JP4673945B2 - Magnetic powder, method for producing the same, and magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium and a magnetic powder, and more particularly to a magnetic recording medium that requires high-density recording, such as a digital video tape and a computer backup tape, a magnetic powder that is optimal for the magnetic recording medium, and a method for manufacturing the same. It is.

A coating type magnetic recording medium obtained by dispersing and binding magnetic powder to a binder is required to further improve the recording density as the recording / reproducing system shifts from an analog system to a digital system. In particular, this demand is increasing year by year for high-density video tapes and computer backup tapes.

In order to cope with the short wavelength recording in order to improve such recording density, fine particles have been developed year by year, and at present, acicular metal magnetic powder having a particle length of 0.1 μm or less has been put into practical use. Yes. Further, in order to prevent a decrease in output due to demagnetization at the time of short wavelength recording, a coercive force is increased year by year. For example, as disclosed in JP-A-3-49026, an iron-cobalt alloy is used to form 199 A coercive force of about 0.0 kA / m (2,500 Oersted) is realized. However, in a magnetic recording medium using acicular particles, since the coercive force depends on the shape, it has become difficult to make the particles significantly smaller from the particle diameter.

Thus, a magnetic recording medium using a granular or elliptical rare earth-iron-boron magnetic powder having an average particle size in the range of 5 to 200 nm, which is different from the needle-shaped magnetic powder, has been proposed (Patent Document 1). reference). Further, as an iron-based magnetic powder having a particle shape that is not needle-shaped, an iron nitride-based magnetic powder having an irregular particle shape and a BET specific surface area of 10 m ² / g or more with an Fe ₁₆ N ₂ phase as a main phase is used. It has been proposed to obtain a high coercive force (see Patent Document 2).
JP 2001-181754 A (4th page, 19th page) Japanese Patent Laid-Open No. 2000-277311 (pages 2 to 5 and FIG. 2)

However, the rare earth-iron-boron magnetic powder of Patent Document 1 is a composite material formed on the balance of high magnetic anisotropy due to the rare earth compound and high saturation magnetization due to the iron-based material as the core. Even if an improvement is made, for example, to increase the coercive force, it is difficult to improve the magnetic characteristics while maintaining the optimum dispersibility and chemical stability for the magnetic recording medium. In addition, the iron nitride magnetic powder of Patent Document 2 shows only a BET specific surface area of 10 to 22 m ² / g in the examples, the particle size is still large, and the obtained coercive force is It is about 94.7 to 179.1 kA / m (1,190 to 2,250 oersted).

Moreover, these known magnetic powders are characterized by high saturation magnetization. For example, in the case of iron nitride-based magnetic powders, those having 190 to 200 Am ² / kg (190 to 200 emu / g) are included in the examples. It is shown. When such a magnetic powder with too high saturation magnetization is applied to a magnetic recording medium for high-density recording, recording demagnetization becomes prominent, and the output in the short wavelength region may be lowered.

In particular, in a high-density recording medium, in order to reduce recording demagnetization, it is essential to lower the saturation magnetization of the magnetic powder and reduce the thickness of the magnetic layer. When the saturation magnetization is lowered, the magnetic flux from the surface of the medium is reduced and the reproduction output is reduced. However, due to the remarkable progress of the recent magnetic head technology, even a small magnetic flux can be reproduced with sufficiently high sensitivity. Therefore, in order to achieve high density recording, it is necessary to set the saturation magnetization of the magnetic powder to an appropriate value lower than the conventionally required value and to increase the coercive force.

In addition, these known magnetic powders are also inferior in storage stability, and when the magnetic powder itself or a magnetic recording medium using the magnetic powder is stored in a high temperature and high humidity environment, the saturation magnetization and the like gradually decrease, resulting in magnetic properties. There was also a problem that was not stable.

In light of such circumstances, the present invention is a digital video tape having finer particles, higher coercive force, moderate saturation magnetization, and excellent storage stability, compared to the prior art, An object of the present invention is to obtain a magnetic powder particularly suitable for a magnetic recording medium for high-density recording such as a computer backup tape.

As a result of intensive studies on the above object, the inventors of the present invention have at least iron and nitrogen as constituent elements and at least an Fe ₁₆ N ₂ phase, and the nitrogen content relative to iron is 1.0 to 20.0 atoms. % Of a granular or elliptical magnetic powder, and the surface of the powder is composed of a compound layer containing a rare earth element or at least one element selected from boron, silicon, aluminum, and phosphorus. It was found that the magnetic powder having a thickness of 1 to 5 nm has a high coercive force and an appropriate saturation magnetization, and also has excellent storage stability.

Further, the magnetic powder having such characteristics uses an iron-based oxide or hydroxide as a starting material, and at least one element selected from rare earth elements, boron, silicon, aluminum, and phosphorus. After depositing a compound containing, a heat reduction treatment is performed, followed by a nitriding treatment at a temperature lower than the reduction treatment temperature, and then an oxidation treatment under an appropriate oxygen concentration. I understand.

Furthermore, by using this magnetic powder, it is possible to realize a coating type magnetic recording medium having an ultra-thin magnetic layer that does not have a problem of output reduction due to recording demagnetization, thereby achieving high output and excellent. It was found that short wavelength recording characteristics can be obtained.

The present invention has been completed based on such knowledge.

That is, the present invention includes at least iron and nitrogen as constituent elements, and Fe ₁₆ N _2.
Granular or elliptical magnetism containing at least a phase, having a nitrogen content with respect to iron of 1.0 to 20.0 atomic%, an average axial ratio of 1 or more and 2 or less, and an average particle size of 15 nm or more and 50 nm or less The powder surface is composed of a compound layer containing a rare earth element or at least one element selected from boron, silicon, aluminum, and phosphorus, and the average thickness of the surface compound layer is 1 to 5 nm. It is related with the magnetic powder characterized by being.

In particular, the present invention relates to a magnetic powder having the above-described configuration having an average particle size of 15 to 20 nm, a magnetic powder having the above-described configuration in which the surface compound layer is an oxide, a rare earth element with respect to iron, or a total content of boron, silicon, aluminum and phosphorus. The magnetic powder having the above-mentioned constitution with an amount of 0.1 to 40.0 atomic%, a saturation magnetization of 50 to 150 Am ² / kg (50 to 150 emu / g), and a coercive force of 119.4 to 318.5 kA / m ( 1,500 to 4,000 oersted), magnetic powder having the above-described configuration, having a saturation magnetization of 129.6 to 144.2 Am ² / kg, and a coercive force of 226.9 to 254.8 kA / m The BET specific surface area of 40 to 100 m ² / g can provide the magnetic powder having the above-described configuration.

In addition, the present invention is a method for producing a magnetic powder having each of the above constitutions, in which an iron-based oxide or hydroxide is used as a starting material, and is selected from rare earth elements, boron, silicon, aluminum, and phosphorus. A method for producing a magnetic powder comprising: depositing a compound containing at least one element, performing a heat reduction treatment, then nitriding at a temperature equal to or lower than the reduction treatment temperature, and then performing an oxidation treatment Can be provided.

Furthermore, the present invention relates to a magnetic recording medium characterized by having a magnetic layer containing the magnetic powder having the above-described configuration and a binder on a nonmagnetic support. In particular, the magnetic recording medium having the above-described structure having at least one undercoat layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer, wherein the magnetic layer has a thickness of 10 nm to 300 nm. Can be provided.

As described above, the present invention provides an iron nitride system having a specific configuration in which the powder surface is composed of a compound layer having a specific thickness containing at least one element selected from rare earth elements or boron, silicon, aluminum, and phosphorus. With magnetic powder, magnetic powder having high coercive force and moderate saturation magnetization and excellent storage stability can be realized, and by using this magnetic powder, there is no problem of output reduction due to recording demagnetization, A coating-type magnetic recording medium having an ultra-thin magnetic layer of 300 nm or less can be realized, which can achieve high output and excellent short wavelength recording characteristics. It can be expressed.

The present inventors have synthesized various magnetic powders and investigated their shapes and magnetic anisotropy in order to improve magnetic properties from a viewpoint different from conventional magnetic powders based on shape magnetic anisotropy. A compound containing at least iron and nitrogen as constituent elements and containing at least an Fe ₁₆ N ₂ phase and the surface of the magnetic powder containing a rare earth element or at least one element selected from boron, silicon, aluminum, and phosphorus It was found that the iron nitride-based magnetic powder composed of (1) exhibited chemically excellent properties at the same time as high magnetic anisotropy.

In this iron nitride-based magnetic powder, the content of nitrogen with respect to iron is preferably 1.0 to 20.0 atomic%, more preferably 5.0 to 18.0 atomic%, more preferably 8.0 to 15. It should be 0 atomic%. If the amount of nitrogen is too small, the amount of Fe ₁₆ N ₂ phase formed will be small and the effect of increasing the coercive force will be small. If the amount of nitrogen is too large, nonmagnetic nitride will be easily formed and the effect of increasing the coercive force will be small. Further, the saturation magnetization is excessively lowered.

The total content of rare earth elements or boron, silicon, aluminum, and phosphorus with respect to iron is preferably 0.1 to 40.0 atomic%, more preferably 1.0 to 30.0 atomic%, more preferably 3.0 to It should be 25.0 atomic%. If the amount of these elements is too small, it becomes difficult to form a surface compound layer, not only the magnetic anisotropy of the magnetic powder is reduced, but also the storage stability is poor. Moreover, when there are too many of these elements, the saturation magnetization will fall excessively easily.

The surface compound layer may be composed of any compound as long as it contains a rare earth element or at least one element selected from boron, silicon, aluminum, and phosphorus. Oxides, nitrides, carbides, and the like are easy to form and have excellent corrosion resistance, so they are highly convenient. Among these, an oxide is particularly preferable.

The thickness of the surface compound layer is preferably 1 to 5 nm. If it is thinner than 1 nm, the storage stability is inferior. If it is thicker than 5 nm, the proportion of the surface compound layer in the magnetic powder increases, and as the particle size becomes smaller, an appropriate saturation magnetization cannot be maintained.

The magnetic powder of the present invention has a granular or elliptical shape different from conventional acicular particles. The particle size is not particularly limited, but it is desirable that the average particle size is 50 nm or less in response to the demand for fine particles. If the particle size is too large, it not only causes an increase in noise but also makes it difficult to obtain a smooth magnetic layer surface.

Spherical or elliptical shape means that the average value of the axial ratio [ratio of major axis length (major axis) to minor axis length (minor axis)] is 1 or more and 2 or less (preferably 1 or more and 1.5 or less). In addition, those having irregularities on the surface and those having a slight deformation are included.

The average particle size is obtained by measuring the particle size of a photograph taken with a transmission electron microscope (TEM) and calculating an average value of 300 particles. Further, the surface compound layer is a compound different from the composition and crystal structure inside the particle existing on the surface of the particle, and the average thickness of the surface compound layer is a magnification (1 million times or more) at which these boundaries can be discriminated at least. For 10 particles of the photographed transmission electron micrograph, the thicknesses of 10 surface compound layers arbitrarily selected are measured and obtained as the average thickness.

It is desirable to select a particle corresponding to the average particle size as the measurement particle, and the boundary between the surface compound and the inside of the particle is a contrast or lattice image of an electron micrograph, or a microscopic analysis using a field emission transmission electron microscope (FE-TEM). It is desirable to discriminate by such as.

The magnetic powder of the present invention thus configured has a saturation magnetization of 50 to 150 Am ² / kg (50 to 150 emu / g), preferably 70 to 150 Am ² / kg (70 to 150 emu / g), more preferably 80. It is ˜145 Am ² / kg (80 to 145 emu / g), and has an appropriate saturation magnetization that is not excessively high as in the conventional magnetic powders (Patent Documents 1 and 2). Further, the coercive force is 119.4 to 318.5 kA / m (1,500 to 4,000 oersted), preferably 159.2 to 278.6 kA / m (2,500 to 3,500 oersted). Compared with magnetic powder (of Patent Documents 1 and 2), it has a coercive force that is about 15 to 25% higher.

Further, this magnetic powder exhibits optimum performance for a magnetic recording medium when the BET specific surface area is in the range of 40 to 100 m ² / g. When the BET specific surface area is too small, the particle size increases, and when applied to a magnetic recording medium, particulate noise increases, the surface smoothness of the magnetic layer decreases, and the reproduction output tends to decrease. Further, if the BET specific surface area is too large, it is difficult to obtain a uniform dispersion in the magnetic paint due to the aggregation of the magnetic powder, and when applied to a magnetic recording medium, the orientation tends to decrease and the surface smoothness tends to decrease. .

In this way, it is a granular or elliptical magnetic powder containing at least iron and nitrogen as constituent elements, containing at least the Fe ₁₆ N ₂ phase, and having a nitrogen content with respect to iron defined in the specific range, and the surface of the powder is the specific element. According to the magnetic powder composed of a compound layer with a specific thickness including, it has finer particles and higher coercive force than the conventional one, and exhibits an appropriate saturation magnetization and excellent storage stability. When stored as it is or in a magnetic recording medium in a high-temperature and high-humidity environment, there is little deterioration in magnetic properties such as saturation magnetization, and coupled with the above properties, high density such as digital video tapes and computer backup tapes. The performance suitable for the magnetic recording medium for recording can be exhibited.

The reason why such an effect is achieved is not necessarily clear, but is considered as follows. That is, by combining the high magnetocrystalline anisotropy of the Fe ₁₆ N ₂ phase with the surface magnetic anisotropy of the surface compound layer, it exhibits a unique performance not found in conventional magnetic powders, This is considered to be based on many factors, such as a higher coercivity being easily obtained when the thickness is in a specific range.

In order to obtain a higher coercive force while maintaining the shape of the magnetic powder of the present invention, the magnetic powder has a multi-layer structure of an inner layer and an outer layer, the inner layer is an Fe phase, and the outer layer portion is a rare earth element or boron, silicon, aluminum. And a compound containing at least one element selected from phosphorus. Inner layer of Fe phase and Fe ₁₆ N ₂ phase, but need not be all the inner Fe ₁₆ N ₂ phase, or a mixed phase of Fe ₁₆ N ₂ phase and alpha-Fe phase or Fe ₄ N phase. Rather, by adjusting these mixing ratios, there is an advantage that desired magnetic characteristics can be set.

In the magnetic powder of the present invention, examples of rare earth elements include yttrium, ytterbium, cesium, praseodymium, lanthanum, europium, and neodymium. Among these, yttrium, samarium or neodymium has a large effect of maintaining the particle shape during reduction as well as an effect of improving the coercive force.

Moreover, carbon, magnesium, titanium, manganese, etc. can also be used as needed as elements other than said rare earth element, and also boron, silicon, aluminum, and phosphorus. By using these elements in combination, it is possible to design a material in consideration of desired magnetic properties, storage stability, and cost.

Next, a method for producing the magnetic powder of the present invention will be described.

As a starting material, an iron-based oxide or hydroxide is used. For example, hematite, magnetite, goethite and the like can be mentioned. The average particle size is not particularly limited, but usually it is preferably about 5 to 100 nm. If the particle size is too small, inter-particle sintering is likely to occur during the reduction treatment, and if the particle size is too large, the reduction treatment tends to be heterogeneous, making it difficult to control the particle size and magnetic properties.

First, a rare earth element or a compound containing at least one element selected from boron, silicon, aluminum, phosphorus and the like is deposited on the starting material. When depositing a rare earth element, a starting material is usually dispersed in an aqueous solution of an alkali or acid, a salt of the rare earth element is dissolved therein, a hydroxide containing a rare earth element in the raw material powder by a neutralization reaction, etc. What is necessary is just to precipitate a hydrate.

When depositing a compound containing at least one element selected from boron, silicon, aluminum, phosphorus, etc., these compounds are dissolved in a solution in which the raw material powder is immersed and deposited by adsorption, The deposition is carried out by precipitation.

A rare earth element and at least one element selected from boron, silicon, aluminum, phosphorus and the like may be simultaneously or alternately deposited on the raw material powder. Moreover, in order to perform these adhesion processes efficiently, you may make it mix additives, such as a reducing agent, a pH buffer agent, and a particle size control agent.

Next, the raw material powder to which the compound is deposited in this way is heated and reduced in a hydrogen stream. The reducing gas to be used is not particularly limited, and a reducing gas such as carbon monoxide gas can be used in addition to the hydrogen gas.

The reduction temperature is preferably 300 to 600 ° C. When the reduction temperature is lower than 300 ° C., the reduction reaction does not proceed sufficiently, and when it exceeds 600 ° C., the powder particles are likely to be sintered, which is not preferable.

After such heat reduction treatment, nitriding treatment is performed. The nitriding treatment is desirably performed using a gas containing ammonia. In addition to ammonia gas alone, a mixed gas using hydrogen gas, helium gas, nitrogen gas, argon gas or the like as a carrier gas may be used. Nitrogen gas is particularly preferred because it is inexpensive.

The nitriding temperature is preferably 100 to 300 ° C. If the nitriding temperature is too low, nitriding does not proceed sufficiently and the effect of increasing the coercive force is small. When nitriding treatment temperature is too high, nitride is excessively accelerated, increasing percentage of such Fe ₄ N and Fe ₃ N phase is rather decreased coercive force, further, tends to cause excessive reduction of the saturation magnetization.

After such nitriding treatment, an oxidation treatment is performed to obtain a magnetic powder having iron and nitrogen as at least constituent elements, at least an Fe ₁₆ N ₂ phase, and an appropriate surface compound layer. The oxidation treatment is desirably performed using a mixed gas containing oxygen. For this, nitrogen gas, argon gas, helium gas, or the like can be used.

The temperature of the oxidation treatment is preferably 200 ° C. or less. If this temperature is too high, the oxidation proceeds excessively, the iron nitride phase is remarkably reduced, and the coercive force and saturation magnetization are liable to be deteriorated.

The magnetic powder of the present invention thus obtained differs from the acicular magnetic powder based only on the conventional shape magnetic anisotropy, and exhibits a large coercive force and an appropriate saturation magnetization even in the granular shape. It has excellent storage stability, and saturation magnetization, coercive force, and particle shape are all essentially suitable for obtaining a thin magnetic layer.

That is, the magnetic recording medium of the present invention in which the magnetic layer containing the magnetic powder and the binder is provided on the nonmagnetic support has a high coercive force and an appropriate saturation within a range in which recording / erasing can be performed with a magnetic head. As a coating type magnetic recording medium having a thin layer area, it exhibits excellent electromagnetic conversion characteristics and excellent storage stability.

As described above, in the present invention, a thin magnetic layer (for example, a magnetic layer having a thickness of 300 nm or less) is formed by using the specific magnetic powder described above, thereby achieving good recording / reproducing characteristics. However, the material has not only high crystal magnetic anisotropy, that is, high coercive force and moderate saturation magnetization, but also high storage stability, although the particle size is very small and spherical or elliptical magnetic powder. The point that has been found is an epoch-making thing that breaks the common knowledge of the material technology of the coating type magnetic recording medium.

The magnetic recording medium of the present invention prepares a magnetic coating material in which a magnetic powder having a specific configuration and a binder described above are dispersed and mixed in a solvent, which is coated on a nonmagnetic support and dried to form a magnetic layer. Can be produced. Prior to the formation of the magnetic layer, an undercoat containing nonmagnetic powder such as iron oxide, titanium oxide, and aluminum oxide and a binder is applied onto the nonmagnetic support and dried to form an undercoat layer thereon. A magnetic layer may be formed.

Hereinafter, (a) a nonmagnetic support, (b) a magnetic layer, and (c) an undercoat layer will be described as components of the magnetic recording medium of the present invention. The (d) binder and (e) lubricant used for the magnetic layer and undercoat layer will be described.

Further, when the magnetic recording medium is a magnetic tape, it is desirable to form a backcoat layer by applying a backcoat paint on the side opposite to the magnetic layer forming surface of the nonmagnetic support and drying it. This back coat layer will also be described.

In addition, (g) Solvents used in magnetic paints, undercoat paints, back coat paints, (h) Dispersion and application methods of the above-mentioned paints, and (li) LRT treatment methods for magnetic layers in the manufacture of magnetic recording media. To do.

(A) Nonmagnetic support As the nonmagnetic support, any conventionally used nonmagnetic support for magnetic recording media can be used. For example, the thickness composed of polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins, cellulose triacetate, polycarbonate, polyamide, polyimide, polyamideimide, polysulfone, aramid, aromatic polyamide and the like is usually 2 to 15 μm, particularly 2 to 2 μm. A 7 μm plastic film is used. If the thickness is less than 2 μm, it is difficult to form a film, and the tape strength is reduced.

In the magnetic tape, a nonmagnetic support having anisotropy in Young's modulus is used. The Young's modulus in the longitudinal direction of the non-magnetic support varies depending on the thickness of the non-magnetic support, but usually 4.9 GPa (500 kg / mm ² ) or more is used. When the thickness of the non-magnetic support is 5 μm or less, a material having a Young's modulus of 9.8 GPa (1,000 kg / mm ² ) or more is preferably used. If the Young's modulus is too small, the strength of the magnetic tape becomes weak or the running of the magnetic tape becomes unstable.

When the Young's modulus in the longitudinal direction of the non-magnetic support is MD and the Young's modulus in the width direction is TD, the ratio (MD / TD) of both is 0.60 to 0.80 in the helical scan system. preferable. This range is preferable because the mechanism is unknown at present, but the output variation (flatness) between the entrance side and the exit side of the track of the magnetic head becomes large. In the linear track system, 1.0 to 1.8 is preferable, and 1.1 to 1.7 is more preferable. This range is preferable because the head touch is improved. Such nonmagnetic supports include polyethylene terephthalate films, polyethylene naphthalate films, aromatic polyamide films, aromatic polyimide films and the like.

(B) Magnetic layer The thickness of the magnetic layer is a thin layer of 300 nm or less in order to solve the problem of output reduction due to demagnetization, which is an essential problem in longitudinal recording. The thickness of the magnetic layer is determined by the relationship with the recording wavelength to be used, and the effect of the present invention is particularly remarkable when applied to a system having the shortest recording wavelength of 1.0 μm or less.

Thus, the thickness of the magnetic layer is preferably 300 nm or less, particularly preferably 10 to 300 nm, more preferably 10 to 250 nm, and most preferably 10 to 200 nm. If it exceeds 300 nm, the reproduction output becomes small due to the thickness loss, or the product of the residual magnetic flux density and the thickness becomes too large, and the reproduction output is distorted due to saturation of the MR head. If it is less than 10 nm, it is difficult to obtain a uniform magnetic layer.

In the present invention, since the magnetic powder is in the form of very fine particles or ellipses, it is possible to realize a very thin magnetic layer thickness that is almost impossible with conventional acicular magnetic powders.

In the case of a magnetic tape, the coercive force in the longitudinal direction of the magnetic layer is 79.6 to 318.4 kA / m (1,000 to 4,000 Oe), preferably 119.4 to 318.4 kA / m (1,500 ~ 4,000 Oe). If the recording wavelength is shorter than 79.6 kA / m, the output is likely to decrease due to demagnetization, and if it exceeds 318.4 kA / m, recording with a magnetic head becomes difficult.

The squareness ratio (Br / Bm) in the longitudinal direction of the magnetic layer is usually 0.6 to 0.9, particularly preferably 0.8 to 0.9.

Further, the product of the saturation magnetic flux density in the longitudinal direction and the thickness of the magnetic layer is 0.001 to 0.1 μTm, preferably 0.0015 to 0.05 μTm. If it is less than 0.001 μTm, the reproduction output is small even when an MR head is used, and if it exceeds 0.1 μTm, it tends to be difficult to obtain a high output in the intended short wavelength region.

Further, the average surface roughness Ra of the magnetic layer is 1.0 to 3.2 nm. When the central value of the unevenness of the magnetic layer is P0 and the maximum protrusion amount is P1, (P1−P0) is When 10th to 30 nm and the 20th convex amount is P20, if (P1 -P20) is 5 nm or less, contact with the MR head is improved when the MR head is used, and the MR head is used. When this is done, the reproduction output becomes high, which is preferable.

For the purpose of improving electrical conductivity and surface lubricity, the magnetic layer preferably contains conventionally known carbon black. As this carbon black, acetylene black, furnace black, thermal black, etc. can be used. The average particle diameter is preferably 5 to 200 nm, more preferably 10 to 100 nm. When the thickness is less than 5 nm, it is difficult to disperse the carbon black. When the thickness exceeds 200 nm, it is necessary to include a large amount of carbon black. In either case, the surface becomes rough, which tends to cause a decrease in output.

As content of carbon black, 0.2 to 5 weight% is preferable with respect to magnetic powder, and 0.5 to 4 weight% is more preferable. If it is less than 0.2% by weight, the effect is small, and if it exceeds 5% by weight, the surface of the magnetic layer tends to be rough.

(C) Undercoat layer The undercoat layer is not an essential component, but is provided between the nonmagnetic support and the magnetic layer for the purpose of improving durability. The thickness of the undercoat layer is preferably from 0.1 to 3.0 μm, more preferably from 0.15 to 2.5 μm.

If the thickness is less than 0.1 μm, the durability of the magnetic tape may be deteriorated. If the thickness exceeds 3.0 μm, the effect of improving the durability of the magnetic tape is saturated, and the total thickness of the tape is increased, resulting in a tape per roll. The length becomes shorter and the storage capacity becomes smaller.

The undercoat layer can contain nonmagnetic powders such as titanium oxide, iron oxide, and aluminum oxide for the purpose of controlling the viscosity of the paint and the tape rigidity.

Nonmagnetic iron oxide is preferably used alone or mixed with aluminum oxide. The content of nonmagnetic iron oxide is usually preferably 35 to 83% by weight, more preferably 40 to 80% by weight. If it is less than 35% by weight, the effect of improving the coating film strength is small, and if it exceeds 83% by weight, the film strength is rather lowered. The content of aluminum oxide is usually 0 to 20% by weight, preferably 2 to 10% by weight.

Nonmagnetic iron oxide is acicular, granular or amorphous. The needle-like one preferably has an average major axis length of 50 to 200 nm and an average minor axis length (average particle size) of 5 to 200 nm, and the granular or amorphous one has an average particle size of 5 to 200 nm. Preferably, it is 5 to 150 nm, more preferably 5 to 100 nm. When the particle size is smaller than the above, uniform dispersion is difficult, and when the particle size is larger than the above, unevenness at the interface between the undercoat layer and the magnetic layer tends to increase.

The average particle diameter of aluminum oxide is preferably 10 to 100 nm, more preferably 20 to 100 nm, and most preferably 30 to 100 nm. When the average particle size is smaller than the above, uniform dispersion becomes difficult. When the average particle size is larger than the above, unevenness at the interface between the undercoat layer and the magnetic layer tends to increase.

The undercoat layer can contain carbon black such as acetylene black, furnace black, and thermal black for the purpose of improving conductivity.

These carbon blacks preferably have an average particle size of usually 5 to 200 nm, more preferably 10 to 100 nm. Carbon black has a structure structure. If the average particle size is too small, it becomes difficult to disperse the carbon black, and if it is too large, the surface smoothness becomes poor.

The carbon black content varies depending on the particle size of the carbon black, but is preferably 15 to 35% by weight. If it is less than 15% by weight, the effect of improving the conductivity is poor, and if it exceeds 35% by weight, the effect is saturated. It is more preferable to use 15 to 35% by weight of carbon black having an average particle diameter of 15 to 80 nm, and it is further preferable to use 20 to 30% by weight of carbon black having an average particle diameter of 20 to 50 nm. By including such a particle size and amount of carbon black, electrical resistance is reduced and running unevenness is reduced.

In addition, it is not excluded to include carbon black having a large particle size with an average particle size exceeding the above range as long as the surface smoothness is not impaired. In this case, the amount of carbon black used is preferably such that the sum of the small particle size carbon black and the large particle size carbon black is within the above-described range.

In the undercoat layer, 15 to 35% by weight of carbon black having an average particle size of 10 to 100 nm, an average major axis length of 50 to 200 nm, an average minor axis length of 5 to 5, based on the weight of all nonmagnetic powders in this layer When 35 to 83% by weight of 200 nm non-magnetic iron oxide and 0 to 20% by weight of aluminum oxide having an average particle diameter of 10 to 100 nm are included, the surface roughness of the magnetic layer formed thereon by wet-on-wet is small. It is preferable.

(D) Binder The binder used for the undercoat layer and magnetic layer is vinyl chloride resin, vinyl chloride-vinyl acetate copolymer resin, vinyl chloride-vinyl alcohol copolymer resin, vinyl chloride-vinyl acetate-vinyl alcohol copolymer. And at least one selected from vinyl chloride resins such as vinyl chloride-vinyl acetate-maleic anhydride copolymer resin, vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin, nitrocellulose, epoxy resin, and the like, polyurethane resin And the combination.

In particular, it is preferable to use a vinyl chloride resin and a polyurethane resin in combination. Among these, it is most preferable to use a vinyl chloride-hydroxyl group-containing alkyl acrylate copolymer resin and a polyurethane resin in combination.

Examples of the polyurethane resin include polyester polyurethane, polyether polyurethane, polyether polyester polyurethane, polycarbonate polyurethane, and polyester polycarbonate polyurethane.

As these binders, those having a functional group are preferable in order to improve the dispersibility of the magnetic powder and the like and to increase the filling property. As this functional group, COOM, SO ₃ M, OSO ₃ M, P═O (OM) ₃ , O—P═O (OM) ₂ (M is a hydrogen atom, an alkali metal salt or an amine salt), OH, NR ¹ R ² , NR ³ R ⁴ R ⁵ (R ¹ , R ² , R ³ , R ⁴ , R ⁵ are hydrogen or hydrocarbon groups, usually having 1 to 10 carbon atoms), epoxy groups, etc. . When two or more resins are used in combination, the polarities of the functional groups are preferably matched, and among them, a combination of —SO ₃ M groups is preferable.

These binders are generally used in an amount of 7 to 50 parts by weight, preferably 10 to 35 parts by weight, based on 100 parts by weight of a solid powder such as magnetic powder or nonmagnetic powder. In particular, it is preferable to use a composite of 5 to 30 parts by weight of a vinyl chloride resin and 2 to 20 parts by weight of a polyurethane resin as a binder.

In addition to these binders, it is desirable to use a thermosetting crosslinking agent that is bonded to a functional group contained in the binder and crosslinked. Examples of the crosslinking agent include tolylene diisocyanate, hexamethylene diisocyanate, isophorone diisocyanate, reaction products of these isocyanates with a plurality of hydroxyl groups such as trimethylolpropane, and condensation products of the above isocyanates. Various polyisocyanates are preferably used. The amount of these crosslinking agents used is usually preferably 10 to 50 parts by weight, more preferably 10 to 35 parts by weight, based on 100 parts by weight of the binder.

The amount of the crosslinking agent used for the magnetic layer is adjusted to 30 to 60% by weight (particularly about 1/2 of the amount of the crosslinking agent used for the undercoat layer) with the total amount of the crosslinking agent used for the undercoat layer. For example, the friction coefficient of the MR head against the slider is small, which is preferable.

This range is preferable if the coating strength of the magnetic layer tends to be weak when it is less than 30% by weight, and if it exceeds 60% by weight, the condition for wiping with a tissue (described later) is used to reduce the coefficient of friction against the slider. This is because it is necessary to increase the LRT processing conditions), leading to an increase in cost.

(E) Lubricant Conventionally known fatty acids, fatty acid esters, fatty acid amides and the like are used as the lubricant to be included in the undercoat layer and the magnetic layer. Among them, it is particularly preferable to use a fatty acid having 10 or more carbon atoms, preferably 12 to 30 carbon atoms, and a fatty acid ester having a melting point of 35 ° C. or lower, preferably 10 ° C. or lower.

The fatty acid having 10 or more carbon atoms may be any of isomers such as linear, branched and cis / trans, but is preferably a linear type having excellent lubricating performance. Examples of such fatty acids include lauric acid, myristic acid, stearic acid, palmitic acid, behenic acid, oleic acid, linoleic acid, and the like. Among these, myristic acid, stearic acid, palmitic acid and the like are preferable.

Fatty acid esters having a melting point of 35 ° C. or lower include n-butyl oleate, hexyl oleate, n-octyl oleate, 2-ethylhexyl oleate, oleyl oleate, n-butyl laurate, heptyl laurate, and n-myristate. Examples thereof include butyl, n-butoxyethyl oleate, trimethylolpropane trioleate, n-butyl stearate, s-butyl stearate, isoamyl stearate, and butyl cellosolve stearate. Since these fatty acid esters can control the oil film strength and the oil output by the difference in molecular weight, structure, and melting point, optimization by combination may be performed. By having the above melting point, even when exposed to low temperature and low humidity, it can easily exude and transfer to the surface of the magnetic layer at the time of high-speed sliding contact between the magnetic layer and the magnetic head, and can effectively exhibit its excellent lubricating action. it can.

In the case of a magnetic tape provided with an undercoat layer, it is desirable to contain lubricants having different roles in the coating layer composed of the undercoat layer and the magnetic layer.

The undercoat layer contains 0.5 to 4% by weight of higher fatty acid and 0.2 to 3% by weight of higher fatty acid ester with respect to the total powder. And the friction coefficient is small, which is preferable. When the amount of the higher fatty acid is less than 0.5% by weight, the effect of reducing the friction coefficient is reduced, and when it exceeds 4% by weight, the undercoat layer is plasticized and the toughness is easily lost. Further, when the amount of higher fatty acid ester is less than 0.5% by weight, the effect of reducing the friction coefficient is reduced, and when it exceeds 3% by weight, the amount of transfer to the magnetic layer is too large. Side effects such as sticking to guides are likely to occur.

The magnetic layer contains 0.2 to 3% by weight of fatty acid amide (for example, amides of higher fatty acids such as palmitic acid and stearic acid) with respect to the magnetic powder, and 0.2 to 3% by weight of higher fatty acid ester. Including this material is preferable because the friction coefficient between the magnetic tape and the guide of the traveling system, the slider of the MR head, etc. becomes small. If the amount of fatty acid amide is less than 0.2% by weight, the friction coefficient (dynamic friction coefficient) of the head slider / magnetic layer tends to increase, and if it exceeds 3% by weight, bleeding occurs and defects such as dropout occur. It's easy to do. If the amount of the higher fatty acid ester is less than 0.2% by weight, the effect of reducing the friction coefficient is small, and if it exceeds 3% by weight, side effects such as sticking of the magnetic tape and the guide of the running system tend to occur.

It does not exclude the mutual movement of the lubricant between the magnetic layer and the undercoat layer.

In the case of the MR head, the friction coefficient (μMsl) with the slider of the MR head is preferably 0.30 or less, and more preferably 0.25 or less. If it exceeds 0.30, spacing loss due to slider contamination is likely to occur. If it is less than 0.10, it is difficult to realize.

The coefficient of friction (SUS) with SUS is preferably 0.10 to 0.25, and more preferably 0.12 to 0.20. If it is less than 0.10, it is slippery at the guide portion and the running becomes unstable, and if it exceeds 0.25, the guide is easily soiled.

[(ΜMsl) / (μMsus)] is preferably 0.7 to 1.3, particularly preferably 0.8 to 1.2. As a result, tracking deviation (off-track) due to meandering of the magnetic tape is reduced.

(F) Backcoat layer The backcoat layer is not an essential component, but in the case of a magnetic tape, it is desirable to form a backcoat layer on the surface opposite to the magnetic layer forming surface of the nonmagnetic support.

The thickness of the back coat layer is preferably 0.2 to 0.8 μm, more preferably 0.3 to 0.8 μm, and still more preferably 0.3 to 0.6 μm. If the thickness is less than 0.2 μm, the effect of improving the running performance is insufficient. If the thickness exceeds 0.8 μm, the total thickness of the tape is increased and the storage capacity per roll is reduced.

Further, the center line surface roughness Ra of the backcoat layer is preferably 3 to 15 nm, and more preferably 4 to 10 nm.

The coefficient of friction (μBsus) between the backcoat layer and SUS is preferably 0.10 to 0.30, and more preferably 0.10 to 0.25. If it is less than 0.10, it will be slippery at a guide part, driving | running | working will become unstable, and if it exceeds 0.30, a guide will become dirty easily.

[(ΜMsl) / (μBsus)] is preferably 0.8 to 1.5, more preferably 0.9 to 1.4. By setting this range, tracking deviation (off-track) due to meandering of the magnetic tape is reduced.

The back coat layer contains carbon black such as acetylene black, furnace black, and thermal black. Usually, carbon black having a small particle size and carbon black having a large particle size are used in combination. The total amount of carbon black having a small particle size and carbon black having a large particle size is usually preferably 60 to 98% by weight and more preferably 70 to 95% by weight based on the weight of the inorganic powder.

As the carbon black having a small particle diameter, those having an average particle diameter of 5 to 100 nm are used, and those having an average particle diameter of 10 to 100 nm are more preferable. If the average particle size is too small, it will be difficult to disperse the carbon black. If the average particle size is too large, it will be necessary to add a large amount of carbon black. It tends to cause embossing.

As carbon black having a large particle size, 5-15% by weight of the carbon black having a small particle size and a carbon black having an average particle size of 300 to 400 nm are used. Become.

The back coat layer may contain additives usually added to the back coat layer such as iron oxide and aluminum oxide having an average particle diameter of 0.05 to 0.6 μm for the purpose of improving the strength. preferable. Those having an average particle diameter of 0.07 to 0.4 μm are more preferable, and those having an average particle diameter of 0.07 to 0.35 μm are more preferable. When the average particle size is less than 0.05 μm, the effect of improving the strength is reduced, and when the average particle size is more than 0.6 μm, the surface roughness of the backcoat layer becomes rough, and the back to the magnetic layer is likely to occur. .

The additive such as iron oxide is preferably 2 to 40% by weight, more preferably 2 to 30% by weight, further preferably 2 to 20% by weight, and 5 to 15% by weight based on the weight of the inorganic powder. Most preferred. If it is less than 2% by weight, the effect of improving the strength is small, and if it exceeds 40% by weight, the surface roughness of the backcoat layer tends to be rough.

Normally, iron oxide or the like is added alone. However, when iron oxide and aluminum oxide are added simultaneously, the amount of aluminum oxide added is preferably 20% by weight or less of iron oxide.

In the backcoat layer, the same resin as that used for the magnetic layer and the undercoat layer can be used as a binder, and among them, a cellulose resin and a polyurethane resin are used in combination in order to reduce the friction coefficient and improve the runnability. Is preferred.

The amount of the binder is usually 40 to 150 parts by weight, particularly preferably 50 to 120 parts by weight, and preferably 60 to 110 parts by weight with respect to 100 parts by weight of the total amount of carbon black and the inorganic nonmagnetic powder. Is more preferable, and 70-110 weight part is further more preferable. If the amount of the binder is too small, the strength of the backcoat layer becomes insufficient, and if the amount of the binder is too large, the friction coefficient tends to be high. It is most preferable to use 30 to 70 parts by weight of cellulose resin and 20 to 50 parts by weight of polyurethane resin.

In the back coat layer, it is desirable to use a crosslinking agent in order to cure the binder. As the crosslinking agent, the same polyisocyanate compound used for the magnetic layer and the undercoat layer can be used. The amount of the crosslinking agent is usually 10 to 50 parts by weight, particularly preferably 10 to 35 parts by weight, and more preferably 10 to 30 parts by weight with respect to 100 parts by weight of the binder. If the amount of the crosslinking agent is too small, the coating strength of the backcoat layer tends to be weak, and if the amount of the crosslinking agent is too large, the dynamic friction coefficient against SUS tends to increase.

(G) Solvents of paints In preparing magnetic paints, undercoat paints, and back coat paints, all conventionally used organic solvents can be used as solvents. For example, aromatic solvents such as benzene, toluene and xylene, ketone solvents such as acetone, cyclohexanone, methyl ethyl ketone and methyl isobutyl ketone, ester solvents such as ethyl acetate and butyl acetate, carbonate esters such as dimethyl carbonate and diethyl carbonate Solvents and alcohol solvents such as ethanol and isopropanol can be used. In addition, various organic solvents such as hexane, tetrahydrofuran and dimethylformamide are used.

(H) Dispersion and coating method of paints In preparing magnetic paints, undercoat paints and back coat paints, conventionally known paint production processes can be used, and it is particularly preferable to use a kneading process using a kneader or the like and a primary dispersion process. In the primary dispersion step, it is desirable to use a sand mill because the surface properties can be controlled while improving the dispersibility of the magnetic powder and the like.

Further, when applying a magnetic paint, an undercoat paint, or a backcoat paint on a nonmagnetic support, conventionally known coating methods such as gravure coating, roll coating, blade coating, and extrusion coating are used. The undercoat paint and magnetic paint can be applied by applying the undercoat paint on the non-magnetic support and drying, then applying the magnetic paint, or by applying the successive overlay coating method or by applying the undercoat paint and the magnetic paint simultaneously. Any of the application methods (wet on wet) may be adopted. Considering the leveling of the thin magnetic layer at the time of coating, it is preferable to adopt a simultaneous multilayer coating method in which the magnetic coating is applied while the undercoat coating is wet.

(L) LRT processing method For the magnetic layer, the surface smoothness, friction coefficient with MR head slider material and cylinder material, surface roughness, and surface shape are optimized by applying the LRT processing, and the magnetic tape travels. Thus, the reduction of the spacing loss and the improvement of the MR reproduction output can be achieved.

The LRT processing includes (a) lapping processing, (b) rotary processing, and (c) tissue processing as described below.

(A) Lapping process The polishing tape (wrapping tape) is moved at a constant speed (standard: 14.4 cm / min) in the opposite direction to the tape feed (standard: 400 m / min) by a rotating roll, and is guided from the top. The magnetic tape is brought into contact with the surface of the tape magnetic layer, and the polishing treatment is performed with the magnetic tape unwinding tension and the tension of the polishing tape being constant (standard: 100 g and 250 g, respectively).

The polishing tape used for this treatment is, for example, a polishing tape having fine abrasive grains such as M20000, WA10000, and K10000. The use of a polishing wheel (wrapping wheel) instead of or in combination with the polishing tape is not excluded, and when frequent replacement is required, only the polishing tape is used.

(B) Rotary treatment A grooved wheel for air venting [standard: width 1 inch (25.4 mm), diameter 60 mm, air venting groove 2 mm width, groove angle 45 degrees, manufactured by Kyowa Seiko Co., Ltd.] and a magnetic layer, The treatment is performed by contacting at a constant contact angle (standard: 90 degrees) at a constant rotational speed (normal: 200 to 3,000 rpm, standard: 1,100 rpm) in the direction opposite to the tape.

(C) Tissue treatment A tissue (for example, a woven cloth Toraysee manufactured by Toray Industries, Inc.) is fed at a constant speed (standard: 14 mm / min) in the opposite direction to the tape feed with a rotating rod on the back coat layer and the magnetic layer surface, respectively. Perform a cleaning process.

Hereinafter, as Examples of the present invention, “Examples 1 to 4” relating to magnetic powder and “Examples 5 to 9” relating to magnetic tapes which are magnetic recording media will be described in more detail.

In addition, “Comparative Examples 1 and 4” as the control examples of “Examples 1 to 4” and “Comparative Examples 3 and 4” as the control examples of “Examples 5 to 9” are also described.

In the following description, “parts” means parts by weight.

10 g of magnetite particles having an average particle size of approximately 25 nm and a substantially spherical shape were dispersed in 500 cc of water for 30 minutes using an ultrasonic disperser. To this dispersion, 3.0 g of yttrium nitrate was added and dissolved, and stirred for 30 minutes. Separately, 0.8 g of sodium hydroxide was dissolved in 100 cc of water.

The above sodium hydroxide aqueous solution was dropped into the above dispersion over about 30 minutes, and after completion of the dropping, the mixture was further stirred for 1 hour. By this treatment, yttrium hydroxide was deposited on the surface of the magnetite particles. This was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which yttrium hydroxide was deposited on the surface of magnetite particles.

The powder obtained by depositing yttrium hydroxide on the surface of the magnetite particles was heated and reduced at 450 ° C. for 2 hours in a hydrogen stream. Next, the temperature was lowered to 150 ° C. over about 1 hour in a state of flowing hydrogen gas. When the temperature reached 150 ° C., the gas was switched to ammonia gas, and nitriding was performed for 30 hours while maintaining the temperature at 150 ° C.

Thereafter, the ammonia gas was switched to nitrogen gas, and the temperature was lowered from 150 ° C to 100 ° C. When the temperature reached 100 ° C., the mixture was switched to a mixed gas of oxygen and nitrogen, and oxidation treatment was performed for 3 hours. Next, the temperature was lowered from 100 ° C. to 30 ° C. in the state of flowing the mixed gas, and the surface compound layer was formed at 30 ° C. for about 12 hours and taken out into the air.

With respect to the iron nitride magnetic powder thus obtained, the contents of yttrium and nitrogen were measured by fluorescent X-ray and found to be 5.3 atomic% and 10.8 atomic%, respectively, with respect to Fe. Further, from the X-ray diffraction pattern to obtain a profile indicating a Fe ₁₆ N ₂ phase. Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were almost spherical and the average particle size was 20 nm.

The thickness of the surface compound layer was 2.0 nm. When the surface compound was analyzed by X-ray photoelectron spectroscopy, it was found that the surface compound layer was an oxide layer containing yttrium. FIG. 1 shows a transmission electron micrograph of this magnetic powder. The specific surface area determined by the BET method was 53.2 m ² / g.

Next, for this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 144.2 Am ² / kg (144.2 emu / g), and the coercive force is 250.8 kA / m (3,150 oersted).

Further, after storing this magnetic powder at 60 ° C. and 90% RH for 1 week, the saturation magnetization was measured in the same manner as described above. As a result, it was 132.4 Am ^{2 /} kg (132.4 emu / g). The magnetization maintenance ratio was 91.8%.

An iron nitride magnetic powder was obtained by the same operation as in Example 1 except that the magnetite particles having an average particle size of 25 nm as the starting material were changed to magnetite particles having an average particle size of 20 nm.

With respect to the iron nitride magnetic powder thus obtained, the contents of yttrium and nitrogen were measured by fluorescent X-ray and found to be 6.1 atomic% and 13.1 atomic%, respectively, with respect to Fe. Further, from the X-ray diffraction pattern to obtain a profile indicating a Fe ₁₆ N ₂ phase. Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were spherical or elliptical and had an average particle size of 15 nm.

The thickness of the surface compound layer was 2.0 nm. When the surface compound was analyzed by X-ray photoelectron spectroscopy, it was found that the surface compound layer was an oxide layer containing yttrium. FIG. 2 shows a transmission electron micrograph of this magnetic powder. The specific surface area determined by the BET method was 60.1 m ² / g.

Next, the magnetic powder, the saturation magnetization was measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 135.8Am ² /kg(135.8emu/g), coercive force 226.9KA / m (2,850 oersted).

In addition, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above, resulting in 121.2 Am ^{2 /} kg (121.2 emu / g). The magnetization maintenance ratio was 89.3%.

An iron nitride magnetic powder was obtained in the same manner as in Example 1 except that the oxidation treatment temperature was changed from 100 ° C to 140 ° C.

The iron nitride magnetic powder thus obtained was measured for the yttrium and nitrogen contents by fluorescent X-ray and found to be 5.5 atomic% and 9.5 atomic%, respectively, with respect to Fe. Further, from the X-ray diffraction pattern to obtain a profile indicating a Fe ₁₆ N ₂ phase. Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were spherical or elliptical and had an average particle size of 20 nm.

The thickness of the surface compound layer was 4.0 nm. When the surface compound was analyzed by X-ray photoelectron spectroscopy, it was found that the surface compound layer was an oxide layer containing yttrium. The specific surface area determined by the BET method was 55.6 m ² / g.

Next, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 129.6 Am ² / kg (129.6 emu / g), and the coercive force is 254.8 kA / m (3,200 oersteds).

In addition, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above. As a result, it was 120.6 Am ^{2 /} kg (120.6 emu / g). The maintenance ratio of magnetization was 93.1%.

10 g of magnetite particles having an average particle size of 25 nm were dispersed in 500 cc of water for 30 minutes using an ultrasonic disperser. To this dispersion, 2.0 g of sodium silicate was added and dissolved, and stirred for 30 minutes. To this, 10 ml of a 1N nitric acid aqueous solution was dropped over about 30 minutes. After completion of dropping, the mixture was further stirred for 2 hours. By this treatment, a silicon compound was deposited on the surface of the magnetite particles. This was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which a silicon compound was deposited on the surface of magnetite particles.

The powder obtained by depositing silicon hydroxide on the surface of the magnetite particles was heated and reduced at 450 ° C. for 2 hours in a hydrogen stream. Next, the temperature was lowered to 150 ° C. over about 1 hour in a state of flowing hydrogen gas. When the temperature reached 150 ° C., the gas was switched to ammonia gas, and nitriding was performed for 30 hours while maintaining the temperature at 150 ° C.

Thereafter, the ammonia gas was switched to nitrogen gas, and the temperature was lowered from 150 ° C to 100 ° C. When the temperature reached 100 ° C., the mixture was switched to a mixed gas of oxygen and nitrogen, and oxidation treatment was performed for 3 hours. Next, the temperature was lowered from 100 ° C. to 30 ° C. in the state of flowing the mixed gas, and the surface compound layer was formed at 30 ° C. for about 12 hours and taken out into the air.

With respect to the iron nitride magnetic powder thus obtained, the silicon and nitrogen contents were measured by fluorescent X-ray and found to be 8.1 atomic% and 11.9 atomic%, respectively, with respect to Fe. Further, from the X-ray diffraction pattern to obtain a profile indicating a Fe ₁₆ N ₂ phase. Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were spherical or elliptical and had an average particle size of 20 nm.

The thickness of the surface compound layer was 2.0 nm. When the surface compound was analyzed by X-ray photoelectron spectroscopy, it was found that the surface compound layer was an oxide layer containing silicon. The specific surface area determined by the BET method was 58.5 m ² / g.

Next, for this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 130.2 Am ² / kg (130.2 emu / g), and the coercive force is 235.7 kA / g. m (2,960 oersteds).

Further, after storing this magnetic powder at 60 ° C. and 90% RH for 1 week, the saturation magnetization was measured in the same manner as described above. As a result, it was 119.7 Am ^{2 /} kg (119.7 emu / g), which was saturated before storage. The maintenance ratio of magnetization was 91.9%.

Comparative Example 1
An iron nitride-based magnetic powder was obtained in the same manner as in Example 1 except that the oxidation treatment was not performed and the sample was held at room temperature for 2 days and then taken out.

With respect to the iron nitride magnetic powder thus obtained, the contents of yttrium and nitrogen were measured by fluorescent X-ray and found to be 4.9 atomic% and 11.8 atomic%, respectively, with respect to Fe. Further, from the X-ray diffraction pattern to obtain a profile indicating a Fe ₁₆ N ₂ phase. Furthermore, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were spherical or elliptical and had an average particle size of 20 nm.

The thickness of the surface compound layer was 0.8 nm. When the surface compound was analyzed by X-ray photoelectron spectroscopy, it was found that the surface compound layer was an oxide layer containing yttrium. The specific surface area determined by the BET method was 52.3 m ² / g.

Next, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 154.3 Am ² / kg (154.3 emu / g), and the coercive force is 221.3 kA / g. m (2,780 oersteds).

Further, after storing this magnetic powder at 60 ° C. and 90% RH for one week, the saturation magnetization was measured in the same manner as described above, resulting in 133.7 Am ^{2 /} kg (133.7 emu / g). The magnetization maintenance ratio was 86.7%.

Comparative Example 2
An iron nitride magnetic powder was obtained in the same manner as in Example 1 except that the oxidation treatment temperature was changed from 100 ° C to 300 ° C.

With respect to the iron nitride magnetic powder thus obtained, the contents of yttrium and nitrogen were measured by fluorescent X-ray and found to be 2.8 atomic% and 1.5 atomic%, respectively, with respect to Fe. Further, from the X-ray diffraction pattern to obtain a profile indicating a Fe ₁₆ N ₂ phase. Further, when the particle shape was observed with a high-resolution analytical transmission electron microscope, it was found that the particles were spherical or elliptical and had an average particle size of 21 nm.

The thickness of the surface compound layer was 6.0 nm. When the surface compound was analyzed by X-ray photoelectron spectroscopy, it was found that the surface compound layer was an oxide layer containing yttrium. The specific surface area determined by the BET method was 57.5 m ² / g.

Next, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 45.6 Am ² / kg (45.6 emu / g), and the coercive force is 182.3 kA / m (2,290 oersteds).

Further, the magnetic powder 60 ° C., then stored for 1 week under 90% RH, results of measuring the saturation magnetization as above, 43.3Am ² /kg(43.3emu/g) next, before storage saturation The maintenance ratio of magnetization was 95.0%.

The production conditions of the iron nitride magnetic powders of Examples 1 to 4 and Comparative Examples 1 and 2 are summarized in Table 1. In addition, the elemental composition (nitrogen, yttrium and silicon atom%), average particle size, surface compound layer thickness, and BET specific surface area of each of the iron nitride magnetic powders of Examples 1 to 4 and Comparative Examples 1 and 2 above. Are summarized in Table 2. Further, Table 3 summarizes the saturation magnetization, coercive force, and storage stability (saturation magnetization and retention rate after storage) of the iron nitride magnetic powders of Examples 1 to 4 and Comparative Examples 1 and 2 described above. It was.

Table 1
┌────┬────┬────────┬────────┬────────┐
│ │ Raw material powder │ Reduction condition │ Nitriding condition │ Oxidation condition │
│ │ average grain ├────┬───┼────┬───┼────┬───┤
│ │ Child size │ Processing temperature │ Time │ Processing temperature │ Time │ Processing temperature │ Time │
│ │ (nm) │ (℃) │ (h) │ (℃) │ (h) │ (℃) │ (h) │
├────┼────┼────┼───┼────┼───┼────┼───┤
│Example 1│ 25 │ 450 │ 2 │ 150 │ 30 │ 100 │ 3 │
│ │ │ │ │ │ │ │ │
│Example 2│ 20 │ 450│ 2 │ 150│ 30│ 100│ 3 │
│ │ │ │ │ │ │ │ │
│Example 3│ 25 │ 450│ 2 │ 150│ 30│ 140│ 3 │
│ │ │ │ │ │ │ │ │
│Example 4│ 25 │ 450 │ 2 │ 150 │ 30 │ 130 │ 3 │
├────┼────┼────┼───┼────┼───┼────┼───┤
│Comparative Example 1│ 25 │ 450 │ 2 │ 150 │ 30 │ None │ │ │
│ │ │ │ │ │ │ │ │
│Comparative Example 2│ 25 │ 450 │ 2 │ 150 │ 30 │ 300 │ 3 │
└────┴────┴────┴───┴────┴───┴────┴───┘

Table 2
┌────┬──────────────┬────┬──────┬────┐
│ │ Composition (atomic%) │Average particle│Surface compound layer│BET │
│ ├────┬────┬────┤Size │Thickness │Specific surface area│
│ │ Nitrogen │ Good │ Silicon │ │ │ │
│ │ │um │ │ (nm) │ (nm) │ (m ² / g) │
├────┼────┼────┼────┼────┼──────┼────┤
│Example 1│10.8│ 5.3│ 0 │ 20 │ 2.0 │53.2│
│ │ │ │ │ │ │ │
│Example 2│13.1│ 6.1│ 0 │ 15 │ 2.0 │60.1│
│ │ │ │ │ │ │ │
│Example 3│ 9.5 │ 5.5 │ 0 │ 20 │ 4.0 │55.6│
│ │ │ │ │ │ │ │
│Example 4│11.9│ 0 │ 8.1│ 20 │ 2.0 │58.5│
├────┼────┼────┼────┼────┼──────┼────┤
│Comparative Example 1│11.8│ 4.9│ 0 │ 20 │ 0.8 │52.3│
│ │ │ │ │ │ │ │
│Comparative Example 2│ 1.5│ 2.8 │ 0 │ 21 │ 6.0 │57.5│
└────┴────┴────┴────┴────┴──────┴────┘

Table 3
┌────┬─────┬─────┬──────────────┐
│ │ │ │ Storage stability │
│ │ Saturation │ Coercive force ├────────┬─────┤
│ │ (Am ² / kg) │ (kA / m) │ Saturation magnetization after storage │ Maintenance ratio │
│ │ │ │ (Am ² / kg) │ (%) │
├────┼─────┼─────┼────────┼─────┤
Example 1 | 144.2 | 250.8 | 132.4 | 91.8 |
│ │ │ │ │ │
│Example 2│135.8│226.9│ 121.2 │ 89.3│
│ │ │ │ │ │
│Example 3│129.6│254.8│ 120.6 │ 93.1│
│ │ │ │ │ │
Example 4 | 130.2 | 235.7 | 119.7 | 91.9 |
├────┼─────┼─────┼────────┼─────┤
│Comparative Example 1│154.3│221.3│ 133.7 │ 86.7│
│ │ │ │ │ │
│Comparative Example 2│ 45.6│182.3│ 43.3 │ 95.0│
└────┴─────┴─────┴────────┴─────┘

As is clear from the results of Tables 1 to 3, the iron nitride magnetic powders of Examples 1 to 4 of the present invention are about 130 to 144 Am compared to the iron nitride magnetic powders of Comparative Examples 1 and 2. ^It has a moderate saturation magnetization of about ² / kg, a high coercive force, a high retention ratio of the saturation magnetization after storage, and a very good storage stability.

The following undercoat paint components were kneaded with a kneader and then subjected to a dispersion treatment using a sand mill with a residence time of 60 minutes. To this, 6 parts of polyisocyanate was added, followed by stirring and filtration to prepare an undercoat paint. Separately, the following magnetic coating component (1) using the iron nitride magnetic powder of Example 1 was kneaded with a kneader, and then dispersed in a sand mill with a residence time of 45 minutes. (2) was added and mixed to prepare a magnetic paint.

<Undercoat paint component>
Iron oxide powder (average particle size: 55 nm) 70 parts

Aluminum oxide powder (average particle size: 80 nm) 10 parts

Carbon black (average particle size: 25 nm) 20 parts

10 parts of vinyl chloride-hydroxypropyl methacrylate copolymer resin (containing -SO ₃ Na group: 0.7 × 10 ^-4 equivalent / g)

Polyester polyurethane resin 5 parts (containing -SO ₃ Na group: 1.0 × 10 ^-4 equivalent / g)

Methyl ethyl ketone 130 parts

80 parts of toluene

Myristic acid 1 part

Butyl stearate 1.5 parts

65 parts of cyclohexanone

<Magnetic paint component (1)>
100 parts of iron nitride-based magnetic powder of Example 1

8 parts of vinyl chloride-hydroxypropyl acrylate copolymer resin (containing-SO ₃ Na group: 0.7 × 10 ⁻⁴ equivalent / g)

Polyester polyurethane resin 4 parts (containing -SO ₃ Na group: 1.0 × 10 ^-4 equivalent / g)

α-alumina (average particle size: 80 nm) 10 parts

Carbon black (average particle size: 25 nm) 1.5 parts

1.5 parts of myristic acid

133 parts of methyl ethyl ketone

100 parts of toluene

<Magnetic paint component (2)>
Stearic acid 1.5 parts

4 parts of polyisocyanate ("Coronate L" manufactured by Nippon Polyurethane Industry Co., Ltd.)

133 parts of cyclohexanone

33 parts of toluene

The above-mentioned undercoat paint is a non-magnetic support and a polyethylene naphthalate film having a thickness of 6 μm (105 ° C., 30 minutes heat shrinkage ratio of 0.8% in the vertical direction and 0.6% in the horizontal direction) The undercoat layer after drying and calendering is applied so that the thickness of the undercoat layer is 2 μm, and the magnetic coating is further coated thereon with a magnetic layer thickness of 80 nm after magnetic field orientation, drying and calendering. As applied.

Next, the back coat paint was applied to the surface opposite to the surface on which the non-magnetic support undercoat layer and magnetic layer were formed so that the thickness of the back coat layer after drying and calendering was 700 nm and dried. . The back coat paint was prepared by dispersing the following back coat paint components in a sand mill with a residence time of 45 minutes, adding 8.5 parts of polyisocyanate, and stirring and filtering.

<Back coat paint component>
Carbon black (average particle size: 25 nm) 40.5 parts

Carbon black (average particle size: 370 nm) 0.5 part

4.05 parts barium sulfate

Nitrocellulose 28 parts

20 parts of polyurethane resin (containing SO ₃ Na group)

100 parts of cyclohexanone

100 parts of toluene

100 parts of methyl ethyl ketone

The magnetic sheet thus obtained was mirror-finished with a five-stage calendar (temperature: 70 ° C., linear pressure: 150 kg / cm), and this was wound on a sheet core at 60 ° C. under 40% RH for 48 hours. Aged. Then, the magnetic layer surface was polished with a ceramic wheel (rotation measure + 150%, winding angle 30 °) while being cut at ½ inch width and running at 100 m / min, and a magnetic tape having a length of 609 m. Was made. This magnetic tape was incorporated into a cartridge and used as a computer tape.

In the production of the magnetic tape, a magnetic tape was produced in the same manner as in Example 5 except that the thickness of the magnetic layer after the magnetic field orientation treatment, drying and calendar treatment was changed to 50 nm. Built-in computer tape.

In place of 100 parts of the iron nitride magnetic powder of Example 1 in the magnetic coating component (1), 100 parts of the iron nitride magnetic powder of Example 2 is used, and the thickness of the magnetic layer after drying and calendering is changed. A magnetic tape was prepared in the same manner as in Example 5 except that the thickness was 80 nm, and this was incorporated into a cartridge to form a computer tape.

Instead of 100 parts of the iron nitride magnetic powder of Example 1 in the magnetic paint component (1), 100 parts of the iron nitride magnetic powder of Example 3 is used, and the thickness of the magnetic layer after drying and calendering is changed. A magnetic tape was prepared in the same manner as in Example 5 except that the thickness was 80 nm, and this was incorporated into a cartridge to form a computer tape.

In place of 100 parts of the iron nitride magnetic powder of Example 1 in the magnetic paint component (1), 100 parts of the iron nitride magnetic powder of Example 4 is used, and the thickness of the magnetic layer after drying and calendering is changed. A magnetic tape was prepared in the same manner as in Example 5 except that the thickness was 80 nm, and this was incorporated into a cartridge to form a computer tape.

Comparative Example 3
In place of 100 parts of the iron nitride magnetic powder of Example 1 in the magnetic coating component (1), 100 parts of the iron nitride magnetic powder of Comparative Example 1 was used, and the thickness of the magnetic layer after drying and calendering was A magnetic tape was prepared in the same manner as in Example 5 except that the thickness was 80 nm, and this was incorporated into a cartridge to form a computer tape.

Comparative Example 4
Instead of 100 parts of the iron nitride magnetic powder of Example 1 in the magnetic coating component (1), 100 parts of the iron nitride magnetic powder of Comparative Example 2 was used, and the thickness of the magnetic layer after drying and calendering was A magnetic tape was prepared in the same manner as in Example 5 except that the thickness was 80 nm, and this was incorporated into a cartridge to form a computer tape.

About each magnetic tape of said Examples 5-9 and Comparative Examples 3 and 4, as a magnetic characteristic, the product of longitudinal coercive force, squareness ratio, saturation magnetic flux density, and magnetic layer thickness was measured, and the following procedure Then, the electromagnetic conversion characteristics were measured. Further, each magnetic tape was also measured for electromagnetic conversion characteristics after storage for 1 week at 60 ° C. and 90% RH. These results were as shown in Table 4. In the table, for reference, the average particle size of the magnetic powder, the thickness of the surface compound layer, and the thickness of the magnetic layer used for the production of each magnetic tape are also shown.

<Measurement of electromagnetic conversion characteristics>
As an electromagnetic conversion characteristic, a random data signal having a shortest recording wavelength of 0.33 μm was recorded after running five times under the conditions of 40 ° C. and 5% RH using an LTO drive manufactured by Hülette Patcard Co. The relative value (dB) with the value of Comparative Example 3 as the reference (0) was obtained.

Table 4
┌──────┬────────────────────┬─────────┐
│ │ Examples │ Comparative examples │
│ ├───┬───┬───┬───┬────┼────┬────┤
│ │ 5 │ 6 │ 7 │ 8 │ 9 │ 3 │ 4 │
├──────┼───┼───┼───┼───┼────┼┼────┼────┤
│ Magnetic powder flat │ 20│ 20│ 15│ 20│ 20 │ 20 │ 21 │
│ Average particle size │ │ │ │ │ │ │ │
│ (nm) │ │ │ │ │ │ │ │
│ │ │ │ │ │ │ │ │
│Surface compound layer│2.0│2.0│2.0│4.0│ 2.0│ 0.8│ 6.0│
│ Thickness │ │ │ │ │ │ │ │
│ (nm) │ │ │ │ │ │ │ │
│ │ │ │ │ │ │ │ │
│ Thickness of magnetic layer │ 80 │ 50 │ 80 │ 80 │ 80 │ 80 │ 80 │
│ (nm) │ │ │ │ │ │ │ │
├──────┼───┼───┼───┼───┼────┼┼────┼────┤
│Coercive force: Hc│ 283.4│ 277.1│ 274.7│ 282.6│ 268.3│ 245.2│ 195.1│
│ (kA / m) │ │ │ │ │ │ │ │
│ │ │ │ │ │ │ │ │
│Square ratio │ 0.89 │ 0.85 │ 0.87 │ 0.91 │ 0.88 │ 0.88 │ 0.85 │
│ ： Br / Bm│ │ │ │ │ │ │ │
│ │ │ │ │ │ │ │ │
│ Saturation magnetic flux density │ │ │ │ │ │ │ │
│ × Magnetic layer thickness │ 33│ 16│ 32│ 25│ 27 │ 36 │ 9 │
│ ： Bm ・ t │ │ │ │ │ │ │ │
│ (μTm) │ │ │ │ │ │ │ │
├──────┼───┼───┼───┼───┼────┼┼────┼────┤
│Output (dB) │0.1│1.2│0.4│0.2│ 0.1│ 0 │-1.2│
│ │ │ │ │ │ │ │ │
│Output after saving│ 0 │0.8│0.1│0.1│-0.4│-1.1│-1.2│
│ (dB) │ │ │ │ │ │ │ │
└──────┴───┴───┴───┴───┴────┴┴────┴────┘

As is apparent from the results of Table 4 above, each of the magnetic tapes of Examples 5 to 9 of the present invention is excellent in storage stability as well as magnetic properties. In particular, the thickness of the magnetic layer is 50 nm (Example 6). It can be seen that even when the thickness is extremely thin, the characteristics are hardly deteriorated, the high output is maintained, and excellent high-density recording characteristics are exhibited. On the other hand, the magnetic tape of Comparative Example 3 is inferior in storage stability, and the output greatly deteriorates under long-term storage. In addition, the magnetic tape of Comparative Example 4 is inferior in magnetic characteristics and cannot be reduced in output.

2 is a transmission electron micrograph (magnification of 3 million times) of the iron nitride-based magnetic powder of Example 1. FIG. 3 is a transmission electron micrograph (magnification of 3 million times) of the iron nitride-based magnetic powder of Example 2. FIG.

Claims (10)

Fe and N at least as constituent elements, and Fe ₁₆ N ₂
Includes at least a phase, the content of nitrogen to the iron is 1.0 to 20.0 atomic%, an average axial ratio is 1 to 2, the average particle size of the particulate or ellipsoidal shape at 15nm or more 50nm or less magnetic The powder surface is composed of a compound layer containing a rare earth element or at least one element selected from boron, silicon, aluminum, and phosphorus, and the average thickness of the surface compound layer is 1 to 5 nm. Magnetic powder characterized by being.

The magnetic powder according to claim 1, wherein the average particle size is 15 to 20 nm.
The magnetic powder according to claim 1, wherein the surface compound layer is an oxide.
The magnetic powder according to any one of claims 1 to 3 , wherein the total content of rare earth elements or boron, silicon, aluminum, and phosphorus with respect to iron is 0.1 to 40.0 atomic%.
Saturation magnetization ^{50~150Am 2 / kg (50~150emu / g} ), the coercive force to any one of claims 1 to 4, which is a 119.4~318.5kA / m (1,500~4,000 oersted) The magnetic powder as described.
Saturation magnetization is 129.6-144.2Am ² The magnetic powder according to claim 5, wherein the coercive force is 226.9 to 254.8 kA / m.
The magnetic powder according to any one of claims 1 to 6 , which has a BET specific surface area of 40 to 100 m ² / g.
Use iron-based oxide or hydroxide as a starting material, and deposit a rare earth element or a compound containing at least one element selected from boron, silicon, aluminum, and phosphorus, and then heat reduction treatment. A method for producing a magnetic powder, characterized in that the magnetic powder according to any one of claims 1 to 7 is obtained by performing nitriding at a temperature equal to or lower than a reduction temperature and then performing an oxidation treatment.
A magnetic recording medium comprising a magnetic layer containing the magnetic powder according to any one of claims 1 to 7 and a binder on a nonmagnetic support.
10. The magnetic recording according to claim 9, wherein the magnetic recording layer has at least one undercoat layer containing a nonmagnetic powder and a binder between the nonmagnetic support and the magnetic layer, and the magnetic layer has a thickness of 10 nm to 300 nm. Medium.

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