JP2001338414A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a smooth magnetic recording medium having very superior electromagnetic transducing characteristics and running durability, retaining high output and ensuring a low error rate. SOLUTION: The magnetic recording medium is obtained by disposing an under layer containing a nonmagnetic powder and a binder on a base and one or more magnetic layers containing a ferromagnetic metal powder having 0.01-0.10 μm average major axis size and 80-180 Å crystallite size or a ferromagnetic hexagonal ferrite powder having 5-40 nm average plate diameter and a binder on the under layer, the thickness of the magnetic layers is 0.01-0.5 μm and an organic phosphorus compound having a specified structure is contained in the magnetic layers.

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 in which a lower layer containing a nonmagnetic powder and a binder is provided on a support, and a magnetic layer containing a ferromagnetic fine powder and a binder is further provided thereon. The present invention relates to a magnetic recording medium comprising an organic phosphorus compound having a specific structure in a magnetic layer and having extremely excellent electromagnetic conversion characteristics and running durability.

[0002]

2. Description of the Related Art Conventionally, magnetic recording media containing various organic phosphorus compounds in a magnetic layer are known. For example, Japanese Patent Laid-Open No. 1-1
No. 89025 discloses a magnetic recording medium comprising a support and a magnetic layer in which ferromagnetic powder is dispersed in a binder.
A magnetic recording medium containing a phosphorous ester in a magnetic layer is disclosed.

JP-A-58-171720 discloses a magnetic recording medium in which a magnetic layer contains a C ≧ 6 substituted or unsubstituted alkyl, alkenyl or arylalkyl phosphate alkyl ester. Have been.

[0004] However, the magnetic recording media described in the examples of JP-A-1-189025 and JP-A-58-171720 are single-layer media having a magnetic layer thickness of 4 μm and 6 μm, respectively. In the compounds described in the examples, the average major axis length of 0.1 μm used for a coating type ultra-thin layer magnetic recording medium corresponding to a recent MR head was used.
The effect is not sufficient for the dispersibility of fine ferromagnetic metal powder having a particle size of m or less or fine ferromagnetic hexagonal ferrite powder having a mean plate diameter of 40 nm or less, and the necessary electromagnetic conversion characteristics and medium surface properties cannot be secured.

JP-A-10-228635 discloses a magnetic recording medium comprising a support and a magnetic layer in which a ferromagnetic metal fine powder or a ferromagnetic hexagonal ferrite fine powder is dispersed in a binder. A magnetic recording medium containing a phosphorus compound such as phosphonic acid, phosphoric acid, and phosphinic acid is disclosed.

In Japanese Patent Application Laid-Open No. Hei 10-228635, Examples describe phenylphosphonic acid as a phosphorus compound to be added.
Dispersibility of fine ferromagnetic metal powder with an average major axis length of 0.1 μm or less and fine ferromagnetic hexagonal ferrite powder with an average plate diameter of 40 nm or less used for coating type ultrathin layer magnetic recording media corresponding to the head The effect is insufficient, and the necessary electromagnetic conversion characteristics and surface properties of the medium cannot be secured.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium having extremely excellent electromagnetic conversion characteristics and running durability. More specifically, an object of the present invention is to provide a magnetic recording medium that maintains a high output, is smooth, and has a low error rate.

Specifically, an object of the present invention is to provide a lower layer containing a nonmagnetic powder on a support, and further form a ferromagnetic metal fine powder having an average major axis length of 0.1 μm or less or an By providing a magnetic layer having a thickness of 0.5 μm or less containing a ferromagnetic hexagonal ferrite fine powder having a plate diameter of 40 nm or less, and using an organic phosphorus compound having a specific structure for the magnetic layer,
An object of the present invention is to provide the following magnetic recording medium. A magnetic recording medium in which the ferromagnetic powder used in the magnetic layer has high dispersibility and excellent electromagnetic conversion characteristics. A magnetic recording medium with excellent magnetic layer smoothness and electromagnetic conversion characteristics. A magnetic recording medium with less running of the magnetic layer and less contamination of the head, and excellent running durability. A magnetic recording medium with excellent storage properties under high temperature and high humidity.

[0009]

According to the present invention, a lower layer containing a non-magnetic powder and a binder is provided on a support, on which an average major axis length of 0.01 μm to 0.10 μm and a crystallite size of 8
0 to 180 ° ferromagnetic metal powder or average plate diameter of 5 nm or more
At least one magnetic layer containing a ferromagnetic hexagonal ferrite powder of 40 nm and a binder is provided, the thickness of the magnetic layer is 0.01 μm to 0.5 μm, and the magnetic layer has the following formula (1): The present invention relates to a magnetic recording medium containing an organic phosphorus compound represented by any one of (1) to (4). (R ¹ ) _n -P (= O) (OH) _3-n (1) (R ¹ -O) _n -P (= O) (OH) _3-n (2) [(R ² ) _m -φ _{] n -P (= O) (} OH) 3-n (3) [(R 2) m -φ-O] n -P (= O) (OH) 3-n (4) wherein, R ¹ is , an aralkyl group having an alkyl chain of 1 to 4 carbon atoms, an aryl group substituted with an alkyl group having 3 to 20 carbon atoms, or represent straight-chain or branched alkyl group having 8 to 20 carbon atoms, R ² is aralkyl Represents an aryl group or an aryl group, φ represents a benzene ring, m = 1 to 5, n = 1,
Represents an integer of 2. In the present invention, the following aspects are preferable. 1. When the magnetic layer contains a ferromagnetic metal powder, the magnetic layer has a thickness of 0.01 to 0.1 μm. 2. When the magnetic layer contains ferromagnetic hexagonal ferrite powder, the magnetic layer has a thickness of 0.01 to 0.2 μm. 3. The ferromagnetic metal powder contains Fe as a main component, 10 to 40 at% of Co, 2 to 20 at% of Al,
Y is contained at 1 to 15 atomic%, and coercive force is 2000 to 300
0 Oersted (Oe) (160-240 kA / m)
And a saturation magnetic flux density of 150 to 300 mT. 4. The coercive force of the ferromagnetic hexagonal ferrite powder is 2000
A magnetic recording medium characterized by being hexagonal barium ferrite having a saturation magnetic flux density of 150 to 300 mT at 〜3000 Oe (160 to 240 kA / m). 5. A magnetic recording medium characterized in that the lower layer contains the organic phosphorus compound represented by the above formulas (1) to (4). 6. A magnetic recording medium, wherein the magnetic recording medium is a magnetic disk or a magnetic tape for digital signal recording applied to a recording / reproducing system equipped with an MR reproducing head.

[0010]

DETAILED DESCRIPTION OF THE INVENTION Organic Phosphorus Compound In the present invention, the magnetic layer and, if necessary, the lower layer contain an organic phosphorus compound represented by the following formulas (1) to (4) as a dispersant. (R ¹ ) _n -P (= O) (OH) _3-n (1) (R ¹ -O) _n -P (= O) (OH) _3-n (2) [(R ² ) _m -φ _{] n -P (= O) (} OH) 3-n (3) [(R 2) m -φ-O] n -P (= O) (OH) 3-n (4) wherein, R ¹ is , an aralkyl group having an alkyl chain of 1 to 4 carbon atoms, an aryl group substituted with an alkyl group having 3 to 20 carbon atoms, or represent straight-chain or branched alkyl group having 8 to 20 carbon atoms, R ² is aralkyl Represents an aryl group or an aryl group, φ represents a benzene ring, m = 1 to 5, n = 1,
Represents an integer of 2.

The aralkyl group having an alkyl chain having 1 to 4 carbon atoms used as R ¹ includes a benzyl group, a phenethyl group, an α-methylbenzyl group, a 1-methyl-1-phenethyl group, a diphenylmethyl group and the like. be able to. Among the above specific examples, a benzyl group and a phenethyl group are particularly preferred.

The aryl group substituted by an alkyl group having 3 to 20 carbon atoms used as R ¹ is a toluyl group,
Examples thereof include a xylyl group, an ethylphenyl group, a cumenyl group, and a nonylphenyl group. Among the above specific examples, an ethylphenyl group and a cumenyl group are particularly preferred.

The linear or branched alkyl group used as R ¹ preferably has 8 to 20 carbon atoms, and may be linear or branched and has 6 to 18 carbon atoms. Particularly preferred are those in the range. Specifically, an isooctyl group such as an octyl group and a 2-ethylhexyl group, an (iso) nonyl group, an (iso) decyl group, an (iso) undecyl group, an (iso) dodecyl group, an (iso) hexadecyl group, and an (iso) octadecyl group. And an (iso) eicosyl group. Among the above specific examples, an octyl group, a dodecyl group and the like are particularly preferred.

The aralkyl group used as R ² includes a benzyl group, an α-cumyl group, a phenethyl group, an α-methylbenzyl group, a 1-methyl-1-phenethyl group, a diphenylmethyl group and the like. Among the above specific examples, a benzyl group and a phenethyl group are particularly preferred.

The aryl group used as R ² includes a phenyl group, a toluyl group, a xylyl group, an ethylphenyl group, a cumenyl group and the like. Among the above specific examples, a phenyl group and a toluyl group are particularly preferred.

Further, an alkyl group, an aryl group, or an aralkyl group substituted with a group other than the above-mentioned hydrocarbon group may be used. Examples of groups other than hydrocarbon groups include methoxy, butoxy, amino, nitro and F, Cl, Br, C
Examples thereof include halogen-containing hydrocarbons such as F ₃ , CCl ₃ , and CBr ₃ .

Examples of the organic phosphorus compound represented by the formula (1) include benzylphosphonic acid, phenethylphosphonic acid, ethylphenylphosphonic acid, cumenylphosphonic acid,
Octylphosphonic acid, dodecylphosphonic acid and the like can be mentioned.

Examples of the organic phosphorus compound represented by the formula (2) include benzyl phosphate, phenethyl phosphate, ethylphenyl phosphate, cumenyl phosphate, octyl phosphate, dodecyl phosphate and the like.

Examples of the organic phosphorus compound represented by the formula (3) include benzylphenylphosphonic acid, phenethylphenylphosphonic acid, ethylbiphenylphosphonic acid, t-
Butylbiphenylphosphonic acid, octylphenylphosphonic acid, dodecylphenylphosphonic acid, and the like.

Examples of the organic phosphorus compound represented by the formula (4) include benzylphenyl phosphate, phenethyl phenyl phosphate, ethyl biphenyl phosphate, t-butyl biphenyl phosphate, octyl phenyl phosphate, dodecyl phenyl phosphate and the like.

Such an organic phosphorus compound has a property of adsorbing or bonding with a polar group, and has a polarizable property mainly on the surface of a ferromagnetic powder in a magnetic layer and mainly on a surface of a nonmagnetic powder in a lower layer. It is presumed that it exists in a state of being adsorbed or bound by the group. In particular, the adsorptive power of metal surfaces, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, etc. on metal compound surfaces is higher than that of carboxylic acids and sulfonic acids. Since the organic phosphorus compound used in the present invention has a strong adsorptive power, the organic phosphorus compound once adsorbed is difficult to desorb from the surface of a metal or a metal compound. Therefore, the surface of the ferromagnetic powder or non-magnetic powder of the present invention is in a state in which the organic phosphorus compound is strongly adsorbed and is covered with a benzene ring or the like. Affinity is improved,
Further, it is presumed that the dispersion stability of the ferromagnetic powder or the non-magnetic powder is also improved.

In addition, since the ferromagnetic powder or non-magnetic powder and the binder cause a strong interaction due to the action of the organic phosphorus compound, desorption of the ferromagnetic powder or non-magnetic powder does not occur, and the running property and running durability are reduced. It is considered that the property is significantly improved. Furthermore, since the organic phosphorus compound used in the present invention has a lower water absorption than other organic compounds such as sulfonic acid, it has good water resistance and durability.

Further, since the thickness of the magnetic layer is very thin compared to about 2 μm of the lower layer, the surface property of the magnetic layer in direct contact with the recording / reproducing head largely reflects the surface property of the lower layer.

In the present invention, by using an organic phosphorus compound for the magnetic layer and, if necessary, for the lower layer as a dispersant, a magnetic recording excellent in magnetic characteristics, surface smoothness, and electromagnetic conversion characteristics, durability and storage stability. Medium can be obtained.

According to the present invention, the dispersibility is improved by using an organic phosphorus compound in the magnetic layer and, if necessary, the lower layer, and the moldability in the calendering step for the purpose of further improving the smoothness is improved. The electromagnetic conversion characteristics,
A magnetic recording medium having excellent durability and storability is provided.

The content of the above organic phosphorus compound in the range of 0.1 to 20 parts by mass per 100 parts by mass of the ferromagnetic powder or nonmagnetic powder is contained in the magnetic layer of the present invention and, if necessary, the lower layer. Is preferably included. In particular, by setting the content in the range of 0.5 to 15 parts by mass, a phenomenon such as an increase in the glossiness of the surface of the magnetic layer or the lower layer appears, and the dispersion state of the ferromagnetic powder or the nonmagnetic powder is good. Become. Further, by setting the content in the range of 1 to 10 parts by mass, the electromagnetic conversion characteristics are remarkably improved.
If the content is less than 0.1 part by mass, the effect of the compounding may not be effectively exhibited, and if the content is more than 20 parts by mass, the dispersion state of the ferromagnetic powder or the nonmagnetic powder is further improved. May not.

As a method for improving the dispersibility of ferromagnetic powder or non-magnetic powder by incorporating the above organic phosphorus compound into the magnetic layer and, if necessary, the lower layer, the organic phosphorus compound is added to a low boiling organic solvent. After dissolving or dispersing, ferromagnetic powder or non-magnetic powder is added to the solution and mixed, and then, after adjusting the ferromagnetic powder or non-magnetic powder pretreated with the organic phosphorus compound by removing the organic solvent, A method for producing a magnetic recording medium using a pretreated ferromagnetic powder or non-magnetic powder, and when preparing a magnetic layer coating solution or a lower layer coating solution, the organic phosphorus compound directly or preferably, It is possible to use a method of kneading and dispersing the mixture by dissolving or dispersing in a part of the solvent for the layer coating liquid or the lower layer coating liquid. When the organic phosphorus compound of the present invention is kneaded and dispersed in a solvent with a ferromagnetic powder or a non-magnetic powder, it is extremely strongly adsorbed on the powder surface.

II. Magnetic Material [Ferromagnetic Metal Powder] The ferromagnetic metal powder used in the present invention is not particularly limited as long as it is mainly composed of Fe (including an alloy). Ferromagnetic alloy powders are preferred. These ferromagnetic metal powders include Al, Si, S, Sc, Ca, Ti,
V, Cr, Cu, Y, Mo, Rh, Pd, Ag, Sn,
Sb, Te, Ba, Ta, W, Re, Au, Hg, P
b, Bi, La, Ce, Pr, Nd, P, Co, Mn,
It may contain atoms such as Zn, Ni, Sr, and B. Al, Si, Ca, Y, Ba, La, Nd, Co,
Preferably, at least one of Ni and B is contained other than α-Fe, and particularly preferably, Co, Al, and Y are contained. More specifically, Co is 10 to 10% of Fe.
It is preferable that 40 atomic%, Al is 2 to 20 atomic%, and Y is 1 to 15 atomic%.

These ferromagnetic metal powders may be previously treated with a dispersant, a lubricant, a surfactant, an antistatic agent, and the like, which will be described later, before dispersion. Further, the ferromagnetic metal powder may contain a small amount of water, hydroxide or oxide. The water content of the ferromagnetic metal powder is 0.0
It is preferable to set it to 1 to 2%. It is preferable to optimize the water content of the ferromagnetic metal powder depending on the type of the binder.

The crystallite size of the ferromagnetic metal powder is 80 to
180 °, preferably 100-180 °,
Particularly preferably, it is 120 to 160 °. When the crystallite size is less than 80 °, the demagnetization increases, and when the crystallite size exceeds 180 °, noise increases, and both are unsuitable. The crystallite size was determined by using an X-ray diffractometer (RINT2000 series manufactured by Rigaku Denki) and using a radiation source CuKα.
1. The average value obtained by the Scherrer method from the half width of the diffraction peak under the conditions of a tube voltage of 50 kV and a tube current of 300 mA was used.

The average major axis length of the ferromagnetic metal powder is 0.01
０．１0.10 μm, preferably 0.03 to 0.09
μm, and particularly preferably 0.05 to 0.08 μm. If the average major axis length is less than 0.01 μm, stable magnetization cannot be obtained due to thermal fluctuation, and the average major axis length is 0.10 μm.
If m exceeds m, noise increases, and all are unsuitable. The average major axis length is determined by taking a transmission electron microscope photograph and directly reading the minor axis length and the major axis length of the ferromagnetic metal powder from the photograph.

Ferromagnetic metal powder used in the magnetic layer of the present invention
The specific surface area (SBET) by the BET method is 30 m^Two
/ G or more 50m^Two/ G is preferred. Moreover 38 ~
48m ^Two/ G is preferred. Thereby, good surface properties and
Low noise compatibility can be achieved.

It is preferable that the pH of the ferromagnetic metal powder is optimized depending on the combination with the binder used. The range is usually from 4 to 12, preferably from 7 to 10. The ferromagnetic metal powder may be subjected to a surface treatment with Al, Si, P, or an oxide thereof, if necessary. The amount is 0.1 to 10% based on the ferromagnetic metal powder, and when the surface treatment is performed, the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less, which is preferable. The ferromagnetic metal powder may contain soluble inorganic ions such as Na, Ca, Fe, Ni, and Sr, but if it is 200 ppm or less, there is little effect on the characteristics. The ferromagnetic metal powder used in the present invention preferably has a small number of vacancies, and its value is 20% by volume or less, more preferably 5% by volume or less.

The shape may be any of acicular, granular, rice granular or plate-like as long as the above-mentioned particle size characteristics are satisfied. In particular, acicular ferromagnetic metal powders should be used. Is preferred. In the case of the acicular ferromagnetic metal powder, the average acicular ratio (the arithmetic average of the acicular ratio (major axis length / minor axis length)) is preferably 4 or more and 12 or less, more preferably 5 or more and 12 or less.

The coercive force Hc of the ferromagnetic metal powder is preferably 2000 to 3000 Oe (160 to 240 kA / m).
And more preferably 2100 to 2900 Oe (17
0 to 230 kA / m), the saturation magnetic flux density is preferably
150 to 300 mT, more preferably 160 to 2 mT
90 mT. σs is preferably 140 to 170A
· M ² / kg, more preferably 145 to 160 A · m ² /
kg.

[Ferromagnetic hexagonal ferrite powder] In particular, when reproducing with a magnetoresistive head to increase the track density,
It is necessary to reduce the noise, and the average plate diameter of the ferromagnetic hexagonal ferrite powder used in the present invention is 5 to 40 nm. However, if the average plate diameter is less than 5 nm, stable magnetization cannot be expected due to thermal fluctuation. . The preferred range of the average plate diameter is 10 nm.
To 35 nm, and a more preferable range of the average plate diameter is 1
5 nm to 30 nm.

The average tabular ratio {the arithmetic average of the plate ratio (plate diameter / plate thickness)} is preferably 1 to 15. More preferably 1 to 7
It is. When the average plate ratio is small, the filling property in the magnetic layer is increased, which is preferable, but sufficient orientation cannot be obtained. If it is larger than 15, noise increases due to stacking between particles. The specific surface area of the particle size range by the BET method is as follows:
10 to ²⁰⁰ m ² / g. The specific surface area generally corresponds to an arithmetic calculation value from the particle plate diameter and the plate thickness. Generally, the narrower the distribution of particle plate diameter and plate thickness, the better. Particle plate diameter and plate thickness are
500 particles are measured from a particle TEM photograph. The distribution is often not a normal distribution, but when calculated and expressed as a standard deviation with respect to the average size, σ / average size = 0.1 to 2.0. In order to sharpen the particle size distribution, the particle generation reaction system is made as uniform as possible, and the generated particles are subjected to a distribution improving treatment. For example, a method of selectively dissolving ultrafine particles in an acid solution is also known.

The coercive force Hc measured on the magnetic material is 500
It can be made up to about 5000 Oe (40 kA / m to 400 kA / m). A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. In the present invention, Hc
Is preferably 2000 to 3000 Oe (160 to 24
0 kA / m), but more preferably 2200-200 kA / m).
It is 2800 Oe (175 to 220 kA / m). When the saturation magnetization of the head exceeds 1.4T, 2000 Oe
(160 kA / m) or more. Hc
Is the particle size (diameter and thickness), the type and amount of contained elements,
It can be controlled by the substitution site of the element, the particle generation reaction conditions and the like. Saturation magnetization σs ^{is, 40A · m 2 / kg~80A ·} m 2
/ Kg is preferred. σs is preferably higher, but tends to be smaller as the particles become finer. It is well known to combine spinel ferrite with magnetoplumbite ferrite to improve σs, and to select the type of element contained and the amount added, etc. It is also possible to use W-type hexagonal ferrite.

When dispersing the magnetic material, the surface of the magnetic material particles is also treated with a substance suitable for the dispersion medium and the polymer. As the surface treatment material, an inorganic compound or an organic compound is used. Typical examples of the main compound include compounds such as Si, Al, and P, various silane coupling agents, and various titanium coupling agents. The amount is 0.1 to 10 based on the magnetic material.
%. The pH of the magnetic material is also important for dispersion. Usually 4 ~
The optimum value is about 12 depending on the dispersion medium and the polymer, but about 6 to 11 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects dispersion. Dispersion medium,
There is an optimum value depending on the polymer, but usually 0.01 to 2.0%
Is selected.

The ferromagnetic hexagonal ferrite powder is prepared by mixing barium oxide, iron oxide, and a metal oxide that replaces iron with boron oxide or the like as a glass-forming substance so as to have a desired ferrite composition, and then melting. A glass crystallization method in which a barium ferrite crystal powder is obtained by quenching to obtain an amorphous body, followed by reheating treatment, followed by washing and pulverization to obtain barium ferrite crystal powder. A hydrothermal reaction method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, heated in a liquid phase at 100 ° C. or higher, washed, dried, and pulverized to obtain barium ferrite crystal powder. A coprecipitation method in which a barium ferrite composition metal salt solution is neutralized with an alkali to remove by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain barium ferrite crystal powder. In the present invention, ferromagnetic hexagonal barium ferrite powder is particularly preferred.

III. Nonmagnetic Powder The magnetic recording medium of the present invention is provided with a lower layer containing a binder and a nonmagnetic powder on a support.

The nonmagnetic powder that can be used for the lower layer may be an inorganic substance or an organic substance. Further, carbon black or the like can be used. Examples of the inorganic substance include metals, metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, metal sulfides, and the like. Specifically, titanium oxide such as titanium dioxide, cerium oxide, tin oxide, tungsten oxide, ZnO, ZrO ₂ , SiO ₂ , Cr ₂ O ₃ , α
Α-alumina, β-alumina, γ with a conversion of 90 to 100%
-Alumina, α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, magnesium oxide, boron nitride, molybdenum disulfide, copper oxide, MgCO ₃ , CaC
O ₃ , BaCO ₃ , SrCO ₃ , BaSO ₄ , silicon carbide, titanium carbide and the like are used alone or in combination of two or more. Preferred are α-iron oxide and titanium oxide.

The shape of the non-magnetic powder may be any of acicular, spherical, polyhedral, and plate shapes. The crystallite size of the nonmagnetic powder is preferably from 0.004 μm to 1 μm, more preferably from 0.04 μm.
m to 0.1 μm is more preferred. If it is smaller than 0.004 μm, dispersion tends to be difficult. If it is larger than 1 μm, the surface roughness tends to increase.

The average particle size of these non-magnetic powders is 0.00
The thickness is preferably from 5 to 2 μm, but if necessary, non-magnetic powders having different average particle diameters may be combined, or even a single non-magnetic powder may have the same effect by broadening the particle diameter distribution. Particularly preferred is 0.01 to 0.2 μm. 0.
If it is smaller than 005 μm, dispersion tends to be difficult, and if it is larger than 2 μm, the surface roughness tends to increase.

The specific surface area of the nonmagnetic powder is 1 to 100 m ^2.
/ G, preferably 5 to 70 m ² / g. And more preferably it is 10-65 m < ² > / g. 1m ² / g
If it is smaller, the surface roughness tends to be large, and if it is larger than 100 m ² / g, it tends to be difficult to disperse, for example, it is impossible to disperse with a desired amount of binder.

The oil absorption using dibutyl phthalate (DBP) is 5 to 100 ml / 100 g, preferably 10 to 100 ml / 100 g.
80 ml / 100 g, more preferably 20-60 ml /
100 g. Specific gravity is 1 to 12, preferably 3 to 6
It is.

The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. 0.05g /
If it is smaller than ml, there is a tendency that the amount of scattered particles is large and the operation becomes difficult. If it is larger than 2 g / ml, it tends to stick to the device and the operation tends to be difficult.

The non-magnetic powder preferably has a pH of 2 to 11, and particularly preferably a pH of 6 to 9. pH
Is smaller than 2, the coefficient of friction under high temperature and high humidity tends to increase. If the pH is higher than 11, the amount of released fatty acids tends to decrease, and the friction coefficient tends to increase.

The water content of the nonmagnetic powder is 0.1 to 5% by mass, preferably 0.2 to 3% by mass, and more preferably 0.1 to 5% by mass.
3 to 1.5% by mass. If it is less than 0.1% by mass, dispersion tends to be difficult. If it is more than 5% by mass, the viscosity of the paint after dispersion tends to be unstable.

The loss on ignition is preferably 20% by mass or less, and the loss on ignition is preferably small.

When the nonmagnetic powder is an inorganic powder, the Mohs' hardness is preferably 4 or more and 10 or less. If the Mohs hardness is smaller than 4, durability tends to be insufficient.

The amount of stearic acid adsorbed on the non-magnetic powder is 1 to
20 μmol / m ² , more preferably ^{2 to} 15 μmol
/ M ² .

The heat of wetting of the nonmagnetic powder in water at 25 ° C. is
200 erg / cm ^{2 to} 600 erg / cm ² (200 to
It is preferably in the range of 600 mJ / m ² ). Further, a solvent having a range of the heat of wetting can be used. The amount of water molecules on the surface at 100 to 400 ° C is 1 to 1
0 pieces / 100 ° is appropriate. PH of isoelectric point in water
Is preferably between 3 and 9.

The surface of these non-magnetic powders is subjected to a surface treatment so that Al ₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , S
Preferably, nO ₂ , Sb ₂ O ₃ and ZnO are present. Particularly preferred for dispersibility are Al ₂ O ₃ , SiO ₂ , T
iO ₂ and ZrO ₂ , more preferably Al ₂ O ₃ ,
SiO ₂ and ZrO ₂ . These may be used in combination or may be used alone. Further, a surface treatment layer coprecipitated may be used according to the purpose, or a method in which alumina is first present and silica is present in the surface layer, or the reverse method may be employed. Also, the surface treatment layer may be a porous layer depending on the purpose,
Homogeneous and dense are generally preferred.

Specific examples of the non-magnetic powder used for the lower layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100 and ZA-G1 manufactured by Sumitomo Chemical, and DPN-2 manufactured by Toda Kogyo.
50, DPN-250BX, DPN-245, DPN-
270BX, DPB-550BX, DPN-550R
X, Titanium oxide manufactured by Ishihara Sangyo TTO-51B, TTO-5
5A, TTO-55B, TTO-55C, TTO-55
S, TTO-55D, SN-100, MJ-7, α-iron oxide E270, E271, E300, ST manufactured by Titanium Industry
T-4D, STT-30D, STT-30, STT-6
5C, Teika MT-100S, MT-100T, MT
-150W, MT-500B, MT-600B, MT-
100F, MT-500HD, FINEX-2 manufactured by Sakai Chemical
5, BF-1, BF-10, BF-20, ST-M, Dowa Mining DEFIC-Y, DEFIC-R, Nippon Aerosil AS2BM, TiO2P25, Ube Industries 100
A, 500A, Y-LOP manufactured by Titanium Kogyo Co., Ltd. and fired products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

For the lower layer, carbon black may be mixed with non-magnetic powder to reduce the surface electric resistance (Rs), reduce the light transmittance, and obtain a desired micro-Vickers hardness. it can.

The micro Vickers hardness of the lower layer is usually
25 to 60 kg / mm ² (245 to 588 MPa), preferably 30 to 50 k
g / mm ² (294 to 490 MPa), and a ridge angle of 80 using a thin film hardness tester (NEC HMA-400).
It can be measured using a diamond triangular pyramid needle with a tip radius of 0.1 μm at the tip of the indenter. The light transmittance is standardized so that the absorption of infrared rays having a wavelength of about 900 nm is generally 3% or less, for example, 0.8% or less for a VHS magnetic tape. For this purpose, a furnace for rubber,
Thermal rubber, black for color, acetylene black and the like can be used.

[0058] The specific surface area of the carbon black used in the lower layer of the present invention is generally, 100 to 500 m ² / g, preferably from 150 to 400 m ² / g, DBP oil absorption, typically, 20 to 400 ml / 100 g, preferably 30-2
It is 00 ml / 100 g. The average particle size of the carbon black is 5 to 80 nm, preferably 10 to 50 nm, and more preferably 10 to 40 nm. The carbon black preferably has a pH of 2 to 10, a water content of 0.1 to 10%, and a tap density of 0.1 to 1 g / ml.

Specific examples of carbon black used in the present invention include BLACKPEAR manufactured by Cabot Corporation.
LS 2000, 1300, 1000, 900, 80
0, 880, 700, VULCAN XC-72, # 3050B, 3150B, 3250B, manufactured by Mitsubishi Kasei Kogyo Co., Ltd.
# 3750B, # 3950B, # 950, # 650B,
# 970B, # 850B, MA-600, CONDUCTEX SC, RAVEN 8 manufactured by Columbia Carbon Co.
800, 8000, 7000, 5750, 5250, 3
500, 2100, 2000, 1800, 1500, 1
255, 1250, Akzo Ketjen Black E
C and the like. Carbon black may be used after being surface-treated with a dispersant or the like or grafted with a resin, or may be used after a part of the surface is graphitized. Further, the carbon black may be dispersed in a binder before adding it to the paint. These carbon blacks can be used in a range not exceeding 50% by mass and not exceeding 40% of the total mass of the lower layer based on the inorganic powder. These carbon blacks can be used alone or in combination. The carbon black that can be used in the lower layer of the present invention can be referred to, for example, "Carbon Black Handbook" edited by Carbon Black Association.

Further, an organic powder can be added to the lower layer according to the purpose. For example, acrylic / styrene-based resin powder, benzoguanamine resin powder, melamine-based resin powder, phthalocyanine-based pigment may be mentioned, but polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can also be used.

IV. Binder In the magnetic recording medium of the present invention, a polar group-containing vinyl chloride resin and a polar group-containing polyurethane resin can be used as a binder used for forming the lower layer or the magnetic layer.

The polar groups used in the present invention include -SO ₃ M, -PO (OM) ₂ , -COO introduced into a binder for the purpose of improving the dispersibility of the ferromagnetic fine powder and the non-magnetic powder.
M (M represents a hydrogen atom, an alkali metal or ammonium), an amino group, and a quaternary ammonium group. Among them -SO ₃ M is preferred particularly excellent dispersibility. The preferred polar group content is 1 × 10 ⁻⁶ to 50 × 10 ^−5.
eq / g, more preferably 5 × 10 ⁻⁶ to 2 × 10 ⁻⁵ eq
/ G-binder. If it is less than 1 × 10 ⁻⁶ eq / g, no effect can be obtained, and if it exceeds 50 × 10 ⁻⁵ eq / g, the viscosity of the paint becomes high, the workability becomes extremely poor, and the handling becomes difficult. Furthermore, polar groups to be introduced, may be two or more, for example, in addition to be performed to introduce -COOM of -SO ₃ M.

The method of introducing a polar group into a polar group-containing vinyl chloride resin used in the present invention can be synthesized, for example, by adding the polar group to a vinyl chloride resin containing no polar group by a reaction. . Specifically when introducing a -SO ₃ M vinyl chloride resin, first with these and optionally a monomer copolymerizable with the vinyl chloride monomer and a glycidyl group other copolymerizable monomers Is copolymerized,
After obtaining a copolymer simultaneously or copolymer, -SO ₃ M
Which is obtained by reacting a compound having a glycidyl group with a glycidyl group. Examples of the copolymerizable monomer having a glycidyl group include glycidyl acrylate, glycidyl methacrylate, and glycidyl vinyl ether. These may be used alone or in combination of two or more. Compounds having —SO ₃ M and reacting with a glycidyl group include sulfurous acid and sodium sulfite, sodium bisulfite, potassium sulfite,
Sulfites such as ammonium sulfite, sulfuric acid and sodium hydrogen sulfate, potassium hydrogen sulfate, hydrogen sulfate such as ammonium hydrogen sulfate, taurine, sodium taurine,
Taurine potassium, taurine ammonium, sulfamic acid, sodium sulfamate, potassium sulfamate, ammonium sulfamate, sulfanilic acid,
Sodium sulfanilate, potassium sulfanilate,
And aminosulfonic acids such as ammonium sulfanilate.

The copolymerizable polar group-containing monomer may be copolymerized with vinyl chloride and other copolymerizable monomers. As the copolymerizable monomer containing a -SO ₃ M, 2-acrylamido-2-methylpropanesulfonic acid, vinylsulfonic acid, acrylic acid, unsaturated hydrocarbons such as methacrylic acid, p- styrenesulfonic acid Examples include hydrogen sulfonic acid and salts thereof, sulfoalkyl esters of acrylic acid or methacrylic acid such as methacrylic acid sulfoethyl ester and methacrylic acid sulfopropyl ester, and salts thereof. These may be used alone or in combination of two or more.

Further, when it is necessary to introduce two or more kinds of polar groups to be introduced, for example, when -COOM is required to be introduced in addition to -SO ₃ M, a copolymerizable monomer containing -COOM, specifically, Acrylic acid, methacrylic acid, maleic acid and the like and salts thereof can also be copolymerized.

The content of the polar group-containing monomer unit is preferably from 0.05 to 5% by mass, and if it is less than 0.05% by mass, there is no effect of improving the dispersibility of the nonmagnetic powder or the magnetic powder. On the other hand, when the content exceeds 5% by mass, the viscosity of the coating material becomes high, and the pot life when the isocyanate compound is added becomes short.

The content of the vinyl chloride unit is preferably from 57 to 98% by mass. If the amount is less than 57% by mass, the strength of the obtained coating film is reduced. If the amount exceeds 98% by mass, the solubility of the resin in organic solvents such as ketones and esters is hindered.

Other copolymerizable monomers that can be used in producing the polar group-containing vinyl chloride resin include vinyl acetate, vinyl propionate, (meth) acrylate, (meth) acrylate, and the like. Acrylic acid, (anhydride) maleic acid, acrylonitrile, vinylidene chloride, hydroxyethyl (meth) acrylate, glycidyl (meth) acrylate and the like can be mentioned. Here, (meth) acryl means a material containing at least one of acryl and methacryl, and (maleic anhydride) means a material containing at least one of maleic acid and maleic anhydride. When other monomer units are contained, the content is preferably set to 26% by mass or less. If it exceeds this range, the mechanical properties and dispersibility of the entire resin will be reduced.

The obtained vinyl chloride resin can be saponified to introduce a hydroxyl group using vinyl acetate, vinyl propionate or the like as a vinyl alcohol component. The content of the vinyl alcohol unit is preferably 2 to 16% by mass. If the amount is less than 2% by mass, solubility in organic solvents such as ketones and esters when preparing coating materials, dispersibility of non-magnetic powder and magnetic powder, reactivity with isocyanate compounds used in combination with the present resin, and other resins No effect on compatibility with
If the amount is more than mass%, the viscosity of the coating material becomes too high, and the pot life when the isocyanate compound is added becomes short, which is disadvantageous in practical use.

The average polymerization degree of the polar group-containing vinyl chloride resin is preferably from 200 to 800. Furthermore, 250 ~
700 is preferred. If it is less than 200, the resulting magnetic layer and the lower layer become brittle and the physical strength is reduced, and the durability of the magnetic tape and the like is affected. If it exceeds 800, the viscosity of the paint at a predetermined concentration becomes high, and the workability becomes extremely poor, and the handling becomes difficult. The polar group-containing vinyl chloride resin used in the present invention includes a polymerization initiator, a suspension stabilizer,
It is produced by adding compounds such as emulsifiers and molecular weight regulators.

The polar group-containing polyurethane resin of the present invention comprises
It can be produced from a polar group-containing polyol such as a polyester polyol having a polar group, a polycarbonate polyol or a polyether polyol, and a polyol having no polar group such as a polyester polyol, a polycarbonate polyol or a polyether polyol, and a diisocyanate. The polar group-containing polyol has the polar group in the main chain or side chain of the polyol. The polar group-containing polyol can be produced by, for example, changing a part of the following dihydric alcohol or dibasic acid into a polar group-containing diol or polar group-containing dibasic acid when producing the polyol. Examples of the polar group-containing diol include sulfo (iso or tere) phthalic acid (Na or K).
EO (ethylene oxide) adduct, PO
Examples include (propylene oxide) adducts, EO adducts of sulfamic acids such as aminoethanesulfonic acid, and PO adducts. Examples of polar group-containing dibasic acids include 5-sodium sulfoisophthalic acid, Examples thereof include potassium sulfoisophthalic acid, 5-sulfoisophthalic acid, 2-sodium sulfoterephthalic acid, 2-potassium sulfoterephthalic acid, and 2-sulfoterephthalic acid.

The above polyester polyol is, for example,
Examples thereof include those obtained by polycondensation of a dihydric alcohol and a dibasic acid, and those obtained by ring-opening polymerization of lactones, for example, caprolactone. Representative dihydric alcohols include ethylene glycol, propylene glycol, butanediol, 1,6-hexanediol,
Glycols such as cyclohexanedimethanol can be exemplified. In addition, typical dibasic acids include adipic acid, pimelic acid, azelaic acid, sebacic acid, phthalic acid, terephthalic acid, and the like.

The polycarbonate polyol is prepared by condensation or transesterification of a polyhydric alcohol with phosgene, chloroformate, dialkyl carbonate or diallyl carbonate.
0000, a polycarbonate polyol having a hydroxyl value of 200 to 300, or 2
Molecular weight 400 to 3 obtained by condensation with a polyvalent carboxylic acid
0000, a polycarbonate polyester polyol having a hydroxyl value of 5 to 300.

Examples of the polyether polyol include polyethylene oxides such as bisphenol A, hydrogenated bisphenol A, bisphenol S, and bisphenol P and / or adducts of polypropylene oxide, and molecular weights of 500 to 500 such as polypropylene glycol, polyethylene glycol, and polytetramethylene glycol. 5000
Can be used.

As the polyol, bisphenol A,
Polyether polyols containing hydrogenated bisphenol A and their ethylene oxide and propylene oxide adducts and containing ether groups in the range of 25% by mass to 45% by mass, more preferably 30% by mass to 40% by mass are preferred. If the amount is less than 25% by mass, the solubility in a solvent is reduced, so that the dispersibility is reduced. If it exceeds 45% by mass, the strength of the coating film is reduced, so that the durability is reduced. Other polyols may be blended with the above polyol up to 90% by mass of the above polyol and used in combination.

The polyisocyanate used for forming the polyurethane by reacting with the above-mentioned polyol is not particularly limited, and those generally used can be used. For example, hexamethylene diisocyanate, tolidine diisocyanate, isophorone diisocyanate, 1,3-xylylene diisocyanate, 1,4
-Xylylene diisocyanate, cyclohexane diisocyanate, toluidine diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4'-diphenylmethane diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1,5-naphthalene Examples thereof include diisocyanate and 3,3-dimethylphenylene diisocyanate.

As the chain extender, substances known per se, polyhydric alcohols, aliphatic polyamines, alicyclic polyamines, aromatic polyamines and the like can be used. Among them, polyhydric alcohols having a molecular weight of 50 to 500 are preferable. If it is less than 50, the coating film becomes brittle and the durability is reduced. If it is 500 or more, the Tg of the coating film decreases, and the coating film becomes soft, so that the durability decreases. Examples of polyhydric alcohols include bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P and their ethylene oxide, propylene oxide adducts, cyclohexanedimethanol, cyclohexanediol, hydroquinone, bis (2-hydroxyethyl) tetrabromobispheno- A, screw (2-
(Hydroxyethyl) tetrabromobisphenol S, bis (2-hydroxyethyl) tetramethylbisphenol-
S, bis (2-hydroxyethyl) diphenylbisphenol S, bis (2-hydroxyethyl) diphenylbiphenol, bis (2-hydroxyethyl) thiodiphenol, bis (2-hydroxyethyl) bisphenol-
Short-chain diols having a cyclic structure, such as F, biphenol, bisphenol fluorene, and bisphenol fluorene hydroxyethyl ether, are preferred. More preferred are aromatic and alicyclic diols such as bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P, and their ethylene oxide, propylene oxide adducts, cyclohexane dimethanol, and cyclohexane diol.

The average molecular weight of the polar group-containing polyurethane resin used in the present invention is preferably 5,000 to 100,000. More preferably, it is 10,000 to 50,000. 5
If it is less than 000, the resulting magnetic layer and the lower layer become brittle and the physical strength is reduced, which affects the durability of the magnetic recording medium. When the molecular weight exceeds 100,000, the solubility in a solvent decreases, and the dispersibility decreases. Further, the viscosity of the paint at a predetermined concentration becomes high, so that workability is remarkably deteriorated and handling becomes difficult.

The OH group of the polar group-containing polyurethane resin used in the present invention preferably has a branched OH group in terms of curability and durability, and preferably has two or more OH groups per molecule.
The number is preferably 40, and more preferably 3 to 20 per molecule.

Other binders used in the present invention include:
Along with the above-mentioned polar group-containing vinyl chloride resin and polar group-containing polyurethane resin, a binder having another polar group may be used in an amount equal to or less than the total amount of these. Other resins that can be used in combination are not particularly limited, and known thermoplastic resins, thermosetting resins, reactive resins, and mixtures thereof, which are conventionally used as binders for magnetic recording media, can be used. In particular,
As a thermoplastic resin, the glass transition temperature is -100 to 1
50 ° C., number average molecular weight of 1,000 to 200,000, preferably 10,000 to 100,000, and degree of polymerization of 50 to 10
It is about 00. Examples of such a polymer include acrylic acid, acrylic acid ester, vinylidene chloride, acrylonitrile, methacrylic acid, methacrylic acid ester, styrene, butadiene, ethylene, vinyl butyral, vinyl acetal, a polymer containing vinyl ether, and the like as constituent units, and copolymers. There are coalescing, polyurethane resin and various rubber resins. In addition, as the thermosetting resin or the reactive resin, phenol resin, phenoxy resin, epoxy resin,
Examples include urea resins, melamine resins, alkyd resins, acrylic reaction resins, formaldehyde resins, silicone resins, epoxy-polyamide resins, and mixtures of polyester resins and isocyanate prepolymers.

In the magnetic recording medium of the present invention, when a polar group-containing vinyl chloride resin and a polar group-containing polyurethane resin are used in combination, the polar group-containing polyurethane resin 100
It is preferred to use 0 to 800 parts by mass of the polar group-containing vinyl chloride resin based on parts by mass.

It is also possible to use a polyisocyanate as a crosslinking agent in the binder to improve the abrasion resistance and the like of the magnetic layer. Examples of the polyisocyanate that can be used as a crosslinking agent include tolylene diisocyanate, 4,4 ′
Diisocyanates such as diphenylmethane diisocyanate, hexamethylene diisocyanate, xylylene diisocyanate, naphthylene-1,5-diisocyanate, o-toluidine diisocyanate, isophorone diisocyanate, triphenylmethane triisocyanate, and the formation of these isocyanates and polyalcohols Products, and polyisocyanates formed by condensation of isocyanates can be used.
Commercially available trade names of these isocyanates include Nippon Polyurethane Co., Ltd., Coronate L, Coronate HL, Coronate 2030, Coronate 2031, Millionate MR, Millionate MTL, Takeda Pharmaceutical Co., Ltd.
Takenate D-102, Takenate D-110N, Takenate D-200, Takenate D-202, manufactured by Sumitomo Bayer, Desmodur L, Desmodur IL, Desmodur N, Desmodur HL, etc. These are used alone. Alternatively, each layer can be used in combination of two or more utilizing the difference in curing reactivity.

V. Other Additives In the magnetic recording medium of the present invention, additives for imparting a lubricating effect, an antistatic effect, a dispersing effect, a plasticizing effect and the like may be used in the magnetic layer or the lower layer. These additives include molybdenum disulfide, tungsten disulfide, graphite, boron nitride, graphite fluoride, silicone oil, polar group-containing silicone, fatty acid-modified silicone,
Fluorine-containing silicone, fluorine-containing alcohol, fluorine-containing ester, polyolefin, polyglycol, alkyl phosphate and its alkali metal salt, alkyl sulfate and its alkali metal salt, polyphenyl ether, fluorine-containing alkyl sulfate and its alkali metal salt A monobasic fatty acid which may contain or be branched to an unsaturated bond having 10 to 24 carbon atoms, and a metal salt thereof (such as Li, Na, K or Cu) or an unsaturated bond having 12 to 22 carbon atoms 1 to 6 alcohols which may contain or be branched, alkoxy alcohols which may contain or have an unsaturated bond having 12 to 22 carbon atoms,
Any one of a monobasic fatty acid which may contain or branch an unsaturated bond having 10 to 24 carbon atoms and a 1 to 6 alcohol which may contain or branch an unsaturated bond having 2 to 12 carbon atoms Mono- or di-fatty acid esters or tri-fatty acid esters, fatty acid esters of monoalkyl ethers of alkylene oxide polymers, fatty acid amides having 2 to 22 carbon atoms, and aliphatic amines having 8 to 22 carbon atoms can be used.

Specific examples thereof include lauric acid, myristic acid, palmitic acid, stearic acid, behenic acid, butyl stearate, oleic acid, linoleic acid, linolenic acid, elaidic acid, octyl stearate, amyl stearate, and stearic acid. Isooctyl, octyl myristate, butoxyethyl stearate, anhydrosorbitan monostearate, anhydrosorbitan distearate, anhydrosorbitan tristearate, oleyl alcohol and lauryl alcohol.

Further, nonionic surfactants such as alkylene oxide, glycerin, glycidol, and alkylphenol ethylene oxide adducts, cyclic amines,
Ester amides, quaternary ammonium salts, hydantoin derivatives, heterocyclics, cationic surfactants such as phosphonium or sulfoniums, and acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, and phosphate group. Included are anionic surfactants, amino acids, aminosulfonic acids, sulfuric acid or phosphate esters of amino alcohols, and amphoteric surfactants such as alkyl betaine type. These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents and the like are not necessarily pure and may contain impurities such as isomers, unreacted products, by-products, decomposition products, oxides, etc. in addition to the main components. These impurities are preferably at most 30% by mass, more preferably at most 10% by mass.

The type and amount of these lubricants and surfactants used in the present invention can be properly used for the lower layer and the magnetic layer as required. For example, the lower layer and the magnetic layer control the bleeding to the surface using fatty acids with different melting points, control the bleeding to the surface using esters with different boiling points and polarities, and adjust the amount of surfactant to apply. It can be considered to improve the stability of the resin and to improve the lubricating effect by increasing the amount of the lubricant added in the lower layer, and it is needless to say that the present invention is not limited to only the examples shown here. Further, all or a part of the additives used in the present invention may be added in any step of producing a coating solution for the magnetic layer or the lower layer.
For example, when mixing with ferromagnetic powder before the kneading step, when adding in the kneading step with ferromagnetic powder, binder and solvent,
There are a case where it is added in the dispersion step, a case where it is added after the dispersion, and a case where it is added just before the application.

Specific examples of these lubricants used in the present invention include NAA-102, castor oil-hardened fatty acid, NAA-42, cation SA, Nymeen L-201, Nonion E-208, manufactured by NOF Corporation. Anon BF, Anone LG, butyl stearate, butyl laurate, erucic acid, manufactured by Kanto Kagaku: oleic acid, manufactured by Takemoto Yushi: FA
L-205, FAL-123, Nippon Rika Co., Ltd .: Nujierubu OL, Shin-Etsu Chemical Co., Ltd .: TA-3, Lion Armor Co .: Armide P, Lion Co., Ltd., Duomin TD
O, manufactured by Nisshin Oil Co., Ltd .: BA-41G, manufactured by Sanyo Kasei Co., Ltd .: Profan 2012E, New Pole PE61, Ionnet MS-400, and the like.

VI. Support The coating solution prepared from the above materials is coated on a support to form a lower layer or a magnetic layer. As the support that can be used in the present invention, a known support such as biaxially stretched polyethylene terephthalate, polyethylene naphthalate, polyamide, polyimide, polyamideimide, aromatic polyamide, and polybenzoxdazole can be used. Preferred are polyethylene terephthalate, polyethylene naphthalate and aromatic polyamide. These supports may be subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, or the like in advance. Further, the support which can be used in the present invention has a center plane average surface roughness by the Mirau method of 0.2 mm at a cutoff value of 0.25 mm.
The surface preferably has excellent smoothness in the range of 1 to 20 nm, preferably 1 to 10 nm. Also,
These supports preferably have not only a small center line average surface roughness but also no coarse projections of 1 μ or more.

The arithmetic mean roughness of the obtained support is (R
a) [JIS B0660-1998, ISO 4
287-1997] is preferably 0.1 μm or less, since noise of the obtained magnetic recording medium is reduced.

The thickness of the support in the magnetic recording medium of the present invention is preferably 3 to 80 μm.

VII. Backcoat layer and undercoat layer A backcoat layer (backing layer) may be provided on the surface of the support used in the present invention where the magnetic layer is not provided. The back coat layer was provided by applying a back coat layer forming paint in which a particulate component such as an abrasive and an antistatic agent and a binder were dispersed in an organic solvent on the surface of the support on which the magnetic layer was not provided. Layer. Various inorganic pigments and carbon black can be used as the particulate component, and resins such as nitrocellulose, phenoxy resin, vinyl chloride resin, and polyurethane can be used alone or as a mixture of these as a binder. . An adhesive layer may be provided on the surface of the support of the present invention on which the magnetic paint and the backcoat layer forming paint are applied.

In the magnetic recording medium of the present invention,
An undercoat layer may be provided. By providing the undercoat layer, the adhesive strength between the support and the magnetic layer or the lower layer can be improved. As the undercoat layer, a polyester resin soluble in a solvent is used. The undercoat layer has a thickness of 0.5
Those having a size of μm or less are used.

VIII. Manufacturing Method The magnetic recording medium of the present invention is manufactured, for example, by applying a lower layer coating solution and a magnetic layer coating solution to the surface of a running support so as to have a predetermined thickness. Here, a plurality of magnetic layer coating solutions may be sequentially or simultaneously multi-layer coated,
The lower layer coating solution and the magnetic layer coating solution may be sequentially or simultaneously multi-layer coated. As a coating machine for applying the magnetic layer coating solution or the lower layer coating solution, air doctor coat, blade coat, rod coat, extrusion coat, air knife coat, squeeze coat, impregnation coat, reverse roll coat, transfer roll coat, gravure coat, Kiss coat, cast coat, spray coat, spin coat and the like can be used. For these, for example, "Latest Coating Technology" (May 31, 1983) published by Sogo Gijutsu Center can be referred to.

When applied to the magnetic recording medium of the present invention, the following can be proposed as an example of a coating apparatus and method. (1) First, a lower layer is applied by a coating apparatus such as gravure, roll, blade, or extrusion which is generally applied in the application of a magnetic layer coating liquid, and the lower layer is dried while the lower layer is in an undried state. No., JP-A-60-23
The upper layer is applied by a support pressure type extrusion coating apparatus as disclosed in JP-A-8179, JP-A-2-265672 and the like. (2) JP-A-63-88080, JP-A-2-1
No. 7971 and Japanese Unexamined Patent Publication No. 2-265672 disclose the upper and lower layers almost simultaneously by one coating head having two coating liquid passage slits. (3) The upper and lower layers are coated almost simultaneously by an extrusion coating device with a backup roll as disclosed in JP-A-2-174965.

The thickness of the magnetic layer of the magnetic recording medium according to the present invention depends on the saturation magnetization of the head used, the head gap length,
Optimized according to the recording signal bandwidth, 0.01-0.5μ
m, when the magnetic layer contains a ferromagnetic metal powder, the thickness of the magnetic layer is preferably 0.01 to 0.1 μm, and when the magnetic layer contains a ferromagnetic hexagonal ferrite powder, Is preferably 0.01 to 0.2 μm. The magnetic layer may be separated into two or more layers having different magnetic characteristics, and a known configuration relating to a multilayer magnetic layer can be applied. When a plurality of magnetic layers are provided, the thickness of the magnetic layer
It is the thickness of each magnetic layer.

In order to stably apply this ultra-thin magnetic layer, a lower layer containing an inorganic powder is interposed on a support,
It is desirable to apply a magnetic layer thereon on a wet-on-wet basis.

In the case of a magnetic tape, the ferromagnetic powder contained in the coating layer of the magnetic layer coating solution is subjected to a magnetic field orientation treatment in the longitudinal direction using a cobalt magnet or a solenoid. In the case of a disk, a sufficient isotropic orientation may be obtained even without orientation using an orientation device, but known random orientation such as alternately arranging cobalt magnets diagonally or applying an AC magnetic field with a solenoid. Preferably, an apparatus is used. In the case of ferromagnetic metal fine powder, isotropic orientation is generally preferably in-plane two-dimensional random,
Three-dimensional randomness can be obtained by adding a vertical component. In the case of ferromagnetic hexagonal ferrite powder, three-dimensional randomness in the in-plane and vertical directions generally tends to occur, but in-plane two-dimensional randomness is also possible. In addition, by using a known method such as a different-magnet opposed magnet and performing vertical alignment, it is also possible to impart isotropic magnetic characteristics in the circumferential direction.
In particular, when performing high-density recording, vertical alignment is preferable. In addition, circumferential orientation may be performed using spin coating.

It is preferable that the drying position of the coating film can be controlled by controlling the temperature, air volume, and coating speed of the drying air. The coating speed is 20 m / min to 1000 m / min, and the temperature of the drying air is 60 ° C. The above is preferred. Also, an appropriate preliminary drying can be performed before entering the magnet zone.

After being dried, the coating layer is subjected to a surface smoothing treatment. For the surface smoothing treatment, for example, a super calender roll or the like is used. By performing the surface smoothing treatment, pores generated by removing the solvent during drying disappear, and the filling ratio of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium with high electromagnetic conversion characteristics can be obtained. Can be. For calendering rolls, epoxy, polyimide,
Heat-resistant plastic rolls such as polyamide and polyamide-imide can be used. Moreover, it can also process with a metal roll. The magnetic recording medium of the present invention has a surface M
The center plane average surface roughness by the irau method is 0.1 to 4 nm at a cutoff value of 0.25 mm, preferably 1 to 4 nm.
It is preferable that the surface has an extremely excellent smoothness in the range of 3 nm. As a method for this, for example, a magnetic layer formed by selecting a specific ferromagnetic powder and a binder as described above is subjected to the above calendering treatment. The calendering conditions are as follows: the temperature of the calender roll is in the range of 60 to 100 ° C., preferably 70 to 100 ° C., particularly preferably 80 to 100 ° C., and the pressure is 100 to 500 kg / cm (98 to 490 kN). / M)
, Preferably 200 to 450 kg / cm
(196 to 441 kN / m), particularly preferably 300 to 400 kg / cm (294 to 392 kN / m).
m). The obtained magnetic recording medium can be used after being cut into a desired size using a cutting machine or the like.

[0100]

The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples. In the examples, “parts” indicates “parts by mass” unless otherwise specified.

Example 1 Preparation of Coating Solution for Magnetic Layer 100 parts of ferromagnetic needle-shaped metal powder Composition: Fe / Co / Al / Y = 68/20/7/5, Surface treatment layer: Al ₂ O ₃ , Y ₂ O ₃ , Hc: 2500 Oe (200 kA / m), crystallite size: 14 nm, average major axis length: 0.08 μm, average needle ratio: 6, BET specific surface area: 46 m ² / g, σs: 150 A · m ² / Kg polyurethane resin 12 parts (UR8200: Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin) Vinyl chloride resin 6 parts (MR110: Nippon Zeon, sulfonic acid group-containing vinyl chloride resin) Benzylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle diameter: 0.15 [mu] m) 2 parts carbon black (average particle size: 20 nm) 2 parts cyclohexanone 110 parts Methyl ethyl ketone 100 parts toluene 10 Parts Butyl stearate 2 parts 1 part of stearic acid

Preparation of lower layer coating liquid Non-magnetic inorganic powder 85 parts α-iron oxide Surface treatment agent: Al ₂ O ₃ , SiO ₂ , average major axis length: 0.15 μm, tap density: 0.8, average needle ratio : 7, BET specific surface area: 52 m ² / g, pH 8, DBP oil absorption: 33 ml / 100 g Carbon black 20 parts DBP oil absorption: 120 ml / 100 g, pH: 8, BET specific surface area: 250 m ² / g, volatile matter: 1 0.5% polyurethane resin 12 parts (UR8200: manufactured by Toyobo Co., Ltd., sulfonic acid group-containing polyurethane resin) Vinyl chloride resin 6 parts (MR110: manufactured by Zeon Corporation, sulfonic acid group-containing vinyl chloride resin) benzylphosphonic acid 3 parts α- Al ₂ O ₃ (average particle size 0.2 μm) 1 part Monolauryl phosphate 3 parts Cyclohexanone 140 parts Methyl ethyl ketone 170 parts Allate 2 parts Stearic acid 1 part

For each of the above-mentioned magnetic layer coating solution and lower layer coating solution composition, each component was treated with an open kneader to 60 parts.
After kneading for 120 minutes, the mixture was dispersed in a sand mill for 120 minutes. To the obtained dispersion, 6 parts of a trifunctional low-molecular-weight polyisocyanate compound (Coronate 3041 manufactured by Nippon Polyurethane) was added, and the mixture was further stirred and mixed for 20 minutes, and then filtered using a filter having an average pore diameter of 1 μm to coat the magnetic layer. A liquid and a lower layer coating liquid were prepared.

The thickness is 6 μm and the average central surface roughness is 5 nm.
On the polyethylene terephthalate support of the above, the lower layer coating solution was applied so that the thickness after drying was 1.8 μm,
Immediately thereafter, the thickness of the dried magnetic layer coating solution was 0.0
Coating was performed simultaneously to form an 8 μm layer. In a state where both layers are not dried, a magnetic field orientation is performed with a magnet of 300 mT, and after drying, a speed of 100 m / min and a linear pressure of 300 kg / cm (29
4 kN / m) and a surface smoothing treatment at a temperature of 90 ° C., followed by a heat curing treatment at 70 ° C. for 24 hours to 3.8 mm
A slit was made to the width to make a magnetic tape.

Examples 2 to 10 In the same manner as in Example 1 except that the organophosphorus compound was changed as shown in Table 1, Example 2 was used.
To 10 magnetic tapes were prepared.

Example 11 A floppy disk was prepared using the same lower layer coating solution as in Example 1 except that the magnetic material was changed as described below. Preparation of Magnetic Layer Coating Solution Ferromagnetic plate-like hexagonal ferrite powder 100 parts Composition (molar ratio): Ba / Fe / Co / Zn = 1 / 9.1 / 0.2 / 0.8, Hc: 2450 Oe (195 kA / m), average plate diameter: 35 nm, average plate ratio: 4, BET specific surface area: 50 m ² / g, σs: 60 A · m ² / kg 12 parts of polyurethane resin (UR8200: manufactured by Toyobo, sulfonic acid group-containing polyurethane resin ) Vinyl chloride resin 6 parts (MR110: a sulfonic acid group-containing vinyl chloride resin manufactured by Zeon Corporation) Benzylphosphonic acid 3 parts α-Al ₂ O ₃ (average particle diameter: 0.15 μm) 2 parts Carbon black (average particle) Diameter: 20 nm) 2 parts Cyclohexanone 110 parts Methyl ethyl ketone 100 parts Toluene 100 parts Butyl stearate 2 parts Stearic acid 1 part

A magnetic layer coating solution was prepared in the same manner as in Example 1 using each component of the magnetic layer coating solution composition. On a polyethylene terephthalate support having a thickness of 62 μm and a center plane average surface roughness of 5 nm, the same lower layer coating solution as in Example 1 was applied to a thickness of 1.5 μm after drying, and immediately thereafter. The thickness of the magnetic layer coating solution after drying is 0.
A simultaneous multi-layer coating was performed so that the thickness became 08 μm, and while both layers were still in a wet state, a frequency of 50 Hz and a magnetic field intensity of 2 were applied.
5 mT, frequency 50 Hz, and 12 mT are passed through an AC magnetic field generator for random orientation treatment. After drying, the temperature is increased to 90 ° C. and a linear pressure of 300 kg / cm (294 kN / m) using a 7-stage calender. Process
After punching into a 3.7-inch and subjecting to a surface polishing treatment, the liner is placed in a 3.7-inch Zip-disk cartridge with a liner installed inside, and predetermined mechanical components are added, and a 3.7-inch floppy (registered trademark) is added. ) I got a disc.

[Examples 12 to 20] Table 2 shows the organic phosphorus compounds.
And the floppy disks of Examples 12 to 20 were prepared in the same manner as in Example 11.

Comparative Examples 1 to 5 Magnetic tapes of Comparative Examples 1 to 5 were prepared in the same manner as in Example 1 except that the magnetic substance and the organic phosphorus compound were changed as shown in Table 1.

Comparative Examples 6 to 8 Floppy disks of Comparative Examples 6 to 8 were prepared in the same manner as in Example 11, except that the magnetic substance and the organic phosphorus compound were changed as shown in Table 2.

[Measurement Method] Magnetic properties (Hc): Vibration sample type magnetometer (Toei Kogyo Co., Ltd.)
And measured at Hm10 kOe (800 kA / m).

Magnetic layer thickness: A magnetic recording medium was cut out to a thickness of about 0.1 μm with a diamond cutter along the longitudinal direction, and the transmission electron microscope was used to magnify 10,000 to 1,000 times.
The photograph was observed at a magnification of 00, preferably 20,000 to 50,000, and photographed. Photo print size is A
4-A5. Thereafter, the interface was visually judged by focusing on the shape difference between the surface of the magnetic layer, the magnetic layer, and the lower layer of the ferromagnetic powder and the non-magnetic powder. Thereafter, the length of the cut line was measured by an image processing apparatus IBAS2 manufactured by Zeiss. If the length of the sample photograph is 21 cm, measure
It was performed 00 times. The average of the measured values at that time was defined as the magnetic layer thickness.

Error rate (initial, after storage): 2
At 3 ° C. and 50% RH, 8-10 for tape-shaped media
It is recorded on a tape by the conversion PR1 equalization method, and measured using a DDS drive.
The data was recorded on a disk by the modulation method and measured. 50 ° C,
After storing at 80% RH for 1 week, the error rate was measured in the same manner.

[0114]

[Table 1]

[0115]

[Table 2] As is clear from Tables 1 and 2, the magnetic recording medium according to the present invention has a stable and low error rate.

[0116]

According to the present invention, a lower layer containing a nonmagnetic powder is provided on a support, and an average major axis length of 0.1 μm is further provided thereon.
0.5 μm in thickness containing ferromagnetic metal fine powder of less than m or ferromagnetic hexagonal ferrite fine powder of less than 40 nm in average plate diameter
m, the use of an organophosphorus compound having a specific structure in the magnetic layer improves the smoothness of the coating film, the electromagnetic conversion characteristics, the surface of the magnetic layer is hardly scraped, and the head dirt is reduced. It is possible to provide a magnetic recording medium in which the storage stability is greatly improved, the increase in error rate is small, the running durability is excellent, and the surface smoothness of the magnetic recording medium is excellent, so that a low error rate can be stably obtained. .

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4J038 CD021 DG001 GA06 GA13 GA14 HA066 HA166 JC21 KA08 KA09 NA17 NA22 PB11 PC08 5D006 BA05 BA06 BA08 BA09 DA02 FA02 FA05 FA09

Claims (1)

[Claims] 1. A lower layer containing a non-magnetic powder and a binder is provided on a support, on which an average major axis length of 0.01 μm to 0.1 μm is provided.
At least one magnetic layer containing a ferromagnetic metal powder having a crystallite size of 80 to 180 ° or a ferromagnetic hexagonal ferrite powder having an average plate diameter of 5 to 40 nm and a binder is provided, and the thickness of the magnetic layer is 0.01 μm to 0.5
μm, and the following formulas (1) to (4)
A magnetic recording medium comprising an organic phosphorus compound represented by the formula: (R ¹ ) _n -P (= O) (OH) _3-n (1) (R ¹ -O) _n -P (= O) (OH) _3-n (2) [(R ² ) _m -φ _{] n -P (= O) (} OH) 3-n (3) [(R 2) m -φ-O] n -P (= O) (OH) 3-n (4) wherein, R ¹ is , an aralkyl group having an alkyl chain of 1 to 4 carbon atoms, an aryl group substituted with an alkyl group having 3 to 20 carbon atoms, or represent straight-chain or branched alkyl group having 8 to 20 carbon atoms, R ² is aralkyl Represents an aryl group or an aryl group, φ represents a benzene ring, m = 1 to 5, n = 1,
Represents an integer of 2.