JPH08255337A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE: To provide a magnetic recording medium excellent in durability under various temp. conditions by successively forming a nonmagnetic layer and a magnetic layer on a substrate and incorporating two or more kinds of electrically conductive powders having prescribed characteristics into the nonmagnetic layer. CONSTITUTION: A nonmagnetic layer and a magnetic layer are successively formed on a substrate. The nonmagnetic layer contains nonmagnetic powder having 10-100nm crystal size and a Mohs hardness of >=5 and two or more kinds of electrically conductive powders different from each other in number average particle diameter by >=5nm. The objective magnetic recording medium excellent in durability over a long period of time under various environmental conditions from high temp. to low temp. is obtd. This medium does not cause an error under various temp. conditions and has high reproduction output and satisfactory overwriting characteristics.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium and a manufacturing method thereof, and more particularly to a magnetic recording medium preferably used as a magnetic recording disk for a floppy disk or a still video floppy disk and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, the development of magnetic recording media using thin metal multi-layer media as W-VHS or high-definition tape has become vigorous.

Japanese Unexamined Patent Publication (Kokai) No. 6-267059 discloses a technique in which two or more kinds of non-magnetic powders are contained in the lower non-magnetic layer in order to improve the running property and electromagnetic conversion characteristics of the tape. However, in order to cope with the high capacity of floppy disks and still video floppy disks, it has become necessary to improve the durability (especially at cycle thermostat) and the error rate as well as to make the density much higher than before. The above technique was not sufficient to solve the above problem. Further, JP-A-2-35625 discloses a technique using two or more kinds of carbon black having different average particle diameters. However, the example in this case had a single layer structure, and the lower layer could not be functionally separated in order to lower the surface resistivity. Therefore, it is necessary to use a relatively large amount of carbon black in the magnetic layer in order to satisfy good surface resistivity, but then it is not possible to densify the magnetic layer and achieve a high level of electromagnetic conversion characteristics. I couldn't.

[0004]

The problems of the present invention are: 1) excellent durability for a long time even under a wide range of environmental conditions from high temperature to low temperature, 2) no error occurs in a wide range of temperature conditions, 3) (4) To provide a magnetic recording medium having a high reproduction output and a good overwrite characteristic, and a method for manufacturing the same.

[0005]

[Means for Solving the Problems]

Invention 1: A nonmagnetic layer and a magnetic layer are formed in this order on a support, and the nonmagnetic layer has a crystallite size of 10 to 100.
A magnetic recording medium comprising a non-magnetic powder A having a Mohs hardness of 5 or more in nm and two or more kinds of electrically conductive powders having a number average particle diameter different by 5 nm or more.

Invention 2: Two or more kinds of electrically conductive fine powders which are composed of a non-magnetic layer and a magnetic layer formed on a support in this order, and have different oil absorptions expressed by DBP values of 10 ml / 100 g or more in the non-magnetic layer. A magnetic recording medium containing:

Invention 3: A method of manufacturing a magnetic recording medium, wherein the magnetic layer is formed while the non-magnetic layer is in a wet state.

Invention 4: The non-magnetic layer has a number average particle size of 10
At least 2 which is ~ 35 nm and 40-500 nm
The magnetic recording medium according to claim 1, comprising a conductive fine powder of a type.

Invention 5: The non-magnetic layer has an oil absorption represented by a DBP (dibutyl phthalate) value of 20 to 100 ml /
The magnetic recording medium according to claim 1, comprising at least two kinds of conductive fine powders of 100 g and 110 to 500 ml / 100 g.

Invention 6: The magnetic recording medium according to claim 1 or 2, wherein the non-magnetic layer and / or the magnetic layer contains α-alumina and / or chromium oxide.

Invention 7: A number average particle diameter of 40 to 40 in the magnetic layer.
The magnetic recording medium according to claim 1 or 2, comprising a conductive fine powder having a size of 500 nm.

Invention 8: The magnetic recording medium according to claim 1 or 2, wherein the magnetic layer contains a conductive fine powder having an oil absorption represented by a DBP value of 110 to 500 ml / 100 g.

[0013]

In the conventional multi-layer medium, carbon black is used as the lower layer in order to lower the surface specific resistance of the medium or to adjust the thixotropy of the lower layer coating material to obtain good rheological properties suitable for multi-layer coating. And other conductive powders have been used. In order to obtain high reproduction output and good overwrite characteristics, which is the subject of the present invention, it is necessary to carry out thin film multilayer coating, but the surface properties of the upper layer substantially reflect the surface properties of the lower layer, so the lower layer Design is important. In order to improve the dispersibility of the non-magnetic powder in the lower layer to improve the surface property, it is considered that the conductive fine powder used in the lower layer is made into fine particles or one having a small oil absorption amount is used. On the other hand, in order to improve durability and error rate at the time of cycle thermography, which is another subject of the present invention, it is necessary to consider the coating property and the lubricating property of the lower non-magnetic layer. The present inventors have variously studied the crystallite size and the number average particle size of the filler used in the lower non-magnetic layer based on the above idea, the Mohs hardness, the oil absorption, the combination of a plurality of fillers, etc. Point became clear. 1. It is difficult to satisfy requirements such as dispersibility and conductivity of the lower layer at a high level by using only one kind of conductive powder such as carbon black contained in the lower layer, and a plurality of conductive powders having different number average particle sizes or different oil absorptions. Must be used together. 2. When the filler contained in the lower layer is only conductive powder such as carbon black, the rheological properties of the upper and lower coating materials are poorly matched and surface roughness occurs during multi-layer coating. Also, the physical properties of the coating film are weak, so the durability is poor. Therefore, it is necessary to improve the rheological properties and coating film physical properties of the coating by adding non-magnetic powder A to the lower layer in addition to the conductive powder. 3. The crystallite size and the Mohs hardness of the above-mentioned nonmagnetic powder A must meet specific conditions.

Then, specifically, they have found that the problems of the present invention can be solved by the following constitution. Hereinafter, the present invention will be described in detail. (Layer Structure) The magnetic recording medium of the present invention basically comprises a nonmagnetic support and a nonmagnetic layer formed on the nonmagnetic support. In addition, on the surface (back surface) on which the above-mentioned magnetic layer is not provided on the non-magnetic support, improvement in running property and durability of the magnetic recording medium,
It is preferable to provide a back coat layer, a writing layer or a print recording layer, or an anti-counterfeiting layer for the purpose of preventing electrification and transfer, and between the non-magnetic layer and the non-magnetic support. It is also possible to provide an undercoat layer. In addition, an overcoat layer may be provided on the uppermost magnetic layer, if necessary.

(Non-magnetic support) As the material for forming the non-magnetic support, for example, polyesters such as polyethylene terephthalate, polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose triacetate, cellulose diacetate, etc. Examples of the cellulose derivative include plastics such as polyamide and polycarbonate.

The form of the non-magnetic support is not particularly limited, and is mainly tape-like, film-like, sheet-like, card-like,
There are disc shape and drum shape.

The thickness of the non-magnetic support is not particularly limited, but usually 3 to 1 in the case of a film or sheet.
00 μm, preferably 5 to 50 μm, about 30 μm to 10 mm in the case of a disk or card, and appropriately selected depending on the recorder etc. in the case of a drum.

The non-magnetic support may have a single structure or a multi-layer structure. Further, the non-magnetic support may be subjected to surface treatment such as corona discharge treatment. A back coat layer may be provided on the surface (front surface) of the non-magnetic support on which the magnetic layer is not provided, for the purpose of improving the running property of the magnetic recording medium, preventing electrification and preventing transfer, and the like. It is preferable to provide a writing layer and a print recording layer.

(Magnetic Layer) In the present invention, the magnetic layer is basically formed by dispersing magnetic powder in a binder resin. Known magnetic powder can be used for this magnetic layer, but it is particularly preferable to contain ferromagnetic metal powder or hexagonal magnetic powder. The thickness of the magnetic layer is usually 0.
05-1.0 μm, preferably 0.05-0.5
μm, and more preferably 0.1 to 0.4 μm.

Examples of the hexagonal magnetic powder include hexagonal ferrite. Such hexagonal ferrite is made of barium ferrite, strontium ferrite, or the like, and a part of iron element is another element (for example, Ti, Co, Zn, In, Mn, Ge, H).
b) or the like). Regarding this ferrite magnetic material, the IEEE Trans, on MAG-1
816 (1982).

In the present invention, a particularly preferable hexagonal magnetic powder is barium ferrite (hereinafter referred to as Ba-ferrite) magnetic powder. A preferable Ba-ferrite magnetic powder that can be used in the present invention is an average particle diameter of Ba-ferrite powder in which a part of Fe is replaced by at least Co and Zn (height of diagonal line of plate surface of hexagonal ferrite). ) 400 to 900Å, plate ratio (value obtained by dividing the length of the diagonal line of the plate surface of the hexagonal ferrite by the plate thickness) 2.0 to 10.0, more preferably 2.0 to
Ba with a coercive force (Hc) of 450 to 1500 Oe of 6.0
-It is ferrite.

The Ba-ferrite powder has a coercive force controlled to an appropriate value by partially substituting Fe for Co, and further partially substituting for Zn, which cannot be obtained only by Co substitution. A magnetic recording medium that realizes saturation magnetization and has a high reproduction output and excellent electromagnetic conversion characteristics can be obtained. Further, by substituting a part of Fe with Nb, it is possible to obtain a magnetic recording medium having a higher reproduction output and excellent in electromagnetic conversion characteristics. Further, in the Ba-ferrite used in the present invention, it does not matter even if a part of Fe is further substituted with a transition metal such as Ti, In, Mn, Cu, Ge or Sn.

The Ba-ferrite used in the present invention is represented by the following general formula. _{BaOn ((Fe 1-m M} m) 2 O 3) [ provided that, m> 0.36 (However, Co + Zn = 0.0
8 to 0.3, Co / Zn = 0.5 to 10), n is 5.4 to 11.0, preferably 5.4 to 6.0, and M represents a substituted metal, Magnetic particles that are a combination of two or more elements having an average valence of 3 are preferable. In the present invention, the reason why the average particle size of Ba-ferrite, the plate ratio, and the coercive force are preferably within the above-mentioned preferred ranges is as follows. That is, the average particle size is 0.04 μm
If it is less than 0.1 μm, the reproduction output when used as a magnetic recording medium becomes insufficient, and conversely, if it exceeds 0.1 μm, the surface smoothness when used as a magnetic recording medium deteriorates significantly, and the noise level becomes too high. If the plate ratio is less than 2.0, a perpendicular orientation ratio suitable for high density recording cannot be obtained when used as a magnetic recording medium, and conversely, if the plate ratio exceeds 6.0, magnetic recording is performed. The surface smoothness when used as a medium is significantly deteriorated,
The noise level becomes too high, and the coercive force is 350.
If it is less than Oe, it becomes difficult to hold the recording signal,
This is because if it exceeds 2000 Oe, the head limit may decrease in saturation and recording may become difficult.

The hexagonal magnetic powder used in the present invention usually has a saturation magnetization (σs) which is a magnetic characteristic of 50e.
It is preferably mu / g or more. If the saturation magnetization is less than 50 emu / g, electromagnetic conversion characteristics may deteriorate.

A preferred specific example of the Ba-ferrite used in the present invention is Co-substituted Ba ferrite.

Further, in the present invention, it is desirable to use Ba-ferrite magnetic powder having a specific surface area of 30 m ² / g or more by the BET method according to the higher recording density.

As a method for producing the hexagonal magnetic powder used in the present invention, for example, an oxide or carbonate of each element necessary for forming the desired Ba-ferrite is used, such as boric acid. The glass melt is melted together with another glass-forming substance, the resulting melt is rapidly cooled to form glass, and the glass is then heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally the glass component is added. In addition to the glass crystallization method of removing by heat treatment,
A coprecipitation-firing method, a hydrothermal synthesis method, a flux method, an alkoxide method, a plasma jet method and the like can be applied.

In the present invention, the ferromagnetic metal powder and the hexagonal magnetic powder may be mixed and used. The content of the ferromagnetic metal powder and / or the hexagonal magnetic powder in this magnetic layer is usually 50 to 99% by weight, preferably 60 to 99% by weight.

In order to obtain a sufficient reproduction output when used as a magnetic recording medium, the average particle size of the Ba-ferrite is 300Å
It is preferably not less than 900 Å or less in order to improve the surface smoothness and reduce the noise level. Further, by setting the plate ratio to 2.0 or more, a vertical orientation ratio suitable for high-density recording when used as a magnetic recording medium can be obtained, and in order to improve surface smoothness and reduce noise level, The plate ratio is preferably 10.0 or less. Further, the coercive force is preferably 450 Oe or more for holding the recording signal, and it is necessary to prevent the head from being saturated.
It is preferably 00 Oe or less.

The ferromagnetic metal powder used in the magnetic layer includes Fe, Co, Fe-Al system, and Fe-Al-.
Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based, F
e-Al-Ca system, Fe-Ni system, Fe-Ni-Al
System, Fe-Ni-Co system, Fe-Ni-Si-Al-M
n-based, Fe-Ni-Si-Al-Zn-based, Fe-Al-
Si-based, Fe-Ni-Zn-based, Fe-Ni-Mn-based, F
e-Ni-Si system, Fe-Mn-Zn system, Fe-Co-
Ferromagnetic powders such as Ni-P-based, Ni-Co-based, metal magnetic powders containing Fe, Ni, Co, etc. as main components are exemplified. Among them, Fe-based metal powder has excellent electrical characteristics.

On the other hand, from the viewpoint of corrosion resistance and dispersibility, Fe-Al type, Fe-Al-Ca type, Fe-Al-type.
Ni-based, Fe-Al-Zn-based, Fe-Al-Co-based, F
e-Ni-Si-Al-Zn system, Fe-Ni-Si-A
Fe-Al-based metal powder such as 1-Mn-based is preferable.

Particularly preferred ferromagnetic metal powder for the purpose of the present invention is a metal magnetic powder containing iron as a main component, and Al or Al and Ca, and Al in a weight ratio of Fe:
Al = 100: 0.5 to 100: 20, and Ca is preferably contained in a weight ratio of Fe: Ca = 100: 0.1 to 100: 10.

By setting the ratio of Fe: Al in such a range, the corrosion resistance is remarkably improved, and by setting the ratio of Fe: Ca in such a range, electromagnetic conversion characteristics are improved and dropout is reduced. Can be made. The reason why the electromagnetic conversion characteristics are improved and the dropout is reduced is not clear, but it is considered that the coercive force is increased and the agglomerates are decreased due to the improved dispersibility.

The preferred ferromagnetic metal powder used in the present invention has an average major axis length observed by a transmission electron microscope of less than 0.25 μm, particularly 0.03 to 0.22 μm,
More preferably 0.05 to 0.17 μm and the X-ray particle size (crystallite size) is less than 200Å, especially 50 to 180Å
It is preferred that The axial ratio (average major axis length / average minor axis length) is 12 or less, preferably 10 or less, and more preferably 4 to 9. When the average major axis length, the crystal size, and the axial ratio of the ferromagnetic metal powder are within the above ranges, the high frequency characteristics, especially the output of the perpendicular recording component can be enhanced.

The average major axis length (in the case of needle-shaped particles) and number average particle diameter (in the case of spherical particles) of the magnetic powder and non-magnetic powder used in the present invention are ferromagnetic powder or It is an average value obtained by measuring 500 major axis lengths or diameters (in the case of spherical particles) of the non-magnetic powder. The crystallite size was measured by the Scherrer method using Si powder as a reference, using the integral width of the (110) diffraction line of Fe with an X-ray diffractometer. Regarding the method of obtaining, the method described in the X-ray diffraction guide (Rigaku Denki Co., Ltd.) was used, and the correction of the spread due to double lines was performed by the correction by A: Jones (integral width) described on page 77. The axial ratio was determined as (average major axis length / average minor axis length) by measuring the average major axis length and the average minor axis length of 500 particles on an electron micrograph.

The ferromagnetic metal powder used in the present invention usually has a coercive force (Hc) of 600 to 5,000.
It is preferably in the range of Oe. This coercive force is 600
If it is less than Oe, the electromagnetic conversion characteristics may be deteriorated, and if the coercive force exceeds 5,000 Oe, recording may not be possible with an ordinary head, which is not preferable.

The ferromagnetic powder preferably has a saturation magnetization amount (σs), which is a magnetic property, of usually 120 emu / g or more, and particularly preferably 130 to 170 emu / g. Further, according to the present invention, the specific surface area by the BET method is 30 m ^{2 as the} recording density is increased.
/ G or more, especially 45 m ² / g or more of a ferromagnetic metal powder is preferably used.

The specific surface area and its measuring method are described in "Measurement of powder" (JM Dallavelle,
Clyeorr Jr. Co-authored by Muta et al. (Translated by Sangyo Tosho Publishing Co., Ltd.)
170-1171 (Edited by Chemical Society of Japan: Maruzen Co., Ltd., Showa 41)
(Published April 30, 2013). To measure the specific surface area, for example, the powder is deaerated while being heated at about 105 ° C. for 13 minutes to remove what is adsorbed on the powder, and then the powder is introduced into a measuring device to reduce the initial pressure of nitrogen to 0. The pressure is set to 0.5 kg / m ² and measurement is performed with nitrogen at a liquid nitrogen temperature (−105 ° C.) for 10 minutes. As the measuring device, for example, a counter soap (manufactured by Yuasa Ionics Co., Ltd.) is used.

The ferromagnetic metal powder preferably contains Fe, Al, and a rare earth element as its constituent elements. Sm, Nd, Y, Pr and La as rare earth elements
It is preferable to contain one or more rare earth elements selected from the group consisting of

The ferromagnetic metal powder according to the present invention comprises Fe, Al, Sm, Nd, Y and P in the entire composition.
The abundance ratio of one or more rare earth elements selected from the group consisting of r and La is such that Al is 100 parts by weight with respect to Al.
Atom is 1 to 20 parts by weight (preferably Sm and Nd
And one or more rare earth elements selected from the group consisting of Y, Pr, and La) are 1 to 16 parts by weight. Further, Fe and Al (preferably Sm, Nd, Y and P on the surface thereof)
The abundance ratio of one or more rare earth elements (selected from the group consisting of r and La) is 70 to 300 for 100 Fe atoms, and the number of rare earth elements is 0.
It is preferably 5 to 100.

More preferably, the ferromagnetic metal powder further contains Na and Ca as constituent elements, and the weight ratio of the elements in the entire ferromagnetic metal powder is Na with respect to 100 parts by weight of Fe atoms. Atoms are less than 0.1 parts by weight, Ca atoms are 0.1 to 2 parts by weight, Al atoms are 2 to 10 parts by weight, rare earth elements are 1 to 8 parts by weight, and The average abundance ratio of elements forming the surface of the magnetic metal powder is 2 to 30 for Na atoms, 5 to 30 for Ca atoms, and 5 to 30 for Ca atoms with respect to 100 Fe atoms.
The number of atoms is 70 to 200, and the number of atoms of rare earth elements is 0.5 to 30.

More preferably, the ferromagnetic metal powder further contains at least one of Co, Ni and Si as its constituent elements, and the weight ratio of the elements in the entire ferromagnetic metal powder is 100 parts by weight of Fe atoms. On the other hand, Co atom is 2 to 40 parts by weight, Ni atom is 2 to 20 parts by weight, Si atom is 0.3 to 5 parts by weight, and Na atom is less than 0.1 parts by weight, Ca atom is 0.1 to 2 parts by weight, Al atom is 1 to 20 parts by weight, rare earth element atom is 1 to 16 parts by weight, and of the elements forming the surface of the ferromagnetic metal powder. Average abundance ratio is 1 Fe atom
00, the Co atom number is less than 0.1, the Ni atom number is less than 0.1, the Si atom number is 20 to 130, the Na atom number is 2 to 30, and the Ca atom number. Is 5
30, the number of Al atoms is 70 to 300, and the number of rare earth element atoms is 0.5 to 100.

(Nonmagnetic Layer) In the lower nonmagnetic layer in the present invention, a nonmagnetic powder A having a crystallite size of 10 to 100 nm and a Mohs hardness of 5 or more is used. Non-magnetic powder A
It is preferable to appropriately select and use from among various known non-magnetic powders used in this type of magnetic recording medium. The crystallite size of the non-magnetic powder A is preferably 15-
It is 80 nm, more preferably 20 to 60 nm. Examples of the non-magnetic powder A include titanium oxide,
Boron nitride, SnO ₂ , SiO ₂ , Cr ₂ O ₃ , α-A
l ₂ O ₃ , α-Fe ₂ O ₃ , α-FeOOH, SiC,
Examples thereof include cerium oxide, corundum, artificial diamond, garnet, garnet, silica stone, silicon nitride, boron nitride and silicon carbide.

Of these, preferred are titanium oxide, barium sulfate, α-Al ₂ O ₃ , α-Fe ₂ O ₃ ,
Inorganic powder such as α-FeOOH, Cr ₂ O _3, etc.,
Among them, α-Fe ₂ O ₃ and α-FeOOH are preferable, and α-Fe ₂ O ₃ is particularly preferable. In the present invention, a non-magnetic powder having a needle-like powder shape can be preferably used. By using the acicular non-magnetic powder, the smoothness of the surface of the non-magnetic layer can be improved, and the smoothness of the surface of the uppermost layer composed of the magnetic layer laminated thereon can also be improved.

The non-magnetic layer here is a layer which is substantially non-magnetic (saturation magnetic flux density Bm is 0) and is substantially non-magnetic (slightly magnetic layer). so,
Bm of 0.01 to 100 Gauss) is also included. In particular, when acicular α-Fe ₂ O ₃ is used as the lower layer filler, the Bm of the layer is usually about 0.01 to 29 Gauss, and in this case also, it is called the nonmagnetic layer in the present invention. I will.

The thickness of the non-magnetic layer is usually 0.2 to
It is 2.5 μm, preferably 0.5 to 2.0 μm. When the thickness is 2.5 μm or less, the surface roughness of the upper layer surface after layering, that is, so-called layer surface roughness is less likely to occur, and preferable electromagnetic conversion characteristics can be obtained.
When it is 2 μm or more, high smoothness can be obtained at the time of calendering, and electromagnetic conversion characteristics are improved.

In order to control the shape and axial ratio of the non-magnetic powder, it is necessary to combine known methods such as selection of starting material as a starting material, selection of oxidation-reduction conditions, and selection of sintering inhibitor. You can

The major axis diameter of the acicular nonmagnetic powder used in the lower layer of the present invention or the number average particle diameter of nonacicular nonmagnetic powder is preferably 10 nm or more and 250 nm or less, and particularly preferably 200 nm or less. Is.

The minor axis diameter of the needle-shaped non-magnetic powder is
It is usually 10 nm or more and 100 nm or less, preferably 80 nm or less, and particularly preferably 60 nm or less.

The axial ratio of the needle-shaped non-magnetic powder is usually 2 to 20, preferably 5 to 15, and particularly preferably 5 to 10. The axial ratio referred to here is the ratio of the major axis diameter to the minor axis diameter (major axis diameter / minor axis diameter).

The specific surface area of the non-magnetic powder is usually 10 to 250 m ² / g, preferably 20 to 150.
m ² / g, particularly preferably 30 to 100 m ² / g
Is.

By using a non-magnetic powder having a major axis diameter, a minor axis diameter, an axial ratio and a specific surface area within the above ranges, the surface properties of the non-magnetic layer can be improved and the top layer of the magnetic layer can be used. It is preferable in that the surface property can be made good.

In the present invention, the non-powdered powder is preferably surface-treated with a Si compound and / or an Al compound. When the non-magnetic powder subjected to such surface treatment is used, the surface condition of the uppermost layer which is the magnetic layer can be improved. The content of Si and / or Al is preferably 0.1 to 10% by weight of Si and 0.1 to 10% by weight of Al, more preferably Si. 0.1-5 wt%, Al 0.1-
5% by weight, preferably 0.1 to 2% by weight of Si and 0.1 to 2% by weight of Al. In the case of non-magnetic powder, the weight ratio of Si and Al is preferably Si <Al. The surface treatment can be performed by the method described in JP-A-2-83219.

The content of the non-magnetic powder in the lower layer is usually 5 with respect to the total of all components constituting the lower layer.
It is 0 to 99% by weight, preferably 60 to 95% by weight, and particularly preferably 70 to 95% by weight. When the content of the non-magnetic powder is within the above range, the surface condition of the uppermost layer and the lower layer which are magnetic layers can be improved.

Conductive Fine Powder As the conductive fine powder used in the present invention, carbon black, Sb deposited conductive tin oxide (SnO ₂ ), and conductive titanium dioxide (TiO 2 coated with Sb and Sn) are used.
₂ ) etc., but carbon black is particularly preferably used.

The conductive fine powder contained in the magnetic layer is preferably a conductive fine powder having a number average particle diameter of 40 to 500 nm or an oil absorption represented by a DBP value of 110 to 500 ml / 100 g. More preferably, the number average particle size is 50 to
350nm, or the oil absorption expressed by DBP value is 140
It is preferable to use conductive fine powder of 400 ml / 100 g. The weight of the conductive fine powder contained in the magnetic layer is preferably 0.1 to 5.0% by weight based on the magnetic powder,
It is more preferably 0.2 to 2.0% by weight.

The non-magnetic layer contains two or more conductive fine powders having a number average particle size different by 5 nm or more or two or more conductive fine powders having an oil absorption represented by a DBP value of 10 ml / 100 g or more. It Here, the number average particle size is 10 nm
As described above, more preferably, two or more kinds of conductive fine powders differing by 20 nm or more or the oil absorption amount represented by the DBP value is 20 m.
1/100 g or more, more preferably 30 ml / 100 g
Two or more different conductive fine powders are contained. More specifically, the non-magnetic layer contains a conductive fine powder having a number average particle size of 10 to 35 nm and 40 to 500 nm, more preferably 10 to 30 nm and 50 to 400 nm, or the non-magnetic layer is represented by a DBP value. Oil absorption is 20-100m
1 / 100g and 110-500ml / 100g, more preferably 30-90ml / 100g and 140-
It is preferable to contain 400 ml / 100 g of conductive fine powder. The total weight of the conductive fine powder contained in the nonmagnetic layer is preferably 5.0 to 30% by weight, and more preferably 7.0 to 20% by weight, based on the total weight of the nonmagnetic powder.
When the non-magnetic layer contains two kinds of conductive fine powders B and C (the powder having a large number average particle size is C), the weight ratio of B and C is 99: 1 to 50:50, and more preferably Is 95: 5
~ 70: 30.

The method of adding carbon black can be variously changed. For example, fine particles and coarse particles of carbon black may be charged into a disperser at the same time and mixed, or only a part thereof may be added first, and the remaining amount may be added when the dispersion has progressed to some extent. When importance is placed on the dispersion of carbon black, it is also possible to knead carbon black together with a magnetic material or filler and a binder by a three-roll mill, Banbury mixer or the like, and then disperse with a disperser to obtain a coating material. When importance is attached to conductivity like layers other than the magnetic layer, the carbon black structure structure is less likely to be broken by adding carbon black in the latter half of the dispersion step and the liquid preparation step as much as possible.

A so-called "carbon master patch" prepared by previously kneading carbon black with a binder may be used.

Here, the particle size of the above carbon black is directly measured visually by an electron microscope. That is, a magnetic recording medium, for example, a tape is cut in the longitudinal direction to a thickness of about 700Å, and the obtained cross section is observed with a transmission electron microscope (applied voltage 200 KV, magnification = 60,000). In this case, measure the diameter of each particle of carbon black,
The number average particle diameter of N = 100 pieces is referred to as “number average particle diameter”.

Regarding the above-mentioned "oil absorption (DBP method)", 100 g of pigment powder is added to DBP (Dibutylph).
The state of the pigment is observed while kneading, and the number of ml of DBP when the point of forming one lump from the dispersed state is found is the DBP oil absorption.

(Binder) The binder used for forming the magnetic layer and the non-magnetic layer is, for example, polyurethane, polyester, vinyl chloride resin such as vinyl chloride copolymer, phenoxy resin, fibrin resin and the resin is a typical example, these resins are -SO ₃ M, -O
It is preferable to include a repeating unit having at least one polar group selected from SO ₃ M, —COOM, and —PO (OM ¹ ) ₂ . However, in the above polar group,
M represents a hydrogen atom or an alkali metal such as Na, K and Li, and M ¹ represents a hydrogen atom, an alkali atom such as Na, K and Li or an alkyl group.

The polar group has the function of improving the dispersibility of the ferromagnetic powder, and the content in each resin is 0.1 to 8.0 mol%, preferably 0.5 to 6.0 mol%. . When the content is less than 0.1 mol%, the dispersibility of the ferromagnetic powder is lowered, and when the content is more than 8.0 mol%, the magnetic coating tends to gel. The weight average molecular weight of each resin is preferably in the range of 15,000 to 50,000.

The content of the binder in the magnetic layer is usually 10 to 100 parts by weight of the ferromagnetic powder.
It is 40 parts by weight, preferably 15 to 30 parts by weight. The binder (binder) is not limited to one kind alone, and two or more kinds can be used in combination. In this case, the ratio of the polyurethane and / or polyester to the vinyl chloride resin is usually 90:10 by weight. 10:90,
It is preferably in the range of 70:30 to 30:70.

The polar group-containing vinyl chloride copolymer used as the binder in the present invention is a compound having a hydroxyl group and the following polar group and chlorine atom, such as a vinyl chloride-vinyl alcohol copolymer. It can be synthesized by addition reaction with.

Cl-CH ₂ CH ₂ SO ₃ M, Cl-CH
_{2 CH 2 OSO 3 M, Cl} -CH 2 COOM, Cl-C
H ₂ -P (= 0) (OM ¹ ) _{2 From} these compounds, Cl-CH ₂ CH ₂ SO ₃ Na is taken as an example, and the above reaction is described as follows. _{-CH 2 C (OH) H- +} ClCH 2 CH 2 SO 3 Na
_{→ -CH 2 C (OCH 2 CH} 2 SO 3 Na) H-.

The polar group-containing vinyl chloride copolymer is prepared by charging a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced into a reaction vessel such as an autoclave to start a general polymerization. Agents, eg BPO
(Benzoyl peroxide), AIBN (azobisisobutyronitrile) and other radical polymerization initiators, redox polymerization initiators, cationic polymerization initiators and the like can be obtained by carrying out a polymerization reaction.

Specific examples of the reactive monomer for introducing the sulfonic acid or its salt include unsaturated hydrocarbon sulfonic acids such as vinyl sulfonic acid, allyl sulfonic acid, methacryl sulfonic acid, p-styrene sulfonic acid and the like. Mention may be made of salt.

When introducing a carboxylic acid or a salt thereof, for example, (meth) acrylic acid or maleic acid is used,
When phosphoric acid or a salt thereof is introduced, for example, (meth) acrylic acid-2-phosphate ester may be used.

It is preferable that an epoxy group is introduced into the vinyl chloride copolymer. This is because the thermal stability of the polymer is improved by doing so.

When the epoxy group is introduced, the content of the repeating unit having an epoxy group in the copolymer is 1
-30 mol% is preferable, and 1-20 mol% is more preferable. As the monomer for introducing an epoxy group, for example, chrysidyl acrylate is preferable.

Regarding the technique for introducing a polar group into a vinyl chloride-based copolymer, JP-A-57-44227 and JP-A-5-44227 have been used.
8-108052, 59-8127, 60-1
No. 01161, No. 60-235814, No. 60-23
No. 8306, No. 60-238371, No. 62-121
No. 923, No. 62-146432, No. 62-1464.
No. 33 and the like are described, and these can be used in the present invention.

Next, the synthesis of polyester and polyurethane used in the present invention will be described. Generally, polyesters are obtained by reacting polyols with polybasic acids. By using this known method, a polyester (polyol) having a polar group can be synthesized from a polyol and a polybasic acid partially having a polar group.

An example of a polybasic acid having a polar group is 5
-Sulfoisophthalic acid, 2-sulfoisophthalic acid, 4-
Examples thereof include sulfoisophthalic acid, 3-sulfophthalic acid, dialkyl 5-sulfoisophthalate, dialkyl 2-sulfoisophthalate, dialkyl 4-sulfoisophthalate, dialkyl 3-sulfoisophthalate, and their sodium salts and potassium salts.

Examples of polyols are trimethylolpropane, hexanetriol, glycerin, trimethylolethane, neopentyl glycol, pentaerythritol, ethylene glycol, propylene glycol, 1.3-butanediol, 1.4-butanediol, 1 6-hexanediol, diethylene glycol, cyclohexanedimethanol and the like can be mentioned. Note that other polar group-introduced polyesters can also be synthesized by a known method.

Next, the polyurethane will be described. It results from the reaction of polyols with polyisocyanates. As the polyol, a polyester polyol obtained by reacting a polyol with a polybasic acid is generally used. Therefore, if a polyester polyol having a polar group is used as a raw material, a polyurethane having a polar group can be synthesized.

In the present invention, it is preferable to use an aromatic polyester polyurethane prepared by using a polyester polyol having an aromatic ring and / or a polyester polyol containing a cyclic hydrocarbon residue or a polyester polyurethane containing a cyclic hydrocarbon residue. It is preferable in achieving the object of the invention.

Examples of polyisocyanates include diphenylmethane-4-4'-diisocyanate (MDI),
Hexamethylene diisocyanate (HMDI), tolylene diisocyanate (TDI), 1.5-naphthalene diisocyanate (NDI), tolidine diisocyanate (TODI), lysine isocyanate methyl ester (LDI) and the like can be mentioned.

As another method for synthesizing a polyurethane having a polar group, an addition reaction between a polyurethane having a hydroxyl group and the following compound having a polar group and a chlorine atom is also effective. _{Cl-CH 2 CH 2 SO 3} M, Cl-CH 2 CH 2 OS
_{O 2 M, Cl-CH 2} COOM, Cl-CH 2 -P (=
0) (OM ¹ ) _{2 As} a technique for introducing a polar group into polyurethane, JP-B-58-41565 and JP-A-57-9242 are known.
No. 2, No. 57-92423, No. 59-8127, No. 59-5423, No. 59-5424, No. 62-12.
It is described in the publications such as 1923, and these can be used in the present invention.

In the present invention, the following resins can be used together as a binder in an amount of 20% by weight or less based on the total amount of the binder. The resin has a weight average molecular weight of 1
Vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer, polyamide resin, polyvinyl butyral, cellulose Derivatives (nitrocellulose etc.), styrene-butadiene copolymers, phenol resins, epoxy resins, urea resins, melamine resins, phenoxy resins, silicone resins, acrylic resins, urea formamide resins, various synthetic rubber resins, etc. .

(Other Components) In the present invention, it is desirable to contain polyisocyanate in order to improve the durability of the magnetic layer and other layers.

Examples of the polyisocyanate include aromatic polyisocyanates such as adducts of tolylene diisocyanate (TDI) and active hydrogen compounds, and fats such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. There are group polyisocyanates. The weight average molecular weight of the polyisocyanate is 100 to
It is preferably in the range of 3,000.

In the present invention, the magnetic layer and other layers may contain additives such as a dispersant, a lubricant, an abrasive, an antistatic agent and a filler, if necessary. First,
Examples of the dispersant include those described in paragraph No. 0093 of JP-A-4-214218. These dispersants are usually added to the ferromagnetic powder at 0.5.
Used in the range of up to 5% by weight.

Next, as the lubricant, a fatty acid and / or a fatty acid ester can be used. In this case, the amount of the fatty acid added is preferably 0.2 to 10% by weight, based on the ferromagnetic powder or nonmagnetic powder that is mainly used, and 0.5 to
5% by weight is more preferred. If the addition amount is less than 0.2% by weight, the running property tends to be lowered, and if the addition amount is more than 10% by weight, the fatty acid is likely to seep out to the surface of the magnetic layer or the output is likely to be lowered.

The amount of the fatty acid ester added is preferably 0.2 to 10% by weight, more preferably 0.5 to 5% by weight, based on the ferromagnetic powder or non-magnetic powder used mainly. If the addition amount is less than 0.2% by weight, the still durability is likely to deteriorate, and if it exceeds 10% by weight, the fatty acid ester is likely to seep out to the surface of the magnetic layer or the output is likely to decrease.

When it is desired to enhance the lubricating effect by using the fatty acid and the fatty acid ester together, the weight ratio of the fatty acid and the fatty acid ester is preferably 10:90 to 90:10. The fatty acid may be a monobasic acid or a dibasic acid,
6-30 are preferable and, as for carbon number, the range of 12-22 is more preferable.

Specific examples of the fatty acid include caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid, elaidic acid, behenic acid, malonic acid, succinic acid. Acid, maleic acid, glutaric acid, adipic acid,
Examples thereof include pimelic acid, azelaic acid, sebacic acid, 1.12-dodecanedicarboxylic acid and octanedicarboxylic acid.

Specific examples of the fatty acid ester include oleyl oleate, isocetyl stearate, dioleyl malate, butyl stearate, butyl palmitate, butyl myristate, octyl myristate, octyl palmitate, pentyl stearate, pentyl palmitate. Tate, isobutyl oleate, stearyl stearate,
Lauryl oleate, octyl oleate, isobutyl oleate, ethyl oleate, isotridecyl oleate, 2-ethylhexyl stearate, 2-ethylhexyl palmitate, isopropyl palmitate, isopropyl myristate, butyl laurate, cetyl-2.
-Ethyl hexalate, dioleyl adipate, diethyl adipate, diisobutyl adipate, diisodecyl adipate, oleyl stearate, 2-ethylhexyl myristate, isopentyl palmitate, isopentyl stearate, diethylene glycol mono-butyl ether palmitate, diethylene glycol mono- Butyl ether palmitate and the like.

In the present invention, it is preferable that the non-magnetic layer contains a fatty acid ester or glycerin ester composed of unsaturated fatty acid and unsaturated alcohol. Oleyl oleate is particularly preferable as the fatty acid ester, and glycerin trioleate is particularly preferable as the glycerin ester.

As the unsaturated fatty acid component in the ester of unsaturated fatty acid and unsaturated alcohol, oleic acid, elaidic acid, linoleic acid, linolenic acid and the like can be mentioned as preferable ones, of which oleic acid is most preferable. It is mentioned as a thing. Examples of the unsaturated alcohol component include oleyl alcohol. Specific examples of esters of these unsaturated fatty acid components and unsaturated alcohol components include, for example, oleyl oleate, oleyl elaidate, oleic linoleate,
Examples include oleyl linolenate and the like.

The glycerin ester is preferably represented by the following general formula.

[0092]

Embedded image (However, at least one of R ¹ , R ² , and R ³ is a monobasic fatty acid residue having 6 to 30 carbon atoms, and the rest may be hydrogen atoms, and R ¹ , R ² , and R ^{3 s} may be the same or different from each other, and more preferably, at least one monobasic fatty acid residue of R ¹ , R ² , and R ³ has 10 to 22 carbon atoms.)

The glycerin ester may be specifically the following. (1) Ester of glycerin and palmitic acid (16 carbon atoms) (however, the ester may be any of monoester, diester and triester (the same applies hereinafter)) (2) Glycerin and stearic acid (carbon atom) Ester of (18) (3) Glycerin and oleic acid (containing one unsaturated carbon-carbon double bond with 18 carbon atoms) (4) Glycerin and linoleic acid (2 of 18 carbon atoms) Esters with unsaturated carbon-carbon double bonds) (5) Olive oil (natural product, a mixture of various glycerin esters) (6) Esters of glycerin and lauric acid (10 carbon atoms) (7) Glycerin Ester of myristic acid with 14 carbon atoms (8) Ester of glycerin with palmitic acid (16 carbon atoms) (9) Glyce Emissions and isostearic acid (1 carbon atoms
Ester with 8) (10) Ester with glycerin and behenic acid (22 carbon atoms) (11) 2-Ethylhexanoic acid triglyceride (12) Behenic acid monoglyceride (13) Oleic acid stearic acid monodiglyceride (14) Diacetylcaprin Acid glyceride (15) Diacetyl palm fatty acid glyceride (16) Acetyl stearic acid glyceride (17) Diacetyl capric acid glyceride (18) Diacetyl palm fatty acid glyceride (19) Caprylic acid monodiglyceride (20) Acetyl stearic acid glyceride (21) Caprylic acid triglyceride (22) in the fatty acid _{(C 8, C 10)} triglycerides above, it may be used in combination of two or more glycerides.

In the present invention, an ester of another polyhydric alcohol such as sorbitan may be used in addition to the glycerin ester.

In the present invention, R ¹ C═OO (CHR ² CHR ³ O) nR ⁴ (R ¹ is a linear or branched hydrocarbon group having 11 to 22 carbon atoms, is further added to the nonmagnetic layer as a lubricant.
It is preferable that R ² and R ³ contain H or CH ₃ , 1 ≦ n ≦ 10, and R contains a saturated or unsaturated hydrocarbon group having 1 to 22 carbon atoms. Further, R ⁵ OC = OR ⁶ (R ⁵ is a straight-chain or branched hydrocarbon group having 1 to 18 carbon atoms, R ⁶ is a straight-chain or branched hydrocarbon group having 11 to 22 carbon atoms) is contained as a fatty acid ester. Is preferably provided. By including several different types of fatty acid ester and glycerin ester in the non-magnetic layer in this way, these lubricants are appropriately replenished to the upper magnetic layer, and stable lubrication is achieved in a wide range of temperatures from high to low. The effect is demonstrated and the durability is significantly improved. It is more preferable that the non-magnetic layer contains a plurality of fatty acids having different melting points in addition to the fatty acid ester and the glycerin ester from the viewpoint of improving durability. Using such a hybrid lubricant system that combines a large number of different lubricants is an important technology for realizing a high-density magnetic disk medium with significantly higher density, higher durability, and an improved error rate than before. Is.

As the lubricant other than the above fatty acids and fatty acid esters, for example, silicone oil, graphite, carbon fluoride, molybdenum disulfide, tungsten disulfide, fatty acid amide, α-olefin oxide and the like can be used.

Specific examples of the polishing agent include α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide, boron carbide, corundum, and oxide. Examples thereof include zinc, cerium oxide, magnesium oxide, and boron nitride. The number average particle diameter of the polishing agent is 0.05 to 0.6 μm.
Is preferable, and 0.05-0.3 μm is more preferable. In the present invention, α is contained in the non-magnetic layer and / or the magnetic layer.
It preferably contains alumina and / or chromium oxide.

As the antistatic agent, conductive powder such as carbon black and graphite; cationic surfactant such as quaternary amine; acid such as sulfonic acid, sulfuric acid, phosphoric acid, phosphoric acid ester and carboxylic acid. Examples thereof include anionic surfactants containing a group; amphoteric surfactants such as aminosulfonic acid; and natural surfactants such as saponin. The above-mentioned antistatic agent is usually added in the range of 0.01 to 40% by weight with respect to the binder.

(Manufacture of Magnetic Recording Medium) In the magnetic recording medium of the present invention, it is preferable that the upper layer is laminated by a so-called wet-on-wet method which is performed when the lower layer is in a wet state. As the wet-on-wet system, a known method used for manufacturing a multilayer structure type magnetic recording medium can be appropriately adopted.

In the present invention, Wet-on-wet.
The production method is not particularly limited except that the coating method is preferably used, and the production can be performed according to a known method used for producing a multilayer structure type magnetic recording medium. For example, generally, magnetic powder, binder, dispersant, lubricant, abrasive, antistatic agent, etc. are kneaded and dispersed in a solvent to prepare a magnetic paint, and then this magnetic paint is applied to a non-magnetic support. Apply to the surface of.

Examples of the solvent include, for example, JP-A-4-21.
The thing etc. which are described in paragraph number 0119 of 4218 can be used.

Various kneading and dispersing machines can be used for kneading and dispersing the components for forming the magnetic layer and other layers. As this kneading disperser, for example, Japanese Patent Laid-Open No. 4-2142
No. 18, Paragraph No. 0112 and the like can be mentioned. Among the above kneading dispersers, kneading dispersers capable of providing a power consumption load of 0.05 to 0.5 KW (per 1 Kg of magnetic powder) include a pressure kneader, an open kneader,
It is a continuous kneader, a two-roll mill, and a three-roll mill.

In order to coat the magnetic layer and other layers on the non-magnetic support, in the production of the magnetic recording medium of the present invention, simultaneous multi-layer coating by the wet-on-wet multi-layer coating method is particularly effective. It is preferable to carry out.

Specifically, as shown in FIG. 1, first, the film-shaped support 1 fed from the supply roll 32 is applied to the coating materials for the magnetic layer and other layers by the extrusion type extrusion coaters 10 and 11. Is applied in multiple layers by the wet-on-wet method, and then passes through the orienting magnet or the vertically orienting magnet 33, is introduced into the dryer 34, and hot air is blown from the nozzles arranged above and below to dry it.
Next, the dried support 1 with each coating layer is combined with a calender roll 38 to form a super calender device 37.
And after performing a calendar process here, it is wound up on a winding roll 39. The magnetic film thus obtained can be cut into a tape having a desired width to produce, for example, a magnetic recording tape for an 8 mm video camera.

In the above method, each paint was extruded through an in-line mixer (not shown), the coater 10,
11 may be supplied. In the figure, arrow D indicates the transport direction of the non-magnetic base film. Extrusion coater 1
0 and 11 are provided with liquid reservoirs 13 and 14, respectively,
Overlay the paint from each coater in a wet-on-wet fashion. That is, the upper layer coating material is applied in multiple layers immediately after the lower magnetic layer coating material is applied (when it is in an undried state). The coater head shown in FIG. 2 (c) is preferable in the present invention.

As the wet-on-wet multilayer coating method, a combination of a reverse roll and an extrusion coater, a combination of a gravure roll and an extrusion coater, and the like can be used. Further, an air doctor coater, blade coater, air knife coater, squeeze coater, impregnation coater, transfer roll coater, kiss coater, cast coater, spray coater and the like can be combined.

In the multi-layer coating by the wet-on-wet method, the upper layer is coated while the lower layer is in a wet state, so that the surface of the lower layer (that is, the boundary surface with the upper layer).
And the surface property of the upper layer is improved, and the contact property between the upper and lower layers is also improved. As a result, the high performance and low noise required for high density recording are satisfied, for example, the performance required as a magnetic disk is satisfied, and film durability is also required for film peeling. It is eliminated, the film strength is improved, and the durability is sufficient. Further, the wet-on-wet multi-layer coating method can also reduce dropout and improve reliability.

As the solvent to be added to the above paint or a diluent solvent for applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone: alcohols such as methanol, ethanol, propanol and butanol: methyl acetate , Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol cenoacetate: ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran: aromatic hydrocarbons such as benzene, toluene, xylene: methylene chloride, Ethylene chloride, carbon tetrachloride, chloroform,
Halogenated hydrocarbons such as dichlorobenzene can be used. These various solvents may be used alone or in combination of two or more. The magnetic field in the orienting magnet or the vertically orienting magnet is about 20 to 10,000 gauss, the drying temperature by the dryer is about 30 to 120 ° C., and the drying time is about 0.1 to 10 minutes.

Surface Smoothing Next, surface smoothing processing is performed by calendering. After that, if necessary, burnishing or blade processing is performed and slitting is performed. On this occasion,
The surface smoothing treatment is effective in achieving the object of the present invention.

In the surface smoothing treatment, temperature, linear pressure, C / S (coating speed) and the like can be mentioned as calendering conditions. To achieve the object of the present invention, the temperature is usually 50 to 140 ° C., the linear pressure is 50 to 400 kg / cm, and the C / S is 20 to 100.
It is preferable to keep it at 0 m / min.

[0111]

According to the present invention, a magnetic recording medium which is excellent in durability for a long time under any environmental condition, does not cause an error in a wide range of temperature conditions, has a high reproduction output, and has a good overwrite characteristic. Can be obtained.

[0112]

Embodiments of the present invention will be described below. The components, ratios, and operation order shown below can be variously changed without departing from the scope of the present invention. In the following examples, all "parts" are parts by weight. (Examples 1 to 15 and Comparative Examples 1 to 5) First, a magnetic layer coating material and a non-magnetic layer coating material having the following composition formulations were kneaded and dispersed using a kneader and a sand mill, and polyisocyanate was added to each of the obtained coating materials. After adding 5 parts (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.), the combination shown in Table 1 was applied on a polyethylene terephthalate film having a thickness of 75 μm by a wet-on-wet method.
~ 15 and the samples of Comparative Examples 1 to 5 were applied, and then a non-orientation treatment was performed while the coating film was undried, followed by drying and then a surface smoothing treatment with a calendar to obtain a thickness of 1.0.
An original fabric was prepared which was composed of a layer containing a non-magnetic powder having a thickness of μm and a magnetic layer having a thickness of 0.2 μm. The magnetic film thus obtained was punched into a disk shape having a diameter of 86 mm and housed in a cassette to obtain a 3.5 inch floppy disk.

: Paint for magnetic layer: (Paint A1) Fe-Al based ferromagnetic metal powder (Fe: Co: Al: Y = 100: 10: 8: 5 (weight ratio), average major axis length: 100 nm, axis Ratio: 6, Hc: 1800 Oe, σs: 140 emu / g, crystallite size: 150Å) 100 parts Sulfonic acid metal salt-containing vinyl chloride resin [manufactured by Nippon Zeon Co., Ltd., MR-110] 10 parts Sulfonic acid metal salt Containing aromatic polyester polyurethane resin (manufactured by Toyobo Co., Ltd., UR-8200, containing cyclohexane ring) 10 parts Alumina (α-Al ₂ O ₃ , number average particle size: 0.2 μm) 5 parts Carbon black (number The average particle size and oil absorption are shown in Table 1.) 0.8 parts Stearic acid 1 part Myristic acid 1 part Butyl stearate 2 parts Butoxyethyl stearate 2 parts Oleyl oleate 5 parts Serine trioleate 2 parts Cyclohexanone 100 parts Methyl ethyl ketone 100 parts 100 parts toluene

(Coating B) Co-substituted barium ferrite (H
c: 1100 Oe, BET: 45 m ² / g, σs: 6
The same as the coating material A except that 4 emu / g and plate ratio: 4) were used.

(Paint A2) Fe-Al in paint A1
Fe: Co: Al: Ni: S as the base ferromagnetic metal powder
Same as A1 except that i: Nd = 100: 10: 8: 5: 3: 5 (weight ratio) was used.

: Paint formulation of non-magnetic layer: (Paint a: Non-magnetic layer) α-Fe ₂ O ₃ (average major axis length: 160 nm, average minor axis length: 20 nm, acicular ratio: 8, crystallite size: 18 nm , Si and _α-Fe 2 _{O 3} 1.0% in a weight ratio with respect to the _{0.2% a l α-Fe 2} O 3 in a weight ratio relative to) 100 parts conductive fine powder B (conductive fine powder The type, number average particle size, and oil absorption amount were changed as shown in Table 1.) 18 parts Conductive fine powder C 2 parts Metal sulfonate vinyl chloride resin [NIPPON ZEON CORPORATION ), MR-110] 6 parts Sulfonic acid metal salt-containing aromatic polyester polyurethane resin [Toyobo Co., Ltd. UR-8300, containing cyclohexane ring] 3 parts Alumina (α-Al ₂ O ₃ , number average) Particle size: 0.3 μm) 6 parts Myristic acid 1 part Butyl Stearate 2 parts Butoxyethyl stearate 2 parts Oleyl oleate 5 parts Glycerine trioleate 2 parts Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts

(Paint b) In sample a, α-Fe ₂ O ₃
Instead of 100 parts titanium oxide (number average particle size 30 nm,
Crystallite size 28nm, 0.2% by weight with respect to TiO ₂ and Si, different only with 1.0% in a weight ratio with respect to TiO ₂₎ Al.

The characteristics of this floppy disk were measured according to the following items. The measurement results are shown in Tables 1, 2, and 3.

(1) Reproduction output Using the following commercially available drive, 25 signals (500 KH)
Recording was performed with the sine wave signal of z), and the reproduction output was measured.

Drive: PD made by TOSHIBA Corporation, PD
-211

Example 13 α-Fe in Example 1
₂ O ₃ has an average major axis length of 300 nm and an average minor axis length of 5
0 nm, acicular ratio: 6, crystallite size 45 nm, Si α
0.2% by weight relative to —Fe ₂ O ₃ , Al is α-Fe
_A sample was prepared in the same manner as in Example 1 except that 100 parts by weight of 1.0 based on ₂ O ₃ were used.

Example 14 α-Fe in Example 1
₂ O ₃ has an average major axis length of 400 nm and an average minor axis length of 8
0 nm, acicular ratio: 5, crystallite size 75 nm, Si α
0.2% by weight relative to —Fe ₂ O ₃ , Al is α-Fe
_A sample was prepared in the same manner as in Example 1 except that 100 parts by weight of 1.0 based on ₂ O ₃ were used.

Example 15 α-Fe in Example 1
₂ O ₃ has an average major axis length of 60 nm and an average minor axis length of 12
nm, acicular ratio: 5, crystallite size 10 nm, Si α-
0.2% by weight relative to Fe ₂ O ₃ , Al is α-Fe ₂
A sample was prepared in the same manner as in Example 1 except that 100 parts of O _{3 in a} weight ratio of 1.0% were used. Measurement track: 79 tracks The measured reproduction output is shown as a relative value when the floppy disk manufactured in Example 1 is 100%. The larger the reproduction output, the better the magnetic disk.

(2) Durability A magnetic head mounted on a recording / reproducing apparatus was used as a magnetic head manufactured by Toshiba Corp. 4
While making sliding contact with the MB drive PD-211 at a clamping pressure of 50 g / cm ² and rotating at a disk rotation speed of 1000 rpm, the running time until the reproduction output reaches 70% of the initial output is set as the durability time, and the temperature and humidity are set. It changed and measured. (0
Cycle between ℃ and 60 ℃ in 24 hours)

<Dropout> Using 100 3.5-inch floppy disk samples, the number of disks in which dropout had occurred after applying vibration for 1 hour was determined as reliability.

<Overwrite characteristics> A signal of 315 KHz was recorded on the demagnetized sample and the reproduction output was measured (Ad
After B), the signal of 1 MHz was overwritten, and the overwrite characteristic B-A (dB) was obtained from the output (B dB) of 315 KHz at that time.

<Overall composition>: Fe, Co, Ni, Nd, Si, Al, Y, in the overall composition of the ferromagnetic metal powder.
Regarding the abundance ratio of each element of Pr, Sm, and La, after measuring the fluorescent X-ray intensity of each element in the sample using a wavelength dispersive fluorescent X-ray analyzer (WDX), the fundamental parameter method (hereinafter, FP Method).

The FP method will be described below. For measuring fluorescent X-rays, WDX system 308 manufactured by Rigaku Denki Co., Ltd.
0 was used under the following conditions. X-ray tube: Rhodium tube output: 50 KV, 50 mA Spectroscopic crystal: LiF (Fe, Co, Ni, Nd, Y, P
r, Sm, La), PET (for Al),
RX-4 (for Si) Absorber: 1/1 (Fe only 1/10) Slit: COARSE Filter: OUT PHA: 15-30 (for Al, Si), 10
~ 30 (Fe, Co, Ni, Nd, Y, Pr, Sm, L
(For a) Counting time: peak = 40 seconds, background = 40
Second (Measure two points before and after the peak) The measurement of the fluorescent X-ray is not limited to the above-mentioned device, and various devices can be used.

The following eight kinds of metal compounds were used as standard samples. Standard sample 1 is Analytical R
effort Materials Intern
alloy SRM1219 (C is 0.1
5 wt%, Mn 0.42 wt%, P 0.03 wt%, Si 0.55 wt%, Cu 0.16 wt%, N
i is 2.16% by weight, Cr is 15.64% by weight, Mo is 0.16% by weight, and V is 0.06% by weight. ).

The standard sample 2 is Analytical R
effort Materials Intern
alloy SRM1250 (Ni 3
7.78 wt%, Cr 0.08 wt%, Mo 0.0
1% by weight, 16.10% by weight of Co, and 0.99% by weight of Al are contained. ).

The standard sample 3 is magnetic iron oxide powder (Mn 0.14 wt%, P 0.15 wt%, S 0.19 wt%, Si 0.36 wt%, Co 3.19). weight%,
It contains 1.26% by weight of Zn, 0.07% by weight of Ca, and 0.02% by weight of Na. ).

Standard sample 4 is a ferromagnetic metal powder (containing 2.73% by weight of Nd).

The standard sample 5 is a ferromagnetic metal powder (containing 0.97% by weight of Sr).

The standard sample 6 is a ferromagnetic metal powder (containing 1.40% by weight of Ba and 0.40% by weight of Ca).

The standard sample 7 is a ferromagnetic metal powder (containing 2.69% by weight of La).

The standard sample 8 is a ferromagnetic metal powder (Y is 1.
Contains 98% by weight. ).

The weight% of the elements in the standard samples 1 and 2 are the values on the data sheet provided by the manufacturer, and the weight% of the elements in the standard samples 3 to 8 are the values analyzed by the ICP emission spectrometer. This value was input as the elemental composition value of the standard sample in the calculation of the FP method below.

For the calculation of the FP method, the fundamental parameter software Version2.1 manufactured by Technos is used.
Was calculated under the following conditions. Sample model: Bulk sample Balance component sample: Fe Input component: Measured X-ray intensity (KCPS) Analytical unit: wt% The calculated abundance ratio of each element (wt%) is Fe atom 1
It is a quantitative value by converting it as the weight% of other elements with respect to 00 weight%.

[0139]

[Table 1]

[0140]

[Table 2]

[Brief description of drawings]

FIG. 1 is a diagram for explaining simultaneous multi-layer coating of magnetic layers by a wet-on-wet coating method.

FIG. 2 is a diagram of a coater head for applying a magnetic layer paint.

Claims (8)

[Claims] 1. A nonmagnetic layer and a magnetic layer are formed in this order on a support, and the nonmagnetic layer has a crystallite size of 10 to 1.
A magnetic recording medium comprising: a non-magnetic powder A having a Mohs hardness of 5 or more at 00 nm and two or more kinds of conductive powders having a number average particle diameter of 5 nm or more. 2. A nonmagnetic layer and a magnetic layer are formed in this order on a support, and two or more kinds of conductive fine powders having different oil absorptions represented by DBP values of 10 ml / 100 g or more are formed on the nonmagnetic layer. A magnetic recording medium characterized by being contained. 3. A method of manufacturing a magnetic recording medium, wherein the magnetic layer is formed while the non-magnetic layer is in a wet state. 4. The non-magnetic layer has a number average particle size of 10 to 35 n.
The magnetic recording medium according to claim 1, comprising m and at least two kinds of conductive fine powder having a particle size of 40 to 500 nm. 5. The non-magnetic layer has an oil absorption represented by a DBP value of 20 to 100 ml / 100 g and 110 to 500 m.
2. The magnetic recording medium according to claim 1, wherein the magnetic recording medium contains at least two kinds of conductive fine powder of 1/100 g. 6. The magnetic recording medium according to claim 1, wherein the non-magnetic layer and / or the magnetic layer contains α-alumina and / or chromium oxide. 7. A number average particle diameter of 40 to 500 n in the magnetic layer.
A conductive fine powder of m is included.
Alternatively, the magnetic recording medium according to 2. 8. The magnetic recording medium according to claim 1, wherein the magnetic layer contains conductive fine powder having an oil absorption represented by a DBP value of 110 to 500 ml / 100 g.