JP2002334416A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium with excellent coating smoothness and an excellent electromagnetic conversion characteristic and having excellent traveling durability. SOLUTION: The magnetic recording medium is provided with at least one magnetic layer containing ferromagnetic powder and a binder on a nonmagnetic supporting body. The ferromagnetic powder is an acicular magnetic material with the long axis length in 10-100 nm range or a tabular magnetic material with the diameter of the tablet in 10-50 nm range. Furthermore, the binder contains a polyether urethane with the weight-average molecular weight in 1,500-25,000 range and with a polar group.

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 having excellent dispersibility, durability and electromagnetic characteristics.

[0002]

2. Description of the Related Art A magnetic recording medium widely used as a recording tape, a video tape, a floppy (registered trademark) disk or the like includes a magnetic layer in which a ferromagnetic powder is dispersed in a binder, and a nonmagnetic support. It is configured by being laminated on top. The magnetic recording medium is required to be at a high level in various characteristics such as electromagnetic conversion characteristics, running durability and running performance.

In order to obtain excellent electromagnetic conversion characteristics and running durability, for example, Japanese Unexamined Patent Application Publication No. 11-259850 discloses a method of combining a fine particle metal magnetic material as a large-capacity and high-recording-density coating type magnetic recording medium. There has been proposed a medium in which a thin magnetic layer dispersed with an agent is provided on a non-magnetic layer, but in order to improve the electromagnetic conversion characteristics and running durability of a magnetic recording medium, a magnetic material of fine particles is further required. It is considered effective to use the magnetic layer having high surface smoothness.

[0004] However, extremely fine magnetic particles have poor dispersibility and tend to aggregate, so it has been difficult to form a smooth magnetic layer with a conventional binder. Further, there is a problem that the magnetic material having extremely fine particles has poor dispersion stability, and the magnetic material is agglomerated with the lapse of time after the dispersion, the viscosity of the coating solution is increased, and it is not possible to apply the film uniformly and thinly.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a magnetic recording medium having excellent coating smoothness and electromagnetic conversion characteristics and excellent running durability.

[0006]

The present inventors have further studied by using a polyether polyurethane having a polar group having a polymerization average molecular weight in the range of 1500 to 25000 as a binder for a magnetic layer. It has been found that an extremely fine-particle magnetic material, that is, a needle-shaped magnetic material having a major axis length in a range of 10 nm to 100 nm, or a flat magnetic material having a plate diameter of 10 to 50 nm can be satisfactorily dispersed. The present invention has been completed.

That is, an object of the present invention is to provide (1) a magnetic recording medium having at least one magnetic layer containing a ferromagnetic powder and a binder on a nonmagnetic support,
The ferromagnetic powder is a needle-shaped magnetic material having a major axis length in a range of 10 nm to 100 nm or a plate-shaped magnetic material having a plate diameter of 10 to 50 nm, and the binder has a weight average molecular weight of 1500. This is achieved by a magnetic recording medium characterized by comprising a polyether polyurethane having a polar group in the range of の 25,000.

[0008] Preferred embodiments of the present invention are as follows. (2) A magnetic recording medium having a magnetic layer containing at least one ferromagnetic powder and a binder on a non-magnetic support via a lower non-magnetic layer, wherein the thickness of the magnetic layer is 0.5 μm
Wherein the ferromagnetic powder has a major axis length of 10 nm to 1
Needle-shaped magnetic material having a diameter of 10 nm or a plate diameter of 10 to 50
A magnetic recording medium which is a plate-shaped magnetic material having a thickness in the range of nm, and wherein the binder comprises a polyether polyurethane having a polar group and having a weight average molecular weight in the range of from 1500 to 25,000. (3) The polyether polyurethane of (1) or (2) is composed of a polyether polyurethane which is a reaction product mainly containing a diol and an organic diisocyanate,
The polyether polyurethane contains a short-chain diol having a cyclic structure in an amount of 17 to 40% by weight, and has an ether group of 1.0 to 5.0 m with respect to the entire polyether polyurethane.
A magnetic recording medium characterized in that a polyether polyurethane contains 10 to 50% by weight of a long chain diol containing mol / g.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the magnetic recording medium of the present invention will be described in more detail. In the present invention, a magnetic recording material having excellent electromagnetic conversion characteristics and running durability is obtained by highly dispersing a very fine magnetic material having a low dispersibility with a binder made of polyether polyurethane having a high molecular weight and a high adsorptivity. Medium can be obtained. [Magnetic Material] The ferromagnetic powder used in the magnetic layer of the present invention is a needle-shaped magnetic material having a major axis length in the range of 10 to 100 nm, or a flat magnetic material having a plate diameter of 10 to 50 nm. . Acicular magnetic body When the ferromagnetic powder used in the magnetic layer of the present invention is an acicular magnetic body, its major axis length is 10 nm to 100 nm,
Preferably 20-90 nm, more preferably 30-80
nm. If the major axis length is less than 10 nm, it is not possible to obtain a magnetic material having a sufficient saturation magnetization σs due to thermal fluctuation, and if the major axis length exceeds 100 nm, the coating film smoothness and electromagnetic conversion characteristics deteriorate. However, the strength of the coating film also decreases.

As the acicular magnetic material used in the magnetic layer of the present invention, a ferromagnetic alloy powder containing α-Fe as a main component is preferable. In these ferromagnetic alloy powders, A
1, Si, S, Sc, Ca, Ti, V, Cr, Cu,
Y, Mo, Rh, Pd, Ag, Sn, Sb, Te, B
a, Ta, W, Re, Au, Hg, Pb, Bi, La,
Ce, Pr, Nd, P, Co, Mn, Zn, Ni, S
It may contain atoms such as r and B. In particular, Al,
Preferably, at least one of Si, Ca, Y, Ba, La, Nd, Co, Ni, and B is contained in addition to α-Fe,
More preferably, it contains at least one of Co, Y, and Al. The Co content is preferably from 0 to 40 at%, more preferably from 15 to 35 at%, even more preferably from 20 to 35 at%. Y
Is preferably 1.5 to 12 atomic%, more preferably 3 to 10 atomic%, and still more preferably 4 to 9 atomic%. Al is 5
At least 30 at%, more preferably at least 5 at% and at most 15 at%, more preferably at least 7 at%.
Not less than 12 atomic%. These ferromagnetic powders may be preliminarily treated with a dispersant, a lubricant, a surfactant, an antistatic agent or the like before dispersion before dispersion. Specifically, Japanese Patent Publication No. 44-14090, Japanese Patent Publication No. 45
No. 18372, Japanese Patent Publication No. 47-22062,
JP-B-47-22513, JP-B-46-2846
No. 6, JP-B-46-38755, JP-B-47
-4286, JP-B-47-12422, JP-B-47-17284, JP-B-47-18509.
JP, JP-B-47-18573, JP-B-39-
No. 10307, Japanese Patent Publication No. 46-39639, U.S. Pat. Nos. 3,026,215, 3,303,341 and 3,
No. 100194, No. 3242005, No. 338901
No. 4, etc.

[0011] The ferromagnetic alloy powder may contain a small amount of hydroxide or oxide. A ferromagnetic alloy powder obtained by a known production method can be used, and the following method can be used. A method of reducing a complex organic acid salt (mainly oxalate) with a reducing gas such as hydrogen, reducing iron oxide with a reducing gas such as hydrogen to reduce Fe or F
a method of obtaining e-Co particles or the like, a method of thermally decomposing a metal carbonyl compound, a method of adding a reducing agent such as sodium borohydride, hypophosphite or hydrazine to an aqueous solution of a ferromagnetic metal to reduce the metal, And evaporating in a low-pressure inert gas to obtain fine powder. The ferromagnetic alloy powder thus obtained is subjected to a known slow oxidation treatment, that is, a method of immersing in an organic solvent and then drying, and immersing in an organic solvent and then feeding an oxygen-containing gas to form an oxide film on the surface and drying. Any of the methods of forming an oxide film on the surface by adjusting the partial pressure of oxygen gas and inert gas without using an organic solvent can be used.

When the ferromagnetic alloy powder is expressed by a specific surface area by the BET method, it is 45 to 80 m ² / g, preferably 50 to 80 m ² / g.
Suitably, it is ７０70 m ² / g. When it is 45 m ² / g or more, noise is reduced, and when it is 80 m ² / g or less, surface properties are good and preferable. The crystallite size of the ferromagnetic alloy powder is 350-80 °, preferably 250-10
It is suitable that the angle is 0 °, more preferably 200 to 140 °. The major axis diameter of the ferromagnetic alloy powder is 10 nm or more and 1
00 nm or less, preferably 20 μm or more and 90 μm
It is appropriate that: The needle ratio of the ferromagnetic alloy powder is preferably 3 or more and 15 or less, and more preferably 5 or more and 12 or less. The s of the ferromagnetic alloy powder is 100 to 180A
m ² / g (100 to 180 emu / g), preferably 110 to 170 Am · m ² / g (110 emu / g to 110 emu / g).
170 emu / g), more preferably 125 to 160
Is suitably an ^{A · m 2 / g (125~160emu} / g). The coercive force of the ferromagnetic alloy powder is 111 to 27
9 kA / m (1400-3500 Oe) is preferable, and 143-239 kA / m (1800-30) is more preferable.
00 Oe) is appropriate.

The water content of the ferromagnetic alloy powder is 0.01 to 2%.
It is preferable that It is preferable to optimize the water content of the ferromagnetic alloy powder depending on the type of the binder. It is preferable that the pH of the ferromagnetic alloy powder be optimized depending on the combination with the binder used. Its range is from 4 to 12, preferably from 6 to 10. The ferromagnetic alloy powder may be subjected to a surface treatment with Al, Si, P, or an oxide thereof, if necessary. The amount thereof is 0.1 to 10% based on the ferromagnetic alloy powder, and it is preferable that the surface treatment is performed because the adsorption of a lubricant such as a fatty acid becomes 100 mg / m ² or less.
Ferromagnetic alloy powder contains soluble Na, Ca, Fe, Ni,
It may contain an inorganic ion such as Sr. It is preferable that these are essentially absent, but if they are 200 ppm or less, they do not particularly affect the characteristics. The ferromagnetic alloy powder used in the present invention preferably has a small number of pores, and the value is preferably 20% by volume or less, more preferably 5% by volume or less. The shape may be any of a needle shape, a rice grain shape, and a spindle shape as long as the characteristics of the particle size described above are satisfied. The SFD of the ferromagnetic alloy powder itself is preferably small, and is preferably 0.8 or less. It is necessary to reduce the distribution of Hc in the ferromagnetic alloy powder. In addition, SFD
Is 0.8 or less, the electromagnetic conversion characteristics are good, the output is high, the magnetization reversal is sharp and the peak shift is small, and this is suitable for high-density digital magnetic recording. In order to reduce the distribution of Hc, there are methods of improving the particle size distribution of goethite in ferromagnetic alloy powder, preventing sintering, and the like.

[Flat Plate Magnetic Material] When the ferromagnetic powder used in the magnetic layer of the present invention is a plate magnetic material, the plate diameter is 1
It is 0 to 50 nm, preferably 15 to 40 nm, and more preferably 20 to 35 nm. When reproducing with a magnetoresistive head, it is necessary to reduce noise, and the plate diameter is 40
However, if the thickness is less than 10 nm, stable magnetization cannot be expected due to thermal fluctuation. If it exceeds 50 nm, noise is high, and neither is suitable for high-density magnetic recording.

As the tabular magnetic material used in the magnetic layer of the present invention, hexagonal ferrite powder is preferable. Examples of hexagonal ferrite include barium ferrite, strontium ferrite, lead ferrite, calcium ferrite, and Co-substitutes. Specific examples include magnetoplumbite-type barium ferrite and strontium ferrite, magnetoplumbite-type ferrite whose particle surface is coated with spinel, and magnetoplumbite-type barium ferrite and strontium ferrite further containing a part of spinel phase. , Other than predetermined atoms, Al, Si, S, Sc, Ti, V, Cr, Cu, Y,
Mo, Rh, Pd, Ag, Sn, Sb, Te, Ba, T
a, W, Re, Au, Hg, Pb, Bi, La, Ce,
Pr, Nd, P, Co, Mn, Zn, Ni, Sr, B,
It may contain atoms such as Ge and Nb. Generally C
o-Ti, Co-Ti-Zr, Co-Ti-Zn, Ni
-Ti-Zn, Nb-Zn-Co, Sb-Zn-Co,
A substance to which an element such as Nb-Zn is added can be used. Some raw materials and production methods contain specific impurities.

The particle size is 10 to 50 nm in plate diameter, and the plate ratio (plate diameter / plate thickness) is preferably 1 to 15. Preferably it is 2-7. When the 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 by the BET method in this particle size range is 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. The crystallite size is 50-450 °, preferably 100-350 °. The distribution of particle plate diameter and plate thickness is generally preferably as narrow as possible. Although it is difficult to make a numerical value, it can be compared by randomly measuring 500 particles 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 40 to 400 kA / m (50
0 to 5000 Oe). A higher Hc is advantageous for high-density recording, but is limited by the capability of the recording head. Normally from 64 kA / m (800 Oe) to 318 k
A / m (4000 Oe), preferably 11
9 kA / m (1500 Oe) or more and 279 kA / m (3
500 Oe) or less. When the saturation magnetization of the head exceeds 1.4 Tesler, 159 kA / m (2000O
e) More preferably. Hc is the particle size (plate diameter / plate thickness), the type and amount of the contained element, the substitution site of the element,
It can be controlled by the particle generation reaction conditions and the like. Saturation magnetization σs is ^{40~80A · m 2 / kg (40~80emu} / g). The higher the value of σs, the better, but the smaller the fine particles, the lower the tendency. 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 to be added. It is also possible to use W-type hexagonal ferrite.

As a method for producing hexagonal ferrite, a metal oxide for replacing barium oxide, iron oxide and iron and boron oxide or the like as a glass-forming substance are mixed so as to have a desired ferrite composition, melted, quenched. A glass crystallization method in which a barium ferrite crystal powder is obtained by forming an amorphous body, followed by reheating treatment, and then washing and pulverizing. 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.
The barium ferrite composition metal salt solution is neutralized with an alkali, and after removing by-products, dried, treated at 1100 ° C. or lower, and pulverized to obtain a barium ferrite crystal powder. We do not choose manufacturing method.

When dispersing the needle-shaped magnetic material and the plate-shaped magnetic material, the surface of the magnetic material particles is sometimes treated with a material suitable for the dispersion medium and the polymer. As the surface treatment material, an inorganic compound or an organic compound is used. The main compound is S
Representative examples include oxides or hydroxides of i, Al, P, etc., 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, about 4 to 12, there is an optimum value depending on the dispersion medium and the polymer, but about 6 to 10 is selected from the chemical stability and storage stability of the medium. Water contained in the magnetic material also affects dispersion. There is an optimum value depending on the dispersion medium and the polymer, but usually 0.01 to 2.0% is selected.

[Polyether Polyurethane] In the magnetic layer of the present invention, the binder has a weight average molecular weight of 1500 to 1500.
A polyether polyurethane with polar groups, in the range of 25,000, is used. The polyether polyurethane used in the present invention has a lower average molecular weight and less entanglement of molecules than those conventionally used as a binder. Therefore, the resin alone has extremely low mechanical strength in the so-called low polymer region, and when applied to a conventional magnetic layer, only a resin having extremely low adhesion and durability was obtained. However, according to the inventor's intensive studies, when the above polyether polyurethane is used as a binder in the magnetic layer of the present invention, extremely fine needle-shaped magnetic substances or flat magnetic substances are highly dispersed, and the dispersion stability is further increased. It was revealed that a very smooth and thin magnetic layer could be applied with a uniform thickness. This is because the polyether polyurethane of the present invention has high mobility and adsorbability during kneading and dispersing with the fine particle magnetic material, and can enter small gaps between the fine particle magnetic materials. The functional groups having adsorptivity are adsorbed on the surface of the magnetic material, and the molecular chains of polyurethane have high solvent solubility and can be surrounded by a protective colloid around the magnetic material to maintain a stable dispersion state. It is thought that.

The polyether polyurethane used as a binder in the magnetic layer of the present invention has a weight average molecular weight of 1
500 to 25000, preferably 2500 to 20
000. If the weight average molecular weight is less than 1500, the dispersibility is poor, and the coating film strength and durability are poor. Also,
When the weight average molecular weight exceeds 25,000, the dispersibility of the ultrafine particle magnetic material used in the present invention is reduced.

The polyether polyurethane used as a binder in the magnetic layer of the present invention contains a polar group in the molecule. By containing a polar group, the adsorbability of the polyether polyurethane to the surface of the magnetic material is increased, and the dispersibility can be improved. Examples of the polar group contained in the polyether _{polyurethane, -SO 3 M, -OSO 3 M} , -COO
_{M, -PO 3 M '2,} -OPO 3 M' 2, -NR 2, -N +
R ₂ R′COO ⁻ (where M is hydrogen, alkali metal, alkaline earth metal, ammonium salt, M ′ is hydrogen,
An alkali metal, an alkaline earth metal, or an ammonium salt, wherein R and R 'are alkyl groups, and X represents a halogen). SO ₃ M, an -OSO ₃ M. The content of the polar group in the polyether polyurethane is preferably 10 to 1000 μeq / g,
More preferably, it is suitably from 100 to 600 μeq / g. When the content of the polar group is 10 μeq / g or more, the adsorptivity of the polyether polyurethane to the magnetic substance is increased, the dispersibility is good, and the polyether polyurethane is 1000 μeq / g.
When the amount is less than g, solvent solubility is high and dispersibility is good, which is preferable.

The polyether polyurethane used as a binder in the magnetic layer of the present invention can be composed of a polyether polyurethane which is a reaction product mainly composed of a diol and an organic diisocyanate. As the diol, a short-chain diol having a cyclic structure can be used. When the diol compound has a cyclic structure, the strength of the coating film is increased. Further, when the diol compound is a short-chain diol, the spread of the alkyl chains is small, the crosslink density is increased, and the strength of the coating film can be further improved.

As the short-chain diol having a cyclic structure,
For example, aromatic and alicyclic diols such as bisphenol A, hydrogenated bisphenol A represented by the following formula (1), bisphenol S, cyclohexanedimethanol, and cyclohexanediol are preferred. More preferably, hydrogenated bisphenol A represented by the formula 1 and its ethylene oxide and propylene oxide adducts are exemplified.

[0024]

Embedded image

The content of the short-chain diol in the polyether polyurethane is preferably from 17 to 40% by weight, and more preferably from 20 to 30% by weight. By containing the short-chain diol in the polyether polyurethane in an amount of 17% by weight or more, sufficient coating film strength can be obtained. When the content is 40% by weight or less, the solubility in a solvent is good, so that the dispersibility of the ferromagnetic powder can be secured, good electromagnetic conversion characteristics can be obtained, and a magnetic layer with high strength can be obtained. Can be. The short-chain diol having a cyclic structure preferably has a molecular weight of 50 to 500, and more preferably 100 to 300. When the molecular weight is 50 or more, the strength of the magnetic layer can be secured and good durability can be obtained.
When it is not more than 00, the glass transition temperature Tg of the magnetic layer is increased, so that a magnetic layer having high hardness and excellent durability can be obtained.

As the diol, a long-chain diol can be used. As long-chain diols, for example, bisphenol A, hydrogenated bisphenol A, bisphenol S, bisphenol P and their polyethylene oxide, propylene oxide adducts, polypropylene glycol, polyethylene glycol, polytetramethylene glycol are preferable, and hydrogenation is more preferable. Bisphenol A and their ethylene oxide and propylene oxide adducts, and particularly preferred are compounds represented by the following formula (2).

[0027]

Embedded image Wherein R is as follows:

Embedded image

In the above equation (2), the values of n and m are
It is suitably from 3 to 24, preferably from 3 to 20, more preferably from 4 to 15. n and m are 3
If it is less than 3, the urethane bond concentration in the polyether polyurethane increases, the solvent solubility decreases, and the coating film tends to become brittle. Therefore, n and m are preferably 3 or more. Furthermore, when n and m are 3 or more, dispersibility and durability are also good. When n and m exceed 24, the coating film becomes soft and the durability of the film decreases, so that n and m are preferably 24 or less.

In the long-chain diol, R is preferably as follows, and more preferably R.

Embedded image

Having a cyclic structure in the long-chain diol
Polyether resin with high coating strength and excellent durability
Urethane can be obtained, and propylene is branched.
CH _ThreeHaving a high solubility in a solvent,
It is possible to obtain polyether polyurethane with excellent dispersibility.
Wear. In the long-chain diol of the above formula (2), X
Is preferably a hydrogen or methyl group, more preferably methyl
Group. Weight average molecular weight (Mw) of long chain diol
Is preferably from 500 to 5,000. 5000
If it is below, the coating film strength is high, the durability is good,
preferable.

The long-chain diol preferably has an ether bond in the molecule. Since the ether bond in the molecule has a high adsorptivity to a magnetic substance or a non-magnetic substance, the obtained binder is favorably adsorbed to the magnetic substance or the non-magnetic substance, and the dispersibility of the coating solution can be improved.

The content of the ether group in the whole polyether polyurethane is preferably 1.0 to 5.0 mmol / g, more preferably 2.0 to 4.0 mm / g.
ol / g. When it is 1 mmol / g or more, the adsorptivity to the magnetic substance is high, the dispersibility is good, and 5 mmol / g
When it is less than g, the solvent solubility is high and the dispersibility is good, which is preferable.

The content of the long-chain diol containing an ether group in the polyether polyurethane is preferably from 10 to 50% by weight, more preferably from 30 to 40% by weight.
It is appropriate that When the content is 10% by weight or more, the solvent solubility is high and the dispersibility is good, and when it is 50% by weight or less, the coating film strength is high and the durability is good, which is preferable.

The organic diisocyanate compound which is the main component of the polyether polyurethane used in the magnetic layer in the present invention includes, for example, MDI (diphenylmethane diisocyanate), 2,4-TDI (tolylene diisocyanate), 2,6-TDI, 1,5-NDI (naphthalene diisocyanate), TODI (tolidine diisocyanate), p-phenylene diisocyanate, XDI
Aromatic diisocyanates such as (xylylene diisocyanate), transcyclohexane 1,4-diisocyanate, HDI (hexamethylene diisocyanate),
IPDI (isophorone diisocyanate), H ₆ XDI
(Hydrogenated xylylene diisocyanate), H ₁₂ MDI
(Hydrogenated diphenylmethane diisocyanate), such as aliphatic and alicyclic diisocyanates, such as MDI, 2,4-TDI, 2,6-TDI, and IPD.
Preferably, I is used.

The urethane group concentration in the polyether polyurethane is preferably from 2.5 to 4.5 mmol / g, and more preferably from 3.0 to 4.0 mmol / g. 2.5mmo urethane group concentration
When it is 1 / g or more, the Tg of the coating film is high and the durability is good, and when it is 4.5 mmol / g or less, the solvent solubility is good and the dispersibility is high, which is preferable. On the other hand, if the urethane group concentration exceeds 4.5 mmol / g, the polyol cannot be contained inevitably, so that synthesis problems such as difficulty in controlling the molecular weight are likely to occur.

The glass transition temperature Tg of the polyether polyurethane used in the present invention is preferably from 40 to 200 ° C., more preferably from 70 to 180 ° C. When the temperature is 40 ° C. or higher, the durability of the coating film is good, and when the temperature is 200 ° C. or lower, calender moldability is good and excellent electromagnetic conversion characteristics can be obtained, which is preferable.

The content of OH groups in the polyether polyurethane is preferably from 2 to 20 per molecule, more preferably from 4 to 5 per molecule. When the number is 2 or more per molecule, the reactivity with the isocyanate curing agent is high, the coating film strength is good, and excellent durability can be obtained. When the number is 20 or less, the solubility in a solvent is high. And good dispersibility, which is preferable. As the compound used for adjusting the content of the OH group in the polyurethane resin, a compound having three or more OH groups can be used. Specific examples include trimethylolethane, trimethylolpropane, trimellitic anhydride, glycerin, pentaerythritol, and hexanetriol.

[Binders that can be used in combination] In the magnetic layer of the present invention,
As a binder, in addition to the above polyether polyurethane,
Polyester resin, polyamide resin, vinyl chloride resin, acrylic resin copolymerized with styrene, acrylonitrile, methyl methacrylate, etc., cellulose resin such as nitrocellulose, epoxy resin, phenoxy resin, polyvinyl acetal, polyvinyl butyral etc. A single resin or a mixture of plural resins can be used from alkylal resin. Preferred among these are vinyl chloride resins and acrylic resins. The binder preferably has a functional group (polar group) adsorbed on the surface of the magnetic substance and the non-magnetic powder in order to improve the dispersibility of the powder. A preferred functional group is -SO _{3
M, -SO 4 M, -PO (} OM) 2, -OPO (O
_{M) 2, -COOM,> NSO} 3 M,> NRSO 3 M, -
^{NR 1 R 2, -N + R} 1 R 2 R 3 X - , and the like. Here, M is hydrogen or an alkali metal such as Na or K, R is an alkylene group, R ¹ , R ² , and R ³ are an alkyl group or a hydroxyalkyl group or hydrogen, and X is a halogen such as Cl or Br. The amount of the functional group in the binder is preferably from 10 to 200 μeq / g, and more preferably from 30 to 120 μeq / g.
When the content is in the above range, the dispersibility is good, which is preferable.

The binder is preferably provided with a radiation-curable functional group. However, the object of the present invention can be sufficiently achieved without having a radiation-curable functional group. As the radiation curing functional group, a (meth) acryloyl group is preferable. The preferred amount is 50 μeq / g to 1 meq / g, and more preferably 100 μeq / g to 800 μeq / g.
g. In addition, the binder may include a functional group having active hydrogen such as an —OH group.

The molecular weight of the binder is 2 in terms of weight average molecular weight.
It is preferably from 000 to 200,000, more preferably from 20,000 to 80,000. When it is 20,000 or more, the coating film strength is high and the durability is good.
It is preferable that the molecular weight is not more than 000 because the viscosity is appropriate and the dispersibility is good.

As the PVC resin, a resin obtained by copolymerizing a PVC monomer with various monomers can be used. As copolymerized monomers, vinyl acetate, fatty acid vinyl esters such as vinyl propionate, methyl (meth) acrylate, ethyl (meth) acrylate, isopropyl (meth) acrylate, butyl (meth) acrylate,
Acrylates such as benzyl (meth) acrylate, methacrylates, alkyl allyl ethers such as allyl methyl ether, allyl ethyl ether, allyl propyl ether, allyl butyl ether, and others styrene, α-methylstyrene, vinylidene chloride, acrylonitrile, ethylene, butadiene, acrylamide, Further, vinyl alcohol, 2
-Hydroxyethyl (meth) acrylate, polyethylene glycol (meth) acrylate, 2-hydroxypropyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, polypropylene glycol (meth) acrylate, 2-hydroxyethyl allyl ether, 2-hydroxy Propyl allyl ether, 3-hydroxypropyl allyl ether, p-vinylphenol, maleic acid, maleic anhydride, acrylic acid, methacrylic acid, glycidyl (meth) acrylate, allyl glycidyl ether, phosphoethyl (meth) acrylate,
Sulfoethyl (meth) acrylate, p-styrenesulfonic acid, and Na salts and K salts thereof can be used.

The composition of the vinyl chloride monomer in the PVC resin is preferably 60 to 95% by weight. When it is 60% by weight or more, the mechanical strength is high, and when it is 95% by weight or less, the solvent solubility is high, an appropriate solution viscosity is obtained, and the dispersibility is good, which is preferable. Preferred amounts of the adsorption functional group (polar group) and the radiation-curable functional group are as described above. These functional groups may be introduced by copolymerizing the above-mentioned functional group-containing monomer, or by introducing a functional group by polymer reaction after copolymerizing a PVC resin. The preferred degree of polymerization is 200 to 60.
0, more preferably 240 to 450. Within the above range, the mechanical strength is high, the solution viscosity is appropriate, and the dispersibility is good, which is preferable.

In the magnetic layer of the present invention, a curing agent such as a polyisocyanate compound can be used together with the binder. Examples of polyisocyanate compounds include:
Reactive product of 3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane (eg, Desmodur L-7)
5 (manufactured by Bayer AG)), a reaction product of 3 mol of a diisocyanate such as xylylene diisocyanate or hexamethylene diisocyanate with 1 mol of trimethylolpropane, a burette addition compound of 3 mol of hexamethylene diisocyanate, and tolylene diisocyanate 5
Moles of isocyanurate compound, 3 moles of tolylene diisocyanate and 2 moles of hexamethylene diisocyanate isocyanurate adduct, polymers of isophorone diisocyanate and diphenylmethane diisocyanate.

The polyisocyanate compound contained in the magnetic layer is preferably contained in the binder in the range of 10 to 50% by weight, more preferably in the range of 20 to 40% by weight. In the case of performing a curing treatment by electron beam irradiation, a compound having a reactive double bond such as urethane acrylate can be used. The total weight of the resin component and the curing agent (that is, the binder) is preferably in the range of usually 15 to 40 parts by weight, more preferably 20 to 40 parts by weight, based on 100 parts by weight of the ferromagnetic powder.
30 parts by weight.

In the present invention, not only a magnetic layer but also a lower non-magnetic layer or a magnetic layer can be provided. When having a lower layer, the binder can be used in the upper magnetic layer and the lower nonmagnetic or magnetic layer. The amount of the binder added is preferably 50 parts by weight to 300 parts by weight, more preferably 100 parts by weight, based on 1000 parts by weight of the magnetic substance in the case of the magnetic layer and 1000 parts by weight of the nonmagnetic powder in the case of the nonmagnetic layer. Suitably, it is from 200 parts by weight to 200 parts by weight.

Each of the above components is kneaded and dispersed together with a solvent such as methyl ethyl ketone, dioxane, cyclohexanone, ethyl acetate and the like which are usually used in preparing a magnetic coating material to obtain a magnetic coating material. The kneading and dispersing can be performed according to a usual method. In addition, in the magnetic paint, in addition to the above components, abrasives such as α-Al ₂ O ₃ and Cr ₂ O ₃ , antistatic agents such as carbon black, lubricants such as fatty acids, fatty acid esters, and silicone oils, and dispersions It may contain a commonly used additive or filler such as an agent.

As the carbon black used in the upper magnetic layer of the present invention, furnace for rubber, thermal for rubber, black for color, acetylene black and the like can be used. Specific surface area is 5 to 500 m ² / g, DBP oil absorption is 10 to 400 ml / 100 g, particle diameter is 5 nm to 30
0 nm, the pH is preferably 2 to 10, the water content is preferably 0.1 to 10% by weight, and the tap density is preferably 0.1 to 1 g / ml. Specific examples of the carbon black used in the magnetic layer of the present invention include BLACKPEARLS200 manufactured by Cabot Corporation.
0, 1300, 1000, 900, 800, 700, V
ULCAN XC-72, # 80, # 6 manufactured by Asahi Carbon Co., Ltd.
0, # 55, # 50, # 35, # 24 manufactured by Mitsubishi Kasei Kogyo
00B, # 2300, # 900, # 1000, # 30,
# 40, # 10B, CONDU made by Columbia Carbon
CTEX SC, RAVEN 150, 50, 40, 1
5 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 one obtained by partially graphitizing the surface. Before adding the carbon black to the magnetic paint, the carbon black may be dispersed in a binder in advance. These carbon blacks can be used alone or in combination.

When carbon black is used, it is preferably used in an amount of 0.1 to 30% by weight based on the ferromagnetic powder. Carbon black has functions such as preventing the magnetic layer from being charged, reducing the coefficient of friction, imparting light-shielding properties, and improving the film strength, and differs depending on the carbon black used. Therefore, these carbon blacks used in the present invention are different in type, amount, and combination between the upper layer and the lower layer, and according to the purpose, based on the above-mentioned properties such as particle size, oil absorption, conductivity, and pH. It is of course possible to use them properly. The carbon black that can be used in the magnetic layer of the present invention can be referred to, for example, “Carbon Black Handbook” edited by Carbon Black Association.

In the magnetic layer, in addition to the non-magnetic powder, α-alumina, β-alumina, silicon carbide, chromium oxide, cerium oxide, α-iron oxide, corundum, artificial diamond having an α conversion of 90% or more are used as abrasives. Known materials mainly having a Mohs hardness of 6 or more such as silicon nitride, silicon carbide, titanium carbide, titanium oxide, silicon dioxide, and boron nitride are used alone or in combination. In addition, a composite of these abrasives (abrasive whose surface has been treated with another abrasive) may be used. These abrasives may contain compounds or elements other than the main component, but the main component is 9
If the content is 0% by weight or more, the effect is not changed. The particle size of these abrasives can be 0.01 to 2 μm, but preferably 0.01 to 0.3 μm because the thickness of the magnetic layer is thin. Further, if necessary, abrasives having different particle sizes may be combined, or the same effect may be obtained by widening the particle size distribution using a single abrasive. Tap density is 0.3
~ 2 g / ml, water content 0.1-5 wt%, pH 2 ~
11. The specific surface area is preferably from 1 to 30 m ² / g. The shape of the abrasive used in the present invention is needle-like, spherical, dice-like,
Although any of these may be used, those having a corner in a part of the shape are preferable because of high abrasiveness.

Specific examples of the abrasive used in the present invention include AKP-20, AKP-30, and A
KP-50, HIT-50, HIT-100, G5, G7, S1, Nippon Kagaku Kogyo Co., Ltd., TF-10, Toda Kogyo Co., Ltd.
0 and TF-140. The abrasive used in the present invention can be of different types, amounts and combinations for the magnetic layer (upper and lower layers) and the non-magnetic layer, and can be used properly according to the purpose. These abrasives may be added to the magnetic paint after being subjected to dispersion treatment with a binder in advance. The abrasive present on the surface of the magnetic layer and the end face of the magnetic layer of the magnetic recording medium of the present invention is preferably 5/100 μm ² or more.

[Lower Layer] Next, the lower non-magnetic layer or lower magnetic layer in the case where the present invention has a multilayer structure will be described. The inorganic powder used in the lower non-magnetic layer of the present invention may be either a magnetic powder or a non-magnetic powder. For example, in the case of non-magnetic powder, it can be selected from inorganic compounds such as metal oxides, metal carbonates, metal sulfates, metal nitrides, metal carbides, and metal sulfides. As the inorganic compound, for example, a pregelatinization rate of 90%
The above α-alumina, β-alumina, γ-alumina, θ
-Alumina, silicon carbide, chromium oxide, cerium oxide,
α-iron oxide, goethite, corundum, silicon nitride, titanium carbide, titanium oxide, silicon dioxide, tin oxide, magnesium oxide, tungsten oxide, zirconium oxide, boron nitride, zinc oxide, calcium carbonate, calcium sulfate, barium sulfate, Molybdenum sulfide or the like is used alone or in combination. Particularly preferred are titanium dioxide, zinc oxide, iron oxide and barium sulfate because of their small particle size distribution and many means for imparting functions, and more preferred are titanium dioxide and α-iron oxide. The particle size of these non-magnetic powders is preferably 0.005 to 2 μm, but if necessary, non-magnetic powders having different particle sizes may be combined, or even a single non-magnetic powder may have a similar particle size distribution to achieve the same effect. You can also. Particularly preferably, the particle size of the nonmagnetic powder is 0.01 μm to 0.2 μm.
m. In particular, when the nonmagnetic powder is a granular metal oxide, the average particle diameter is preferably 0.08 μm or less, and when it is an acicular metal oxide, the major axis length is preferably 0.3 μm or less. The tap density is 0.05 to 2 g / ml, preferably 0.2 to 1.5 g / ml. The water content of the non-magnetic powder is 0.1 to 5% by weight, preferably 0.2 to 3% by weight, more preferably 0.3 to 1.5% by weight. The pH of the non-magnetic powder is from 2 to 11, and the pH is particularly preferably from 5.5 to 10. The specific surface area of the non-magnetic powder is 1 to 100 m ² /
g, preferably 5 to 80 m ² / g, more preferably 10 m ² / g.
Suitably, it is ７０70 m ² / g. The crystallite size of the nonmagnetic powder is preferably 0.004 μm to 1 μm,
0.04 μm to 0.1 μm is more preferable. The oil absorption using DBP (dibutyl phthalate) is 5 to 100 ml /
It is suitable that the amount is 100 g, preferably 10 to 80 ml / 100 g, and more preferably 20 to 60 ml / 100 g. The specific gravity is suitably from 1 to 12, preferably from 3 to 6. The shape may be any of a needle shape, a spherical shape, a polyhedral shape, and a plate shape.

It is preferable that the ignition loss is 20% by weight or less, and it is considered that it is most preferable that there is no ignition loss. The Mohs hardness of the nonmagnetic powder used in the present invention is preferably 4 or more and 10 or less. The roughness factor of the surface of these powders is preferably 0.8 to 1.5, and more preferably 0.9 to 1.2. Non-magnetic powder adsorbs SA (stearic acid) from 1 to 20 μm
ol / m ² , preferably ² to 15 μmol / m ² , more preferably 3 to 8 μmol / m ² . The heat of wetting of the nonmagnetic powder in water at 25 ° C. is 2 × 10 ^−5.
~ 6 × 10 ^-5 J / cm ² (200-600erg / c
m ² ). Further, a solvent having a range of the heat of wetting can be used. pH 3 ~
Preferably between 6. Water-soluble Na of non-magnetic powder
Is preferably 0 to 150 ppm, and the water-soluble Ca is suitably 0 to 50 ppm.

On the surface of these non-magnetic powders, Al
₂ O ₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb
It is preferable to perform a surface treatment with ₂ O ₃ , ZnO, and Y ₂ O ₃ .
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. Also,
Depending on the purpose, a co-precipitated surface treatment layer may be used,
A method of treating the surface layer with silica after treating with alumina first, or vice versa may be employed. Although the surface treatment layer may be a porous layer depending on the purpose, it is generally preferable that the surface treatment layer be homogeneous and dense.

Specific examples of the non-magnetic powder used in the lower layer of the present invention include Nanotite manufactured by Showa Denko, HIT-100, ZA-G1 manufactured by Sumitomo Chemical, α-hematite DPN-250 and DPN-250BX manufactured by Toda Kogyo. , DPN-24
5, DPN-270BX, DBN-SA1, DBN-S
A3, Ishihara Sangyo Titanium Oxide TTO-51B, TTO-
55A, TTO-55B, TTO-55C, TTO-5
5S, TTO-55D, SN-100, α hematite E
270, E271, E300, E303, Titanium Oxide STT-4D, STT-30D, STT-3
0, STT-65C, α hematite α-40, MT-100S, MT-100T, MT-150W, M manufactured by Teika
T-500B, MT-600B, MT-100F, MT
-500HD, Sakai Chemical FINEX-25, BF-1,
BF-10, BF-20, ST-M, Dowa Mining DEF
IC-Y, DEFIC-R, AS2B made by Nippon Aerosil
M, TiO2P25, Ube Industries 100A, 500A,
And baked products thereof. Particularly preferred non-magnetic powders are titanium dioxide and α-iron oxide.

By mixing carbon black in the lower layer, it is possible to lower the surface electric resistance Rs, which is a known effect, to reduce the light transmittance, and to obtain a desired micro Vickers hardness. In addition, it is possible to bring about the effect of storing the lubricant by including carbon black in the lower layer. As the type of carbon black, furnace for rubber, thermal for rubber, black for color, acetylene black, and the like can be used. The following characteristics of the carbon black in the lower layer should be optimized depending on the desired effect, and the combined effect may provide more effects.

The specific surface area of the lower carbon black is 10
0~500m ² / g, preferably 150~400m ² /
g, DBP oil absorption is suitably 20 to 400 ml / 100 g, preferably 30 to 200 ml / 100 g. The particle size of the carbon black is suitably from 5 to 80 nm, preferably from 10 to 50 nm, and more preferably from 10 to 40 nm. PH of carbon black is 2 ~
10, water content 0.1 ~ 10%, tap density 0.1 ~
It is preferably 1 g / ml. Specific examples of the carbon black used in the present invention include BLACKPEARLS 2000, 1300, 1
000, 900, 800, 880, 700, VULCA
N XC-72, manufactured by Mitsubishi Kasei Kogyo Co., Ltd. # 3050B, #
3150B, # 3250B, # 3750B, # 3950
B, # 950, # 650B, # 970B, # 850B,
MA-600, MA-230, # 4000, # 401
0, CONDUCTEX S made by Columbia Carbon
C, RAVEN 8800, 8000, 7000, 57
50, 5250, 3500, 2100, 2000, 18
00, 1500, 1255, 1250, manufactured by Akzo
Ketjen Black EC 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 one obtained by partially graphitizing the surface. 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 weight and not exceeding 40% of the total weight of the nonmagnetic 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 present invention can be referred to, for example, “Carbon Black Handbook” (edited by Carbon Black Association).

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 pigments, but also polyolefin-based resin powder, polyester-based resin powder, polyamide-based resin powder, polyimide-based resin powder, and polyfluoroethylene resin Can be used. Its manufacturing method is disclosed in
Those described in JP-A-2-18564 and JP-A-60-255827 can be used.

In the lower layer of the present invention, a magnetic powder can also be used (lower magnetic layer). As magnetic powder, γ-
An alloy mainly composed of Fe ₂ O ₃ , Co-modified γ-Fe ₂ O ₃ , α-Fe, CrO ₂ or the like is used. In particular, Co-modified γ
-Fe ₂ O ₃ is preferable. The ferromagnetic powder used in the lower layer of the present invention preferably has the same composition and performance as the ferromagnetic powder used in the upper magnetic layer. However, it is known that the performance is changed between the upper and lower layers according to the purpose. For example, in order to improve long-wavelength recording characteristics, the Hc of the lower magnetic layer
Is preferably set lower than that of the upper magnetic layer,
It is also effective to make Br of the lower magnetic layer higher than that of the upper magnetic layer. In addition to the above, an advantage obtained by adopting a known multilayer structure can be provided.

In the present invention, known additives can be added to each layer. Lubricating effect as additive,
Those having an antistatic effect, a dispersing effect, a plasticizing effect and the like are used. Molybdenum disulfide, tungsten graphite disulfide, boron nitride, graphite fluoride, silicone oil, polar group 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 having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and metal salts thereof (such as Li, Na, K, and Cu) or 12 to 22 carbon atoms Mono-, di-, tri-, tetra-, penta-, hexa-hydric alcohols (including unsaturated bonds,
It may be branched), an alkoxy alcohol having 12 to 22 carbon atoms, a monobasic fatty acid having 10 to 24 carbon atoms (which may contain an unsaturated bond or may be branched) and 2 carbon atoms. ~ 12 monovalent, divalent, trivalent, tetravalent,
Mono-fatty acid ester or di-fatty acid ester or tri-fatty acid ester comprising any one of pentahydric and hexahydric alcohols (which may contain an unsaturated bond or may be branched), monoalkyl of alkylene oxide polymer Fatty acid esters of ethers, fatty acid amides having 8 to 22 carbon atoms, aliphatic amines having 8 to 22 carbon atoms, and the like 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, lauryl alcohol.
Also, nonionic surfactants such as alkylene oxides, glycerin, glycidol, alkylphenol ethylene oxide adducts, cyclic amines, ester amides, quaternary ammonium salts, hydantoin derivatives,
Heterocycles, cationic surfactants such as phosphonium or sulfoniums, anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfate group, and phosphate group, amino acids, aminosulfonic acids, amino Sulfuric acid or phosphoric acid esters of alcohol, amphoteric surfactants such as alkylbedine type and the like can also be used.

These surfactants are described in detail in "Surfactant Handbook" (published by Sangyo Tosho Co., Ltd.). These lubricants, antistatic agents, etc.
It is not 0% pure and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, etc. in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less.

The type and amount of these lubricants and surfactants used in the present invention can be properly used in the upper layer and the lower layer as required. For example, upper and lower layers use fatty acids with different melting points to control bleeding to the surface, use esters with different boiling points and polarities to control bleeding to the surface, and adjust the amount of surfactant to control coating. It is conceivable that the stability is improved, and the amount of the lubricant added is increased in the lower layer to improve the lubrication effect, and it is needless to say that the present invention is not limited to the examples shown here. Further, all or a part of the additives used in the present invention may be added at any step of the production of the magnetic paint, for example, when mixed with the ferromagnetic powder before the kneading step, the ferromagnetic powder and the binder , A kneading step with a solvent, a dispersing step, a dispersing step, a dispersing step, and a dissolving step immediately before coating.
In some cases, the purpose may be achieved by applying a part or all of the additive simultaneously or sequentially after applying the magnetic layer according to the purpose. Further, depending on the purpose, a lubricant can be applied to the surface of the magnetic layer after calendering or after the slit is completed.

Commercial examples of these lubricants used in the present invention include NAA-102 and NAA-41 manufactured by NOF Corporation.
5, NAA-312, NAA-160, NAA-18
0, NAA-174, NAA-175, NAA-22
2, NAA-34, NAA-35, NAA-171, N
AA-122, NAA-142, NAA-160, NA
A-173K, castor hardened fatty acid, NAA-42, NA
A-44, Cation SA, Cation MA, Cation A
B, Cation BB, Nimeen L-201, Nimeen L-202, Nimeen S-202, Nonion E-20
8, Nonion P-208, Nonion S-207, Nonion K-204, Nonion NS-202, Nonion NS-
210, nonion HS-206, nonion L-2, nonion S-2, nonion S-4, nonion O-2, nonion LP-20R, nonion PP-40R, nonion SP
-60R, Nonion OP-80R, Nonion OP-85
R, Nonion LT-221, Nonion ST-221, Nonion OT-221, Monogly MB, Nonion DS-6
0, Anone BF, Anone LG, butyl stearate, butyl laurate, erucic acid, oleic acid manufactured by Kanto Chemical Co.,
Takemoto Yushi FAL-205, FAL-123, Nippon Rika Co., Ltd. Engelbu LO, Engelbu IPM, Sansocizer E4030, Shin-Etsu Chemical TA-3, KF-
96, KF-96L, KF96H, KF410, KF4
20, KF965, KF54, KF50, KF56, K
F907, KF851, X-22-819, X-22
822, KF905, KF700, KF393, KF-
857, KF-860, KF-865, X-22-98
0, KF-101, KF-102, KF-103, X-
22-3710, X-22-3715, KF-910,
KF-3935, Armamide P manufactured by Lion Armor,
Armide C, Armoslip CP, Duomin TDO manufactured by Lion Yushi, BA-41G manufactured by Nisshin Oil, Profan 2012E manufactured by Sanyo Chemical, New Pole PE61,
IONET MS-400, IONET MO-200, IONET DL-200, IONET DS-300, IONET DS-1000, and IONET DO-200.

The organic solvent used in the present invention may be any ratio of ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclohexanone, isophorone and tetrahydrofuran, methanol, ethanol, propanol, butanol, isobutyl alcohol, isopropyl alcohol, and the like. Alcohols such as methylcyclohexanol, methyl acetate, butyl acetate, isobutyl acetate, isopropyl acetate, ethyl lactate, esters such as glycol acetate, glycol dimethyl ether, glycol monoethyl ether, glycol ethers such as dioxane, benzene, toluene, Aromatic hydrocarbons such as xylene, cresol, chlorobenzene, methylene chloride, ethylene chloride, carbon tetrachloride, Chloroform, ethylene chlorohydrin, chlorinated hydrocarbons such as dichlorobenzene, N,
N-dimethylformamide, hexane and the like can be used. These organic solvents are not necessarily 100% pure, and may contain impurities such as isomers, unreacted products, by-products, decomposed products, oxides, and moisture in addition to the main components. These impurities are preferably 30% or less, more preferably 10% or less. The type of the organic solvent used in the present invention is preferably the same in the upper layer and the lower layer. The amount added may be changed. It is important to improve the coating stability by using a solvent having a high surface tension (cyclohexanone, dioxane, etc.) for the lower layer. Specifically, it is important that the arithmetic average value of the upper solvent composition does not fall below the arithmetic average value of the lower solvent composition. In order to improve the dispersibility, it is preferable that the polarity is somewhat strong, and it is preferable that the solvent composition contains 50% or more of a solvent having a dielectric constant of 15 or more. Further, the dissolution parameter is preferably from 8 to 11.

[Non-magnetic support] As the non-magnetic support usable in the present invention, biaxially stretched polyethylene naphthalate, polyethylene terephthalate, polyamide, polyimide, polyamideimide, aromatic polyamide, polybenzoxdazole And the like can be used. Preferred are polyethylene naphthalate and aromatic polyamide. These non-magnetic supports may be subjected to corona discharge, plasma treatment, easy adhesion treatment, heat treatment, or the like in advance. The non-magnetic support which can be used in the present invention has a center line average surface roughness of a cutoff value of 0.25 mm.
It is preferable that the surface has excellent smoothness in the range of 0.1 to 20 nm, preferably 1 to 10 nm. It is preferable that these non-magnetic supports have not only a small center line average surface roughness but also no coarse protrusions of 1 μm or more.

[Layer Structure] The thickness structure of the magnetic recording medium of the present invention is such that the nonmagnetic support has a thickness of 1 to 100 μm, preferably 4 to 8 μm.
Suitably, it is 0 μm. The thickness of the magnetic layer (in the case of a single layer) or the upper magnetic layer (in the case of two or more layers)
0.01 to 0.5 μm is preferred. If the upper layer is too thin, a uniform recording layer will not be formed, and if it is too thick, the surface will be rough and the electromagnetic conversion characteristics will be reduced. The thickness of the lower layer (magnetic layer or non-magnetic layer) is preferably 0.5 to 3 μm. If it is too thin, the durability decreases. If it is too thick, the surface becomes rough and the electromagnetic conversion characteristics deteriorate. The total thickness of the upper layer and the lower layer is suitably in the range of 1/100 to 2 times the thickness of the nonmagnetic support.

An undercoat layer may be provided between the non-magnetic support and the lower layer (non-magnetic layer or magnetic layer) for improving adhesion. The thickness of the undercoat layer is 0.01 to 2 μm, preferably 0.02 to 0.5 μm.

Further, a back coat layer may be provided on the surface of the non-magnetic support used in the present invention on which the magnetic paint is not applied. Normally, the back coat layer is formed by applying a back coat layer forming paint in which a particulate component such as an abrasive and an antistatic agent and a binder are dispersed in an organic solvent, on the surface of the non-magnetic support on which the magnetic paint is not applied. It is a layer provided. Note that an adhesive layer may be provided on the surface of the nonmagnetic support on which the magnetic paint and the backcoat layer forming paint are applied. When a backcoat layer is provided on the side of the nonmagnetic support opposite to the magnetic layer, the thickness of the backcoat layer is suitably from 0.1 to 2 μm, preferably from 0.3 to 1.0 μm. Known undercoat layers and backcoat layers can be used.

[Production Method] The production method of the magnetic recording medium of the present invention is, for example, a method in which a magnetic layer coating solution is applied to the surface of a running non-magnetic support, preferably the thickness of the magnetic layer after drying is 0.05 to 3 μm. .
0 μm, more preferably 0.07 to 1.0 μm
Apply so that Here, a plurality of magnetic paints may be sequentially or simultaneously applied in a multilayer manner. Examples of the coating machine for applying the magnetic paint include 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, and spray. Coat, spin coat, etc. can be used. These are, for example, "Latest coating technology" published by Sogo Gijutsu Center.
(May 31, 1983).

When the present invention is applied to a magnetic recording medium having two or more layers, the following can be proposed as an example of a coating apparatus and method. (1) Gravure generally applied in the application of magnetic paint,
First, the lower layer is applied by a coating device such as a roll, a blade, an extrusion or the like, and while the lower layer is in an undried state, it is disclosed in Japanese Patent Publication No. 46186/1994, Japanese Patent Application Laid-Open No. 60-238179.
The upper layer is applied by a support pressurization type extrusion coating device as disclosed in Japanese Patent Application Laid-Open No. 2-265672 and JP-A-2-265672. (2) JP-A-63-88080, JP-A-2-179
No. 71 and Japanese Patent Application Laid-Open 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 applied layer of the applied magnetic paint is dried after subjecting the ferromagnetic powder contained in the applied layer of the magnetic paint to a magnetic field orientation treatment. After being dried in this manner, 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, voids generated by the removal of the solvent during drying disappear, and the filling rate of the ferromagnetic powder in the magnetic layer is improved, so that a magnetic recording medium having high electromagnetic conversion characteristics can be obtained. it can. As the calendering roll, a heat-resistant plastic roll such as epoxy, polyimide, polyamide, or polyamideimide is used. Moreover, it can also process with a metal roll.

The magnetic recording medium of the present invention has a center line average roughness of 0.1 to 0.1 at a cutoff value of 0.25 mm.
It is preferable that the surface has an extremely excellent smoothness of 4 nm, preferably 1 to 3 nm. As a method for this, for example, as described above, a magnetic layer formed by selecting a specific ferromagnetic powder and a binder is subjected to the above-described calendering treatment. As the calendering conditions, the temperature of the calender roll is in the range of 60 to 100 ° C, preferably in the range of 70 to 100 ° C, particularly preferably 80 to 10 ° C.
0 ° C. range and the pressure is 9.8-49 MPa (100
~500kg / cm ²⁾ And preferably 1
9.6-44.1 MPa (200-450 kg / c
m ² ) And particularly preferably 29.4 to 39.
2MPa (300-400kg / cm ² ) It is preferable to carry out the operation by operating under the conditions of the following range.
Note that, as described above, it is preferable that the irradiation be performed after the non-magnetic layer and the magnetic layer are applied, dried, and calendered. The laminate thus cured is then cut into a desired shape.

[0073]

EXAMPLES Examples of the present invention will be shown below, and the present invention will be described in more detail. "Parts" described below are "parts by weight".
Is shown. Synthesis Example of Polyether Polyurethane A polyether polyol and a diol compound shown in Table 1 were placed in a vessel previously equipped with a reflux condenser and a stirrer and purged with nitrogen.
And dissolved. Next, 60 ppm of dibutyltin dilaurate was added as a catalyst, and the mixture was further dissolved for 15 minutes. Table 1
Was added and reacted by heating at 90 ° C. for 6 hours to obtain polyurethane resin solutions PU1 to PU9.

[0074]

[Table 1]

[0075]

[Table 2]

[0076]

Embedded image

[Preparation of magnetic liquid for upper layer] Magnetic substance 1 shown in Tables 3 and 4
00 parts were pulverized with an open kneader for 10 minutes, and then 15 parts (solid content) of the polyurethane resin shown in Table 1 and 10 parts of cyclohexanone were added and kneaded for 60 minutes.
Next, 10 parts of α-alumina HIT55 (manufactured by Sumitomo Chemical), 3 parts of carbon black # 50 (manufactured by Asahi Carbon), and 3 parts of methyl ethyl ketone / toluene = 1/200 parts were added and dispersed by a sand mill for 120 minutes. To this, 1 part of stearic acid, 1 part of oleic acid, 2 parts of 2-ethylhexyl myristate, 2 parts of oleyl oleate, 1 part of methyl ethyl ketone, and 50 parts of methyl ethyl ketone were further stirred and mixed for 20 minutes. A magnetic paint was prepared.

[0078]

[Table 3]

[0079]

[Table 4]

[Preparation of Nonmagnetic Liquid for Lower Layer] Titanium oxide (mean particle size 0.035 μm, crystalline rutile, TiO ₂ content 90% or more, surface treatment layer; alumina, S _BET 35-42)
m ² / g, true specific gravity 4.1, pH 6.5 to 8.0) 85 parts, and carbon black (Ketjen Black EC)
(Japan EC) 15 parts were pulverized with an open kneader for 10 minutes, then 7 parts of vinyl chloride copolymer MR110 (manufactured by Nippon Zeon) and 15 parts of UR8700 manufactured by Toyobo Co., Ltd., a polyurethane resin containing SO ₃ Na group ( (Solid content) and 60 parts of cyclohexanone, and kneaded for 60 minutes. Then, 200 parts of methyl ethyl ketone / cyclohexanone = 6/4 200 parts were added and dispersed in a sand mill for 120 minutes. To this, 1 part of stearic acid, 1 part of oleic acid, 2 parts of 2-ethylhexyl myristate, 2 parts of oleyl oleate, 1 part of methyl ethyl ketone, and 50 parts of methyl ethyl ketone were further stirred and mixed for 20 minutes. A magnetic paint was prepared.

The obtained non-magnetic paint was reduced to a thickness of 1.2 μm.
Immediately thereafter, the thickness of the dried magnetic paint is 0.10 μm.
Was simultaneously coated on the surface of a 3.8 μm thick aramid support. A magnetic field orientation treatment is performed in a state where both layers are not dried, and after the solvent is dried, a speed of 10 is applied by a seven-stage calender.
The test was performed under the conditions of 0 m / min, a linear pressure of 300 kgf / cm, and a temperature of 90 ° C. Thereafter, an electron beam having an acceleration voltage of 150 kV was absorbed in an atmosphere having an oxygen concentration of 200 ppm or less and the absorbed dose was 5 M.
Irradiation was performed to obtain rad. Thereafter, the tape was slit to a width of 6.35 mm and assembled into a DVC cartridge. Table 5 shows the properties of the obtained tape.

[Measurement Method] Electromagnetic Conversion Characteristics Using a drum tester on a sample tape, a recording wavelength of 0.5
Recording and reproduction were performed under the conditions of μ and a head speed of 10 m / sec. When the C / N of the reference tape (Comparative Example 5) was set to 0 dB, the relative C / N of the tape was evaluated. Magnetic Layer Surface Roughness Ra The center line average roughness was defined as Ra by a light interference method using a digital optical profilometer (manufactured by WYKO) with a cutoff of 0.25 mm. Magnetic Layer Thickness and Standard Deviation The thickness of the magnetic layer was measured at 50 points from a transmission electron micrograph of an ultra-thin section of the tape cross section, and the average value and standard deviation were determined. Alumina scratch test A tape sample was stuck on a glass plate, and 23 ° C, 50% R
In a H atmosphere, alumina balls having a diameter of 5 mm were reciprocated 10 times in a 2 cm length at a speed of 10 mm / sec under a load of 50 gf, and then the scratches on the tape surface were observed. X indicates that a scratch was visually observed, and ○ indicates that no scratch was observed. Adhesive force The magnetic layer surface of the tape sample was stuck on a glass plate via a double-sided adhesive tape, and the tip was peeled off by 180 degrees. The tape sample which was peeled between the magnetic layer (including the non-magnetic lower layer) / base was designated as X, and the tape sample which was not peeled between the magnetic layer (including the non-magnetic lower layer) / base but the base was cut was marked as ○.

[0083]

[Table 5]

Comparison of Examples and Comparative Examples In Examples 1 to 4, the same polyether polyurethane was used for the magnetic layer (PU3), and different needle-like magnetic materials having a long axis length within the range of the present invention were used. Here is an example (MP
1-4). Examples 5 to 7 are examples in which the same polyether polyurethane was used for the magnetic layer (PU3) and different hexagonal barium ferrites having a plate diameter within the range of the present invention were used (BF1 to 3). Examples 8 to 12
The needle-shaped magnetic materials used are the same (MP3), and are examples in which different polyether polyurethanes having a polar group and having a molecular weight within the range of the present invention are used (PU1 to PU3).
6). In each of the examples, the dispersibility of the magnetic material was good, and the smoothness of the magnetic layer was high. The results of alumina scratch and adhesion were good, the durability and film strength were excellent, and the electromagnetic conversion characteristics were also high. In Comparative Examples 1 and 2, the same polyether polyurethane (PU3) as in Examples 1 to 4 was used, but a needle-shaped magnetic material having a major axis length exceeding the range of the present invention (Comparative Example 1; MP5, Comparative Example 2; MP
This is an example using 6). The magnetic layer smoothness and electromagnetic conversion characteristics were inferior to those of the examples. Further, the results of the alumina scratch and the adhesion were poor, and the durability and the film strength were inferior to those of the examples. Comparative Examples 3 and 4 are the same polyether polyurethane (PU3) as Examples 5-7.
However, this is an example in which a plate-like magnetic material (Comparative Example 3; BF4, Comparative Example 4; BF5) having a plate diameter exceeding the range of the present invention was used. The magnetic layer smoothness and electromagnetic conversion characteristics were significantly inferior to the examples. Further, the results of the alumina scratch and the adhesion were poor, and the durability and the film strength were inferior to those of the examples. Comparative Examples 5 to 7 are Examples 9-1.
2, the same magnetic substance (MP3) was used, but the polyether polyurethane used was different (Comparative Example 6; PU7,
Comparative Example 7; PU8, Comparative Example 8; PU9) Each of the polyether polyurethanes used in Comparative Examples 5 to 7 has an average molecular weight exceeding the range of the present invention. The magnetic layer smoothness was inferior to the examples. Also, the electromagnetic conversion characteristics were lower than those of the examples. In particular, an average molecular weight of 70
Comparative Example 7 using 000 polyether polyurethane
Of the magnetic layer was significantly inferior to the examples in the magnetic layer smoothness and the electromagnetic conversion characteristics, the results of the alumina scratch and the adhesion were poor, and the durability and the film strength were also inferior to the examples.

[0085]

According to the present invention, it is possible to satisfactorily disperse an extremely fine magnetic material, which has conventionally been difficult to obtain good dispersibility, and to obtain a smooth magnetic layer when using an extremely fine magnetic material. Could be improved. Further, it is possible to obtain a magnetic recording medium having improved dispersion stability and excellent durability and electromagnetic conversion characteristics. The magnetic coating solution according to the present invention has a high dispersion stability, a small increase in viscosity over time, particularly a low viscosity increase at a low shear rate, and a stable and uniform coating in a thin layer.

The magnetic recording medium of the present invention achieves extremely high electromagnetic conversion characteristics as compared with the conventional one. Speaking of tapes, tapes for video systems with extremely high recording density, such as DVC and DVC-PRO, or DD
Although there are computer backup tapes such as S4 and LTO which can transfer large-capacity data at high speed, a larger-capacity recording medium is required. According to the present invention, such advanced electromagnetic conversion characteristics and high-density recording can be achieved. Can be achieved.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing at least one ferromagnetic powder and a binder on a nonmagnetic support, wherein the ferromagnetic powder has a major axis length in the range of 10 nm to 100 nm. Needle-like magnetic material or plate-like magnetic material having a plate diameter in the range of 10 to 50 nm, and the binder contains a polyether polyurethane having a polar group and having a weight average molecular weight in the range of 1500 to 25000. A magnetic recording medium characterized by the above-mentioned.