JPH03219422A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve durability and traveling property by incorporating hexagonal plate-shaped magnetic powder into the uppermost layer and incorporating hexagonal plate-shaped magnetic powder which is same as the powder in the uppermost layer or has larger planer ratio into the second layer. CONSTITUTION:The first magnetic layer 2 containing hexagonal ferrite magnetic powder and the second magnetic layer 4 are successively formed on the both sides of a nonmagnetic supporting body 1. The layer 2 is made 0.01 - 1.9mum thick and the layer 4 is made 0.01 - 1.5mum thick, preferably. The planer ratio (d/t, diameter (d) to thickness (t) ratio) of the layer 2 is made same as or larger than that of the layer 4, which prevents oozing of a lubricant to the upper layer or plasticization of the layers and avoides sucking of a head. Moreover, the magnetic powder of small particle size in the layer 4 contributes to increase of S/N, while the magnetic powder of large particle size in the layer 2 enables high output and proper surface property.

Description

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

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, improving high-frequency recording characteristics,
Moreover, since low noise is required, high He
Magnetic powder with a high BET value is used.

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 become insufficient.

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. 59172142, Special Publication No. 32-
No. 2218, JP-A-51-64901, JP-A-56-
No. 12937, JP-A-58-56228, JP-A-63
-146211 publications, etc.).

According to these known techniques, relatively fine particles of magnetic powder are used in the upper layer of the magnetic layer, and larger magnetic particles are used in the lower layer, so that the upper layer receives video output on the short wavelength side, and the lower layer receives video output on the long wavelength side. It was designed to have chroma audio output.

Until now, in magnetic recording media in which the magnetic layer is of a coated type, γ-Fe20. However, recently, in order to improve the magnetic recording density, plate-shaped magnetic powder made of hexagonal ferrite and having an average particle size of 0.2 μm or less has been used as a magnetic powder that allows perpendicular magnetic recording. is proposed.

A medium in which such hexagonal ferrite is applied to a plurality of magnetic layers as described above is disclosed in JP-A-1-128228. According to this medium, the saturation magnetization is 70em
A lower layer mainly consisting of acicular ferromagnetic powder of u/g or more and conductive powder, and a main layer consisting of hexagonal ferromagnetic powder with a number average particle size of 0.03 to 0.1 μm and a platelet ratio of 3 to 5. An upper layer is provided, the lower layer has a thickness of 1 to 5 μm, and the upper layer has a thickness of 0 μm.
．． It is 1 to 0.5 μm.

Although the second medium is said to have good recording characteristics for short and long wavelength signals and to provide high durability, it is still insufficient. Moreover, no measures have been taken for other required performance such as running performance, and sticking and running problems are likely to occur. This can lead to serious problems, especially since the top layer of the magnetic layer is very thin. In addition, from a manufacturing point of view, since the above-mentioned hexagonal ferrite is a small plate-shaped particle, it is difficult to distribute the hexagonal ferrite in the magnetic layer (especially the thin top layer) so that its surface preferably follows the magnetic layer surface. Cannot achieve sufficient orientation. As a result, the electromagnetic conversion characteristics deteriorate overall including the high frequency range (short wave side). Furthermore, the adhesiveness between the uppermost layer and the lower layer is insufficient, resulting in poor durability.

An object of the present invention is to provide a medium having a plurality of magnetic layers that generally improves electromagnetic conversion characteristics, durability, runnability, etc., and a method for manufacturing the same. .

20 Structure of the Invention That is, in the present invention, a magnetic layer provided on a non-magnetic support is formed of an uppermost layer and a lower layer consisting of at least one layer, and the uppermost layer comprises hexagonal plate-shaped magnetic powder. a magnetic recording medium in which at least the second layer from the top layer of the lower layer contains hexagonal plate-like magnetic powder having a plate-like ratio equal to or larger than that of the plate-like magnetic powder; This is related to.

Further, the present invention provides that the magnetic layer provided on the non-magnetic support is formed of an uppermost layer and a lower layer consisting of at least one layer, and the uppermost layer contains hexagonal plate-shaped magnetic powder, At least the second layer from the top layer of the lower layer contains hexagonal plate-like magnetic powder with a plate-like ratio equal to or larger than that of the plate-like magnetic powder, and the surface roughness of the magnetic layer is As, 0.01 from the average line of the surface roughness cross-sectional curve
Ns/N which is the ratio between the number of spikes Ns that protruded by μm or more and the total number of peaks Ns (t) that protruded from the same average line
5(1) is 0.10 to 0.35.

The present invention also provides a top layer containing a hexagonal plate-like magnetic powder; and at least a second layer from the top layer is a hexagonal crystal with a plate-like ratio equal to or larger than that of the plate-like magnetic powder. When producing a magnetic recording medium having a small (at least one lower layer) on a non-magnetic support, the magnetic paint for the lower layer is coated on the non-magnetic support. The present invention also provides a method for manufacturing a magnetic recording medium in which the magnetic coating material for the uppermost layer is coated in a wet state in a multilayer manner.

In the medium of the present invention, the magnetic layer is composed of a plurality of layers, and since the top layer uses the above-mentioned hexagonal magnetic powder, high-frequency recording and playback characteristics such as video output are improved. Since the lower layer uses hexagonal magnetic powder with the above-mentioned plate ratio, it is possible to record high output, especially relatively low range recording such as chroma and audio output. The reproduction characteristics can be improved, and the electromagnetic conversion characteristics can be improved over the entire region.

Examples of the hexagonal magnetic powder used in the uppermost layer and the lower layer (at least the second layer from the uppermost layer) include hexagonal ferrite 9 as shown in FIG.

This hexagonal ferrite has a flat plate shape (the ratio d/l between the diameter d and the thickness t is called the plate ratio), and the axis of easy magnetization is perpendicular to the plate surface (that is, in the C-axis direction), so it is or can be easily oriented in the vertical direction by mechanical orientation;
A recording medium suitable for perpendicular magnetic recording can be obtained. Moreover, hexagonal ferrite can efficiently record even short wavelengths. In the present invention, with respect to the plate ratio (this is referred to as d1/ll) of the plate-shaped magnetic powder such as hexagonal ferrite in the uppermost layer of the magnetic layer, at least the second layer from the uppermost layer among the lower layers The plate ratio of plate-shaped magnetic powder such as hexagonal ferrite (
Let this be dt/lz. ) is dl /l+ = dz
/lz or d+/l+<dz/tz, the lubricant is prevented from seeping into the upper layer or becoming plasticized, eliminating head adsorption and improving running performance. Moreover, the magnetic powder in the top layer has a small particle size and contributes to increasing the S/N ratio.
The magnetic powder in the lower layer can be expected to have high output due to its relatively large particle size, and can provide an appropriate surface roughness to obtain good electromagnetic conversion characteristics.

Regarding this plate ratio, d1/ll is preferably from 1 to 10, and even more preferably from 3 to 8. dt/lt is 1-15 is 0.5-
1 is good, and 0.7 to 1 is even better. Also, usually, the above t is 0.005 to 5 μm, and t2 is 0.005 to 5 μm.
S dI is 0.01-0.1 am, d z
is 0.01 to 0.1 μm.

The hexagonal ferrite magnetic material described above is composed of barium ferrite, strontium ferrite, calcium ferrite, lead ferrite, etc. (especially barium ferrite), and a part of the iron element is composed of other elements (for example, Ti5Co, Zn
, InSMn, Ge.

Nb, etc.), or multiple types of hexagonal ferrite magnetic materials may be used in combination. Also,
The types of hexagonal ferrite magnetic materials in the uppermost layer and the lower layer may be the same or different.

Regarding this ferrite magnetic material, please refer to IEEE Trans.
, on Mag,, MAG-1816 (19B2
) is described in detail.

In the present invention, the film thickness (or layer thickness) of the above-mentioned top layer is preferably 0.01 to 1.5 Bm.
．． It is desirable that the thickness be 0 μm, particularly 0.5 μm or less.

If it is less than 0.01 μm, it is too thin and difficult to coat;
If it exceeds μm, it is too thick and tends to impair the performance of the underlying layer.

The thickness of the lower layer adjacent to this upper layer is 0.01 to 1.
It is desirable that the thickness be 9 μm. Further, it is preferable that the medium constituent layers including the magnetic layer (excluding the support) have a thickness of 2.0 μm or less; if it is thicker than this, problems with runnability etc. tend to occur. In the present invention, it is desirable that the plurality N (uppermost layer and lower layer) constituting the magnetic layer are adjacent to each other. The lower layer may be one layer, or may be two or more layers. 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.

(9) (10) Running performance can be further improved. In a multi-layer magnetic layer as in the present invention, if the particle size of the non-magnetic powder (for example, abrasive) in the top layer is too coarse, the surface of the magnetic layer becomes rough, increasing noise and head wear during reproduction. . However, if the particle size is small, for example, the polishing power will decrease, and it will be easier to stick to the head, causing a decrease in output, and the surface will become too smooth, increasing friction and increasing sliding noise or media noise. Become. However, in the present invention, in the uppermost layer of the magnetic layer, non-magnetic powder with a relatively small particle size of less than 0.3 μm and a Mohs hardness of 6 or more is added, while in the lower layer, a relatively small particle size of less than 0.3 μm is added. When using non-magnetic powder with a large diameter and a Mohs hardness of 5 or more, the surface of the magnetic layer can be roughened to an appropriate degree, maintaining polishing power and reducing sliding noise or media noise. can also be made even better.

In the uppermost layer, the above-mentioned non-magnetic powder has a particle size of 0.01 to 0.25 tt mO, more preferably 0.05 tt mO.
-0.209 is good, and in the lower layer, the particle size is 0.209.
3 to 1.0 μm, and more preferably 0.5 to 1.0 $71. The number of nonmagnetic powders having the above particle size and Mohs hardness is preferably 50% or more of the total nonmagnetic powder, and more preferably 60% or more (or 60 to 80%). The content of non-magnetic particles is 0.01 to 20 parts by weight in the uppermost layer, more preferably 0.1 to 20 parts by weight, per 100 parts by weight of magnetic powder.
10 parts by weight, 0.01 to 20 parts by weight in the lower layer, and even 0.01 to 20 parts by weight in the lower layer.
The amount is preferably 05 to 10 parts by weight.

In the above, the particle size of the non-magnetic powder means the particle size of the non-magnetic powder measured with a caliper after taking an electron micrograph of a cross section of a tape or the like at a magnification of 20,000 times.

Examples of the non-magnetic powder having a Mohs hardness of 5 or more used in the present invention include α-alumina, chromium oxide, titanium oxide, tin oxide, α-iron oxide, silicon oxide, silicon nitride, silicon oxide, zirconium oxide, zinc oxide, Cerium oxide, magnesium oxide, boron nitride, etc. are used. Among these, the non-magnetic powders with a Mohs hardness of 6 or more include α-alumina (Mohs hardness 9), nichrome dioxide (Mohs hardness 9)
, titanium dioxide (Mohs hardness 6.5), tin dioxide (Mohs hardness 6.5), α-iron oxide, silicon dioxide (1
1) (12) (Mohs hardness: 7), silicon nitride, silicon carbide, zinc oxide, cerium oxide, magnesium oxide, boron nitride, etc.

In the present invention, the above-mentioned spike ratio N s / N
5(1) is 0.10≦Ns/Ns(t)≦0.35, preferably 0.15≦Ns/Ns(t)≦0.3.
It is 0.

With this Ns/Ns(t) range, sliding noise and head cloudiness can be effectively reduced without impairing electromagnetic conversion characteristics.

The spike ratio Ns/Ns(t) described above simply, clearly, and concretely expresses the physical meaning of the surface roughness situation.

On the other hand, the center line average surface roughness Ra that includes the four parts below the average line and the maximum roughness Rmax that includes the height of no harm or benefit are as follows:
The definition content is different for each, and the recess that sinks below the average line is an essential requirement, and the ratio Rmax
/Ra is difficult to grasp its significance as far as electromagnetic conversion is concerned.

Therefore, Ns/Ns (t) and Rmax/Ra specify different types of surface states, at least with regard to electromagnetic conversion characteristics.

In order to adjust the surface roughness based on the spike ratio, consideration must be given to the dispersion of the magnetic powder, the selection of the binder, and the plasticity of the coating film.

The magnetic recording medium of the present invention is, for example, a floppy disk, as shown in FIG. Magnetic layer 2, second
The magnetic layers 4 are laminated in this order. 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.

In the magnetic recording media shown in FIGS. 1 and 2, the thickness of the first magnetic layer 2 is 0.01 to 1.9 μm (for example, 1.5 μm).
m), and the thickness of the second magnetic layer 4 or the total thickness of the second and third magnetic layers 5.6 is preferably 0.01-1.
It is preferably 5 μm (for example, 0.2 μm).

Furthermore, FIG. 3 shows an example in which a layer 7 other than the above-mentioned layer 2 is provided as a lower layer, and the layer 7 includes a magnetic layer containing magnetite magnetic powder to improve light shielding properties (13) (14). Alternatively, a nonmagnetic layer containing carbon black may be used (light-shielding properties and conductivity are improved). In the example shown in Fig. 4, a layer 8 is added below layer 7, and layer 8 is a non-magnetic layer containing carbon black similar to the above, and layer 7 is a magnetic layer containing magnetite magnetic powder. good.

In addition to the above-mentioned magnetic powder and non-magnetic powder, each magnetic layer is coated with lubricant (
Examples include silicone oil, graphite, molybdenum disulfide, tungsten disulfide, monobasic fatty acids with 12 to 20 carbon atoms (e.g. stearic acid), fatty acid esters with 13 to 40 carbon atoms, antistatic agents (e.g. carbon Black, graphite), dispersant (lecithin powder), etc. may be added.

In addition, the binder that can be used in each of the above magnetic layers preferably has an average molecular weight of about 10,000 to 200,000.
For example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-
Vinylidene chloride copolymer, vinyl acrylonitrile chloride 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 resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic reactive resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers,
Examples include 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 -303M, -COOM.

PO(OM')z (where M is hydrogen or lithium,
Alkali metals such as potassium and sodium, M' is hydrogen,
It is preferable that the resin contains a hydrophilic polar group such as a polar group containing (15) (16) a nitrogen atom or an alkali metal such as lithium, potassium, or sodium or a hydrocarbon residue. In other words, these resins have polar groups in their molecules that
Compatibility with the magnetic powder is improved, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the magnetic powder, further improving the stability of the coating liquid, which in turn improves the durability of the medium. It can be done. It is particularly preferable to use the above-mentioned binder having a polar group in the uppermost layer.

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, if necessary, other copolymerizable monomers. can.

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 such as sulfonic acid or phosphoric acid is an alkali metal (particularly sodium, potassium, lithium).

Note that the present invention is applicable not only to magnetic disks but also to other media (for example, video tapes); however, in this case, the above-mentioned magnetic layer is provided only on one side of the support, and is not provided on the other side. A back coat layer (the above-described binder containing non-magnetic particles such as barium sulfate) can be applied.

Further, according to the manufacturing method of the present invention, the magnetic paint for the lower layers other than the top layer and the magnetic paint for the top layer are coated in a wet state in a multilayer (simultaneous or sequential wet multilayer coating). That is,
Since it is a wet on wet coating method, it is easy to coat the uppermost layer on the lower layer, and in particular, the thinner uppermost layer can be coated uniformly and with good adhesion, and multiple layers can be coated in multiple layers with good reproducibility. Moreover, although the hexagonal magnetic powder in the layer is plate-shaped, since the uppermost layer is applied while the lower layer is wet, the particles tend to be oriented so that the plate surfaces of the particles are aligned along the layer surface. Therefore,
Although the top layer is thin, it is possible to apply the hexagonal magnetic powder while fully orienting and dispersing it, and it is possible to omit the magnetic field orientation treatment after coating.

Further, when oriented, the orientation becomes easier, which is advantageous for the squareness ratio (and thus the output).

(17) (18) On the contrary, conventional media (Japanese Unexamined Patent Publication No. 1-1282
As mentioned above, with No. 28, etc., the lower layer is dried and rolled up after being applied, so the surface of the lower layer is rough, making it difficult to apply the top layer well, and the hexagonal magnetic powder cannot be properly oriented. . In the present invention, such a problem does not occur, and a multilayer structure can be produced satisfactorily.

FIG. 6 shows an example of the manufacturing method according to the present invention.

In this manufacturing method, for example, when manufacturing the medium shown in FIG. After applying, for example 20
It is oriented by a 00 Gauss front-stage orientation magnet 33 (this can be omitted), and is further introduced into a dryer 34 equipped with, for example, a 2000 Gauss rear-stage orientation magnet 35 (this can be omitted), where hot air is applied from nozzles arranged above and below. Spray and dry.

Next, the dried support 1 with each coated layer is applied to a super calender device 3 consisting of a combination of calender rolls 38.
7, where it is calendered and then wound onto a winding roll 39.

Thereafter, the magnetic layer 2.4 is coated on the other side of the support 1 in the same manner as described above, dried, and calendered. For example, the magnetic film obtained in this way has a diameter of 3
．． A 5-inch disk is punched out and placed in a cassette to produce a floppy disk.

In the above method, each paint may be fed to the 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. The extrusion coaters 10.11 are each provided with a reservoir 13.14 to deposit the paint from each coater in a wet-on-wet manner. To manufacture the media shown in FIG. 2 and the like, an extrusion coater may be added in FIG. 3.

FIG. 7 shows an example of an extrusion coater. Same figure (A)
is similar to that shown in Fig. 6 (for sequential wet multi-layer coating with 2 heads); C) is 1
This head discharges both magnetic paints 2' and 4' in an overlapping manner in the cross direction inside the head (for simultaneous wet multilayer coating). In either case, the purpose of the present invention can be fully realized.

Note that the device used for the multilayer coating described above does not necessarily have to be an extrusion coater; other known coating devices can be used.

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. Also,
"Actual" represents an example, and "ratio" represents a comparative example.

First, coating solutions (1), (2), (2) and (2) consisting of the following compositions were prepared.

CO-substituted Ba ferrite from Nobu (BET value 60ffl/g, average particle size 0.04 tt m) 1
00 parts Vinyl chloride copolymer (MRIIO: manufactured by Zeon Corporation) 10 parts Polyurethane resin (toluene diisocyanate, 1.4-
Consisting of butanediol and adipic acid, -3o, Na group 0.05mmo I! , /g content, molecular weight 50,000) 15
1 part carbon black (particle size 100 mμ) 5 parts abrasive 3 parts lecithin
1 part butyl stearate 4 parts myristic acid
2 parts methyl ethyl ketone
150 parts toluene
150 parts blood 1 Co containing r-Fez Os (BET value 45rrf/
g) 100 parts vinyl chloride copolymer (MRIIO: manufactured by Zeon Corporation) 10 parts polyurethane resin (toluene diisocyanate, 1.6
-Hexanediol, adipic acid (21) (22) Li, -303Na group 0.03 mm.

Quantity: 30,000) Carbon black (particle size: 100, abrasive lecithin, myristate, stearate, butyl methyl ethyl ketone, toluene saturation and Co-containing Fe3 O4 (BET value: 35 M/g) I!, containing 7 g, molecule: 15 parts mμ) 5 parts 3 parts 1 Part 3 Part 3 150 parts 150 parts 100 parts Vinyl chloride copolymer (MRIIO: manufactured by Nippon Zeon ■) 15 parts Polyurethane resin (same as that used in coating liquid ■) 1
0 parts carbon black 3 parts alumina powder 2 parts lecithin
1 part myristic acid
1 part butyl stearate
1 part methyl ethyl ketone
150 parts toluene 1
50 parts coating 5 times 1 carbon black (particle size 80 mμ) 100 parts nitrocellulose 15 parts polyurethane resin (4,4'-diphenylmethane diisocyanate, 1,
Consisting of 6-hexanediol and adipic acid, molecular weight 4
10,000 parts lecithin
1 part myristic acid 1 part butyl stearate 1 part methyl ethyl ketone 150 parts cyclohexanone 100 parts toluene
After thoroughly stirring and mixing 150 parts of each component of the above composition in a ball mill, 5 parts of a polyfunctional isocyanate: Coronate L (manufactured by Nippon Polyurethane Co., Ltd.) were added.

Then, using the coating liquid in combination as shown in Table 1 below, dry thickness, coating method, plate ratio of Ba ferrite, (23) (24) and abrasive as shown in Table 1, polyethylene film with a film thickness of 75 μm was applied. After coating on a terephthalate base and drying, it was calendered using a super calender roll. Thereafter, each coating solution was similarly applied to the opposite side of the polyethylene terephthalate base film, and after drying, calendering was performed.

The magnetic film thus obtained was punched out into a disk shape with a diameter of 3.5 inches and housed in a cassette.

Note that Ns/Ns(t) was measured as follows. As a measuring device, a Christetub roughness meter (manufactured by Rank Taylor Hobson) was used.
was used.

<Specifications and measurement conditions> Stylus...2.5 Xo, 1μm
Needle pressure: 2mg cut-off
Filter... 0.33Hz measurement speed
... 2.5 μm/sec reference length
... 0.5 improvement, 0.005 μ in roughness curve
Irregularities smaller than m are cut.

From the above, calculate the number of spikes Ns that protruded by 0.01 μm or more from the average line of the roughness curve, and the number Ns (t) of spikes that protrude beyond the average line, and calculate Ns / N 5 (1)
Calculate.

(The following is a blank space) (25) (26) The following performance evaluations were performed for each of the above disks, and the results are shown in Table 2 below.

(a), Initial 2F floppy disk drive F
Relative ratio (%) when Example 1 is taken as 100% for D-1135-D (manufactured by NEC Corporation) (b), Running durability: FD-1135, D at a temperature of 5°C
Thermocycle is performed for 24 hours under environmental conditions of /relative humidity 10% to temperature 50°C/humidity 30%.

(C) Test to see if noise occurs at 5°C (d) Head adsorption at 60°C, 130% RH, and whether or not adhesion occurs between the head and the floppy disk.

(e) Media noise: Relative ratio (%) when the noise is measured at the innermost 2F output at room temperature and the standard sample is taken as 100%. From this result, it is found that each layer is configured based on the present invention. By putting hexagonal magnetic powder with a high plate-like ratio in at least the second layer and macrogonal magnetic powder with a small plate-like ratio in the top layer, lubricant seepage or plasticization can be weakened. This makes it possible to eliminate head adhesion at high temperatures and improve running durability.

In this case, it is possible to achieve both initial 2F output and running durability, and the top layer is an abrasive with a Mohs hardness of 6 or more and a particle size of 0.3 μm or less, and the next layer is an abrasive with a Mohs hardness of 5 or more and a particle size of 0.3 μm or more. By using , the running at low temperatures is stable, and furthermore, the polishing effect does not deteriorate even after repeated use.

Furthermore, by setting Ns/Ns(t) to 0.10 to 0.35, sliding noise and the like can be improved.

In addition, a multilayer coating method in a wet state (wet on we
By performing the extrusion coating method (extrusion coating method at t) and dispersing each layer separately, good surface roughness can be obtained and durability can also be improved.

9. Effects of the Invention As described above, in the present invention, the uppermost layer contains hexagonal plate-shaped magnetic powder, and at least two layers from the uppermost layer among the lower layers
Since the second layer contains hexagonal plate-shaped magnetic powder with a plate-like ratio equal to or larger than that of the plate-shaped magnetic powder, it is possible to weaken lubricant seepage or plasticization. This eliminates head adhesion and improves running durability. Furthermore, since the surface properties can be appropriately achieved, electromagnetic conversion characteristics and runnability can also be improved. Further, by performing a multilayer coating method in a wet state and dispersing each layer separately, good surface roughness can be obtained and durability can also be improved.

[Brief explanation of drawings]

The drawings are for illustratively explaining the present invention, and FIGS. 1, 2, 3, and 4 are cross-sectional views of each side of a magnetic recording medium, and FIG. 5 is a hexagonal ferrite. An enlarged perspective view of particles, FIG. 6 is a schematic diagram of a magnetic recording medium manufacturing apparatus, and FIG. 7 (A), (
B) and (C) are sectional views of each side of the coating head (30) (31) (extrusion coater). In addition, in the symbols shown in the drawings, 1...Nonmagnetic support 2...Lower magnetic layer 2', 4'...Magnetic Paint 4.6...
......Upper magnetic layer 7.8...Lower layer 9...Hexagonal ferrite 10.11.
......It is an extrusion coater.

Claims (1)

[Claims] 1. A magnetic layer provided on a non-magnetic support is formed of an uppermost layer and a lower layer consisting of at least one layer, the uppermost layer containing hexagonal plate-shaped magnetic powder, and a magnetic recording medium in which at least the second layer from the uppermost layer of the lower layer contains hexagonal plate-shaped magnetic powder having a plate-like ratio equal to or greater than that of the plate-shaped magnetic powder. 2. The magnetic layer provided on the non-magnetic support is formed of an uppermost layer and a lower layer consisting of at least one layer, and the uppermost layer contains hexagonal plate-shaped magnetic powder, and among the lower layers, At least the second layer from the top layer contains hexagonal plate-like magnetic powder with a plate-like ratio equal to or larger than that of the plate-like magnetic powder, and the surface roughness of the magnetic layer is Ns/Ns(t), which is the ratio of the number of spikes Ns that protruded by 0.01 μm or more from the average line of the cross-sectional curve to the total number of peaks Ns(t) that protruded from the same average line, is 0.1.
0 to 0.35. 3. A top layer containing a hexagonal plate-shaped magnetic powder; at least the second layer from the top layer is a hexagonal plate-shaped layer with a plate-like ratio equal to or larger than that of the plate-shaped magnetic powder; When manufacturing a magnetic recording medium having on a non-magnetic support a lower layer consisting of at least one layer containing magnetic powder,
A method for manufacturing a magnetic recording medium, which comprises coating the magnetic paint for the lower layer and the magnetic paint for the uppermost layer in a wet state in a multilayer manner on the nonmagnetic support.