JPH08263835A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE: To improve durability under conditions of a wide temp. range by forming lower layers comprising plural nonmagnetic layers or magnetic layers and layers including magnetic layers on a supporting body and incorporating lubricants having different melting points from each other into the respective layer of the lower layers. CONSTITUTION: This magnetic recording medium is formed of lower layers 1, 2 comprising plural nonmagnetic layers or magnetic layers and layers including magnetic layers on a supporting body. Each layer of the lower layers 1, 2 contains a lubricant having different melting point from each other. By forming plural nonmagnetic layers or magnetic layers as the lower layers, the shape or physical characteristics of additives contained in each layer can be controlled to increase the latitude of design. Namely, by controlling the melting point of the lubricant or the number, average particle size and oil absorption amt. expressed by DBP value of the conductive fine powder contained in each layer of the lower layers, such requirements as an increase in durability and decrease in error rate can bee satisfied.

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 more particularly to a magnetic recording medium preferably used as a magnetic recording disk for a floppy disk or a still video floppy disk.

[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.

JP-A-5-242461 and JP-A-5-325
Nos. 172 and 6-301964 disclose a technique for increasing the density and running durability of a magnetic recording medium by using a specific lubricant in the lower non-magnetic layer. Since the upper layer is thin in the prescription design of a thin multilayer medium, the characteristics of the medium largely depend on the characteristics of the lower non-magnetic layer. However, in these examples, since the non-magnetic layer constituting the lower layer has a single-layer structure, it is difficult to design the formulation with a degree of freedom in which the lower layer is functionally separated according to the purpose. JP-A-6
In No. 195682, the lower layer is composed of a plurality of layers,
Techniques for improving electromagnetic conversion characteristics and head touch characteristics by optimizing the crystallite size and average major axis length of the filler are disclosed. However, in order to cope with the recent increase in capacity of floppy disks and still floppy disks, it has become necessary to improve durability (especially at cycle thermostat) and error rate as well as to achieve much higher density than before. The above-mentioned technology was not sufficient for solving high-level technical problems.

[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, and 2) no error occurs in a wide range of temperature conditions. ) To provide a magnetic recording medium having a high reproduction output and 4) having a good overwrite characteristic.

[0005]

The problems of the present invention are as follows. A magnetic recording medium comprising a support and a layer including a magnetic layer and a lower layer composed of a plurality of non-magnetic layers formed on the support, and each of the lower layers containing lubricants having different melting points. ,

2. When the lower layer is composed of n layers (n is an integer of 2 or more), and the melting point of the lubricant contained in each layer is T1, T2, ... Tn in order from the layer closest to the support, T1 <T2
<... <Tn, The magnetic recording medium as described in 1 above,

3. A lower layer consisting of a plurality of non-magnetic layers or magnetic layers and a magnetic layer on a support, the upper layer is formed while the lower layer is in a wet state, and each coating material for the lower layer contains a lubricant having a different melting point. A method for manufacturing a magnetic recording medium,

4. When the lower layer is composed of n layers (n is an integer of 2 or more), and the melting point of the lubricant contained in each layer is T1, T2, ... Tn in order from the layer closest to the support, T1 <T2
<... <Tn, The method of manufacturing a magnetic recording medium according to the above item 3,

5. 3. The magnetic recording medium as described in 1 or 2 above, wherein the lubricant is a fatty acid.

6. 3. The magnetic recording medium as described in 1 or 2 above, wherein the lubricant is a fatty acid ester.

7. A layer comprising a lower layer composed of a plurality of non-magnetic layers or magnetic layers and a magnetic layer is formed on a support, and each of the lower layers contains conductive fine powders having different number average particle diameters from each other. The magnetic recording medium according to 1 or 2 above,

8. When the lower layer is composed of n layers (n is an integer of 2 or more), and the number average particle diameter of the conductive fine powder contained in each layer is L1, L2, ... Ln in order from the layer closer to the support, L1> L2 >> ... >> Ln, wherein the magnetic recording medium is

9. 9. The magnetic recording medium as described in 7 or 8 above, wherein the upper layer is formed while the lower layer is in a wet state, and the lower layer and the magnetic layer that are composed of the plurality of non-magnetic layers or magnetic layers.

10. A support is provided with a layer including a lower layer composed of a plurality of non-magnetic layers or magnetic layers and a magnetic layer, and each of the lower layers contains conductive fine powders having different oil absorptions expressed by DBP values. A magnetic recording medium characterized by

11. The lower layer is composed of n layers (n is an integer of 2 or more), and the oil absorption amount represented by the DBP value of the conductive fine powder contained in each layer is A1, A2, ...
The magnetic recording medium as described in 10 above, wherein when An, A1> A2 >> ... >> An,

12. 12. The magnetic recording medium as described in 10 or 11 above, wherein an upper layer is formed while the lower layer is wet and the lower layer composed of the plurality of non-magnetic layers or magnetic layers and the magnetic layer are in a wet state.

13. A support is provided with a plurality of non-magnetic layers or a lower layer composed of magnetic layers and a layer including a magnetic layer, and each of the lower layers contains non-magnetic powder having a Mohs hardness of 5 or more and different number average particle diameters. A magnetic recording medium characterized by

14. The lower layer is composed of n layers (n is an integer of 2 or more), and the number average particle size of the non-magnetic powder contained in each layer and having a Mohs hardness of 5 or more is X1, X2, ...
.. when Xn, X1>X2>...> Xn,

15. The magnetic recording medium according to any one of 13 and 14 above, wherein the upper layer is formed while the lower layer is in a wet state, and the lower layer consisting of the plurality of non-magnetic layers or the magnetic layers and the magnetic layer are formed. To be done.

[0020]

As a result of various studies to solve the above problems, it is difficult to solve the above problems as long as the support is composed of only two layers, a lower layer and an uppermost magnetic layer. I understand. That is, as the uppermost magnetic layer is made thinner, the role played by the lower layer increases to improve durability and electromagnetic conversion characteristics, but as long as the lower layer is a single layer structure, the role played by the lower layer is delicately controlled. do it,
It is difficult to provide the uppermost magnetic layer with a property suitable for the purpose. However, by forming the lower layer from a plurality of non-magnetic layers or magnetic layers, it becomes possible to control the shape and physical characteristics of the additive contained in each layer, and the degree of freedom in designing the lower layer is greatly increased. The present inventor has made various investigations on the shape and physical properties of the additive in the lower layer, and found that the melting point of the lubricant contained in each of the lower layers, the number average particle diameter of the conductive fine powder, and the DBP.
By controlling the oil absorption represented by the value and the number average particle diameter of the non-magnetic powder having a Mohs hardness of 5 or more, the above-mentioned problems can be achieved.

As a preferred embodiment for carrying out the present invention, in the present invention 1 or 3, it is preferable that each lower layer or each coating material contains a lubricant having a different melting point of 5 ° C. or more. It is more preferable to contain lubricants having different melting points of not less than ° C.

In the present invention 7, the thickness of each lower layer is 5 nm.
The conductive fine powders having different number average particle diameters are preferably contained, and the conductive fine powders having different number average particle diameters of 10 nm or more are more preferably contained.

In the tenth aspect of the present invention, DB is provided in each lower layer.
It is preferable to contain conductive fine powders having different oil absorptions represented by P values of 10 ml / 100 g or more, and 20 ml.
/ 100 g or more It is more preferable to contain conductive fine powders having different oil absorptions represented by DBP values.

In the thirteenth aspect of the present invention, it is preferable that each of the lower layers contains a non-magnetic powder having a Mohs hardness of 5 or more different in the number average particle size of 0.05 μm or more, and the number average particle size of 0.1.
It is more preferable to contain a non-magnetic powder having a Mohs hardness of 5 or more that is different by at least μm.

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 non-magnetic support and a lower layer composed of a plurality of non-magnetic layers or magnetic layers and a magnetic layer. In the present invention, the lower layer preferably comprises a plurality of nonmagnetic layers. 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 also to provide a lower layer between the lower layer and the non-magnetic support. A pulling layer can also be provided. Also,
If necessary, an overcoat layer can be provided on the uppermost magnetic layer.

(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. As described above, it is preferable to provide a writing layer or a print recording layer, and an undercoat layer can be provided between the magnetic layer and the non-magnetic support.

(Magnetic Layer) In the present invention, the magnetic layer is
Basically, magnetic powder is dispersed in a binder resin. Known magnetic powder can be used for this magnetic layer, but it is particularly preferable that the uppermost magnetic layer contains ferromagnetic metal powder or hexagonal magnetic powder. When a magnetic layer is used as the lower layer, it is preferable to contain Co-deposited iron oxide. The thickness of the uppermost magnetic layer is usually 0.05 to 1.
It is 0 μm, preferably 0.05 to 0.5 μm, and more preferably 0.05 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, 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 that at least part of Fe in the Ba-ferrite powder is C.
average particle size (height of diagonal of plate surface of hexagonal ferrite) replaced with o and Zn 400 to 900Å, plate ratio (diagonal length of plate surface of hexagonal ferrite divided by plate thickness) Value) 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.

In the Ba-ferrite powder, the coercive force is controlled to an appropriate value by partially substituting Fe with Co, and further by partially substituting with Zn, it is not possible to obtain it 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 diameter 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 is
The saturation magnetization (σs), which is a magnetic property, is usually 50 emu.
/ G or more is desirable. This saturation magnetization is 50
If it is less than emu / g, the 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 as measured by the BET method according to the higher recording density.

As the method for producing the hexagonal magnetic powder used in the present invention, for example, the oxides and carbonates of the respective elements necessary for forming the desired Ba-ferrite are 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 diameter 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 preferable 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, and more preferably 0.05. ~ 0.17μm and X-ray particle size (crystallite size) is less than 200Å, especially 50-180Å
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 acicular 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 O.
It is preferably in the range of e. This coercive force is 600
When it is less than Oe, the electromagnetic conversion characteristics may be deteriorated, and when 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 (σs), which is a magnetic characteristic, 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 Dallavele,
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 at least one of Fe, Al, and a rare earth element as its constituent element. That is, it is preferable to contain at least one rare earth element selected from the group consisting of Sm, Nd, Y, Pr and La.

The ferromagnetic metal powder preferably used in the present invention has an abundance ratio of Fe, Al and at least one rare earth element selected from the group consisting of Sm, Nd, Y, Pr and La in the overall composition. , Al atoms are 1 to 20 parts by weight with respect to 100 parts by weight of Fe atoms, and the rare earth element (preferably one or more kinds selected from the group consisting of Sm, Nd, Y, Pr and La) is 1 ~ 16 parts by weight.
Further, the existence ratio of rare earth elements of Fe and Al (preferably one or more kinds selected from the group consisting of Sm, Nd, Y, Pr, and La) on the surface thereof is 100 for Fe atoms and 100 for Al atoms. Is 70 to 300, and the number of atoms of the rare earth element is preferably 0.5 to 100.

More preferably, the ferromagnetic metal powder further contains Na and Ca as its 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.

Preferably, the ferromagnetic metal powder contains at least one element selected from 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. Against C
o 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 is
Atoms are less than 0.1 parts by weight and Ca atoms are 0.1-2.
Parts by weight, Al atoms are 1 to 20 parts by weight, atoms of rare earth elements are 1 to 16 parts by weight, and the average abundance of elements forming the surface of the ferromagnetic metal powder is the number of Fe atoms. The number of Co atoms is less than 0.1 with respect to 100,
The number of Ni atoms is less than 0.1 and the number of Si atoms is 20 to 1
30, the number of Na atoms is 2 to 30, the number of Ca atoms is 5 to 30, the number of Al atoms is 70 to 300,
The number of atoms of the rare earth element is 0.5 to 100.

(Lower Layer) The lower layer of the present invention comprises a plurality of non-magnetic layers or magnetic layers, but the lower layer preferably comprises a plurality of non-magnetic layers. For the lower non-magnetic layer in the present invention, it is preferable to use non-magnetic powder A having a crystallite size of 10 to 100 nm and a Mohs hardness of 5 or more. 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, it is possible to improve the surface smoothness of the non-magnetic layer,
The smoothness of the surface of the uppermost layer composed of the magnetic layer laminated thereon can also be improved.

The term "nonmagnetic layer" used herein means a layer which is substantially nonmagnetic (saturation magnetic flux density Bm is 0) and a layer which is substantially nonmagnetic (slightly magnetized 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 100 Gauss, but 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 redox 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 20 nm or more and 250 nm or less, preferably 22.
It is 0 nm or less, and particularly preferably 200 nm or less.

The minor axis diameter of the acicular 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 acicular 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.

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

In the present invention, the non-magnetic powder is Si
Surface treatment with a compound and / or an Al compound is preferred. 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 nonmagnetic powder in the lower layer is usually 5 with respect to the total amount 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 contained in the magnetic layer, carbon black, Sb deposited tin oxide, and titanium dioxide (TiO 2 coated with Sb and Sn) are used.
₂ ) and the like, but as the carbon black B having a DBP oil absorption of 110 ml / 100 g to 500 ml / 100 g, which is particularly preferably used, there are, for example, Asahi # 80 (23 nm, 113 ml / 100 g) manufactured by Asahi Carbon Black Co., Ltd., Colombian Carbon Co., Ltd. Conductex SC (17n)
m, 115 ml / 100 g), Conductex 975
(20 nm, 183 ml / 100 g), Monarch 1300 (13 nm, 121 ml / 100) manufactured by Cabot.
g), Vulcan XC-72 (30 nm, 178 ml / 1
00g), Vulcan P (20nm, 116ml / 100
g), Vulcan 9 (19 nm, 114 ml / 100)
g), Black Pearls 2000 (15nm, 330m
1/100 g) and the like.

The carbon black contained in the non-magnetic layer is a DBP oil absorption amount of 20 ml / 100 g to 110 ml.
/ 100 g of carbon black A is preferred, for example
Raven 5000 (12n made by Colombian Carbon Co., Ltd.
m, 95 ml / 100 g), Raven 1255 (23
nm, 58 ml / 100 g), Raven1035 (2
7nm, 60ml / 100g), Raven2000
(18nm, 70ml / 100g), Cabot Black Pearl 1400 (13nm, 80ml / 100g)
g), Black Pearl 1300 (13 nm, 91 ml /
100 g), Black Pearl 1100 (14 nm, 50
ml / 100g), Black Pearl 900 (15nm,
64 ml / 100 g), Black Pearl L (24 nm,
55ml / 100g), Regal 400 (25nm, 7
0 ml / 100 g) etc.

The carbon black B contained in the magnetic layer preferably has a number average particle diameter of 10 to 40 nm, more preferably 10 to 30 nm for the purpose of smoothing the surface of the magnetic layer and obtaining high output. is there.

As for the carbon black A contained in the non-magnetic layer, the surface property of the upper magnetic layer greatly depends on the surface property of the lower layer as the thickness of the upper magnetic layer becomes thinner. For this reason, the characteristics of the carbon black A contained in the lower non-magnetic layer are important, the number average particle diameter is 10 to 40 nm, and the oil absorption is a DBP value of 20 ml / 100 g to 100.
It is preferable to select carbon black of ml / 100 g in order to improve the dispersibility of the nonmagnetic layer and obtain good surface properties.

The number average particle size of carbon black A is preferably 10 to 40 nm, more preferably 10 to 30 nm. The oil absorption of carbon black A is preferably 30 to 90 ml / 100 g, more preferably 40 to 80 ml / 100 g in terms of DBP value.

The weight of carbon black B contained in the magnetic layer is preferably 0.1 to 5.0% by weight, and more preferably 0.2 to 2.0% by weight, based on the magnetic powder. The weight of carbon black A contained in the nonmagnetic layer is preferably 5.0 to 30% by weight, more preferably 7.0 to 20% by weight, based on the nonmagnetic powder.

The oil absorption of carbon black B is preferably 130 to 350 ml / 100 g in terms of DBP value.
More preferably, it is 50 to 250 ml / 100 g.

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 average of N = 100 pieces is defined as "number average particle diameter".

With respect to 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) Typical binders used for forming the magnetic layer and the non-magnetic layer are, for example, polyurethane, polyester and vinyl chloride resins, and these resins are --SO ₃ M, -OSO ₃
M, -COOM, -PO (OM ¹ ) ₂ and -OPO (O
It preferably contains at least one polar group selected from M ¹ ) ₂ . However, in the 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 a 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 a binder in the present invention is, for example, a vinyl chloride-vinyl alcohol copolymer or other copolymer having a hydroxyl group and a compound having the following polar group and chlorine atom. 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-.

In addition, in the polar group-containing vinyl chloride-based copolymer, a predetermined amount of a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced is charged 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, and these. Mention may be made of salt.

When the carboxylic acid or its salt is introduced, 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 disclose.
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.

Examples of the polybasic acid having a polar group include 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 include 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 produced by using a polyester polyol having an aromatic ring in order to achieve the object of the present 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, additives such as a dispersant, a lubricant, an abrasive, an antistatic agent and a filler can be added to the magnetic layer and other layers, 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, a fatty acid and / or a fatty acid ester can be used as a lubricant. 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 nonmagnetic powder that is mainly used. 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 a fatty acid and a fatty acid ester are used in combination to further enhance the lubricating effect, 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.

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 0.1-0.3 μm is more preferable.

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, carboxylic acid and the like. 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 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.

To coat the uppermost magnetic layer and a plurality of lower layers on the non-magnetic support, specifically, as shown in FIG. 1, first, as shown in FIG. 1, extrusion-type extrusion coater 10, 1
1 and 12, the uppermost layer magnetic coating material and the lower layer coating material are multi-layered by a wet-on-wet method, and then passed through an orientation magnet or a non-orientation magnet 33 and introduced into a drier 34, where Hot air is blown from the nozzles arranged above and below to dry. Next, the dried non-magnetic support 1 with each coating layer is guided to a super calender device 37 composed of a combination of calender rolls 38, subjected to calendering here, and then wound on a winding roll 39. The magnetic film thus obtained is cut into a tape or disk having a desired width,
For example, 8 mm video magnetic recording tape or 3.5 "floppy disks can be manufactured.

In the above method, each paint is extruded through an in-line mixer (not shown), and the coaters 10, 11,
12 may be supplied. It should be noted that in the figure, the arrow indicates the transport direction of the nonmagnetic support. Extrusion coater 10, 11, 12
Are provided with liquid reservoirs 13, 14, and 15, respectively, and the coating materials from the coaters are superposed in a wet-on-wet system. That is, the magnetic coating material for the uppermost layer is applied in multiple layers immediately after the application of the coating material for the lower layer (when it is in an undried state).

As the extrusion coater, in addition to the three extrusion coaters shown in FIG. 2A, the extrusion coaters of the types shown in FIGS. 2B and 2C can also be used. Of these, the extrusion coater shown in (b) is preferred in the present invention. With the extrusion coater, a plurality of lower layer coating materials and the uppermost layer magnetic coating material are extruded to form multiple layers.

FIG. 3 is a sectional view of a magnetic recording medium coated by the above method.

In 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, 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.

[0122]

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.

[0123]

Embodiments of the present invention will be described below.

The following components, ratios, and operation order 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 13 and Comparative Examples 1 to 4) 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.), Examples 1 to 13 and Comparative Example 1 were combined by a wet-on-wet method on a polyethylene terephthalate film having a thickness of 75 μm in a combination shown in Table 1. After applying the sample of ~ 4,
Non-orientation treatment was performed while the coating film was undried, followed by drying, and then surface smoothing treatment with a calendar to obtain a thickness of 1.0 μm (changed as shown in Tables 1 and 2). A raw material was prepared which was composed of lower layers 1 and 2 of the intermediate layer containing non-magnetic powder and a magnetic layer having a thickness of 0.2 μm (changed as shown in Tables 1 and 2). 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: 135 emu / g, crystallite size: 150 Å) 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-8300) 5 parts Alumina (α-Al ₂ O ₃ , number average particle size: 0.2 μm) 5 parts Carbon black (number average particle size 20 nm, oil absorption (DBP value) ) 60 ml / 100 g) 0.8 part Stearic acid 1 part Myristic acid 1 part Butyl stearate 2 parts Oleyl oleate 5 parts Cyclohexanone 100 parts Methyl ethyl ketone 00 parts of toluene 100 parts

(Paint B) Instead of the Fe--Al based ferromagnetic metal powder in the paint A, 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 the paint A1
Fe: Co: Al: Ni: S as the base ferromagnetic metal powder
i: Nd = 100: 10: 8: 5: 3: 5 (weight ratio)
(Average major axis length: 100 nm, axial ratio: 6, Hc: 1800
Oe, σs: 135 emu / g, crystallite size: 15
Same as A1 except that 0Å) was used.

Non-magnetic layer paint formulation: (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, Si to α-Fe 0.2% by weight relative to ₂ O _3, 1.0% content) 100 parts carbon black Al against Shi weight ratio _α-Fe 2 _{O 3} (number average particle diameter, Table 1 for oil absorption, It was modified as described in 2.) 15 parts Vinyl chloride resin containing sulfonic acid metal salt [MR-110 manufactured by Nippon Zeon Co., Ltd.] 6 parts Aromatic polyester polyurethane resin containing sulfonic acid metal salt [Toyobo Co., Ltd., UR-8300] 3 alumina: 6 parts fatty acids (Table _(α-Al 2 _{O 3,} the number average particle size. was also used to was changed as shown in Table 1 and 2) What was changed as described in 1 and 2 was used.) 2 parts Fatty acid Ether (Tables 1 and 2 was used modified as described.) 5 parts Cyclohexanone 100 parts Methyl ethyl ketone 100 parts 100 parts toluene

(Paint b) In sample a, α-Fe ₂ O ₃
Instead of 100 parts titanium oxide (number average particle size 30 nm,
0.2% by weight of Si to TiO ₂ and Al of TiO 2
_The difference is that the content of 1.0% by weight is used for ₂ ).

(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: manufactured by Toshiba Co., Ltd., PD-211, Measurement track: 79 tracks The measured reproduction output is shown as a relative value when the floppy disk manufactured in Example 1 was set to 100%. The larger the reproduction output, the better the magnetic disk.

(2) Durability A magnetic head mounted on a recording / reproducing apparatus was used and 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 the measurement of fluorescent X-ray, WDX system 3080 manufactured by Rigaku Denki Co., Ltd. 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. ).

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% by weight, P 0.15% by weight, S 0.19% by weight, Si 0.36% by weight, Co 3.19% by weight). weight%,
It contains 1.26% by weight of Zn, 0.07% by weight of Ca, and 0.02% by weight of Na. ).

The 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 wt% of Ba and 0.40 wt% of Ca). The standard sample 7 is a ferromagnetic metal powder (containing 2.69% by weight of La). Standard sample 8 is a ferromagnetic metal powder (containing 1.98% by weight of Y).

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%.

[0143]

[Table 1]

[0144]

[Table 2]

[0145]

[Table 3]

[Brief description of drawings]

FIG. 1 is a simultaneous multilayer coating diagram of a magnetic layer by wet-on-wet coating by an extrusion coating method.

FIG. 2 is a sectional view of an extrusion coater head.

FIG. 3 is a sectional view of a magnetic recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-magnetic support 10, 11, 12 Extrusion coater 13, 14, 15 Liquid pool part 32 Supply roll 33 Orientation magnet or non-orientation magnet 34 Dryer 37 Super calendar device 38 Calendar roll 39 Winding roll

Claims (15)

[Claims] 1. A support is provided with a layer including a lower layer composed of a plurality of nonmagnetic layers or magnetic layers and a magnetic layer, and each of the lower layers contains lubricants having different melting points. And a magnetic recording medium. 2. When the lower layer is composed of n layers (n is an integer of 2 or more), and the melting point of the lubricant contained in each layer is T1, T2, ... Tn in order from the layer closer to the support, T1 < T2 <
... <Tn, The magnetic recording medium according to claim 1. 3. A lubricant comprising a lower layer composed of a plurality of non-magnetic layers or magnetic layers and a magnetic layer on a support, the upper layer being formed while the lower layer is in a wet state, and each coating material for the lower layer having a different melting point. A method of manufacturing a magnetic recording medium, comprising: 4. The lower layer is composed of n layers (n is an integer of 2 or more), and when the melting point of the lubricant contained in each layer is T1, T2, ... Tn in order from the layer closer to the support, T1 < T2 <
... <Tn, The manufacturing method of the magnetic recording medium according to claim 3. 5. The magnetic recording medium according to claim 1, wherein the lubricant is a fatty acid. 6. The magnetic recording medium according to claim 1, wherein the lubricant is a fatty acid ester. 7. A support is provided with a layer including a lower layer composed of a plurality of non-magnetic layers or magnetic layers and a magnetic layer, and each of the lower layers contains conductive fine powders having different number average particle diameters. The magnetic recording medium according to claim 1 or 2, wherein 8. The lower layer comprises n layers (n is an integer of 2 or more), and the number average particle diameter of the conductive fine powder contained in each layer is L1, L2, ... Ln in order from the layer closer to the support. and when,
The magnetic recording medium according to claim 7, wherein L1>L2>...> Ln. 9. The magnetic recording according to claim 7, wherein an upper layer is formed while the lower layer is wet and the lower layer consisting of the plurality of non-magnetic layers or magnetic layers and the magnetic layer are formed. Medium. 10. A support, on which a lower layer composed of a plurality of non-magnetic layers or magnetic layers and a layer including a magnetic layer are formed,
A magnetic recording medium, characterized in that each of the lower layers contains conductive fine powders having different oil absorptions expressed by DBP values. 11. The lower layer comprises n layers (n is an integer of 2 or more), and the oil absorption represented by the DBP value of the conductive fine powder contained in each layer is A1, A2 ,. ..A
11. The magnetic recording medium according to claim 10, wherein when A is n, A1> A2 >> ... >> An. 12. The lower layer composed of a plurality of non-magnetic layers or magnetic layers and the magnetic layer, wherein the upper layer is formed while the lower layer is in a wet state.
1. The magnetic recording medium according to 1. 13. A support, on which a lower layer composed of a plurality of non-magnetic layers or magnetic layers and a layer including a magnetic layer are formed.
A magnetic recording medium characterized in that each of the lower layers contains a non-magnetic powder having a Mohs hardness of 5 or more having different number average particle diameters. 14. The lower layer comprises n layers (n is an integer of 2 or more), and the number average particle diameter of the non-magnetic powder contained in each layer and having a Mohs hardness of 5 or more is X1, X2 ,.・ ・
The magnetic recording medium according to claim 13, wherein when Xn, X1>X2>...> Xn. 15. The lower layer composed of the plurality of non-magnetic layers or magnetic layers and the magnetic layer are formed while the upper layer is being formed while the lower layer is in a wet state.
4. The magnetic recording medium according to 4.