JPH04117618A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve electromagnetic conversion characteristics and traveling property by providing two layers of respectively specific magnetic layers and specifying the distribution and sizes of the projections on a base back layer. CONSTITUTION:At least the two layers 2, 4 are provided on the same side on a nonmagnetic base 1. At least one layer 2 exclusive of the outermost layer 4 is formed of layer consisting of a carbon block as an essential filler. These layers are so formed that the average projection height of the projections existing on the surface of the nonmagnetic base 1 on the side opposite from the surface formed with the magnetic layers is 0.01 to 0.20mum, that the number of the projections having >=0.01mum height on this surface is >=200 pieces per 1mm measured length; that the number of the projections having >=0.30mum height is <=500 pieces per 400mm measured length, and that the ratio of the max. projection height and the average projection height is <=5. The electromagnetic conversion characteristics and the traveling durability are compatibly obtd. at a high level in this way.

Description

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

BACKGROUND OF THE INVENTION Generally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. 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.

On the other hand, in magnetic recording media for video, media having multiple magnetic layers have been proposed in order to increase the magnetic recording capacity or to improve and balance the magnetic recording characteristics of the medium in both the high frequency region and the low frequency region. (Unexamined Japanese Patent Publication No. 48-9
No. 8803, Japanese Patent Publication No. 172142/1983, Special Publication No. 172142
-2218, JP-A-51-64901, JP-A-56
-12937, JP-A No. 58-56228, JP-A No. 6
No. 3-146211, various 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, so that the upper layer receives video output and the lower layer receives the video output. It was designed to have chroma audio output.

On the other hand, in JP-A No. 63-187418, a plurality of layers are formed on a support, with an upper layer being a magnetic layer and a lower layer formed by dispersing non-magnetic powder (e.g. carbon black) in a binder. Further technology has been disclosed.

According to the conventional technology, in order to improve electromagnetic conversion characteristics of multiple layers on a support, carbon black, etc. is removed from the uppermost layer, and a lower layer or back coat layer of carbon black, etc. is added to meet the light transmittance standard. It is known to use On the other hand, magnetic recording media require a back coat layer to ensure running performance. The backcoat layer becomes more important as the magnetic layer is smoothed.

C.9 Purpose of the Invention An object of the present invention is to ensure running durability in a magnetic recording medium in which multiple layers are provided on the same side of a non-magnetic support, and to improve electromagnetic conversion characteristics and running durability at a high level. The objective is to provide magnetic recording media that are compatible with both.

20 Structure of the invention, that is, the present invention provides at least two layers provided on the same side on a non-magnetic support.
of these layers, the outermost layer is a magnetic layer containing magnetic powder, and at least 1 mm of the layer other than the outermost layer is a layer containing carbon blank as a main filler, and the magnetic layer forming surface The average protrusion height of the protrusions present on the surface of the non-magnetic support opposite to the above is 0.01 to 0.20 μm, and the protrusion is 0.01 μm on the surface of the non-magnetic support.
The number of protrusions with a length of m or more is 200 per 1 am of measuring length.
The number of protrusions with a height of 0.30 μm or more is 500 or less per 400 mm of measurement length, and the ratio of the maximum protrusion height to the average protrusion height (maximum protrusion height /
This invention relates to a magnetic recording medium having an average protrusion height of 5 or less.

According to the present invention, the outermost layer of the plurality of layers on the same side on the non-magnetic support is a magnetic layer, and at least often the main filler in the layers other than the outermost layer is carbon black.
This carbon black provides the medium with sufficient light-shielding properties (satisfying the light transmittance standard), and the amount of carbon black in the magnetic layer can be minimized. For this reason,
The electromagnetic conversion characteristics are greatly improved, and the running durability can also be maintained.

In particular, the magnetic layer is composed of multiple layers, the outermost layer is made of relatively fine magnetic powder, and the layers other than the outermost layer are made of larger magnetic powder, so that the former layer receives video output and the latter layer receives video output. If it is designed to handle chroma audio output, the characteristics in all frequency bands can be improved.

In this case, a layer in which carbon black is the main filler according to the present invention is provided further below the latter layer, or by adding carbon black as the main filler to the magnetic layer itself of the latter layer. The amount of carbon blank in the outermost magnetic layer can be reduced compared to the black main filler layer.For example, in the case of the outermost magnetic layer, the output characteristic is on the high frequency side, and in the case of the magnetic layer other than the outermost layer, the output characteristic is on the medium and low frequency side. In particular, since the outermost layer is thin and requires high-density packing, it is possible to achieve both the required electromagnetic conversion characteristics and durability even under such restrictive conditions for the outermost layer. Very meaningful.

However, this can be improved by the above-mentioned protrusion characteristics on the opposite side of the support.

In the present invention, with respect to the layer containing carbon black as the main filler, "r main filler" means that carbon black desirably occupies 10 to 80 parts by weight based on 100 parts by weight of the total amount of the constituent components of the layer. However, the more desirable amount of carbon black is 30 to 60 parts by weight. If the amount is too small, the light shielding effect will not be sufficient, and if it is too large, the strength and adhesion of the layer will be poor. Further, the average particle size of carbon black is preferably 10 to 100 mμ, more preferably 20 to 80 mμ.

If a light shielding carbon black is used as the usable carbon black, the degree of light shielding can be increased. As the light-shielding carbon black, for example, Laben 2000 (specific surface area: 19
0 rrr/g, particle size 18 mμ), 2100.1170.
1000, Mitsubishi Kasei/Kasei #100, #75, #4
0, #35, #30, etc. can be used.

Further, as conductive carbon black, for example, Conductex (Conduc) manufactured by Columbia Carbon Co., Ltd.
tex 975 (BET value (hereinafter abbreviated as BET)
250 bo/g, DBP oil absorption (hereinafter abbreviated as DBP) 170
d/100gr, particle size 24 mμ), :7 Dactex 900 (BET 125rrf/g, particle size 27 m, cz), Near 7 Dactex 40-220
(particle size 20mm), Conductex SC (B
E T 220nf/gr, D B P 115d/
loogr, particle size 20 mμ), Cabot Vulcan X C-72 (specific surface area 254rrf/g, particle size 30 mμ), Pulcan P
(BET 143rrf/gr, DBP 11
8a+j! /100gr, particle size 20mμ), Raven 1040.420, Black Pearls 2000 (particle size 15mμ), and #44 manufactured by Mitsubishi Kasei Corporation.

Other carbon blacks that can be used in the present invention include Conductex (manufactured by Columbia Carbon) (
Conductex) -S C, (B E T 22
0n(/g, D B P 115m1/100
g, particle size 20 mμ), Palcan (Vu
lcan) 9 (BET140 rrf/g,
DBP 114m/100g, particle size 19mu)
, #80 manufactured by Asahi Carbon Co., Ltd. (B E7117 bo/g,
DBP 113d/100g, particle size 23mμ), H3100 manufactured by Denki Kagaku Co., Ltd. (BET32i/g, D B
P 180af/100g.

Particle size: 53 m u ), 422B (B
ET55n(/g,,D B P 131at/1
00g, particle size 40mμ), #20B (BE756 Bo/
g, D B P 115111/loog, particle size 40 mμ), #3500 (BET47rrf/g
, DBP187 II+1/100g, particle size 40m
g), and in addition, CF-9 manufactured by Mitsubishi Chemical Corporation,
#4000. MA-600, Cabot Black Pearls L, Monarch 800, Black Pearls 7
00, Black Pearls 1000, Black Burls 880, Black Burls 900, Black Burls 1300, Black Pearls 2000, Sterling V, Columbian Carbon Raven 410, Raven 3200, Raven 430, Raben 450, Raben 825, Raben 1255, Raben 1035, Raben 1000, Raben 5000, Ketchen Black FC, and the like.

Among the multiple layers in the present invention, the outermost layer has a thickness of 0.1 to
The thickness is preferably 1.0 μm, and more preferably 0.1 to 0.7 am. The thickness of the layers other than the outermost layer is preferably 0.1 to 4.0 μm, and preferably 0.3 to 3.0 μm. OtIm is more preferred.

Note that, in the present invention, it is desirable that the plurality of layers (the outermost layer and the other layers) are adjacent to each other.

However, in addition to cases where there is substantially a clear boundary between each layer, there may be a boundary area where components of both layers are mixed at a certain thickness, and such boundary areas are excluded. The upper or lower layer is each of the above layers. In particular, the media of the present invention provide wet-on-n coating of each layer.
et) is suitable for coating and forming. Of course, an et-on-dry method may also be used, in which the upper layer is applied after drying the lower layer.

In the present invention, in the medium having multiple layers described above, since the protrusions according to the present invention are uniformly formed particularly on the surface of the nonmagnetic support opposite to the surface on which the magnetic layer is formed, the backcoat layer Even without providing the support, the friction coefficient of the back surface of the support is small, and the running performance of the medium against the guide etc. is very good.

That is, the average protrusion height (H) on the opposite surface is set to 0.
．． By setting the thickness to 01 μm or more, for example, it is possible to prevent the occurrence of meandering or hardness in the magnetic layer coating process or calendering process, thereby improving runnability and improving durability. Furthermore, by setting the average protrusion height (H) on the opposite surface to 0.20 μm or less, surface waviness of the magnetic layer can be reduced and electromagnetic conversion characteristics can be improved. In other words, if the average protrusion height (H) on the surface opposite to the magnetic layer forming surface exceeds 0.20 μm, transfer to the magnetic layer will occur, resulting in increased surface waviness of the magnetic layer. This will lead to deterioration of conversion characteristics. This average projection height (H) is 0.0
2-0.15 am < , 0.05-0.1 μm
is even better.

Furthermore, in the non-magnetic support of the present invention, the number of projections having a height of 0.01 μm or more on the opposite surface is 200 or more (preferably 20
0 or more and 2000 or less), and the number of protrusions having a height of 0.30 μm or more on the opposite surface is 500 or less (preferably 100 or less) per 400 mm of measurement length, and It is essential that the ratio of (maximum protrusion height)/(average protrusion height) on the opposite surface is 5 or less (preferably 3 or less).

By setting the number of projections having a height of 0.01 μm or more on the opposite surface to 200 or more per measuring length, the magnetic recording medium has excellent running properties, is less likely to be scratched, and has improved durability. can be provided. Furthermore, by setting the number of protrusions with a height of 0.30 μm or more on the opposite surface to 500 or less per 400 mm of measurement length, the surface waviness of the magnetic layer is reduced and the electromagnetic conversion characteristics are improved. be able to. Furthermore, (maximum protrusion height)/(average protrusion height) on the opposite surface
By setting the ratio to 5 or less, running performance and durability can be improved without deteriorating the improved electromagnetic conversion characteristics.

First, inert particles (for example, silica particles, α-
alumina) from 0.1 to 10% by weight, preferably from 0.1 to 10% by weight
Contains 5% by weight, and has an average film thickness of 0.01~
A protrusion layer having a thickness of 1 pm, preferably 0.01 to 0.5 μm may be laminated. Here, this protrusion layer does not necessarily have to form a film (for example, it may be mesh-like) as long as the particles are wrapped in a polymer. The protrusions can also be formed by mechanically forming irregularities on the opposite surface of the nonmagnetic support without laminating them.

Another way to control the number of projections is to change the amount or particle size distribution of the filler contained in the base (non-magnetic support).

The distribution and size of the protrusions on the opposite surface as described above are particularly important in a medium that has a plurality of magnetic layers and has good frequency characteristics over the entire region. In other words, the uppermost magnetic layer is particularly densely packed with fine magnetic powder and is required to have excellent durability, but as mentioned above, the coating and running properties of the magnetic layer are improved, and there is less surface waviness. From becoming,
The film quality and surface properties of the uppermost layer of the magnetic layer are improved, and electromagnetic conversion characteristics can be improved. Furthermore, the surface of the magnetic layer is not scratched by transfer from the back surface, and the durability of the top layer in particular is greatly improved. Further, by reducing the surface waviness of the magnetic layer, electromagnetic conversion characteristics such as chroma S/N in particular become better.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
Non-magnetic support 1 made of polyethylene terephthalate etc.
A first layer 2 and a second layer 4 are laminated in this order on top. The first layer 2 is a carbon black main filler II according to the invention (which may be a Gff-like layer), and the second layer 4 is a magnetic layer. Further, no back coat layer is provided on the support surface opposite to the laminated surface, and protrusions having a uniform distribution and size according to the present invention are provided on the support surface. An overcoat layer may be provided on the second magnetic layer. In the example shown in FIG. 2, the layer 2 is a magnetic layer, and the lower layer 7 is a layer mainly made of carbon black filler. In the example of FIG. 3, the upper layer in FIG. 1 is further divided into layers 5 and 6. In Figure 2,
Also in layer 2, and in the example in Figure 3, layer 2 (and even 5)
, carbon black may be contained as the main filler.

In the magnetic recording media shown in FIGS. 1 to 3, the thickness of the first layer 2 or layer 7 is 0.1 to 4.0 μm (for example, 2.0 μm
), and the thickness of the second layer 4 or the second layer 4 is preferably
The total film thickness of the third layer 5.6 is 1.0 μm or less (for example, 0
．． 7 μm).

The magnetic layer described above can contain magnetic powder, but the magnetic powder used is Co-containing FeOx (F e”/F e”≧
0.10), 7 F ez02 , co-containing 1-F
e2O.

Iron oxide magnetic powder such as; Fe, Ni, Co, Fe-Ni-C
o alloy, Fe-Ni alloy, Fe-A1 alloy, Fe-Al
-Ca alloy, Fe-AN-Ni alloy, Fe-An-Co
alloy, Fe-Mn-Zn alloy, Fe-Ni-Zn alloy,
Fe-Al2-NiCo alloy, Fe-Af-Ni-Cr
alloy, FeAl2-Co-Cr alloy, Fe-Co-Ni
-Cr alloy, Fe-Co-N1-P alloy, Co-Ni alloy, and various other ferromagnetic powders including metal magnetic powders containing Fe, Ni, Co, etc. as main components.

Among these magnetic powders, one suitable for each of the above magnetic layers can be selected.

Each magnetic layer also contains lubricants such as silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 20 carbon atoms (such as stearic acid), and lubricants with a total of 13 to 40 carbon atoms. fatty acid esters, abrasives (e.g. fused alumina), antistatic agents (e.g. carbon black, graphite), dispersants (
For example, powdered lecithin) etc. may be added.

The binder that can be used in the magnetic layer and the layer containing carbon black as the main filler preferably has an average molecular weight of about 10,000 to 200,000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl chloride copolymer, etc. vinylidene copolymer, 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 Coalescing, polyester resins, various synthetic rubber systems, phenolic resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic reactive resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, polyester polyols and polyisocyanates Examples include mixtures of , urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof.

These binders are -3o, M, -COOM, PO(O
A resin containing a hydrophilic polar group such as M' L (where M is hydrogen or an alkali metal such as lithium, potassium, or sodium, and M' is an alkali metal such as hydrogen, lithium, potassium, or sodium, or a hydrocarbon residue). It's good to have one. In other words, the polar groups in the molecules of these resins improve their compatibility with magnetic powder, etc., which further improves their dispersibility and prevents agglomeration of magnetic powder, etc., further improving coating liquid stability. This can also 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, carboxylic acid, or phosphoric acid, and other copolymerizable monomers as necessary. Obtainable. Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymer components can be selected, so that the properties of the copolymer can be optimally adjusted.

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

Further, as the material of the support body 1, plastics such as polyethylene terephthalate and polypropylene, Aj
l! , metals such as Zn, glass, BN, Si carbide,
Ceramics such as porcelain and pottery are used. The thickness of the nonmagnetic support is usually 3 to 150 μm, preferably 4 to 100 μm when it is in the form of a tape or sheet.

In addition, in the case of disk-shaped or card-shaped, usually 30~
It is 100 μm. Furthermore, in the case of a drum shape, it can be made into a cylindrical shape, etc., depending on the recorder used.

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. 1, the film-like support 1, which is first fed out from the supply roll 32 and provided with the protrusions of the present invention on the back surface, is coated with the above-mentioned layer 2 by the extrusion coater 10. After each paint for No. 4 is applied, it is oriented by a front-stage orientation magnet 33 of, for example, 2000 Gauss, and is further introduced into a dryer 34 equipped with a rear-stage orientation magnet 35 of, for example, 2000 Gauss, where hot air is applied from nozzles arranged above and below. Spray and dry. 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 supplied to the extrusion coater 10 through an in-line mixer (not shown). In addition, in the figure, the arrow indicates the conveyance direction of the nonmagnetic base film. The extrusion coater 10 has a liquid reservoir 1.
3.14 are provided and the paint from each is applied in a wet-on-wet manner. To produce the media of FIG. 2, one more extrusion coater or outlet may be added in FIG. 4.

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.

<Preparation of paint for lower layer> Carbon black (average particle size 20 mμ, oil absorption 115
a+1/100g, product name Conductex-S
C) 20 parts and 15 parts of polyurethane containing sodium sulfonate (trade name UR-8300, manufactured by Toyobo ■) are kneaded together with a small amount of solvent in a Ni-Goo, and further diluted with solvent to give a viscosity of 10 to 50 centiboise. , disperse each component with a sand mill, and prepare polyisocyanate (product name: Coronate L, manufactured by Nippon Polyurethane Industry ■; the same applies hereinafter).
A paint was prepared by adding 5 parts of.

<Preparation of paint for upper layer> 100 parts of ferromagnetic powder (listed in Table 2 below) 10 parts of vinyl chloride resin containing potassium sulfonate (trade name MR-110 manufactured by Nippon Zeon) 5 parts of polyurethane containing sodium sulfonate [Toyo Product name made by spinning ■ UR-83
00) Alumina (average particle size 0.2μm)
5 parts carbon black 1 part myristic acid 1 part stearic acid 1 part butyl stearate 1 part methyl ethyl ketone
100 parts cyclohexanone
100 parts toluene
A magnetic paint having the above composition was prepared using a 100-part kneader and a sand mill, and a polyisocyanate compound [trade name: Corone-1, manufactured by Nippon Polyurethane Co., Ltd.] was added to this dispersion.
-3041L) was added and mixed to prepare a magnetic paint.

Next, in the method shown in FIG. 4, the upper layer and lower layer were simultaneously coated on the support in multiple layers using a wet-on-wet coating method using an extrusion type coater.

The support was a polyethylene terephthalate base film with a thickness of 10 μm, and had protrusions on the back surface with the height and number shown in Table 1 below. Such a support is applied to a base film in a known manner to a thickness of 0.01 to 2.5 μm using ethylene terephthalate or ethylene α,β-bis(2).
-chlorophenoxy)ethane-4,4'-dicarboxylate as a main component was laminated by laminating polyester layers. The height, size, and number of protrusions on the surface of the support can be controlled using inert particles (
This was done by adjusting the particle size, particle size distribution, content, type, etc. of the silica particles.

After coating, orientation, drying, and calendering were performed.

The manufacturing conditions of the medium are shown in Table 2 below.

In this way, a wide magnetic film was obtained and wound up. This film was cut to the width shown in Table 2 below to produce a videotape.

Then, the following performance evaluation was performed, and the results are shown in Table 3 below.

<RF-output, Lumi-3/N, chroma-output, chroma-
3/N> Color video noise meter rShibasoku 9
25D/1", and the 8-tape is Sony's RY-9.
00", the z inch tape is "HR-3" made by Japan Victor Co., Ltd.
Using 7000J, the value (d
B). The frequencies of each signal are as follows.

<Number of protrusions and height of protrusions on the surface opposite to the magnetic layer forming surface of the non-magnetic support> A surface roughness curve was obtained using a tally step surface roughness meter (manufactured by Taylor Hovenon), and this curve was taken as the peak. For those recognized (protrusions exceeding the peak count value), the height from the average line was measured, and the number of protrusions of 0.010 μm or more and 0.30 μm or more were measured under the following conditions.

Measurement length: 1m Cutoff: 0.337 (bypass filter) Peak count value: 0.005μm In addition, 0.30
Since protrusions with a height of μm or more occur infrequently, the above measurement was repeated 400 times to determine the number of protrusions.

<Runability> rEV-3IJ manufactured by Sony (8th printing tape), 'HR-37000J manufactured by Victor Japan (+A inch tape)
Using a deck, the entire length of the tape was repeatedly run for 100 hours under conditions of a temperature of 40° C. and a tW degree of 80%, and the edge damage of the tape was evaluated in the following three grades.

○: No edge damage occurred.

△: Edge damage occurred on a small portion of the tape.

×: Edge damage occurs over the entire length of the tape.

<Scratch on non-magnetic support surface> Sony rEV-3I J (8+n+a tape)
, using the rHR57000J (y2 inch tape) deck made by Victor Japan Co., Ltd., to record the video tape from the beginning.
It was repeatedly run 400 times for 1 minute, and the scratches on the back surface after running were observed and evaluated in the following four stages.

A: There are no scratches on the back side.

B: There are some scratches on the back, but there are no problems C: D= Good level.

There are many scratches on the back, but the playback quality is good. level that has no effect on

There are many scratches on the back, and the playback screen There is noise.

(Margin below, continued on next page) table table In the above, Magnetic material (I) Two ferromagnetic metal powders (composition: Fe:Al2=100:5 Hc: 15800e.

σS: 120 emu/g BET Specific surface area 56 m”/g) Magnetic material (■) Digonal barium ferrite magnetic material (II
I): Co-containing 7-Fe, O, iron oxide (Hc: 8000
e, BET 50m2/g) The amount of carbon black in the lower layer of Example Shio was 10 parts of the total components.

The amount of carbon black in the lower layer of the example material was 80 parts of the total components.

The amount of carbon black in the lower layer of comparative example Shio is 1 part (
The amount of carbon black in the upper layer is 5 parts per 100 parts of magnetic powder).

The amount of carbon black in the lower layer of the comparative example was 95 parts of the total components.

(Margins below, continued on next page) Table From this result, it is possible to provide a lower layer of carbon black main filler under the upper magnetic layer and to control the distribution and size of protrusions on the base back surface, based on the present invention. It can be seen that a magnetic recording medium with overall excellent performance can be obtained.

Next, in the above Example 1, there are two magnetic layers, the uppermost layer is formed by applying the above-mentioned upper layer paint, and the lower magnetic layer is formed using CO-containing iron oxide (BET30rrf/g,
It was formed by applying the same paint as the upper layer except that Hc: 6500 e) was used as the magnetic powder. In this case, as shown in Figure 2, the layer 7 of the lower layer paint (carbon blank main filler), the lower magnetic layer 2, and the uppermost magnetic layer 4 are sequentially coated on the support using a wet-on-wet coating method as shown in Figure 2. Simultaneous multilayer coating was performed. The protrusions on the back surface of the support were the same as in Example 1, and the magnetic material in the uppermost layer was as shown in Table 4 below. The results are shown in Table 5 below.

(Margin below, continued on next page) From the results in Table 2, it can be seen that by setting the magnetic layer to 2N and controlling the distribution and size of the protrusions on the base bank surface, the electromagnetic conversion characteristics and running properties can be improved. I understand.

Next, in the above Example 1, the upper layer was formed by applying the above upper layer paint, and the lower layer (corresponding to 2 in FIG. 1) was formed using CO-containing iron oxide (BET30rTf/g, Hc: 650
It was formed by applying the same paint as the upper layer except that 0e) was used as the magnetic powder. In this case, the amount of carbon black in the lower N magnetic layer was 15 parts per 100 parts of the magnetic layer composition. The results are shown in Table 6 below.

Table 6 Next, in Example IS, when the upper magnetic layer is layer 5.6 as shown in FIG. As a result of the evaluation, the results shown in Table 8 below were obtained.

According to this, it can be seen that the performance is sufficient as in the case of two layers.

(The following is a margin, continued on the next page) In the above table, the magnetic material of the intermediate layer is CO-containing γF et
Os (Hc: 8000e, BET50r
rf/g). The upper and lower layers are the same as described above.

Table-8

[Brief explanation of the drawing]

The drawings illustrate the present invention by way of example, and FIGS. 1, 2, and 3 are sectional views of two sides of a magnetic recording medium, and FIG. 4 is a schematic diagram of a magnetic recording medium manufacturing apparatus. It is. In addition, in the symbols shown in the drawings, 1......Nonmagnetic support 2.7...Lower layer 4.6...Upper layer 5.・・・・・・Middle class.

Claims (1)

[Scope of Claims] 1. The layers provided on the same side of the non-magnetic support consist of at least two layers, the outermost layer of these layers is a magnetic layer containing magnetic powder, and At least one layer other than the outermost layer is a layer containing carbon black as a main filler, and the average height of the protrusions present on the surface of the non-magnetic support opposite to the magnetic layer forming surface is 0.01 to 0. .20 μm, and the height is 0.01 μm on the surface of the non-magnetic support.
The number of protrusions with a height of m or more is 200 or more per 1 mm of measurement length, and the number of protrusions with a height of 0.30 μm or more is 500 or less per 400 mm of measurement length, and
A magnetic recording medium having a ratio of maximum protrusion height to average protrusion height (maximum protrusion height/average protrusion height) of 5 or less.