JPH09161261A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium having excellent durability over a long period of time even under a wide environment from a high temp. to a low temp., high reproduced output, a good taking-up characteristic of a raw sheet and excellent process adaptability. SOLUTION: This magnetic recording medium is constituted by providing the surface of a base with >=2 layers of constituting layers including magnetic layers. The film thickness of the magnetic layer of the uppermost layer is <=1.0μm. The center line average height (expressed by Ra, nm) and max. roughness (expressed by Rt, nm) of the base are 12<=Ra<=28, 95<=Rt<=220, Rt/Ra<=10. The layer in contact with the underside of the magnetic layer is so formed as to contain fatty acid ester.

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 specifically, for example, 8 mm tape, digital V
The present invention relates to a magnetic recording medium preferably used as a TR tape, a data tape, a floppy disk or a still video floppy disk.

[0002]

2. Description of the Related Art In recent years, the development of thin-film metal multi-layer media for large-capacity floppy disks and large-capacity data tapes has become vigorous. Japanese Patent Application Laid-Open No. 57-198536 discloses a technique in which a non-magnetic undercoat layer is provided under the magnetic layer in order to prevent the influence of the support that appears when the magnetic layer is thinned. Further, Japanese Patent Application Laid-Open No. 3-176807 discloses a magnetic recording medium which is excellent in electromagnetic conversion characteristics as well as in running properties and durability by providing a large number of uniform protrusions on the surface of a support. However, the recent increase in the density of magnetic recording media is remarkable, and it is necessary to minimize the losses such as self-demagnetization loss, film thickness loss, and separation loss in order to achieve high density of the medium. For that purpose, it is essential to make the magnetic layer thin and achieve ultra-smoothness. On the other hand, such thinning and ultra-smoothing tend to impair the reliability of the medium (jitter on tape, edge breakage, error rate on disk) under high temperature and high humidity, and to achieve ultra-smoothness of the magnetic layer. When an ultra-smooth base without large protrusions is used as the support, the winding property of the original fabric is deteriorated, and it becomes impossible to satisfy the process suitability. To solve the problem, Japanese Patent Laid-Open Nos. 57-198536 and 3-176.
The technique disclosed in Japanese Patent No. 807 is not sufficient, and it is necessary to deal with it from the viewpoint of the composition of the magnetic layer, the layer constitution, and the surface characteristics of the support.

[0003]

The problems to be solved by the present invention are as follows: 1) excellent durability for a long time in a wide range of environments from high temperature to low temperature, 2) high reproduction output, 3) winding property of original fabric Is excellent and has excellent process suitability,
It is to provide a magnetic recording medium.

[0004]

As a result of repeated studies for solving the above problems, the present inventor has found that a specific center line average roughness (R
a, hereinafter may be simply referred to as Ra. ), A support having a maximum roughness (Rt, hereinafter sometimes simply referred to as Rt), an additive to be contained in the magnetic layer, and a synergistic effect by selecting a specific combination from the viewpoint of the layer structure of the medium. The effect was obtained and the above problems could be solved.

That is, the above problems of the present invention are as follows. Two or more constituent layers including a magnetic layer are provided on a support, and the thickness of the uppermost magnetic layer is 1.0 μm or less,
In addition, the center line average roughness (Ra, nm) and the maximum roughness (Rt, nm) of the support are 12 ≦ Ra ≦ 28, 9
5 ≦ Rt ≦ 220, Rt / Ra ≦ 10, wherein the layer underlying the magnetic layer contains a fatty acid ester, and the magnetic recording medium is characterized.

[0006] 2. 2. The magnetic recording medium as described in 1 above, wherein the number of protrusions having a height of the support surface of 0.01 μm or more is 200 or more per measurement length of 1 mm,

[0007] 3. 2. The magnetic recording medium as described in 1 above, wherein the layer underlying the magnetic layer contains a fatty acid having a melting point of 50 ° C. or higher.

4. A magnetic layer having a film thickness of 1.0 μm or less is provided on a support, and the center line average roughness (Ra,
nm) and maximum roughness (Rt, nm) are 12
≦ Ra ≦ 28, 95 ≦ Rt ≦ 220, Rt / Ra ≦ 10
And a magnetic recording medium characterized by containing a fatty acid ester and carbon black in the magnetic layer,

[0009] 5. 5. The magnetic recording medium as described in 4 above, wherein the number of protrusions having a support surface height of 0.01 μm or more is 200 or more per 1 mm of measurement length,

[0010] 6. 5. The magnetic recording medium as described in 4 above, wherein the magnetic layer contains a fatty acid having a melting point of 50 ° C. or higher.

7. The magnetic recording medium according to item 4, wherein the magnetic layer contains carbon black having a number average particle diameter of 30 nm or more.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below. (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 a material for forming the non-magnetic support, for example, polyethylene terephthalate,
Examples thereof include polyesters such as polyethylene-2,6-naphthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, and plastics such as polyamide and polycarbonate.

The center line average roughness (Ra) of the support is 12 to.
The thickness is 28 nm, preferably 14 to 26 nm, and more preferably 16 to 24 nm. The maximum roughness (Rt) of the support is 95 to 220 nm, but
It is preferably 0 to 200 nm, and 120 to 180 n
More preferably m. Rt / Ra is 10 or less, but is preferably 5 to 9, and more preferably 7 to 9. The number of protrusions having a protrusion height of 0.01 μm or more on the surface of the support is preferably 200 or more per measured length of 1 mm, more preferably 250 to 1000.

In order to adjust Ra, Rt and the number of protrusions of the non-magnetic support, for example, on the smooth and unwound back surface of the non-magnetic support, the particle size should be as uniform as possible and as close to spherical as possible. Particles of 0.1 to 10% by weight, preferably 0.1 to 5% by weight, and an average film thickness of 0.01 to 1 μm, preferably 0.01.
A protrusion layer having a thickness of 0.5 μm may be laminated. here,
The projection layer does not necessarily have to form a film as long as the particles are wrapped with a polymer, and may have a mesh shape, for example. Further, the protrusions can also be formed by mechanically forming irregularities on the back surface of the nonmagnetic support without laminating such a protrusion layer.

In the present invention, the total of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction is preferably 1300 kg / mm ² or more, 1400 kg / mm ² or more, 400
It is more preferably 0 kg / mm ² or less. The form of the non-magnetic support is not particularly limited, and may be mainly tape, film, sheet, card, disk, drum or the like. The thickness of the non-magnetic support is not particularly limited, but is 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, or may be subjected to an undercoat layer. A back coat layer may be provided on the surface (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, 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 0.08 to 0.3 μm.

The hexagonal magnetic powder may be, for example, 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 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, by partially substituting for Zn, it cannot be obtained by only 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, if the average particle size is less than 0.04 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. The noise level may become too high, and 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 it exceeds 6.0, the surface smoothness of the magnetic recording medium is significantly deteriorated, the noise level becomes too high, and the coercive force is 350 O.
If it is less than e, it becomes difficult to hold the recording signal, and
This is because if it exceeds 00 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 preferable specific example of the Ba-ferrite used in the present invention is Co-substituted Ba ferrite. Further, in the present invention, the specific surface area by the BET method is 30 m as the recording density increases.
It is desirable to use ² / g or more of Ba-ferrite magnetic powder.

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, for example, 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.

Ferromagnetic metal powders used in the magnetic layer include 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.

In particular, the preferred ferromagnetic metal powder for the purpose of the present invention is a metal magnetic powder containing iron as a main component, and contains Al or Al and Ca in a weight ratio of Al to 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,
It is more preferably 0.05 to 0.12 μm and the X-ray particle size (crystallite size) is less than 20 nm, and particularly preferably 5 to 17 nm. 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 crystallite 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 powders as determined by transmission electron micrograph. Alternatively, it is an average value of 500 long-axis lengths or diameters (in the case of spherical particles) of the non-magnetic powder. The crystallite size was measured by an X-ray diffractometer by the Scherrer method using Si powder as a reference, using the integral width of the (110) diffraction line of Fe.

Regarding the method of obtaining, according to the method described in the X-ray diffraction manual (Rigaku Denki Co., Ltd.), the correction of the spread due to double lines is described in A. It was determined by correction (integral width) by Jones. The axial ratio was determined as the ratio of (average major axis length / average minor axis length) by measuring the average major axis length and the average minor axis length of 500 particles with 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 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 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.

(Non-Magnetic Layer) In the lower non-magnetic layer in the present invention, it is preferable to use non-magnetic powder having a crystallite size of 10 to 100 nm and a Mohs hardness of 5 or more. As the non-magnetic powder, a known non-magnetic powder used in this type of magnetic recording medium can be appropriately selected and used.
The crystallite size of the non-magnetic powder is preferably 15 to 80 nm
And more preferably 20 to 60 nm. Examples of this non-magnetic powder include titanium oxide, boric acid nitride,
_{SnO 2, SiO 2, Cr 2} O 3, α-Al 2 O 3, α
—Fe ₂ O ₃ , α-FeOOH, SiC, cerium oxide, corundum, artificial diamond, garnet, garnet, silica stone, silicon nitride, silicon carbide and the like can be mentioned.

Among these, preferable are titanium oxide, barium sulfate, α-Al ₂ O ₃ , α-Fe ₂ O ₃ ,
It is an inorganic powder such as α-FeOOH and Cr ₂ O ₃ , and 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. When the acicular non-magnetic powder is used,
The surface smoothness of the non-magnetic layer can be improved, and the surface smoothness of the uppermost layer composed of the magnetic layer laminated thereon can also be improved.

The term "nonmagnetic layer" as used herein means a layer which is substantially nonmagnetic (saturation magnetic flux density Bm is 0) and a layer which is substantially nonmagnetic (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 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 a starting material as a starting material, selection of oxidation-reduction conditions, and selection of a sintering inhibitor. You can

The major axis diameter of the acicular non-magnetic powder used in the lower layer of the present invention or the number average particle diameter of non-acicular non-magnetic 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 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,
It is 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, and particularly preferably 30 to 100 m ² / g. 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 surface property of the uppermost layer which is the magnetic layer is It is preferable in that it can be in a good state.

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 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) In the present invention as set forth in claim 4, carbon black is contained in the magnetic layer together with the fatty acid ester described later. It is particularly preferable that the carbon black has a number average particle diameter of 30 nm or more.

The conductive fine powder preferably used in the present invention as defined in claim 1 has an average particle size of 30 to 500 nm, preferably 45 to 300, if contained in the magnetic layer.
nm, more preferably 85-200 nm powder,
With respect to 100 (wt) of magnetic powder, preferably 0.1 to 1.
0 (wt), and at least 1 other than the magnetic layer
It is included in the layer, and usually has an average particle size of 5 to 50 nm, preferably 10 to 40 nm, more preferably 10 to 30 n.
m powder, and preferably 1.0 (wt) or more and 50 (wt) or less with respect to 100 (wt) of the filler of the layer,
The content is preferably 3.0 (wt) or more and 30 (wt) or less, more preferably 5.0 (wt) or more and 20 (wt) or less.

Examples of the conductive fine powder include carbon black, SnO _{2 and the} like, and the following conductive pigments. That is, silver powder, silver oxide, silver nitrate, an organic compound of silver, metal particles such as copper powder, etc .; zinc oxide, barium sulfate,
There are pigments such as metal oxides such as titanium oxide coated with a conductive material such as tin oxide coating or antimony solid solution tin oxide coating. There are pigments coated with a conductive material. It is preferable. Of these, carbon black is preferable.

When the average particle size of carbon black contained in the magnetic layer is larger than 500 nm, the electromagnetic conversion characteristics deteriorate. Examples of carbon black contained in the magnetic layer include Asahi # 60 (51n manufactured by Asahi Carbon Black Co., Ltd.).
m), Asahi # 55 (77 nm), Asahi Thermal (90n
m), Asahi # 50 (94 nm), Asahi # 35 (115n)
m), Mitsubishi Kasei's Diablack G (84 nm), Cabot's Regal SR
F-S (60nm), Sterling (STERLIN
G) NS (75 nm), HS100 (5 manufactured by Denki Kagaku)
3 nm) and the like. Two or more of these may be used in combination.

As carbon black to be contained in layers other than the uppermost magnetic layer, Seagull 600 manufactured by Tokai Electrode Co., Ltd.
(23 nm), seed 6H (24 nm), seed 6
H (28 nm), Seast 116 (30 nm), Asahi # 80 (23 nm) manufactured by Asahi Carbon Black, Conductivtex SC (17 nm), Conductex 975 (20 nm), Conductex 4 manufactured by Colombian Carbon.
0-220 (20 nm), Mitsubishi Kasei Co., Ltd. Diablack A (18 nm), Diablack I (21 nm), Diablack H (30 nm), Showa Denko Shawaraku O (30 nm), Cabot Monarch (MONAR).
CH) 1300 (13 nm), Regal (REGAL)
400 (25 nm), VULCAN XC-
72 (30 nm), Vulcan P (20 nm), Vulcan 9 (19 nm), Black Pearls 2000 (15n)
m) and the like. Two or more of these may be used in combination.

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 the dispersion of carbon black is particularly important, carbon black may be kneaded together with a magnetic material or a filler and a binder by a three-roll mill, Banbury mixer or the like, and then dispersed by 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 kneading carbon black with a binder in advance 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”.

(Binder) Typical binders used for forming the magnetic layer and the non-magnetic layer are, for example, polyurethane, polyester, vinyl chloride resin, phenoxy resin and fibrin resin. There, these _{resins -SO 3 M, -OSO 3 M,} -COOM, -
It is preferable to contain at least one polar group selected from PO (OM ₁ ) ₂ and —OPO (OM ₁ ) ₂ . However, in the above polar group, M is a hydrogen atom or Na,
K represents an alkali metal such as Li, and M ₁ represents a hydrogen atom, an alkali metal atom such as Na, K and Li, or an alkyl group.

The above 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, for example, a vinyl chloride-vinyl alcohol copolymer, a 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-.

For the polar group-containing vinyl chloride 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 a salt thereof 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 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 introducing an epoxy group, the content of the repeating unit having an epoxy group in the copolymer is preferably 1 to 30 mol%,
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-57-42727 are cited.
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 preferably 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 polybasic acids having polar groups 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 prepared by using a polyester polyol having an aromatic ring and / or a polyester polyol containing a cyclic hydrocarbon residue 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 aliphatic polyisocyanates such as adducts of hexamethylene diisocyanate (HMDI) and active hydrogen compounds. There is. The weight average molecular weight of the polyisocyanate is preferably in the range of 100 to 3,000.

According to the present invention described in claim 1, the layer under the magnetic layer contains a fatty acid ester, and in the present invention described in claim 4, the magnetic layer contains a fatty acid ester and the aforementioned carbon black.

Fatty acids and / or fatty acid esters can be used as the lubricant. In this case, the amount of fatty acid added is preferably 0.2 to 10% by weight, and 0.5 to 5% by weight, based on the ferromagnetic powder or non-magnetic powder that is mainly used.
Is more preferred. If the added amount is less than 0.2% by weight,
The runnability tends to decrease, and when it exceeds 10% by weight, the fatty acid tends to exude to the surface of the magnetic layer and the output tends to decrease.

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 and 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.

Particularly, in the present invention described in claim 1, it is preferable that the layer underlying the magnetic layer, and in the present invention described in claim 4, each contain a fatty acid having a melting point of 50 ° C. or higher. Specific examples of fatty acids having a melting point of 50 ° C. or higher include:
Examples thereof include myristic acid, palmitic acid, pentadecylic acid, heptadecyl acid, stearic acid, behenic acid, arachidic acid, lignoceric acid, cerotic acid, heptacosanoic acid, montanic acid, melicinic acid and laxeric acid. Of these, stearic acid is particularly preferable.

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 preferred as the fatty acid ester, and glycerin trioleate is particularly preferred 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, and among them, oleic acid is most preferable. It is mentioned as a thing. Further, 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,
Examples thereof include oleyl elaidate, oleyl linoleate, and oleyl linolenate. The glycerin ester is preferably represented by the following general formula.

[0083]

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.)

Specifically, the glycerin ester is preferably the following. (1) Ester of glycerin and palmitic acid (having 16 carbon atoms) (However, the ester may be any of monoester, diester and triester (the same applies below)) (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) Ester with unsaturated carbon-carbon double bond) (5) Olive oil (natural product, mixture of various fatty acid esters) (6) Ester with 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) Glycerin with a Stearate (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) Fatty acid (C ₈ , C ₁₀ ) triglyceride In the above, two or more kinds of glycerin esters may be used in combination. In the present invention, in addition to glycerin ester, other polyhydric alcohol ester such as sorbitan may be used in combination.

In the present invention, R is used as a lubricant in the non-magnetic layer.
¹ C = OO (CHR ² CHR ³ O) _n R ⁴ (R ¹ is a linear or branched hydrocarbon group having 11 to 22 carbon atoms, R ² ,
R ³ is H or CH ₃ , 1 ≦ n ≦ 10, and R ⁴ has 1 carbon atom
-22 saturated or unsaturated hydrocarbon groups) are preferably contained.

Further, as a fatty acid ester, R ⁵ OC = OR
⁶ (wherein R ⁵ is a linear or branched hydrocarbon group having 1 to 18 carbon atoms, and R ⁶ is a linear or branched hydrocarbon group having 11 to 22 carbon atoms) is preferably contained. By including several different fatty acid esters and glycerin esters in the non-magnetic layer in this way, these lubricants are appropriately replenished to the upper magnetic layer, and a stable lubricating action is achieved in a wide range of temperatures from high to low. It is demonstrated and its durability is dramatically 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 number of different lubricants is an important technology for realizing a high-density magnetic recording medium with significantly higher density, higher durability, and higher 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.

In the present invention, a dispersant, the above-mentioned other lubricant, abrasive, and
Additives such as antistatic agents and fillers can be included.

First, as the dispersant, for example, JP-A-4-
The thing etc. which are described in paragraph number 0093 of 214218 can be mentioned. These dispersants are usually used in the range of 0.5 to 5% by weight based on the ferromagnetic powder.

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.

In the present invention, it is preferable that α-alumina and / or chromium oxide is contained in the non-magnetic layer and / or the magnetic layer. Further, it is preferable that the non-magnetic layer contains two or more kinds of non-magnetic powder having a Mohs hardness of 5 or more.

Next, 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 manufacturing method is not particularly limited except that the coating method is preferably used, and the manufacturing method can be carried out according to the known method used for manufacturing 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 coating material, and then this magnetic coating material is applied to a non-magnetic support. It is applied to the surface of the non-magnetic layer provided on the top. Examples of the solvent include paragraph 0 of JP-A-4-214218.
119 etc. 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 Application Laid-Open No. 4-214
No. 218, paragraph No. 0112, and the like. Of the above kneading dispersers, 0.05-0.5 kW
The kneading dispersers capable of providing a power consumption load (per 1 kg of magnetic powder) are a pressure kneader, an open kneader, 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, from the standpoint of the effect, the simultaneous multi-layer coating by the wet-on-wet multi-layer coating method. It is preferable to apply.

Specifically, as shown in FIG. 1, first, the film-like support 1 fed from the supply roll 32 is coated with the coating materials for the magnetic layer and other layers by the extrusion type extrusion coaters 10 and 11. After multi-layer coating by the wet-on-wet method, the coating liquid passes through the orientation magnet or the oblique orientation 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 introduced into a super calender device 37 including a combination of calender rolls 38, subjected to calendering here, and then wound 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 may be supplied to the extrusion coaters 10 and 11 through an in-line mixer (not shown). Note that, in the figure, the arrow D indicates the transport direction of the non-magnetic base film. Extrusion coaters 10 and 11 are provided with liquid pools 13 and 14, respectively, and the coating materials from the coaters are stacked in a wet-on-wet system. That is, immediately after the coating of the lower layer constituent layer coating material (when it is in a non-dried state), the upper layer magnetic layer coating material and the lubricant layer (overcoat layer) coating material are finally coated in multiple layers. The coater head is
The head (c) shown in FIG. 2 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 also 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 this wet-on-wet multi-layer coating, since the upper layer is applied while the lower layer is in a wet state, 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, especially for high-density recording, the performance required for high output and low noise, such as a magnetic tape, 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 blended in the above paint or a diluent solvent when this paint is applied, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone: methanol, ethanol, propanol,
Alcohols such as butanol: Esters such as methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol cenoacetate, etc .: Ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran: Benzene, toluene, xylene, etc. Aromatic hydrocarbons: 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. Is.

(Smoothing of Surface) In the present invention, the surface may be smoothed 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 calendar conditions. To achieve the object of the present invention,
Usually, the temperature is 50 to 140 ° C. and the linear pressure is 50 to 140 ° C.
It is preferable to maintain 400 kg / cm and the above C / S at 20 to 1000 m / min.

[0103]

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, "parts" are all parts by weight. (Examples 1-1 to 1-8, 2-1 to 2-8, Comparative example 1-
1 to 1-5, 2-1 to 2-6) First, a magnetic layer coating material and a non-magnetic layer coating material having the following compositional formulations are kneaded and dispersed using a kneader and a sand mill, respectively, and each of the obtained coating materials is coated with a poly After adding 5 parts of isocyanate (Coronate L, manufactured by Nippon Polyurethane Industry Co., Ltd.), a thickness of 8 μm is obtained by a wet-on-wet method.
Examples (1-1 to 1-8, 2-1 to 2-8) and Comparative Examples (1-
1 to 1-5, 2-1 to 2-6), the magnetic field orientation treatment is performed while the coating film is undried, and then the coating is dried, and then the surface is smoothed with a calendar. Done, table 1
An original fabric having a film thickness shown in to 4 was prepared. The magnetic film thus obtained was slit into a width of 8 mm,
It was housed in a cassette to obtain an 8 mm video tape. Note that Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-5 have a multilayer structure, and Examples 2-1 to 2-8 and Comparative Examples 2-1 to 2-6 have a single layer structure.

Magnetic Layer Coating Formulation: (Paint A1) Fe-Al based ferromagnetic metal powder (Fe: Co: Al: Y = 100: 20: 8: 5 (weight ratio), average major axis length: 65 nm, axis Ratio: 5, Hc: 2000 Oe, σs: 140 emu / g, crystallite size: 12 nm) 100 parts Sulfonic acid metal salt-containing vinyl chloride resin [manufactured by Nippon Zeon Co., Ltd., MR-105] 10 parts Sulfonic acid metal salt Containing aromatic polyester polyurethane resin [Toyobo Co., Ltd., UR-8200: containing cyclohexane ring] 10 parts Alumina (α-Al ₂ O ₃ , number average particle diameter: 0.1 μm) 5 parts Carbon black (number average) Particle size: 90 nm) 0.8 part Stearic acid 1 part Myristic acid 1 part Butyl stearate 1 part Butoxyethyl stearate 1 part Oleyl oleate 1 part Glycerin Triolate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts

(Paint B) Instead of the Fe—Al based ferromagnetic metal powder in Paint A, Co-substituted barium ferrite (H)
c: 1100 Oe, BET: 45 m ² / g, average particle size: 0.05 μm, σs: 64 emu / g, plate ratio: 4) The same as the coating material A except that 4) was used.

(Paint A2) In the paint A1, Fe-Al
Fe: Co: Al: Ni: S as the base ferromagnetic metal powder
i: Nd = 100: 20: 8: 5: 3: 5 (weight ratio)
(Average major axis length: 65 nm, axial ratio: 5, Hc: 2000
Oe, σs: 140 emu / g, crystallite size: 12n
Same as A1 except that m) was used.

(Paint A3) Same as Paint A1 except that butyl stearate, butoxyethyl stearate, oleyl oleate, and glycerin trioleate were not used in paint A1.

Non-magnetic layer paint formulation: (Paint a1: 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 0.2 percent by weight relative to the _{Si α-Fe 2 O 3,} 1.0% in a weight ratio of Al to _α-Fe 2 _{O 3)} 100 parts carbon black (number average particle diameter, 20 nm) 16 parts Vinyl chloride resin containing sulfonic acid metal salt [manufactured by Nippon Zeon Co., Ltd., MR-110] 6 parts Aromatic polyester polyurethane resin containing sulfonic acid metal salt [manufactured by Toyobo Co., Ltd., UR-8300: containing cyclohexane ring] to] 3 parts of alumina _(α-Al 2 _{O 3,} the number average particle diameter: 0.3 [mu] m) 6 parts 1 part butyl stearate 1 part but-stearate 1 part myristate carboxyethyl stearate 1 part Oreiruore Sheet 1 parts of glycerol trioleate 1 part 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,
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.

(Paint a2) The paint a1 is the same as the paint a1 except that butyl stearate, butoxyethyl stearate, oleyl oleate, and glycerin trioleate are not used.

The characteristics of the obtained 8 mm video tape were measured according to the following items. The measurement results are shown in Tables 1 to 4.

<Reproduction output (RF output)> 7MH by Sony 8mm video camera CCDV-900
The RF output (dB) at z was measured.

<Running durability at high temperature> S-550 (manufactured by Sony Corporation) under the environment of temperature 40 ° C and relative humidity 80%.
Was recorded for full length, and output reduction (dB) and jitter value (μsec) were measured after running for 50 passes.

<Running durability at low temperature> Output reduction of 2 dB or more, 1 second or more by using S-550 (manufactured by Sony Corp.) in an environment of temperature 0 ° C. and relative humidity 20% to perform full-length recording / playback. When it continued, it was set as a head clog, and the number of occurrences was measured.

<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. ).

Standard Sample 2 is Analytical R
effort Materials Intern
alloy SRM1250 (Ni of 0.3
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% 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%.

<Measurement Method of Ra and Rt> Ra and Rt were measured with a three-dimensional surface roughness meter (3FK) manufactured by Kosaka Laboratory.
(The cutoff is 0.25 mm). The definitions of Ra and Rt are based on JIS surface roughness (B061).

<Regarding the Number of Protrusions with a Height of 0.01 μm or More> A surface roughness curve is obtained with a Tally-step surface roughness meter (manufactured by Taylor Hobson), and this curve is recognized as a peak (peak count). (Protrusion exceeding the value)
About, the height from the average line was measured, and 0.010 μm
The number of protrusions of the above was measured under the following conditions. Measurement length: 1 mm Cutoff: 0.33 Hz

(High-pass filter) Peak count value: 0.005 μm

[0126]

[Table 1]

[0127]

[Table 2]

[0128]

[Table 3]

[0129]

[Table 4]

With the constitution of the present invention, the durability is excellent for a long time under any environmental condition, no error occurs in a wide range of temperature conditions, and the reproduction output is high,
It is possible to obtain a magnetic recording medium having a good dropout, a good winding property of an original fabric and an excellent process suitability.

[0131]

According to the present invention, the durability is excellent for a long time even in a wide range of environments from high temperature to low temperature,
It is possible to obtain a magnetic recording medium having a high reproduction output, a good winding property of the original fabric, and excellent process suitability.

[Brief description of the 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 view of a coater head for applying a magnetic layer coating material.

[Explanation of symbols]

 1 Support 10, 11 Extrusion Coater 13, 14 Liquid Reservoir 32 Supply Roll 33 Orientation Magnet 34 Dryer 37 Super Calender Device 38 Calender Roll 39 Winding Roll

Claims (7)

[Claims] 1. A support comprising two or more constituent layers including a magnetic layer, wherein the uppermost magnetic layer has a thickness of 1.0 μm or less, and the support has a center line average roughness ( Ra, nm) and the maximum roughness (Rt, nm) are 12 ≦ Ra ≦
28, 95 ≦ Rt ≦ 220, Rt / Ra ≦ 10,
A magnetic recording medium, characterized in that a layer underlying the magnetic layer contains a fatty acid ester. 2. The magnetic recording medium according to claim 1, wherein the number of protrusions having a height of the support surface of 0.01 μm or more is 200 or more per 1 mm of measurement length. 3. The magnetic recording medium according to claim 1, wherein the layer underlying the magnetic layer contains a fatty acid having a melting point of 50 ° C. or higher. 4. A magnetic layer having a film thickness of 1.0 μm or less provided on a support, and the center line average roughness (Ra, nm) of the support.
, And the maximum roughness (displayed in Rt and nm) is 12 ≦ R
a ≦ 28, 95 ≦ Rt ≦ 220, Rt / Ra ≦ 10, wherein the magnetic layer contains a fatty acid ester and carbon black. 5. The magnetic recording medium according to claim 4, wherein the number of protrusions having a height of the support surface of 0.01 μm or more is 200 or more per 1 mm of measurement length. 6. The magnetic recording medium according to claim 4, wherein the magnetic layer contains a fatty acid having a melting point of 50 ° C. or higher. 7. The magnetic recording medium according to claim 4, wherein the magnetic layer contains carbon black having a number average particle diameter of 30 nm or more.