Oe) 1650 2230
1750 1780 1800 - Saturation magnetic density (Gauss) 3080 3650
2900 4600 3020 - Surface roughness R10Z (nm) 19 24
26 35 19 - <Lower layer> Magnetic powder particle size (Å) 250 350
400 300 - 300 R
F output (dB) 0.5 -0.5
0.5 0.0 2.0 -2.0 Chroma output (dB) 0.0 1.0
2.0 4.0 -2.5 3.0 Dropout 100 60
35 75 80 300 Output drop (dB) -3.5 -2.0
-1.8 -2.0 -1.5 -4.5 From the above results, it can be seen that the magnetic recording medium of the present invention has high electromagnetic conversion characteristics, reduced dropout, and low output after running durability test. It is clear that the degree of deterioration is small and is excellent.

[Brief explanation of drawings]

FIG. 1 is an example of a cross-sectional view of a multilayer coated magnetic tape.

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

FIG. 3 is a diagram illustrating a situation when measuring the surface roughness R10Z of a magnetic layer.

[Explanation of symbols]

1 Support 2 Magnetic layer (lower layer) 3 Back coat layer 4 Magnetic layer (upper layer) 10, 11 Extrusion coater 13, 14 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 (3)

[Claims] 1. A magnetic recording medium in which at least two magnetic layers containing magnetic powder are stacked on a support, wherein the outermost magnetic layer has a coercive force of 1700 Oe or more, 2
200 Oe or less, the saturation magnetic flux density is 3000 Gauss or more and 4500 Gauss or less, and the magnetic powder contained in at least one layer of the magnetic layer other than the outermost layer is iron oxide magnetic with a particle size measured by X-rays of 350 Å or less. A magnetic recording medium characterized by being a powder. 2. A magnetic recording medium in which at least two magnetic layers containing magnetic powder are stacked on a support, the outermost magnetic layer having a coercive force of 1700 Oe or more, 2
200 Oe or less, the saturation magnetic flux density is 3000 Gauss or more and 4500 Gauss or less, the magnetic powder contained in the outermost layer has a particle size measured by X-ray of 200 Å or less, and has an average major axis length of 0.25 μm or less. A magnetic recording medium comprising a ferromagnetic metal powder, and further comprising an iron oxide magnetic powder having a measured particle size of 350 Å or less, and the magnetic powder contained in at least one of the magnetic layers other than the outermost layer. 3. A magnetic recording medium in which a support is provided with at least two magnetic layers containing magnetic powder, the outermost magnetic layer having a coercive force of 1700 Oe or more, 2
200 Oe or less, saturation magnetic flux density is 3000 Gauss or more and 4500 Gauss or less, and surface roughness R10Z
is 5 nm or more and 20 nm or less, and furthermore, the magnetic powder contained in at least one layer of the magnetic layer other than the outermost layer is X
A magnetic recording medium characterized in that it is an iron oxide magnetic powder having a particle diameter measured by a wire of 350 Å or less. (However, R10Z refers to the straight line parallel to the horizontal line that cuts the outer surface contour curve of the cut surface when a magnetic recording medium is cut perpendicularly by a reference length in the longitudinal direction within a range of ±2 mm from the midpoint in the width direction.) Of these, choose the one that passes through the 10th lowest peak from the highest and the one that passes through the 10th shallowest valley bottom from the highest, and calculate the value of the distance between these two straight lines measured in the direction of the vertical magnification of the surface contour curve. say.)