JPH03219423A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve durability and conductivity by incorporating hexagonal magnetic powder and carbon black into an upper layer and incorporating needle- like magnetic powder and carbon black into a lower layer and specifying the total thickness of the medium layers to <=4.5mum. CONSTITUTION:On a nonmagnetic supporting body 1, the first magnetic layer 2 and the second magnetic layer 4 are successively formed and a back coating layer 3 is provided on the other side of the supporting body 1. The layer 2 is made 1.5 - 4.0mum thick and the layer 4 is made 0.01 - 1.5mum thick. Carbon black of not too fine powder, 20 - 500mmu particle size, is incorporated into the layer 4 by >=50% of the all carbon black particles in the layer 4, so that the proper surface property is obtained to improve durability. Since the layer 2 contains rather fine carbon black of 5 - 30mmu particle size by >=50% of the total amt. of the carbon black, the surface resistivity of the medium is reduced and reduction of light-shielding property due to the layer 4 is prevented. The total thickness including the layers 2, 4 is made <=4.5mum so as to improve kthe traveling property, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks, 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, magnetic powders with high Hc and high BET values are used because recording characteristics in high frequencies are improved and low noise is required.

However, since magnetic recording media are composed of a single type of magnetic powder (magnetic layer), high-H
c. Since it is necessary to use magnetic powder with a high BET value, the low-frequency characteristics 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. 172142/1983, Special Publication No. 172142
-2218, JP-A-51-64901, JP-A-56
-12937, JP-A No. 58-56228, JP-A No. 6
3-146211, 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, magnetic recording media with coated magnetic layers have used oxide magnetic powder such as γ-F6203, but recently, in order to improve magnetic recording density, perpendicular magnetic recording has been used. As the magnetic powder, a plate-shaped magnetic powder made of hexagonal ferrite and having an average particle size of 0.2 μm or less has been 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 this medium is said to have good recording characteristics for short-wavelength and long-wavelength signals and to provide high durability, it is still insufficient. Moreover, no measures have been taken to address other required performances such as conductivity and runnability, and sticking and run 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 are improved in the high range (
Overall deterioration occurs, including the shortwave side).

C.6 Purpose of the Invention The purpose of the present invention is to provide a medium having a plurality of magnetic layers that generally improves electromagnetic conversion characteristics, durability, conductivity, runnability, etc., and a method for manufacturing the same. There is a particular thing.

20 Structure of the Invention That is, in the present invention, 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 has a thickness of 0.01 to 1.5 μm. having a hexagonal magnetic powder and a particle size of 20 to 50 carbon black, which accounts for 50% or more of the total number of carbon blacks in the uppermost layer.
0 mμ of carbon black, and at least the second layer from the top layer of the lower layer contains acicular magnetic powder and the carbon black in the at least second layer (in each layer if there are multiple layers). The total thickness of the media constituting layers on the nonmagnetic support, which contains carbon black with a particle size of 5 to 30 mμ accounting for 50% or more of the total number of carbon blacks, and further includes the uppermost layer and the lower layer. This relates to a magnetic recording medium in which the diameter is 4.5 μm or less.

Further, in the present invention, 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 has a thickness of 0.01 to 1.5 μm. , a hexagonal magnetic powder, and a particle size of 20 to 50 particles accounting for 50% or more of the total number of carbon blacks in the top layer.
0 mμ of carbon black, and at least the second layer from the top layer of the lower layer contains acicular magnetic powder and the carbon black in the at least second layer (in each layer if there are multiple layers). Contains carbon black with a particle size of 5 to 30 mμ accounting for 50% or more of the total number of carbon blacks, and furthermore, the surface roughness of the magnetic layer protrudes by 0.01 μm or more from the average line of the surface roughness cross-sectional curve. The number of spikes N's and the total number of peaks that stick out from the average line NS (t)
This relates to a magnetic recording medium in which the ratio Ns/Ns(t) is 0.1 to 0.35.

In addition, the present invention has a thickness of O0 inch to 1.5 μm, hexagonal magnetic powder, and carbon having a particle size of 20 to 500 μm, which accounts for 50% or more of the total number of carbon blacks in the layer. At least the second layer from the top layer contains acicular magnetic powder and 50% of the total number of carbon blacks in the at least second layer (in each layer in the case of multiple layers). Particle size 5-30 occupies more than %
a lower layer consisting of at least one layer containing mμ of carbon black; The total thickness of the magnetic recording medium is 4.5 μm or less. A method of manufacturing the media is also provided.

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. In addition, the lower layer has acicular magnetic powder to improve relatively low-frequency recording and playback characteristics such as chroma and audio output.
Electromagnetic conversion characteristics are improved over the entire area.

In particular, the hexagonal magnetic powder used for the top layer is, for example, the fifth layer.
Examples include hexagonal ferrite 9 as shown in the figure. Idiohexagonal ferrite has a flat plate shape (diameter d is 0.01 to 0.1
The magnetic field 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 short wavelengths and is suitable for use as the top layer. These hexagonal ferrite magnetic materials are 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, Ti, Co, Zn, In, Mn). , Ge5
Nb, etc.), or multiple types of hexagonal ferrite magnetic materials may be used in combination. Regarding this ferrite magnetic material, IEEE Trans,
on Mag.

It is described in detail in MAG-1816 (19B2).

In addition, the acicular magnetic powder used in the lower layer side of the magnetic layer (at least the second layer from the top layer) is suitable for long wavelength recording, and has a 7F
ew O3, Co-containing 7-Fe2O3, r-Fe304
, Co-containing Fe, O, etc. (especially Co-containing iron oxide), as well as Fe.

N1, Co5Fe-Ni-Co alloy, Fe-Ni alloy,
Fe-A/! alloy, Fe-Affi-Ni alloy, Fe-
Al1-Co alloy, Fe-Mn-Zn alloy, Fe-Ni
-Zn alloy, Fe-AN-Ni-C.

(9) (10) Alloy, Fe-Al! , -Ni-Cr alloy, Fe-Al!
.

Co-Cr alloy, Fe-Co-Ni-Cr alloy, Fe-
Co-N1-P alloy, Co-Ni alloy, etc. Fe, Ni, C
It may be a metal magnetic powder or the like whose main component is O or the like.

In the media of the present invention, the carbon black contained in the multiple magnetic layers is specifically selected, thereby improving durability, conductivity, and runnability, which were insufficient in conventional media. There is.

That is, it is not good to use carbon black with a large particle size in the top layer, but if the particle size is too small, friction will increase and durability will deteriorate.

On the other hand, according to the present invention, carbon black particles with a particle size of 20 to 500 mμ, which is not too fine, can be used to
% or more, it is possible to obtain appropriate surface properties and improve durability. In this case, since the lower layer (at least the second layer from the top layer) contains carbon black with a relatively fine particle size of 5 to 30 mμ, which accounts for 50% or more of the total carbon black, the surface ratio of the medium is It is also possible to lower the resistance (improve conductivity) and prevent the top layer from deteriorating its light-shielding properties.

As for the above carbon black, in the top layer,
Those with a particle size of 40 to 200 mμ, and even 50 to 100 m
μ particles are best, and in the lower layer, the particle size is 40 to 200 m.
It is preferable to use μ, more preferably 40 to 100 mμ. The number of carbon blacks having the above particle size should be at least 50% of the total number of carbon blacks, and preferably at least 60% (or 60 to 90%). In addition, the total content of carbon black is 0.1 to 20 parts by weight in the uppermost layer, further 0.2 to 10 parts by weight, and 0.1 to 20 parts by weight in the lower layer, based on 100 parts by weight of the magnetic powder. Furthermore, the amount is preferably 0.5 to 15 parts by weight.

This refers to the particle size of carbon black, which appears black, measured using a caliper. When the average particle diameter is meant, it is the average value of 50 or more particles.

Furthermore, as the carbon black used in the present invention, (11
) (12) If a light-shielding carbon black is used, the degree of light-shielding can be further increased, and if a conductive carbon black is used, there is an effect of preventing the magnetic layer from being charged.

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 condition.

On the other hand, the center line average surface roughness Ra including the concave portions below the average line and the maximum roughness Rmax including 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 Rma
x/Ra specifies a different type of surface state at least regarding 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.

In the present invention, the film thickness (or layer thickness) of the above-mentioned top layer should be 0.01 to 1.5 am;
, Ottm, particularly preferably 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 will be too thick and will impair the performance of the underlying layer. In addition, the thickness of the lower layer adjacent to this upper layer is 1.5 to 4.0
It is desirable to set it to μm. In addition, the media constituent layers including the magnetic layer (excluding the support) should have a thickness of 4.5 μm or less; if it is thicker than this, problems will arise in runnability and the like.

This thickness is further preferably 4.0 μm or less. In addition, in the present invention, multiple layers (uppermost layer and lower layer) constituting the magnetic layer
are preferably adjacent to each other. The lower layer may be one layer, or may be two or more layers. However, in addition to cases in which there is substantially a clear boundary between each layer, there may also be a boundary area where magnetic powder from both layers coexists at a certain thickness (13) (14) However, the upper or lower layer excluding these boundary areas is defined as each of the above layers.

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 magnetic layer 2 and a second magnetic layer 4 are laminated thereon in this order. Further, although a back coat layer 3 is provided on the support surface opposite to the laminated surface, this need not necessarily be provided. An overcoat layer may be provided on the second magnetic layer. In the example of FIG. 2, the upper layer is further divided into layers 5 and 6.

In the magnetic recording media shown in FIGS. 1 and 2, the thickness of the first magnetic layer 2 is 1.5 to 4.0 μm (for example, 3.0 μm).
It is preferable that the film thickness of the second magnetic layer 4 or the second
, the total thickness of the third magnetic layer 5.6 is 0.01 to 1.5
am (for example, 0.75 μm).

Further, 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 is a magnetic layer containing magnetite magnetic powder to improve the light shielding property (in this case, the magnetic layer 2 For example, Co-containing γFezes may be used as the magnetic powder.) Further, the layer 7 may be a non-magnetic layer containing carbon black instead of a magnetic layer (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 carbon black, each magnetic layer contains
Lubricants (e.g. silicone oil, graphite, molybdenum disulfide, tungsten disulfide, 12 or more carbon atoms)
20 monobasic fatty acids (e.g. stearic acid), fatty acid esters with a total number of carbon atoms of 13 to 40, abrasives (e.g. ffl alumina), antistatic agents (e.g. carbon black, graphite), dispersants (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 chloride (15) (16) acrylonitrile copolymer, polyvinyl chloride, urethane resin, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose derivative (
cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer, polyester resin, various synthetic rubbers, phenolic resin, epoxy resin, urea resin, melamine resin, Phenoxy resins, silicone resins, acrylic reactive resins, mixtures of high molecular weight polyester resins and isocyanate prepolymers, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/isocyanates, and mixtures thereof. etc. are exemplified.

These binders are -3o, M, -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 an alkali metal such as lithium, potassium, or sodium, or a hydrocarbon residue, or a polar group containing a nitrogen atom. In other words, the polar groups in the molecules of these resins improve their compatibility with the magnetic powder, which further improves the dispersibility of the magnetic powder and prevents agglomeration of the magnetic powder, further improving the stability of the coating liquid. This can also improve the durability of the medium.

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).

(17) (18) When providing the back coat layer 3, non-magnetic particles such as barium sulfate are added to the binder described above, and the mixture is coated on the back surface of the support.

Moreover, the material of the support 1 mentioned above includes plastics such as polyethylene terephthalate and polypropylene, A!
, metals such as Zn, glass, BN.

Ceramics such as St carbide, porcelain, and earthenware are used. The Young's modulus of this support 1 in the width direction is 600 k
g/n+m” is desirable for reducing head clogging.

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. Furthermore, although the hexagonal magnetic powder in the uppermost layer has a plate shape, 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, even though the uppermost 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 application. Further, when oriented, the orientation becomes easier, which is advantageous for the squareness ratio (and thus the output).

On the contrary, conventional media (Japanese Unexamined Patent Publication No. 112822 mentioned above)
As mentioned above, with No. 8, etc., the surface of the lower layer is rough because it is dried and rolled up after coating the lower layer.
The top layer cannot be applied 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 a 2000 Gauss rear-stage orientation magnet 35 (this can be omitted). It is dried by blowing hot air from a nozzle placed on it.

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.

Each paint may be fed to extrusion coater 10.11 through an in-line mixer (not shown).

In addition, in the figure, the arrow indicates the conveyance direction of the nonmagnetic base film. 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 Figure 6 (for sequential wet multi-layer coating with two heads), (B) is for one head (for sequential wet multi-layer coating), and (C) is for one head. Both magnetic paint 2
', 4' are discharged in a crosswise overlapping manner 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, and 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 consisting of the following compositions ■, ■, ■, ■,
(2) was prepared.

1 piece of CO-substituted Ba ferrite (BET value 60 rrr/g, average particle size 0.04 μm, plate ratio 4, Hc 6000e) 10
0 parts (21) (22) Vinyl chloride copolymer (degree of polymerization: 300, negative functional group 0
．． 05 mmo j2/g) 15 parts polyurethane resin (toluene diisocyanate, 1.6
- Consists of hexanediol, adipic acid, molecular weight 30,000, negative functional group 0.05 mmo42/g) 10 parts 3 parts 2 parts 1 part 1 part 1 part 150 parts 150 parts Carbon black alumina powder Lecithin Myristate Stearate Butyl methyl ethyl ketone Toluene and Co-containing 7-Fe2O3 (BET value 45nf/g.

Hc6000e) 100 parts vinyl chloride copolymer (same as used in coating liquid ■) 15 parts polyurethane resin (same as 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
1 part toluene 15
0 copies! Cloth blood Ω Co-containing Fe50. (BET value 35nf/g.

Hc6500e) 100 parts vinyl chloride copolymer (same as used in coating liquid ■) 15 parts polyurethane resin (same as 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 (23) (24) Toluene 150 parts Rifu-sanka Fe-Al! , (BET value 45nf/gXHc600
0 e) 100 parts vinyl chloride copolymer (same as used in coating liquid ■) 15 parts polyurethane resin (same as 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
1 part toluene 150
Department! Keishin Ω Carbon black 100 parts Nitrocellulose 15 parts Polyurethane resin (consisting of 4,4'-diphenylmethane diisocyanate, 1,6-hexanediol, adipic acid,
Molecular weight: 40,000) 10 parts lecithin
1 part alumina powder 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: Coronet 1-L (manufactured by Nippon Polyurethane Co., Ltd.) were added. Using each coating solution in combination as shown in Table 1 below, the dry thickness, carbon black particle size, functional group of polyurethane, and coating method were set as shown in Table 1, and a film thickness of 14 μm was obtained.
After coating on a polyethylene terephthalate base of
Calendar treatment was carried out under the treatment conditions of b.

Thereafter, a paint for the BC layer having the following composition was applied to the surface opposite to the magnetic layer to a dry thickness of 0.8 μm (25) (26).

Carbon black (Raven1035)
40 parts barium sulfate (average particle size 300 mμm) 1
0 parts Nitrocellulose 25 parts N-2301 (manufactured by Nippon Polyurethane Co., Ltd.) 25 parts Coronate (manufactured by Nippon Polyurethane Co., Ltd.) 10 parts Cyclohexanone 400 parts Methyl ethyl ketone 250 parts Toluene
250 copies of a wide magnetic film was thus obtained and wound up. This film was cut to a width of A inch to produce video tapes shown in Table 1 below.

Note that Ns/Ns(t) was measured as follows.

As a measuring device, we used a Christetub roughness needle (Rank Taylor).
Bobson (manufactured by Rank Taylor Hobson) was used.

Specifications and measurement conditions> Stylus 2.5 Xo, 1 μm stylus force 2 mg cut-off filter 0.33 Hz measurement speed
゛2.5μm/sec reference length
0.5mm, and in the roughness curve, 0.00
Calculate the number Ns of spikes with protruding irregularities of 5 μm or less and the total number of spikes Ns (t) with protrusions on the average line, and calculate Ns/
Calculate Ns(t).

(The following is a blank space) (27) (28) The following performance evaluations were performed for each of the above tapes, and the results are shown in Table 2 below.

(a), RF output crab JVC r HR-D120 J
is used, and the value when the reference tape value is set to 0 at 7MHz.

(b) The value when the reference tape value is O at 500 kHz using rHR-D120J manufactured by Chromadekani JVC.

(C), H3Fi audio output crab JVC rHR-DI
Value when using 20J and setting the reference tape to 0 at 1.7M7.

(d) Squareness ratio: Residual magnetic flux density (Br) and saturation magnetic flux density (Bm) were measured in the longitudinal direction using a vibrating magnetometer manufactured by Toei Kogyo ■, and a value of (5 kOe) Br78m was determined.

(e), OR: ratio of the squareness ratio in the longitudinal direction to the squareness ratio in the width direction.

Dynamic friction coefficient: 20°C, 165% RH: The inlet tension was set to 20g using a running performance tester rTDT 300D manufactured by Yokohama System Research, and the diameter was 3.
Wrap a magnetic tape around an 8-rib stainless steel bottle at 180 degrees, run it at 3.3 cm/sec, measure the outlet tension after 4 minutes, and calculate it from the following formula (odor, powder drop: 100 at 40°C, 180% RH). After running for an hour, the head was observed for dirt.A: no dirt, B: a little dirt, C: a lot of dirt, and D: very dirty.

(c),3μs,,D,O,(dropout)=1'
The number of dropouts of −12 dB or more was measured for 3 μs per minute.

(i) 9 Surface resistivity: As shown in Figure 8, two rod-shaped metal electrodes 22 whose cross section forms a quarter circle with a radius of approximately 1 cm are separated by a gap d (12,7 cylinders). Place the magnetic surface of the tape 21 in contact with these at right angles, hang weights of weight w (160 g) from both ends of the tape, and use an insulation resistance meter to measure the measurement voltage of 500 ± 50 V DC on these (31 ) (32) In addition to the electrode, the resistance value was measured, and this was taken as the surface specific resistance. Measurements are made after the material has been left at a relative humidity of 30% for 24 hours.

(j) Light-shielding property The light-shielding property of the tape was measured using a light source with a dual wavelength of 900 nm.

○ Runs smoothly until the end of the tape × Stops or cannot run midway (G), sliding noise: 20°C 110% RHt'lOM
We saw an increase from 1 bus run around Hz to 10 bus runs.

(1) Head cloudiness: 20°C 110% RHT: The degree of dirt on the head was observed after running for 20 hours. No stains at all ◎, No stains ○, Some stains △, Extremely dirty ×.

(33) From this result, by forming each layer based on the present invention, output improvement from long wavelength side to short wavelength side, squareness ratio, orientation, surface specific resistance, coefficient of dynamic friction, durability at high temperature and high humidity, etc. It is possible to provide a magnetic recording medium with good quality.

Effects of the Invention As described above, in the present invention, the uppermost layer of the magnetic layer has a thickness of 0.01 to 1
．． It has a thickness of 5 μm, contains hexagonal magnetic powder, and carbon black with a particle size of 20 to 500 mμ, which accounts for 50% or more of the total number of carbon blacks in the uppermost layer, and At least 2 from the top layer of
The second layer contains acicular magnetic powder and carbon black having a particle size of 5 to 30 mμ, which accounts for 50% or more of the total number of carbon blacks in the at least second layer, and further, the top layer The thickness of the medium constituting layer on the non-magnetic support including the lower layer and the lower layer is 4.5 μm or less. Therefore, by using different magnetic powders between each layer of the magnetic layer, it is possible to achieve good recording from the long wavelength side to the short wavelength side, strengthen the durability of the top layer, and reduce powder falling off. By changing the particle size of carbon black and creating different layers of magnetic powder, we can improve the surface roughness and promote the movement of wetting agents to the surface, maintaining appropriate surface roughness and improving runnability. A magnetic recording medium with a low coefficient of friction can be provided. In addition, carbon black lowers the surface resistivity and reduces small dropouts as much as possible. Since each layer is separately dispersed and applied by wet multilayer coating (wet on wet) using an extrusion method or the like, the squareness ratio can be increased and orientation can be easily achieved.

[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 (extrusion coater), and FIG. 8 is a schematic perspective view of a surface resistivity measuring meter. (36) (37) In the symbols shown in the drawings, 1...Nonmagnetic support 2...Lower magnetic layer 2', 4'... ...Magnetic paint 3...
...Back coat layer 4.6... Upper magnetic layer 7.8... Lower layer 9... Hexagonal ferrite 10 .11・
......It is an extrusion coater.

Claims (1)

[Claims] 1. 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 has a thickness of 0.01 to 1.5 μm. and contains hexagonal magnetic powder and carbon black having a particle size of 20 to 500 mμ accounting for 50% or more of the total number of carbon blacks in the uppermost layer, and the uppermost layer of the lower layers At least the second layer includes acicular magnetic powder and particles having a particle size of 5 to 30 mμ that account for 50% or more of the total number of carbon blacks in the at least second layer (in each layer if there are multiple layers). carbon black, and further has a total thickness of the medium constituent layers on the nonmagnetic support, including the uppermost layer and the lower layer, of 4.5 μm or less. 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, the uppermost layer has a thickness of 0.01 to 1.5 μm, and has a hexagonal crystal structure. and carbon black having a particle size of 20 to 500 mμ, which accounts for 50% or more of the total number of carbon blacks in the uppermost layer, and at least the second layer from the uppermost layer among the lower layers. contains acicular magnetic powder and carbon black with a particle size of 5 to 30 mμ, which accounts for 50% or more of the total number of carbon blacks in at least the second layer (in each layer in the case of multiple layers). , Furthermore, as the surface roughness of the magnetic layer, Ns is the ratio of the number of spikes Ns that protrude by 0.01 μm or more from the average line of the surface roughness cross-sectional curve to the total number of peaks Ns (t) that protrude from the average line.
/Ns(t) is 0.10 to 0.35. 3. It has a thickness of 0.01 to 1.5 μm, hexagonal magnetic powder, and carbon black with a particle size of 20 to 500 μm, which accounts for 50% or more of the total number of carbon blacks in the layer. At least the second layer from the top layer contains acicular magnetic powder and at least 50% of the total carbon black number in the at least second layer (in each layer if there are multiple layers). A magnetic recording medium having, on a non-magnetic support, at least one lower layer containing carbon black with a particle size of 5 to 30 mμ;
The total thickness of the medium constituent layers on the nonmagnetic support, including the uppermost layer and the lower layer, is 4.5 μm or less. ), in which the magnetic paint for the lower layer and the magnetic paint for the uppermost layer are coated in a wet state on the non-magnetic support in a multilayer manner.