JPH0991673A - Magnetic recording medium and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the clogging of a head even after repeated running of a medium over the full length at high temp. and humidity and the reduction of output due to the clouding of the head at low humidity, to reduce dropout and to increase reproduction output by specifying the dry film thickness of a recording layer, the coefft. of dynamic friction to a metallic pin and the Young's modulus of the substrate. SOLUTION: This magnetic recording medium has one or more recording layers including a magnetic layer on one side of the substrate, the total dry film thickness of the recording layers is <=0.5μm and the top magnetic layer contains carbon black of >=30nm number average particle diameter. The coefft. of dynamic friction to a metallic pin at 20 deg.C and 60% relative humidity is <=0.3. A layer in contact with the bottom of the top magnetic layer contains a lubricant contg. fatty acid and fatty acid ester and nonmagnetic powder having a Mohs hardness of >=5. The total Young's modulus of the substrate in the longitudinal and transverse directions is >=1,400kg/mm<2> .

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 suitable for use as a magnetic recording disk such as a floppy disk or a still video floppy disk, a data tape and a digital VTR tape.

[0002]

2. Description of the Related Art In recent years, magnetic recording media using thin metal multi-layer media have been actively developed for large capacity floppy disks and large capacity data tapes. Japanese Patent Laid-Open No. 5-2
No. 34068 proposes a magnetic recording medium excellent in high frequency characteristics, overwrite characteristics, and weather resistance by forming a thin nonmagnetic layer having a thickness of 0.5 μm or less as a lower layer. However, the performance of personal computers has been remarkably improved in recent years, and the capacity of recording media has been increased accordingly. In particular, it is an essential task to achieve a large capacity of a recording medium for data backup, but for that purpose, the above-mentioned technique is insufficient for achieving the task.

[0003]

The problems of the present invention are: 1) No clogging of the head even after repeated running over the entire length under high temperature and high humidity, 2) no reduction in output due to cloudiness of the head at low humidity, and 3) 4) To provide a magnetic recording medium with low dropout and 4) High reproduction output.

[0004]

In order to design a large capacity recording medium for data backup, it is necessary to achieve high density of the medium from the medium side. Therefore, the total thickness of the medium should be as thin as possible. Doing is an essential requirement. For that purpose, it is necessary to make each of the support and the recording layer or the back coat layer as thin as possible. On the other hand, for data applications, high reliability under various environments is required. That is, it is a necessary condition to realize high reliability with a high density thin film medium. Conventionally, the development in this direction has been centered on thin film media using the vacuum deposition method, but it has problems in that it is superior in electromagnetic conversion characteristics to the coating type media but increases cost and is inferior in durability. .

On the other hand, even in the case of a coating type medium, thin film coating has become possible by using an extrusion coating device without a back roll in recent years.
Furthermore, multi-layer coating is also possible as its application. In order to achieve high reliability in the high-density medium mentioned in the above 1) to 4), the inventor of the present invention has friction characteristics of the medium, layer constitution, lower layer design, support surface design, protective layer, coating method. As a result of examining from various aspects, it was found that the task can be achieved if the following conditions are met.

(1) 1 including a magnetic layer on one surface of a support 1
A recording layer composed of at least two layers, the total thickness of the recording layer is 0.5 μm or less, and the uppermost magnetic layer contains carbon black having a number average particle diameter of 30 nm or more,
The coefficient of dynamic friction with respect to the metal pin at a temperature of 20 ° C. and a relative humidity of 60% is 0.3 or less, and the total of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the support is 1400 kg.
/ Mm ² or more magnetic recording medium.

(2) 2 including a magnetic layer on one surface of the support
A recording layer composed of at least two layers, the total dry thickness of the recording layer is 0.5 μm or less, and the layer underlying the uppermost magnetic layer is a lubricant containing fatty acid or fatty acid ester and Mohs hardness It is a layer containing 5 or more non-magnetic powder, and the sum of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the support is 1
A magnetic recording medium of 400 kg / mm ² or more.

(3) The magnetic recording medium according to (2), wherein the fatty acid contains a saturated fatty acid and an unsaturated fatty acid.

(4) 1 including a magnetic layer on one surface of the support
A recording layer consisting of two or more layers, the dry thickness of the recording layer is 0.5 μm or less in total, and the average protrusion height of the protrusions present on the surface of the support opposite to the magnetic layer forming surface. Is 0.01 to 0.20 μm, the number of protrusions having a height of 0.01 μm or more is 200 or more per measurement length 1 mm, and the number of protrusions having a height of 0.30 μm or more is a measurement length. A magnetic recording medium having 500 or less per 400 mm and having a ratio of maximum protrusion height to average protrusion height (maximum protrusion height / average protrusion height) of 5 or less.

(5) Including a magnetic layer on one surface of the support 1
And a recording layer having a total thickness of 0.5 μm or less and an average protrusion height of protrusions present on the surface of the support on the same side as the magnetic layer forming surface. Is 0.01 to 0.20 μm, the number of protrusions having a height of 0.01 μm or more is 200 or more per measurement length 1 mm, and the number of protrusions having a height of 0.30 μm or more is a measurement length of 400 mm. A magnetic recording medium in which the number is 500 or less and the ratio of the maximum protrusion height to the average protrusion height (maximum protrusion height / average protrusion height) is 5 or less.

(6) 1 including a magnetic layer on one surface of the support
A recording layer having at least 0.5 layers is provided, the total thickness of the recording layer is 0.5 μm or less, and the average protrusion height of the protrusions present on both surfaces of the support is 0.01 to 0. .20
The number of protrusions having a height of 0.01 μm or more is 200 or more per 1 mm of the measurement length, and the height is 0.
A magnetic recording medium in which the number of protrusions having a size of 30 μm or more is 500 or less per 400 mm of the measurement length, and the ratio of the maximum protrusion height to the average protrusion height (maximum protrusion height / average protrusion height) is 5 or less.

(7) The total of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the support is 1400 kg / mm ² or more, according to any one of (4) to (6). Magnetic recording medium.

(8) Including a magnetic layer on one surface of the support 1
A recording layer consisting of two or more layers is provided, the total thickness of the recording layer is 0.5 μm or less, and a protective layer containing a lubricant is provided on the uppermost magnetic layer. While the upper magnetic layer is in a wet state, the protective layer is wet-on-
A method of manufacturing a magnetic recording medium, wherein the method is provided by wet-type multi-layer coating.

(9) 2 including a magnetic layer on one surface of the support
A layer having two or more layers is provided, the dry film thickness of the two or more layers including the magnetic layer is 0.5 μm or less in total, and the layer underlying the uppermost magnetic layer contains a fatty acid or a fatty acid ester. A layer containing an agent and a non-magnetic powder having a Mohs hardness of 5 or more,
The total of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the support is 1400 kg / mm ² or more, and the magnetic properties of the uppermost layer are obtained by the wet-on-wet multi-layer coating using two or more extrusion coaters. A method of manufacturing a magnetic recording medium, wherein the uppermost magnetic layer is provided while the layer underlying the layer is in a wet state.

(10) The magnetic recording medium according to any one of (1) to (7), wherein the support is a polyamide film.

(11) The method for producing a magnetic recording medium according to (8) or (9), wherein the support is a polyamide film.

(12) The method for producing a magnetic recording medium according to (11), wherein the support has a thickness of 5 μm or less.

(13) The ferromagnetic powder contained in the uppermost magnetic layer contains Fe, Al, Co and a rare earth element, as described in any one of (1) to (7). Magnetic recording medium.

(14) Manufacturing of the magnetic recording medium as described in (8) or (9), wherein the ferromagnetic powder contained in the uppermost magnetic layer contains Fe, Al, Co and a rare earth element. Method.

(15) The magnetic recording medium according to any one of (1) to (7), wherein the total thickness of the magnetic recording medium is 5 μm or less.

(16) The method for producing a magnetic recording medium according to (8) or (9), wherein the total thickness of the magnetic recording medium is 5 μm or less.

The present invention will be described in detail below.

(Layer Structure) Basically, the magnetic recording medium of the present invention is preferably formed by forming a nonmagnetic layer and a magnetic layer on a nonmagnetic support. A back coat layer is provided on the surface (back surface) of the non-magnetic support on which the magnetic layer is not provided for the purpose of improving the running property and durability of the magnetic recording medium, and preventing static charge and transfer. It is preferable to provide a writing layer, a print recording layer or an anti-counterfeiting layer, and an undercoat layer may be provided between the non-magnetic layer and the non-magnetic support. In addition, an overcoat layer may be provided on the uppermost magnetic layer, if necessary.

(Non-magnetic support) As the material for forming the non-magnetic support, for example, polyesters such as polyethylene terephthalate and 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.

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 1400 kg / mm ² or more, and 1600 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 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 in the case of a film or sheet, it is usually 3 to 10.
0 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, this non-magnetic support may be subjected to surface treatment such as corona discharge treatment, or may be subjected to undercoating treatment.

A backcoat layer is formed on the surface (surface) of the non-magnetic support on which the above-mentioned magnetic layer is not provided, for the purpose of improving the running property of the magnetic recording medium, preventing charging and preventing transfer. It is preferable to provide a writing layer or 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 in 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 to 1.0 μm, preferably 0.05 to 1.0 μm.
0.5 μm, more preferably 0.08 to 0.3
0 μm.

Examples of the hexagonal magnetic powder include hexagonal ferrite. Such hexagonal ferrite is composed of barium ferrite, strontium ferrite, etc., and a part of iron element is other element (for example, Ti, Co, Zn, In, Mn, Ge, Hb, etc.).
May be replaced with. Regarding this ferrite magnetic material, the IEEE Trans, on MAG-18 1
6 (1982).

In the present invention, particularly preferable hexagonal magnetic powder is barium ferrite (hereinafter referred to as Ba-ferrite) magnetic powder.

Preferred B which can be used in the present invention
a-ferrite magnetic powder is Ba-ferrite powder, Fe
Average particle size (height of diagonal of plate surface of hexagonal ferrite) in which at least a part of Co is replaced by Co and Zn 400-
900Å, plate ratio (value obtained by dividing the length of the diagonal of the plate surface of hexagonal ferrite by the plate thickness) 2.0 to 10.0, more preferably 2.0 to 6.0, coercive force (Hc) 450-150
It is 0 Oe of Ba-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.

BaO _n ((Fe1-mMm) 2O3) [where m> 0.36 (where 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 recording capability of the head is limited and recording may become difficult.

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

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

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

As a method for producing the hexagonal magnetic powder used in the present invention, for example, an oxide or carbonate of each element necessary for forming the desired Ba-ferrite is used, such as boric acid. The glass melt is melted together with another glass-forming substance, the resulting melt is rapidly cooled to form glass, and the glass is then heat-treated at a predetermined temperature to precipitate the desired Ba-ferrite crystal powder, and finally the glass component is added. Besides 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, in terms of corrosion resistance and dispersibility,
Fe-Al system, Fe-Al-Ca system, Fe-Al-Ni
System, Fe-Al-Zn system, Fe-Al-Co system, Fe-
Ni-Si-Al-Zn system, Fe-Ni-Si-Al-
Fe—Al based metal powder such as Mn based is preferable.

Particularly preferred ferromagnetic metal powders for the purpose of the present invention are metal magnetic powders containing iron as a main component, and Al or Al and Ca, where Al is Fe: A in a weight ratio.
1 = 100: 0.5 to 100: 20, and Ca is preferably contained in a weight ratio of Fe: Ca = 100: 0.1 to 100: 10.

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

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

The average major axis length (in the case of needle 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, the method described in X-ray Diffraction Guide (Rigaku Denki Co., Ltd.) is used to correct the spread due to double lines. 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, in the present invention, a ferromagnetic metal powder having a specific surface area by the BET method of 30 m ² / g or more, particularly 45 m ² / g or more is preferably used according to the higher recording density.

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).

The specific surface area is measured, for example, by measuring the powder at 105 ° C.
Degassed while heating for 13 minutes before and after to remove those adsorbed on the powder, and then introduce this powder into the measuring device to set the initial pressure of nitrogen to 0.5 kg / m ² and The measurement is performed at the liquid nitrogen temperature (-105 ° C) for 10 minutes.

As the measuring device, for example, a counter soap (manufactured by Yuasa Ionics Co., Ltd.) is used.

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

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

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

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. In contrast, Co atom is 2
˜40 parts by weight, Ni atoms 2 to 20 parts by weight, Si atoms 0.3 to 5 parts by weight, Na atoms less than 0.1 parts by weight, Ca atoms 0.1 to 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 ratio of elements forming the surface of the ferromagnetic metal powder is Fe atoms. Number 1
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 the non-magnetic powder include titanium oxide, boron 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, preferred are titanium oxide, barium sulfate, α-Al ₂ O ₃ , α-Fe ₂ O ₃ and α-.
Inorganic powders such as FeOOH and Cr ₂ O ₃ are included. Among them, α-Fe ₂ O ₃ and α-FeOOH are preferable, and α-Fe ₂ O ₃ is particularly preferable.

In the present invention, a non-magnetic powder having a needle-like powder shape can be preferably used. By using the acicular non-magnetic powder, the smoothness of the surface of the non-magnetic layer can be improved, and the smoothness of the surface of the uppermost layer composed of the magnetic layer laminated thereon can also be improved.

The term "nonmagnetic layer" as used herein means a layer that is substantially nonmagnetic (saturation magnetic flux density Bm is 0) and a layer that 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 the 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 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 needle-shaped nonmagnetic 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.
a m ² / g, 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 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) The conductive fine powder used in the present invention includes carbon black, Sb deposited conductive tin oxide (SnO ₂ ), and conductive titanium dioxide (TiO 2 coated with Sb and Sn). ₂ ) etc., but carbon black is particularly preferably used.

The conductive fine powder contained in the magnetic layer is preferably a conductive fine powder having a number average particle diameter of 40 to 500 nm or an oil absorption represented by a DBP value of 110 to 500 ml / 100 g. More preferably, the number average particle size is 50.
~ 350nm, or the oil absorption represented by DBP value is 14
It is preferable to use a conductive fine powder of 0 to 400 ml / 100 g. The weight of the conductive fine powder contained in the magnetic layer is preferably 0.1 to 5.0% by weight, and more preferably 0.2 to 2.0% by weight, based on the magnetic powder.

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 masterbatch" in which carbon black is kneaded in advance 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, such as 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, the diameter of each particle of carbon black is measured, and N = 1
The average particle size of 00 pieces is referred to as "number average particle size".

As for 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, vinyl chloride resin, phenoxy resin and fibrin resin. There, these resins _{-SO 3 M, -OSO 3 M,} -COOM, -P
It preferably contains at least one polar group selected from O (OM ¹ ) ₂ and —OPO (OM ¹ ) ₂ .

However, in the above polar group, M represents a hydrogen atom or an alkali metal atom such as Na, K and Li, and M ¹ represents a hydrogen atom, an alkali metal atom such as Na, K and Li or an alkyl group. .

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

The content of the binder in the magnetic layer is usually 10 to 100 parts by weight of the ferromagnetic powder.
It is 40 parts by weight, preferably 15 to 30 parts by weight.

The binder (binder) is not limited to one kind alone, and two or more kinds may be used in combination. In this case, the ratio of polyurethane and / or polyester to vinyl chloride resin is usually a weight ratio. 90:10
10:90, preferably 70:30 to 30:70
Range.

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

For example, Cl-CH ₂ CH ₂ SO ₃ M, Cl
_{-CH 2 CH 2 OSO 3 M,} Cl-CH 2 COOM, Cl-
_{CH 2 -P (= O) (} OM 1) is ₂ or the like. M and M ¹ represent a hydrogen atom or an alkali metal atom.

From these compounds, Cl--CH ₂ CH ₂ SO
₃ Na is taken as an example, describing the reaction is as follows.

--CH ₂ C (OH) H-+ ClCH ₂ CH ₂
SO ₃ Na → -CH ₂ C (OCH ₂ CH ₂ SO ₃ Na) H- The polar group-containing vinyl chloride copolymer is a reactive monomer having an unsaturated bond into which a repeating unit containing a polar group is introduced. Was charged into a reaction vessel such as an autoclave, and a general polymerization initiator, for example, a radical polymerization initiator such as BPO (benzoyl peroxide) and AIBN (azobisisobutyronitrile), a redox polymerization initiator,
It can be obtained by carrying out a polymerization reaction using a cationic polymerization initiator or the like.

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

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

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

When an 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, see JP-A-57-44227 and JP-A-5-44227.
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.

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 5-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.

Incidentally, other polar group-introduced polyesters can also be synthesized by a known method.

Next, the polyurethane will be described.

It is obtained 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, when 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 having 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.

For example, Cl-CH ₂ CH ₂ SO ₃ M, Cl-
_{CH 2 CH 2 OSO 2 M,} Cl-CH 2 COOM, Cl-C
_{H 2 -P (= O) (} OM 1) is ₂ or the like. M and M ¹ are as defined above.

As a technique relating to the introduction of a polar group into polyurethane, Japanese Patent Publication No. 58-41565 and Japanese Patent Laid-Open No.
7-92422, 57-92423, 59-8
No. 127, No. 59-5423, No. 59-5424,
It is described in Japanese Patent Publication No. 62-121923 and the like, 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, in order to improve the durability of the magnetic layer and other layers, it is desirable to contain polyisocyanate.

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

In the present invention, the magnetic layer and other layers may contain additives such as a dispersant, a lubricant, an abrasive, an antistatic agent and a filler, if necessary.

First, 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.

Next, a fatty acid or a fatty acid ester can be used as the lubricant. In this case, the amount of the fatty acid 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 running property tends to be lowered, and if the addition amount is more than 10% by weight, the fatty acid is likely to seep out to the surface of the magnetic layer or the output is likely to be lowered.

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

When 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 and preferably has 6 to 30 carbon atoms.
The range of -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, octanedicarboxylic acid and the like.

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

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

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

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

[0124]

Embedded image

[0125] (wherein, R ^1, at least one of R ^2, R ³ is a monobasic fatty acid residue having 6 to 30 carbon atoms, and the other may be hydrogen atom, and R ^1, R ² ,
R ³ may be the same as or different from each other. More preferably, the number of carbon atoms in at least one monobasic fatty acid residue of R ¹ , R ² and R ³ is 10 to 22. ) The glycerin ester may be specifically the following.

(1) Ester of glycerin and palmitic acid (having 16 carbon atoms) (however, the ester may be a monoester, diester or triester (the same applies hereinafter)) (2) Glycerin and stearic acid (Ester with 18 carbon atoms) (3) Ester with glycerin and oleic acid (containing one unsaturated carbon-carbon double bond with 18 carbon atoms) (4) Glycerin and linoleic acid (18 carbon atoms) With two unsaturated carbon-carbon double bonds) (5) Ester of glycerin and lauric acid (10 carbon atoms) (6) Ester of glycerin and myristic acid (14 carbon atoms) 7) Ester of glycerin and palmitic acid (16 carbon atoms) (8) Glycerin and isostearic acid (1 carbon atom)
Ester with 8) (9) Ester with glycerin and behenic acid (22 carbon atoms) (10) 2-Ethylhexanoic acid triglyceride (11) Behenic acid monoglyceride (12) Oleic acid stearic acid monodiglyceride (13) Diacetylcaprin Acid glyceride (14) Diacetyl palm fatty acid glyceride (15) Acetyl stearic acid glyceride (16) Diacetyl capric acid glyceride (17) Diacetyl palm fatty acid glyceride (18) Caprylic acid monodiglyceride (19) Acetyl stearic acid glyceride (20) Caprylic acid triglyceride (21) (a natural product, various mixtures of glycerol esters) fatty (C _8, C ₁₀₎ triglycerides (22) olive oil at least, two or more glycerin S. You may use tell together.

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 ¹ C═OO (CHR ² CHR ³ O) nR ⁴ (R ¹ is a linear or branched hydrocarbon group having 11 to 22 carbon atoms, R ^{2 is} used as a lubricant in the nonmagnetic layer. , R ³
Is H or CH ₃ , 1 ≦ n ≦ 10, and R has 1 to 2 carbon atoms
2 saturated or unsaturated hydrocarbon groups) are preferably contained.

Further, as a fatty acid ester, R ⁵ OC═O
R ⁶ (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 types of fatty acid ester and glycerin ester in the non-magnetic layer in this way, these lubricants are appropriately replenished to the upper magnetic layer, and stable lubrication is achieved in a wide range of environments from high temperature to low humidity. The effect is demonstrated and the durability is significantly improved. It is more preferable that the non-magnetic layer contains a plurality of fatty acids having different melting points in addition to the fatty acid ester and the glycerin ester from the viewpoint of improving durability. Using such a hybrid lubricant system that combines a large number of different lubricants is an important technology for realizing a high-density magnetic disk medium with significantly higher density, higher durability, and an improved error rate than before. Is.

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

Specific examples of the polishing agent include α-alumina, fused alumina, chromium oxide, titanium oxide, α-iron oxide, silicon oxide, silicon nitride, tungsten carbide, molybdenum carbide, boron carbide, corundum, and oxide. Examples thereof include zinc, cerium oxide, magnesium oxide, and boron nitride. The Mohs hardness of the abrasive is 5 or more, preferably 8 or more.

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 types of non-magnetic powder having a Mohs hardness of 5 or more.

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, the production method is not particularly limited, except that the wet-on-wet coating method is preferably used, and it is in accordance with the known method used for producing a multilayer structure type magnetic recording medium. Can be manufactured.

For example, generally, ferromagnetic powder, binder,
A magnetic coating material is prepared by kneading and dispersing a dispersant, a lubricant, an abrasive, an antistatic agent and the like in a solvent, and then the magnetic coating material is applied to the surface of the non-magnetic support.

Examples of the solvent include, for example, JP-A-4-4-2.
The thing etc. which are described in paragraph No. 0119 of 14218 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.
-214218, Paragraph No. 0112 etc. are mentioned.

Of the above kneading dispersers, 0.05 to 0.5
The kneading dispersers capable of providing a power consumption load of KW (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, simultaneous multi-layer coating by the wet-on-wet multi-layer coating method is particularly effective. It is preferable to carry out.

Specifically, as shown in FIG. 1, first, the film-shaped support 1 fed from the supply roll 32 is applied to the coating materials for the magnetic layer and other layers by the extrusion type extrusion coaters 10 and 11. Is applied in multiple layers by the wet-on-wet method, then passes through the orientation magnet or the vertical 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 combined with a calender roll 38 to form a super calender device 37.
And after performing a calendar process here, it is wound up on a winding roll 39. The magnetic film thus obtained can be cut into a tape having a desired width to produce, for example, a tape for an 8 mm data cartridge.

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

The coater head shown in FIG. 2A is preferable in the present invention.

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

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

As the solvent to be added to the above paint or a diluent solvent for applying this paint, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone: alcohols such as methanol, ethanol, propanol and butanol: methyl acetate , Esters such as ethyl acetate, butyl acetate, ethyl lactate, ethylene glycol cenoacetate: ethers such as glycol dimethyl ether, glycol monoethyl ether, dioxane, tetrahydrofuran: aromatic hydrocarbons such as benzene, toluene, xylene: methylene chloride, Ethylene chloride, carbon tetrachloride, chloroform,
Halogenated hydrocarbons such as dichlorobenzene can be used. These various solvents may be used alone or in combination of two or more.

The magnetic field in the oriented magnet or the vertical orientation 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.

Surface Smoothing Next, surface smoothing processing is performed by calendering.

After that, if necessary, burnishing or blade processing is performed for slitting.
At this time, the surface smoothing treatment is effective for 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 above temperature is usually 50 to 140 ° C., and the linear pressure is 50 to 400 k.
It is preferable to keep g / cm and the above C / S at 20 to 1000 m / min.

[0154]

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.

(Example 1) 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, respectively, and each of the obtained coating materials was polyisocyanate (Coronate L, Japan). After adding 5 parts of Polyurethane Industry Co., Ltd., a wet-on-wet method was used to form an aramid film having a thickness of 4 μm.
After coating the sample of Example 1 with the combination shown in, the magnetic field orientation treatment was performed while the coating film was undried, followed by drying, and then surface smoothing treatment with a calendar to give a thickness of 0.2.
An original fabric was prepared from a layer containing a non-magnetic powder of μm and a magnetic layer having a thickness of 0.1 μm. The magnetic film thus obtained was cut to a width of 8 mm, placed in a cassette, and
mm cassette tape was obtained.

Magnetic layer paint formulation: (Paint A1) Fe-Al based ferromagnetic metal powder 100 parts (Fe: Co: Al: Y = 100: 20: 8: 5 (weight ratio), average major axis length: 60 nm , Axial ratio: 5, Hc: 1800 Oe, σs: 140 emu / g, crystallite size: 100Å) Vinyl chloride resin containing sulfonic acid metal salt 10 parts [Nippon Zeon Co., Ltd., MR-110] Sulfonic acid metal salt Containing aromatic polyester polyurethane resin 10 parts [Toyobo Co., Ltd., UR-8200: containing cyclohexane ring] Alumina (α-Al ₂ O ₃ , number average particle size: 0.1 μm) 5 parts Carbon black (number average Particle size 70 nm) 0.8 part Stearic acid 1 part Oleic acid 1 part Butyl stearate 1 part Butoxyethyl stearate 1 part Oleyl oleate 1 part Glycerin trio Rate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts (Paint B) Co-substituted barium ferrite (Hc: 110) instead of the Fe-Al based ferromagnetic metal powder in paint Al
0 Oe, BET: 45 m ² / g, average particle size 0.05 μ
m, σs: 64 emu / g, plate ratio: the same as the paint Al except that 4) was used.

(Paint A2) Fe-Al in paint A1
Fe: Co: Al: Ni: S as the base ferromagnetic metal powder
Same as A1 except that i: Nd = 100: 20: 8: 5: 3: 5 (weight ratio) was used.

Non-magnetic layer paint formulation: (Paint a: non-magnetic layer) α-Fe ₂ O ₃ 100 parts (average major axis length: 80 nm, average minor axis length: 15 nm, acicular ratio: 5, crystallite size : 14 nm, 0.2% by weight relative to the _{α-Fe 2 O 3 Si,} 1.0% contained) carbon black 1 16 parts by weight with respect to the α-Fe ₂ O ₃ Al (number average particle diameter 23 nm, oil absorption; 60 ml / 100 g in DBP value) Vinyl chloride resin containing sulfonic acid metal salt 6 parts [MR-110 manufactured by Nippon Zeon Co., Ltd.] Aromatic polyester polyurethane resin containing metal sulfonate 3 parts [TOYOBO ( UR-8300: containing cyclohexane ring] Alumina (α-Al ₂ O ₃ , number average particle size: 0.3 μm) 6 parts Myristic acid 1 part Oleic acid 1 part Butyl stearate 1 part Butoxyethyl stearate 1 part Oleyl oleate 1 part Glycerin trioleate 1 part Cyclohexanone 100 parts Methyl ethyl ketone 100 parts Toluene 100 parts (Paint b) Titanium oxide 100 parts instead of α-Fe ₂ O ₃ in paint a (number average particle size 30 nm, crystallite size Two
8 nm, 0.2% by weight of Si to TiO ₂ , Al
Is used in a weight ratio of 1.0% to TiO ₂ ).

(Paint c) The difference is that in the paint a, 100 parts of ZnO was used instead of α-Fe ₂ O ₃ .

Example 2 The same as Example 1 except that the lower layer film thickness was 0.3 μm.

Example 3 The same as Example 1 except that A2 was used as the upper layer coating material in Example 1.

Example 4 Same as Example 1 except that B was used as the upper layer coating material in Example 1.

(Example 5) The same as Example 1 except that b was used as the lower layer coating material in Example 1.

(Example 6) The same as Example 1 except that the carbon black in Example 1 was changed to have a number average particle size of 100 nm.

(Example 7) The same as Example 1 except that the Young's modulus of the support in Example 1 was changed to that shown in Table 1.

(Embodiment 8) Same as Embodiment 1 except that the thickness of the upper layer is changed to 0.08 μm.

Comparative Example 1 The same as Example 1 except that stearic acid and oleic acid were not used in Example 1.

(Comparative Example 2) The same as Example 1 except that the Young's modulus of the support in Comparative Example 1 was changed to that shown in Table 2.

Comparative Example 3 The same as Example 1 except that the thickness of the upper layer was changed to 0.3 μm.

Comparative Example 4 The same as Example 1 except that carbon black was not used in Example 1 but C was used as the lower layer coating material.

(Examples 9 to 11) Instead of using stearic acid and oleic acid as the upper layer coating in Example 1, dimethyl silicone oil was used, and the surface of the support opposite to the surface on which the magnetic layer is provided is shown in Table 3. Same as Example 1 except that the support provided with the protrusion shown in FIG.

(Example 12) The same as Example 9 except that A2 was used as the upper layer coating material.

(Example 13) The same as Example 9 except that B was used as the upper layer coating material in Example 9.

(Example 14) The same as Example 9 except that b was used as the lower layer coating material in Example 9.

(Example 15) Example 15 was repeated except that a support having protrusions of 0.30 µm or more as shown in Table 3 was used on the surface of the support opposite to the surface on which the magnetic layer was provided. Same as 9.

(Example 16) The same as Example 9 except that the Young's modulus of the support in Example 9 was changed as shown in Table 3.

Comparative Examples 5 to 7 The same as Example 9 except that the support having the protrusions shown in Table 4 was used in Example 9.

(Comparative Example 8) The same as Example 9 except that the upper layer film thickness in Example 9 was 0.30 μm.

(Examples 17 to 19) Instead of using stearic acid and oleic acid as the upper layer coating in Example 1, dimethyl silicone oil was used, and the surface of the support on the same side as the surface on which the magnetic layer was provided was used. Same as Example 1 except that the support shown in FIG.

(Example 20) The same as Example 17 except that A2 was used as the upper layer coating material in Example 17.

(Example 21) The same as Example 17 except that B was used as the upper layer coating material in Example 17.

(Example 22) Same as Example 17 except that b was used as the lower layer coating material in Example 17.

(Example 23) Example 23 is the same as Example 17 except that a support having protrusions of 0.30 μm or more as shown in Table 5 is used on the surface of the support opposite to the surface on which the magnetic layer is provided. Same as 17.

(Example 24) The same as Example 17 except that a support in which the Young's modulus of the support was changed as shown in Table 5 was used.

Comparative Examples 9 to 11 The same as Example 17 except that the support having the projections shown in Table 6 was used in Example 17.

(Comparative Example 12) The same as Example 17 except that the upper layer film thickness was 0.30 μm.

(Examples 25 to 27) A support in which dimethyl silicone oil was used in place of stearic acid and oleic acid in the upper layer coating in Example 1 and the projections shown in Table 7 were provided on both sides of the support. Example 1 except that
the same as.

(Example 28) Same as Example 25 except that A2 was used as the upper layer coating material in Example 25.

(Example 29) The same as Example 25 except that B was used as the upper layer coating material in Example 25.

(Example 30) The same as Example 25 except that b was used as the lower layer coating material in Example 25.

(Example 31) Example 31 except that a support having a protrusion of 0.30 μm or more as shown in Table 7 was used on the surface of the support opposite to the surface on which the magnetic layer was provided. Same as 25.

(Example 32) The same as Example 25 except that a support in which the Young's modulus of the support was changed as shown in Table 7 was used.

(Comparative Examples 13 to 16) The same as Example 25 except that the support having the projections shown in Table 8 was used in Example 25.

(Comparative Example 17) The same as Example 25 except that the upper layer film thickness was 0.30 μm.

(Example 33) In Example 1, dimethyl silicone oil was used instead of stearic acid and oleic acid as the upper coating material, and a protective layer having the following composition was applied by wet-on-wet multi-layer coating. Same as the example except that the uppermost magnetic layer was provided while the layer underlying the upper magnetic layer was in a wet state.

<Composition of Protective Layer> Myristic acid 2 parts by weight Stearic acid 2 parts by weight Cyclohexanone 100 parts by weight Methyl ethyl ketone 100 parts by weight Toluene 100 parts by weight The properties of 8 mm tapes of the obtained samples were measured according to the following items. The measurement results are shown in Tables 1-8.

(1) Running performance at high temperature and high humidity (clogging of head) Full length recording and reproduction were performed using S-550 (manufactured by Sony Corporation) in an environment of temperature 40 ° C. and relative humidity 80%. Occasionally, when the output dropped by 2 dB or more, the head was clogged, and the number of occurrences was measured.

(2) Output drop due to head turbidity under low humidity (dB) Using S-550 (manufactured by Sony Corp.) in an environment of temperature 20 ° C. and relative humidity 20%, full-length running was performed for 2 passes. After that, the value of RF output reduction was calculated by comparison with the initial value.

(3) Dropout Using an 8 mm video camera CCDV-900 (manufactured by Sony Corporation), the number of dropouts at -20 dB and 15 μs was calculated as an average value for 1 minute.

(4) RF Output An RF output of 7 MHz was measured with an 8 mm video camera CCDV-900 (manufactured by Sony Corporation), and a reference tape (manufactured by Konica Corporation) was evaluated as 0 dB.

(5) Measurement of dynamic friction coefficient Tape running tester T at a temperature of 20 ° C. and a relative humidity of 60%
A BT-300D (Yokohama System Testing Laboratory) was used to wind a tape around a chrome-plated stainless steel 4φ pin at 180 °, and the tape speed was measured at 3.33 cm / sec and the inlet tension was 20 g, and μ _k was calculated by the following formula.

[0203]

[Equation 1]

<Overall Composition> Fe, Co, Ni, Nd, Si, Al, Y, P in the overall composition of the ferromagnetic metal powder.
Regarding the abundance ratio of each element of r, Sm, and La, after measuring the fluorescent X-ray intensity of each element in the sample using a wavelength dispersive X-ray fluorescence 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 (1/10 for Fe only) 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 wt%, P 0.15 wt%, S 0.19 wt%).
% By weight, 0.36% by weight of Si, 3.19% by weight of Co, 1.26% by weight of Zn, 0.07% by weight of Ca, N
a is contained in an amount of 0.02% by weight. ).

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

The standard sample 5 is a ferromagnetic metal powder (Sr.
Contains 97% by weight. ).

The standard sample 6 is a ferromagnetic metal powder (Ba containing 1.
It contains 40% by weight and 0.40% by weight of Ca. ).

The standard sample 7 is a ferromagnetic metal powder (La is 2.
Contains 69% by weight. ).

The standard sample 8 is a ferromagnetic metal powder (Y is 1.9).
Contains 8% 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 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) Analysis 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%.

The evaluation results are shown below.

[0221]

[Table 1]

[0222]

[Table 2]

[0223]

[Table 3]

[0224]

[Table 4]

[0225]

[Table 5]

[0226]

[Table 6]

[0227]

[Table 7]

[0228]

[Table 8]

The sample of the present invention does not cause head clogging even during repeated running over the entire length under high temperature and high humidity, has no drop in output due to cloudiness of the head under low humidity, has little dropout, and has high reproduction output.

[0230]

According to the present invention, there is no head clogging even during repeated running over the entire length under high temperature and high humidity, there is no drop in output due to head turbidity under low humidity, there is little dropout, and there is a high magnetic reproduction output. A recording medium can be obtained.

[Brief description of drawings]

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

FIG. 2 is a view of a coater head for applying a magnetic layer coating material.

[Explanation of symbols]

 DESCRIPTION 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 (16)

[Claims] 1. A recording layer comprising one or more magnetic layers including a magnetic layer is provided on one surface of a support, and the total dry thickness of the recording layer is 0.5 μm or less, and the highest magnetic layer is formed. The layer contains carbon black having a number average particle size of 30 nm or more, the coefficient of dynamic friction with respect to the metal pin at a temperature of 20 ° C. and a relative humidity of 60% is 0.3 or less, and the Young's modulus in the longitudinal direction and the Young's direction in the width direction of the support. The total rate is 1400kg / m
A magnetic recording medium of m ² or more. 2. A recording layer comprising two or more magnetic layers including a magnetic layer is provided on one surface of a support, and the total dry thickness of the recording layers is 0.5 μm or less, and the highest magnetic layer is formed. The layer underlying the layer is a layer containing a lubricant containing a fatty acid or a fatty acid ester and a non-magnetic powder having a Mohs hardness of 5 or more, and the total of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the support is 140.
A magnetic recording medium of 0 kg / mm ² or more. 3. The magnetic recording medium according to claim 2, wherein the fatty acid contains a saturated fatty acid and an unsaturated fatty acid. 4. A recording layer comprising one or more layers including a magnetic layer is provided on one surface of a support, and the total dry thickness of the recording layer is 0.5 μm or less. Has an average protrusion height of 0.
The number of protrusions having a height of 0.01 to 0.20 μm and a height of 0.01 μm or more is 200 or more per measurement length of 1 mm, and the number of protrusions having a height of 0.30 μm or more is 500 per a measurement length of 400 mm. A magnetic recording medium having a ratio of maximum protrusion height to average protrusion height (maximum protrusion height / average protrusion height) of 5 or less. 5. A recording layer comprising one or more layers including a magnetic layer is provided on one surface of a support, and the dry film thickness of the recording layer is 0.5 μm or less in total, and the recording layer is formed on the magnetic layer forming surface. The average protrusion height of the protrusions present on the surface of the support on the same side is 0.0
The number of projections having a height of 0.01 μm or more is 200 or more per measurement length 1 mm, and the number of projections having a height of 0.30 μm or more is 500 per 400 mm of measurement length. A magnetic recording medium having a ratio of maximum protrusion height to average protrusion height (maximum protrusion height / average protrusion height) of 5 or less. 6. A support is provided with a recording layer comprising one or more layers including a magnetic layer on one surface of the support, and the total dry thickness of the recording layer is 0.5 μm or less, and both sides of the support are provided. The average protrusion height of the protrusions present on the surface of the is 0.01 to 0.20 μm
The number of protrusions having a height of 0.01 μm or more is 200 or more per 1 mm of the measurement length, and the height is 0.30.
The number of protrusions that are more than μm is 5 per 400 mm of measurement length
A magnetic recording medium having no more than 00 and having a ratio of maximum protrusion height to average protrusion height (maximum protrusion height / average protrusion height) of 5 or less. 7. The magnetic recording medium according to claim 4, wherein the total of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the support is 1400 kg / mm ² or more. . 8. A recording layer comprising one or more layers including a magnetic layer is provided on one surface of a support, and the total dry thickness of the recording layer is 0.5 μm or less, and the topmost magnetic layer is formed. A protective layer containing a lubricant is provided on the layer, and the protective layer is provided by wet-on-wet multi-layer coating while the uppermost magnetic layer is in a wet state. Manufacturing method of magnetic recording medium. 9. A support is provided with two or more layers including a magnetic layer on one surface thereof, and the total dry thickness of the two or more layers including the magnetic layer is 0.5 μm or less, The layer underlying the uppermost magnetic layer is a layer containing a lubricant containing a fatty acid or a fatty acid ester and a non-magnetic powder having a Mohs hardness of 5 or more, and the total of the Young's modulus in the longitudinal direction and the Young's modulus in the width direction of the support is 1
400 kg / mm ² or more and by wet-on-wet multi-layer coating using two or more extrusion coaters, the uppermost magnetic layer while the layer under contacting the uppermost magnetic layer is in a wet state. A method of manufacturing a magnetic recording medium, comprising: 10. The magnetic recording medium according to claim 1, wherein the support is a polyamide film. 11. The method for producing a magnetic recording medium according to claim 8, wherein the support is a polyamide film. 12. The method for manufacturing a magnetic recording medium according to claim 11, wherein the support has a thickness of 5 μm or less. 13. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder contained in the uppermost magnetic layer contains Fe, Al, Co, and a rare earth element. . 14. The method of manufacturing a magnetic recording medium according to claim 8, wherein the ferromagnetic powder contained in the uppermost magnetic layer contains Fe, Al, Co, and a rare earth element. 15. The magnetic recording medium according to claim 1, wherein the total thickness of the magnetic recording medium is 5 μm or less. 16. The method for manufacturing a magnetic recording medium according to claim 8, wherein the total thickness of the magnetic recording medium is 5 μm or less.