JPH1166550A - Magnetic recording medium and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium of high-quality recording and its manufacture which has superior electromagnetic conversion characteristics for outputs, noises, etc., and good head touch performance. SOLUTION: This magnetic recording medium has on a support a first magnetic layer, and a second magnetic layer as an outermost layer. The first and second magnetic layers are obtained by applying a coating in many layers in which magnetic particles or ferromagnetic particles and a binder are at least dispersed. In this case, a thickness of the second magnetic layer is not larger than 0.3 μm, a thickness of the first magnetic layer is not smaller than 0.7 μm, and the second magnetic layer contains at least iron-based ferromagnetic particles and a polar group-containing urethane binder. Barium ferrite is used as the magnetic particles of the first magnetic layer. Non-magnetic acicular inorganic particles are added by not smaller than 20 pts.wt. and smaller than 100 pts.wt. to 100 pts.wt. of the barium ferrite.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer magnetic recording medium and a method for manufacturing the same, and more particularly, to a high recording magnetic recording medium having high rigidity using barium ferrite as a magnetic powder used for a first magnetic layer. The present invention relates to the manufacturing method.

[0002]

2. Description of the Related Art In recent years, the characteristics required for tapes and disks have become extremely high with the increase in density of recording media.
In order to increase the output of the entire media, the powder used for the purpose of high coercive force and high magnetization has been used for the magnetic powder itself, which has undergone changes such as γ-iron oxide, Co-coated iron oxide, and metal powder. . In addition, reduction of noise accompanying an increase in output has become a problem, and finer powder has been developed. This kind of technology is a method of manufacturing magnetic powder, additional elements, moisture adjustment,
It is a content proposed in many documents regarding aspects such as improvement of pH and specific surface area.

Attempts have been made to improve the characteristics of magnetic recording media. The effects of the multilayered medium having the magnetic layer and the intermediate layer include an improvement in output of short-wavelength recording and a reduction in noise. For example, JP-A-62-154
No. 225 and Japanese Unexamined Patent Publication (Kokai) No. 62-212933 describe the advantages of the multilayer medium.

[0004] In the case of this multilayered medium, it is common that the intermediate layer is made non-magnetic, or the intermediate layer is made magnetic by using acicular magnetic powder. For example, U.S. Pat.
As shown in US Pat. No. 3,793,397, the advantage of using a non-magnetic intermediate layer is effective for short-wavelength recording, and the recording demagnetization loss can be minimized. In the case of digital recording such as a DAT tape, the wavelength reaches nearly 10 MHz, and the intermediate layer has little meaning in terms of a recording area. Also, as disclosed in U.S. Pat. No. 4,874,633, a high degree of orientation can be obtained during wet-on-wet orientation because there is little in the intermediate layer that hinders the orientation magnetization movement of the magnetic powder due to viscosity. Has been confirmed.

On the other hand, the main advantage of using magnetic powder for the intermediate layer is that the recording area for short wavelengths and long wavelengths are separated, but servo signals and VTR audio signals correspond to long wavelengths. Is known in many documents. In the recording region of 10 MHz or less, the short-wavelength magnetization component extends to the intermediate layer, and an effect that cannot be obtained when the intermediate layer is made nonmagnetic has been confirmed. Further, conventional magnetic powders used for the intermediate layer are mostly acicular powders, for example, US Pat. No. 4,091,158 and US Pat. No. 4,439,796.
However, there are few products and technologies using barium ferrite, which is a plate-like magnetic powder, in the intermediate layer. This is because barium ferrite is difficult to disperse and has low rigidity as a medium. However, the present invention solves the above problem and provides a magnetic recording medium having extremely high recording characteristics. .

[0006]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a high-recording magnetic recording medium which has excellent electromagnetic conversion characteristics such as output and noise and has good head touch characteristics, and a method of manufacturing the same. It is in.

[0007]

Means for Solving the Problems As a result of diligent research, the present inventors have made the thickness of a magnetic layer extremely thin, used barium ferrite as a magnetic powder of a first magnetic layer, and obtained a nonmagnetic acicular inorganic material. It has been found that the above object can be achieved by containing a certain amount of powder.

That is, the present invention has been made on the basis of the above findings, and comprises a first magnetic layer and a second magnetic layer as an outermost layer on a support, wherein the first magnetic layer And the second magnetic layer is a magnetic recording medium obtained by layer-applying a coating material in which at least a magnetic powder or a ferromagnetic powder and a binder are dispersed, wherein the thickness of the second magnetic layer is 0.3 μm or less, The thickness of the first magnetic layer is 0.7 μm
As described above, the second magnetic layer contains at least an iron-based ferromagnetic powder and a polar group-containing urethane binder, and uses barium ferrite as the magnetic powder of the first magnetic layer, based on 100 parts by weight of the barium ferrite. It is intended to provide a magnetic recording medium characterized by containing not less than 20 parts by weight and less than 100 parts by weight of nonmagnetic acicular inorganic powder.

The present invention also provides, as a preferred method of manufacturing the magnetic recording medium of the present invention, a first magnetic paint in which at least a magnetic powder and a binder are dispersed, and a first magnetic paint in which at least a ferromagnetic powder and a binder are dispersed. In the method for producing a magnetic recording medium, wherein each of the magnetic paints is prepared on a support, the second magnetic paint contains at least an iron-based ferromagnetic powder and a polar group-containing urethane binder, The first magnetic paint contains barium ferrite as a magnetic powder, and contains not less than 20 parts by weight and less than 100 parts by weight of a nonmagnetic acicular inorganic powder with respect to 100 parts by weight of the barium ferrite. While applying the first magnetic paint so that the dry thickness becomes 0.7 μm or more, while the obtained first magnetic layer is in a wet state,
It is another object of the present invention to provide a method for producing a magnetic recording medium, wherein the second magnetic paint is applied simultaneously or sequentially so that the dry thickness becomes 0.3 μm or less.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.
The magnetic recording medium of the present invention comprises a non-magnetic support, a first magnetic layer located on the support, and a second magnetic layer as an uppermost layer located on the first magnetic layer. At least be. Further, a back coat layer is provided on the back surface of the support as necessary. Further, the magnetic recording medium of the present invention includes:
In addition to the support, the first magnetic layer, the second magnetic layer, and the backcoat layer, a primer layer provided between the support and the first magnetic layer or the backcoat layer, or a long-wavelength signal Another layer such as another magnetic layer provided for recording a servo signal or the like corresponding to a hardware system using the same may be provided.

In the magnetic recording medium of the present invention, the first magnetic layer located on the support is a layer having magnetism. The first magnetic layer needs to have a thickness of 0.7 μm or more. If the thickness is less than 0.7 μm, sufficient tape rigidity cannot be obtained, and sufficient output cannot be obtained due to the problem of head touch. Also, the coercive force (H
c) is preferably 1200 to 3000 Oe.
Such a first magnetic layer is formed by preparing a first magnetic paint in which at least a magnetic powder, a non-magnetic acicular inorganic powder, a binder and a solvent are dispersed, and applying the paint to a support. .

In the present invention, hexagonal barium ferrite is used as the magnetic powder of the first magnetic layer. This barium ferrite is in the form of a fine flat plate and has a plate diameter of 100 to 1
Those having a plate-like ratio of 2 to 7 at 000 ° are preferably used. The barium ferrite has a coercive force (Hc) of 1200 to 3000 Oe, preferably 1500 to 220 Oe.
It is preferably 0 Oe. If the coercive force of barium ferrite is less than the lower limit, demagnetization tends to occur, so short-wavelength RF
If the output decreases or exceeds the upper limit, the head magnetic field becomes insufficient and the write performance becomes insufficient, and further the overwrite characteristics are reduced.

The barium ferrite may contain a rare earth element or a transition metal element as required. Further, barium ferrite may be subjected to a surface treatment in order to improve the dispersibility of the barium ferrite. This surface treatment is called "Characterization of Powder S
urfaces "; a method similar to the method described in Academic Press and the like, for example, a method of coating the surface of barium ferrite with an inorganic oxide. At this time, inorganic oxides that can be used include Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , and Sn.
O ₂ , Sb ₂ O ₃ , ZnO and the like can be mentioned, and when used, they can be used alone or as a mixture of two or more kinds. The surface treatment can be performed by an organic treatment such as a silane coupling treatment, a titanium coupling treatment, and an aluminum coupling treatment, in addition to the above methods.

The first magnetic layer contains a nonmagnetic acicular inorganic powder. A plate-like material such as barium ferrite does not have an aggregate effect, and therefore contains a certain amount of nonmagnetic acicular inorganic powder. The content of the nonmagnetic acicular inorganic powder is from 20 parts by weight to less than 100 parts by weight, preferably from 50 parts by weight to less than 100 parts by weight, based on 100 parts by weight of barium ferrite. When the content of the nonmagnetic acicular inorganic powder is 100 parts by weight or more, the surface properties of the magnetic layer are affected, and the output is reduced or the surface becomes poor. When the content is less than 20 parts by weight, the effect of the aggregate is weak. As a result, sufficient head touch cannot be obtained, and both are not desirable.

[0015] Such non-magnetic acicular inorganic powders include:
α-iron oxide, titanium oxide, barium sulfate, zinc sulfide, magnesium carbonate, calcium carbonate, zinc oxide, calcium oxide, magnesium oxide, tungsten disulfide, molybdenum disulfide, boron nitride, tin dioxide, silicon dioxide, non-magnetic oxidation Chromium, alumina, silicon carbide, cerium oxide, corundum, artificial diamond, garnet, garnet, silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, titanium carbide, diatomaceous earth, dolomite, graphite, resinous powder, etc. And, among them, α-iron oxide is preferably used. The size of these nonmagnetic acicular inorganic powders is such that the major axis length is 20 to 300 nm,
Preferably, the axial ratio is from 3 to 20. Further, those having Mohs hardness of 4 or more are desirable.

The first magnetic layer is appropriately blended with a non-magnetic inorganic powder having a shape other than a needle shape, for example, a spherical, plate, or amorphous shape. Examples of such an inorganic powder include the same α-iron oxide, titanium oxide, barium sulfate, zinc sulfide and the like as described above. The size of these nonmagnetic inorganic powders is 5
Preferably it is 200 nm. It is desirable that the Mohs' hardness is 4 or more as described above. In order to improve the dispersibility and the like of these nonmagnetic inorganic powders, a surface treatment similar to the above-described surface treatment performed on barium ferrite can be performed.

It is desirable that the first magnetic layer contains carbon black. Examples of the carbon black include furnace for rubber, thermal for rubber, black for color, acetylene black, ketchen black and the like, and details thereof are described in “Carbon Black Handbook” (edited by Carbon Black Association).

Examples of the binder used for the first magnetic layer include a thermoplastic resin, a thermosetting resin, and a reactive resin. When used, they can be used alone or as a mixture. Specific examples of these binders include:
Examples thereof include vinyl chloride-based resins, polyesters, polyurethanes, nitrocellulose, epoxy resins, and the like. In addition, JP-A-57-162128, page 2, upper right column, line 19 to page 2, lower right column, line 19 Resins and the like described in the rows and the like are included. Further, the binder may contain a polar group for improving dispersibility and the like. The mixing ratio of the binder is preferably 5 to 200 parts by weight, more preferably 5 to 100 parts by weight, based on 100 parts by weight of the magnetic powder (barium ferrite).

The solvents used for forming the first magnetic layer include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, and chlorinated hydrocarbon solvents. Solvents described specifically in JP-A-57-162128, page 3, lower right column, line 17 to page 4, lower left column, line 10, etc. it can. The mixing ratio of the solvent is preferably from 80 to 500 parts by weight, more preferably from 100 to 350 parts by weight, based on 100 parts by weight of the magnetic powder (barium ferrite).

Further, the first magnetic paint for forming the first magnetic layer contains a usual magnetic recording material such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust inhibitor, a fungicide, and a hardener. Additives used in the medium can be added as needed. As these additives, specifically, JP-A-57-
No. 162128, page 6, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6, to page 3 upper right column, first
Various additives described in line 8 and the like can be mentioned.

In the magnetic recording medium of the present invention, the second magnetic layer is an uppermost layer of the magnetic recording medium, that is, a layer provided as a layer located on the surface of the magnetic recording medium. 2 is formed by applying the magnetic paint. As the second magnetic paint, a paint mainly containing a ferromagnetic powder, a binder and a solvent is preferably used. This second magnetic layer needs to have a thickness of 0.3 μm or less. When the thickness exceeds 0.3 μm, the output decreases.
The coercive force (Hc) of the second magnetic layer is 1500 to
It is desirably 3000 Oe, more preferably 1800 to 2300 Oe. The saturation magnetic flux density is preferably 30
00-4500 gauss, more preferably 3200-40
00 Gauss.

As the ferromagnetic powder used here, an iron-based ferromagnetic alloy powder, that is, a hard magnetic metal powder is used.
Examples of the iron-based ferromagnetic alloy powder include a ferromagnetic alloy powder mainly composed of iron in which a metal content is 70% by weight or more and 80% by weight or more of the metal is Fe. Are, for example, Fe-Co, Fe-N
i, Fe-Al, Fe-Ni-Al, Fe-Co-N
i, Fe-Ni-Al-Zn, Fe-Al-Si and the like.

The iron-based ferromagnetic alloy powder has a needle-like or spindle-like shape, and its major axis preferably has a length of 0.05 to 0.25 μm.
m, more preferably 0.05 to 0.2 μm, a preferred needle ratio of 3 to 20, and a preferred crystallite size of 100.
It is desirably about 450 °. Further, in order to improve the dispersibility and the like of these iron-based ferromagnetic alloy powders, a surface treatment similar to the surface treatment performed on the barium ferrite contained in the first magnetic layer is applied to the iron-based ferromagnetic alloy powder. Can be applied.

The coercive force (Hc) of the iron-based ferromagnetic metal powder is 1
It is preferably 500 to 3000 Oe,
More preferably, it is 2400 Oe. If the coercive force of the iron-based ferromagnetic alloy powder is less than the above lower limit, the short-wavelength RF output is reduced due to easy demagnetization. In addition, overwrite characteristics deteriorate. Therefore, it is preferable to be within the above range.

The saturation magnetization of the iron-based ferromagnetic alloy powder is
Preferably, it is 100 to 180 emu / g.
More preferably, it is 60 emu / g. If the saturation magnetization of the ferromagnetic metal powder is less than the lower limit, the filling rate of the magnetic powder becomes low, and the output decreases.If the saturation magnetization exceeds the upper limit, the binder needs to be reduced, and the interaction between the magnetic powders occurs. Is large, and as a result, the magnetic powder is in an agglomerated state, and it is difficult to obtain a desired output.

The second magnetic layer can also contain a nonmagnetic inorganic powder or carbon black. As the nonmagnetic inorganic powder or carbon black, the first
The same materials as those used for the magnetic layer can be used.
As the nonmagnetic inorganic powder, those having a Moh's hardness of 6 or more are preferably used.

The binder and the solvent used in the second magnetic paint forming the second magnetic layer are the same as the binder and the solvent used in the first magnetic paint forming the first magnetic layer. Although it can be used, it is necessary to use at least a polar group-containing urethane binder as the binder. The use of the polar group-containing urethane binder improves the magnetic characteristics of the magnetic recording medium.

The amount of the binder used is preferably about 5 to 100 parts by weight, particularly preferably 5 to 70 parts by weight, per 100 parts by weight of the iron-based ferromagnetic alloy powder. The solvent is preferably used in an amount of 80 to 500 parts by weight, preferably 100 to 3 parts by weight, per 100 parts by weight of the iron-based ferromagnetic alloy powder.
50 parts by weight are more preferred.

The second magnetic coating composition contains additives, such as a dispersant, a lubricant, an abrasive, an antistatic agent, a rust inhibitor, a fungicide, and a hardener, which are commonly used in magnetic recording media. Can be added as needed. As such additives, specifically, JP-A-57-162128, page 2, upper left column, line 6 to page 2, upper right column, line 10 and page 3, upper left column, line 6 to line 3 Various additives described on page 3, upper right column, line 18, etc. can be mentioned.

To prepare the second magnetic paint, for example,
The iron-based ferromagnetic alloy powder and the binder are put into a Nauta mixer or the like together with a part of the solvent and preliminarily mixed to obtain a mixture, and the obtained mixture is kneaded by a continuous pressure kneader or the like, and then the solvent After partially diluting and dispersing using a sand mill or the like, mixing an additive such as a lubricant, filtering, and further mixing a curing agent such as polyisocyanate and the remaining solvent may be mentioned. it can.

As the non-magnetic support used in the magnetic recording medium of the present invention, any known non-magnetic support can be used without any particular limitation. Specifically, a flexible film made of a polymer resin is used. And disks; Cu, Al, Zn
Films, disks, cards and the like made of non-magnetic metals such as non-magnetic metals, glass, ceramics such as porcelain and ceramics can be used.

Examples of the polymer resin forming the flexible film or disk include polyesters such as polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polycyclohexylene dimethylene terephthalate and polyethylene bisphenoxycarboxylate, polyethylene, polypropylene and the like. Polyolefins, cellulose derivatives such as cellulose acetate butyrate, cellulose acetate propionate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, or polyamides, polyimides, polycarbonates, polysulfones, polyether ether ketones, polyurethanes, etc. When used, they can be used alone or in combination of two or more.

In the magnetic recording medium of the present invention, the back coat layer provided on the back surface of the non-magnetic support as needed can be formed using a known back coat paint without any particular limitation.

The magnetic recording medium of the present invention has a recording wavelength of 8 μm.
m and over 8mm video tape and DA
It is suitable as a magnetic tape such as a T tape, but can also be applied as another magnetic recording medium such as a floppy disk.

Next, an outline of the method for manufacturing a magnetic recording medium of the present invention will be described. First, a first magnetic paint for forming a first magnetic layer on a nonmagnetic support and a second magnetic paint for forming a second magnetic layer
The magnetic paint is wet-on-dry so that the dry thicknesses of the first magnetic layer and the second magnetic layer each become the aforementioned thickness.
Simultaneous multilayer coating is performed by a wet method to form a coating film of the first magnetic layer and the second magnetic layer. That is, the second magnetic layer is preferably applied and formed when the first magnetic layer is wet. The coating speed at this time is 100 to 300 m / s
ec is desirable.

Next, after the obtained coating film is subjected to a magnetic field orientation treatment, a drying treatment is performed and the film is wound up. Thereafter, after performing a calendering treatment, a back coat layer is further formed as necessary. Then, if necessary, for example, when obtaining a magnetic tape, 6 to 72 ° C. at 40 to 70 ° C.
After time aging, slit to desired width.

The above simultaneous multi-layer coating method is described in JP-A-5-73.
No. 883, column 42, line 31 to column 43, line 31, etc., wherein the second magnetic layer is formed before the first magnetic paint forming the first magnetic layer is dried. A method of applying a second magnetic paint, which has a smooth boundary surface between the first magnetic layer and the second magnetic layer and also has a good surface property of the second magnetic layer. , High density recording, and a coating film (the first magnetic layer and the second
A magnetic recording medium having excellent durability.

The magnetic field orientation treatment is performed before the first magnetic paint and the second magnetic paint are dried. For example, when the magnetic recording medium of the present invention is a magnetic tape, the second magnetic paint is used. A method of applying a magnetic field of about 500 Oe or more, preferably about 1000 to 10000 Oe, in a direction parallel to the coating surface, or a solenoid of 1000 to 10000 Oe while the first magnetic paint and the second magnetic paint are wet. And the like.

The drying treatment can be performed, for example, by supplying a heated gas. At this time, the degree of drying of the coating film can be controlled by controlling the temperature of the gas and the amount of the supplied gas. As the drying conditions, for example, a hot air temperature of 6
Preferably, the temperature is 0 to 120 ° C., the wind speed is 5 to 35 m / sec, and the drying time is 1 to 60 seconds.

The calendering treatment can be performed by a super calendering method in which a metal roll and a cotton roll or a synthetic resin roll, a metal roll and a metal roll are passed between two rolls. The calendar processing conditions are as follows: the calendar speed is 50 to 300 m / mi.
n, the pressure is preferably 50 to 450 kg / cm, and the roll temperature is preferably 60 to 120 ° C.

The back coat layer, which is provided as needed, is formed on the back surface of the non-magnetic support (the first magnetic layer and the second magnetic layer).
On the side on which the magnetic layer is not provided), and can be obtained by applying a back coat paint, which is usually used for forming a back coat layer, on a non-magnetic support.

When the magnetic recording medium of the present invention is manufactured, a finishing step such as a polishing or cleaning step for the surface of the second magnetic layer can be performed, if necessary. Also, the first
The application of the magnetic paint and the second magnetic paint can also be performed by a generally known sequential multilayer coating method.

[0043]

Next, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. In the following formulation, all “parts” are based on weight.

Example 1 <Second Magnetic Paint A> 100 parts of acicular ferromagnetic metal powder mainly composed of iron (Fe: Al: Ba: Si: Ni: Co (weight ratio) = 88: 2: 1: 1: 3: 5, coercive force: 1840 Oe, saturation magnetization: 134 emu / g, average major axis length: 0.12 μm, specific surface area: 58 m ² / g) Alumina (average particle size: 0.2 μm) 8 parts ・ Carbon black (average primary particle diameter 20 nm) 2 parts ・ Sulfonate group-containing polyurethane resin 13 parts (trade name “UR8300”, manufactured by Toyobo Co., Ltd.) ・ Sulfonate group-containing vinyl chloride resin 10 parts ( (Trade name: MR110, manufactured by Zeon Corporation) 2 parts 2-ethylhexyl stearate 2 parts palmitic acid 4 parts curing agent (Coronate L) 120 parts MEK 80 parts toluene 100 parts cyclohexanone 40 parts

<First Magnetic Coating B> 60 parts of hexagonal barium ferrite powder (hexagonal plate-shaped Co—Ti substituted barium ferrite powder, coercive force: 1670 Oe, saturation magnetization: 56 emu / g, average plate diameter: 600 °) , Plate ratio: 4) α-Fe ₂ O ₃ 40 parts Alumina (average particle diameter 0.2 μm) 5 parts Carbon black (average primary particle diameter 20 nm) 2 parts Sulfonate group-containing polyurethane resin 15 parts (Trade name "UR8300", manufactured by Toyobo Co., Ltd.)-7 parts of vinyl chloride copolymer resin containing sulfonic acid group (trade name "MR104", manufactured by Zeon Corporation)-2-ethylhexyl stearate 5 parts ・ 1.5 parts of palmitic acid ・ 4 parts of curing agent (Coronate L) ・ 90 parts of MEK ・ 90 parts of toluene ・ 30 parts of cyclohexanone

Second magnetic paint A and first magnetic paint B
Knead the above components in a continuous pressure kneader,
After diluting and dispersing, adding a lubricant and filtering,
It was prepared by adding a curing agent to form a coating.

A first magnetic layer having a thickness of 1.8 was formed on a polyethylene terephthalate film having a thickness of 7 μm and a width of 150 mm.
μm and the thickness of the second magnetic layer is 0.3 μm.
Of the magnetic paint B and the second magnetic paint A at a line speed of 100
Simultaneous multi-layer coating was performed using an extrusion die under the conditions of m / min. 5000 Oe D when applying paint
After performing C orientation and drying at 90 ° C., 100 ° C., 30 ° C.
After calendering under the condition of 0 kg / cm, 4k
g The film was wound under tension conditions. The roll is 1
It was cut to 2.6 mm to obtain a magnetic tape, and the obtained magnetic tape was loaded into a cassette, and the electromagnetic conversion characteristics (output after the cassette) were evaluated. The results are shown in Table 1 together with the recording frequency and the results of the post-coating cloth. In addition, these characteristics were evaluated by the following methods.

<Characteristics evaluation method>-Gloss after coating Measure the incident angle-reflection angle 60 ° -60 using a gloss meter manufactured by Suga.
The light reflectance with respect to the standard plate in ゜ was measured.・ Output after cassette Using a fixed-head data cartridge drive, at the shortest recording wavelength of 0.8 μm and 0.6 μm, the optimum recording current at each recording wavelength was written by the write head, and the reproduction output from the read head was measured. . The relative speed was set at 3 m / sec.

[Examples 2 to 4] As shown in Table 1, the thicknesses of the second magnetic layer and the first magnetic layer, the content of the nonmagnetic acicular inorganic powder in the first magnetic layer, and the coating speed were as follows. Except for the change
A web was manufactured in the same manner as in Example 1, and the electromagnetic conversion characteristics (output after the cassette) were evaluated in the same manner as in Example 1. The results are shown in Table 1 together with the recording frequency and the results of the post-coating cloth.

[Comparative Examples 1-2] As shown in Table 1, except that the content of the non-magnetic acicular inorganic powder of the first magnetic layer and the coating speed were changed, the same procedure as in Example 1 was carried out. Manufacture anti
The evaluation of the electromagnetic conversion characteristics (output after the cassette) was performed in the same manner as in Example 1. The results are shown in Table 1 together with the recording frequency and the results of the post-coating cloth.

[Comparative Examples 3 and 4] A raw material was produced in the same manner as in Example 1 except that the thicknesses and coating speeds of the second magnetic layer and the first magnetic layer were changed as shown in Table 1. Example 1
Evaluation of the electromagnetic conversion characteristics (output after the cassette) was performed in the same manner as in the above. The results are shown in Table 1 together with the recording frequency and the results of the post-coating cloth.

Comparative Example 5 A raw material was produced in the same manner as in Example 1, except that the coating material for the second magnetic layer was changed to the following second magnetic coating material C. The electromagnetic conversion characteristics (output after the cassette) were evaluated. The results are shown in Table 1 together with the recording frequency and the results of the post-coating cloth.

<Second Magnetic Coating C> 100 parts of acicular ferromagnetic metal powder mainly composed of iron (Fe: Al: Zn: Ni (weight ratio) = 90: 5: 5, coercive force: 1450 Oe, Saturation magnetization: 130 emu / g, average major axis length: 0.18 μm, specific surface area: 58 m ^Two ・ Alumina (average particle diameter 0.3 μm) 5 parts ・ Carbon black (average primary particle diameter 20 nm) 1 part ・ Sulfonic acid group-containing polyurethane resin 10 parts (trade name “UR8300”, manufactured by Toyobo Co., Ltd.)・ Sulfonate group-containing vinyl chloride resin 10 parts (trade name “MR110”, manufactured by Nippon Zeon Co., Ltd.) ・ 2-ethylhexyl stearate 2 parts ・ Palmitic acid 2 parts ・ Curing agent 4 parts (Coronate L) ・ MEK 120 parts ・ Toluene 80 parts ・ Cyclohexanone 40 parts

[Reference Example 1] A raw material was produced in the same manner as in Example 1 except that the thickness and the coating speed of the second magnetic layer were changed as shown in Table 1, and The electromagnetic conversion characteristics (output after the cassette) were evaluated. The results are shown in Table 1 together with the recording frequency and the results of the post-coating cloth. However,
The output after the cassette was evaluated at 0.6 μm.

[0055]

[Table 1]

As shown in Table 1, Examples 1 to 5
A multilayer tape having rigidity and excellent head touch properties was obtained. On the other hand, in Comparative Example 1 in which the content of the nonmagnetic acicular inorganic powder in the first magnetic layer was small, sufficient head touch properties could not be obtained. In Comparative Example 2 in which the content of the nonmagnetic acicular inorganic powder in the first magnetic layer was large, the surface properties were affected, the surface became rough, and the output was reduced. In Comparative Example 3, although the thickness of the second magnetic layer was too large, a decrease in output was observed. On the other hand, in Comparative Example 4, although the thickness of the first magnetic layer was too small, sufficient tape rigidity was not obtained, and sufficient output was not obtained due to the problem of head touch. In Reference Example 1, the cassette output was evaluated at a short magnetic recording wavelength, but no remarkable effect was expected at this magnetic recording wavelength.
This means that the shorter the recording wavelength, the smaller the recording depth,
This is because the recording signal does not reach the first magnetic layer.

[0057]

As described above, the magnetic recording medium of the present invention is excellent in electromagnetic conversion characteristics such as output and noise, has good head touch properties, and has high recording. Further, by the method for manufacturing a magnetic recording medium of the present invention, the above-mentioned magnetic recording medium can be obtained in high yield.

Claims (8)

[Claims] 1. A first magnetic layer and a second magnetic layer as an outermost layer are provided on a support, wherein the first magnetic layer and the second magnetic layer are magnetic powder or ferromagnetic powder. A magnetic recording medium obtained by applying a coating in which at least a binder and a binder are dispersed, wherein the thickness of the second magnetic layer is 0.3 μm or less, the thickness of the first magnetic layer is 0.7 μm or more, The second magnetic layer contains at least an iron-based ferromagnetic powder and a polar group-containing urethane binder, and uses barium ferrite as the magnetic powder of the first magnetic layer, and is non-magnetic with respect to 100 parts by weight of the barium ferrite. A magnetic recording medium comprising at least 20 parts by weight and less than 100 parts by weight of acicular inorganic powder. 2. The method according to claim 1, wherein the multilayer coating is performed at a coating speed of 100 to 300.
2. The magnetic recording medium according to claim 1, wherein the speed is set at m / min. 3. The magnetic recording medium according to claim 1, wherein the recording wavelength is 0.8 μm or more. 4. The Hc of the second magnetic layer is 1500-3.
000 Oe, and Hc of the first magnetic layer is 1200 to 30
4. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 00 Oe. 5. The method according to claim 1, wherein the first magnetic layer contains at least 50 parts by weight and less than 100 parts by weight of the nonmagnetic acicular inorganic powder with respect to 100 parts by weight of barium ferrite. 3. The magnetic recording medium according to claim 1. 6. The non-magnetic acicular inorganic powder is α-Fe ₂ O.
6. The magnetic recording medium according to claim 1, wherein the number is ₃ . 7. A first magnetic paint in which at least a magnetic powder and a binder are dispersed and a second magnetic paint in which at least a ferromagnetic powder and a binder are dispersed are prepared, and these paints are formed on a support. In the method for manufacturing a magnetic recording medium to be applied, the second magnetic paint contains at least an iron-based ferromagnetic powder and a polar group-containing urethane binder, and the first magnetic paint contains barium ferrite as a magnetic powder, The nonmagnetic acicular inorganic powder contains at least 20 parts by weight and less than 100 parts by weight with respect to 100 parts by weight of the barium ferrite.
7 μm or more.
The method of manufacturing a magnetic recording medium, wherein the second magnetic paint is applied simultaneously or sequentially so that the dry thickness is 0.3 μm or less while the magnetic layer is in a wet state. 8. The method according to claim 7, wherein the application with the first magnetic paint and the second magnetic paint is performed at a coating speed of 100 to 300 m / min.