JP4242402B2 - Magnetic recording medium - Google Patents

Description

The present invention relates to a magnetic recording medium using magnetic powder containing at least iron and nitrogen as constituent elements, and more particularly to a magnetic recording medium optimal for ultrahigh density recording such as a digital video tape and a backup tape for a computer.

Coating type magnetic recording media, that is, magnetic recording media having a magnetic layer containing a magnetic powder and a binder on a non-magnetic support, have a higher recording density as the recording / reproducing system shifts from analog to digital. Improvement is demanded. In particular, the demand for video tapes for high recording density and backup tapes for computers is increasing year by year.

In order to cope with short wavelength recording, which is indispensable for improving the recording density, it is effective to reduce the thickness of the magnetic layer to 300 nm or less, particularly 100 nm or less in order to reduce the thickness loss during recording. As a reproducing magnetic head used in such a high recording density medium, an MR head capable of obtaining a high output is generally used.

Further, in order to reduce noise, the magnetic powder is becoming finer every year, and at present, acicular metal magnetic powder having a particle diameter of about 100 nm is in practical use. Furthermore, in order to prevent a decrease in output due to demagnetization during short wavelength recording, a high coercive force has been achieved year by year, and a coercive force of about 238.9 A / m (3,000 Oe) has been realized by forming an iron-cobalt alloy. (See Patent Documents 1 to 3).

However, in a magnetic recording medium using acicular magnetic particles, since the coercive force depends on the shape, it is difficult to further reduce the particle size from the above particle diameter. That is, when the particle size is further reduced, the specific surface area is remarkably increased and the saturation magnetization is greatly reduced. Therefore, the merit of high saturation magnetization, which is the greatest feature of metal or alloy magnetic powder, is lost, and the use of metal or alloy itself is meaningless.

Therefore, a magnetic recording medium using a rare earth-transition metal-based granular magnetic powder, for example, a granular or elliptical rare earth-iron-boron-based magnetic powder as a magnetic powder completely different from the acicular magnetic powder has been proposed. (See Patent Document 4). This medium can make ultrafine particles of magnetic powder, can realize high saturation magnetization and high coercive force, and greatly contributes to high recording density.

Further, as an iron-based magnetic powder whose particle shape is not needle-shaped, a magnetic material using an iron nitride-based magnetic powder having an irregular particle shape and a BET specific surface area of about 10 m ² / g with a Fe ₁₆ N ₂ phase as a main phase. A recording medium has also been proposed (see Patent Document 5).

JP-A-3-49026 (Page 4) JP 10-83906 A (page 3) Japanese Patent Laid-Open No. 10-340805 (second page) JP 2001-181754 A (4th page, 22nd page) Japanese Unexamined Patent Publication No. 2000-277311 (3rd page, FIG. 4)

However, the rare earth-iron-boron magnetic powder disclosed in Patent Document 4 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 5 has a BET specific surface area of 10 to 22 m ² / g in the examples. However, the particle size is too large and high noise reduction is aimed at reducing noise. Not suitable for density magnetic recording.

Furthermore, the iron nitride magnetic powder of Patent Document 5 is characterized by a high saturation magnetization, and in the examples, those of 190 to 200 Am ² / kg (190 to 200 emu / g) are shown. Thus, a magnetic powder with too high saturation magnetization is not suitable for a magnetic recording medium for high-density recording. This is because if the saturation magnetization is too high, the magnetic flux density of the medium becomes too large and recording demagnetization becomes remarkable. Since this tendency becomes more prominent as the recording wavelength becomes shorter, it is not suitable for high density recording.

In particular, in a high-density recording medium, in order to reduce recording demagnetization, it is essential to appropriately reduce the saturation magnetization of the magnetic powder and reduce the thickness of the magnetic layer. When the magnetic flux density is lowered, the magnetic flux from the medium surface is reduced and the reproduction output is reduced. However, due to the remarkable progress of recent magnetic head technology such as MR head, it is possible to reproduce with a sufficiently high sensitivity even with a small magnetic flux. 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 light of such circumstances, the present invention uses a magnetic powder having an extremely high coercive force and an optimum saturation magnetization for high-density recording, thereby achieving higher output, lower noise, and excellent performance. An object of the present invention is to obtain a magnetic recording medium having a short wavelength recording characteristic.

As a result of diligent investigations for the above object, the present inventors have found that in the iron nitride magnetic powder containing at least the Fe ₁₆ N ₂ phase, a rare earth element is formed in the outer layer portion in a multilayer configuration of the inner layer and the outer layer. The specific magnetic powder that contains the Fe ₁₆ N ₂ phase has an extremely high coercive force and the optimum saturation magnetization for high-density recording. By using this magnetic powder, the output is reduced due to recording demagnetization. It has been found that an ultra-thin magnetic layer free from the above problem can be realized, the output can be increased, the noise can be reduced, and excellent short wavelength recording characteristics can be obtained.

  In addition, by adding at least one element selected from silicon and aluminum together with rare earth elements to the outer layer portion in such iron nitride magnetic powder, the shape of the magnetic particles in the heat treatment process can be maintained and the particles in the magnetic paint can be maintained. It was also found that the dispersibility of the magnetic layer can be improved, the magnetic layer can be made even thinner, and the high output and low noise, which are difficult with the conventional technology, can achieve extremely excellent short wavelength recording characteristics. .

The present invention has been completed based on the above findings.

That is, the present invention has a magnetic layer containing magnetic powder and a binder on a nonmagnetic support, and has at least one undercoat layer between the magnetic layer and the nonmagnetic support. In a magnetic recording medium having a backcoat layer on the side opposite to the magnetic layer forming surface of the magnetic support, the magnetic powder has a multilayer structure of an inner layer and an outer layer, and the outer layer portion contains at least a rare earth element, and the inner layer portion at least Fe ₁₆ N ₂ phase only contains, contains a magnetic powder as the axial ratio (major axis diameter / minor axis diameter) of 1 to 2, the thickness of the magnetic layer has a 300nm or less, and longitudinally The coercive force (Hc) of the magnetic recording medium is 79.6 to 318.4 kA / m (1,000 to 4,000 Oe).

Further, the present invention has a magnetic layer containing magnetic powder and a binder on a nonmagnetic support, and has at least one undercoat layer between the magnetic layer and the nonmagnetic support. In a magnetic recording medium having a backcoat layer on the side opposite to the magnetic layer forming surface of the magnetic support, the magnetic powder has a multilayer structure of an inner layer and an outer layer, and the outer layer portion contains at least a rare earth element, and the inner layer portion at least Fe ₁₆ N ₂ phase only contains, contains a magnetic powder as the axial ratio (major axis diameter / minor axis diameter) of 1 to 2, the thickness of the magnetic layer has a 300nm or less, and longitudinally The product (Bm · t) of the saturation magnetic flux density and the magnetic layer thickness is 0.001 to 0.1 μTm.

Furthermore, the present invention can provide a magnetic recording medium having both the above-mentioned constitutions, wherein the outer layer portion includes at least one element selected from silicon and aluminum in a magnetic powder having a multilayer structure of an inner layer and an outer layer. It is.

As described above, the present invention uses a magnetic powder having the above-mentioned specific configuration as a magnetic powder in forming an extremely thin magnetic layer of 300 nm or less that does not have a problem of lowering the output. Therefore, it is possible to provide a magnetic recording medium that can achieve higher output, lower noise, and excellent short wavelength recording characteristics.

The present inventors have synthesized various magnetic powders and investigated the shape and magnetic anisotropy in order to improve the magnetic characteristics from a viewpoint different from the magnetic powder based on the conventional shape magnetic anisotropy. It was found that the magnetic powder containing at least iron and nitrogen as constituent elements and containing at least the Fe ₁₆ N ₂ phase exhibits high magnetic anisotropy.

In the magnetic powder used in the present invention, the content of nitrogen relative to iron is 1.0 to 20.0 atomic%, preferably 5.0 to 18.0 atomic%, more preferably 8.0 to 15.0 atomic%. It is good to be. 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 is too large, nonmagnetic nitride will be easily formed, and the effect of increasing the coercive force will be small. Magnetization decreases excessively.

Further, this iron nitride-based magnetic powder has an essentially spherical or elliptical shape different from conventional acicular particles, and its particle size is 5 to 50 nm on average with respect to the demand for fine particles. It has been found that it is optimal to set the range of 5 to 30 nm, particularly preferably 5 to 30 nm, more preferably 7 to 25 nm, and most preferably 8 to 23 nm. When the particle size is too small, the dispersibility at the time of preparing the magnetic coating material is deteriorated, and it becomes unstable thermally, and the coercive force is likely to change with time. 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.

The above “essentially spherical or elliptical” shape means that the magnetic powder has an axial ratio (major axis diameter / minor axis diameter) of 1 to 2, particularly preferably 1 to 1.5. When the axial ratio exceeds 2, a part of the magnetic powder stands in the surface direction of the magnetic layer when the magnetic paint is applied, so that the surface smoothness of the magnetic layer is deteriorated and the electromagnetic conversion characteristics are deteriorated. The above-mentioned shape does not exclude magnetic powder having slight irregularities on the powder surface as shown in FIG.

The “average particle size” is obtained by measuring the particle size of a photograph taken with a transmission electron microscope (TEM) and calculating the average value of 300 particles.

Such an iron nitride-based magnetic powder has a saturation magnetization of 80 to 160 Am ² / kg (80 to 160 emu / g), and is not excessively high like conventional magnetic powders (Patent Documents 4 and 5). It was found that it has a moderate saturation magnetization. In addition, the coercive force reaches 318.4 kA / m (4,000 Oe), and a high coercive force of about 25% is obtained compared to the conventional magnetic powders (Patent Documents 4 and 5). .

By using such magnetic powder, the coercive force in the longitudinal direction is 79.6 to 318.4 kA / m (1,000 to 4,000 Oe), and the squareness ratio is 0.6 to 0.9. It was found that a magnetic recording medium having a product of the saturation magnetic flux density and the magnetic layer thickness of 0.001 to 0.1 μTm can be produced.

Furthermore, by incorporating rare earth elements in the iron nitride magnetic powder, the surface of the magnetic powder is modified, and not only the shape maintaining effect in the heat treatment process of the magnetic powder but also the improvement in dispersibility in the paint is achieved. I found it effective.

The content of rare earth elements relative to iron is 0.05 to 20.0 atomic%, preferably 0.1 to 15.0 atomic%, and more preferably 0.5 to 10.0 atomic%. If the amount of the rare earth element is too small, the effect of improving the dispersibility by the rare earth element is reduced, and the effect of maintaining the particle shape during reduction is reduced. On the other hand, if the amount is too large, the unreacted portion of the added rare earth element increases, which not only hinders the dispersion and coating process, but also tends to cause an excessive decrease in coercive force and saturation magnetization.

It was also found that dispersibility can be improved by adding not only rare earth elements but also silicon and aluminum. Since these are cheaper than rare earth elements, they are advantageous in terms of cost. Furthermore, the surface state can be designed in more detail by using these elements in combination. Moreover, boron, phosphorus, etc. can also be included as other elements as needed.

Thus, an essentially spherical or elliptical iron nitride system having a specific particle size that contains iron and nitrogen at least as constituent elements and includes at least the Fe ₁₆ N ₂ phase and the nitrogen content relative to iron is defined in the above range. It has been found that the magnetic powder is finer and has a higher coercive force than that of the prior art, and exhibits an appropriate saturation magnetization. It was also found that by adding rare earth elements, silicon, or aluminum, high dispersibility can be obtained, and excellent thinning can be realized.

Such iron nitride-based magnetic powder has excellent storage stability, and when it is 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 magnetic flux density. It has also been found that, in combination with the above characteristics, it exhibits a performance that is very suitable for magnetic recording media for high-density recording such as digital video tapes and computer backup tapes.

The reason why such an effect is achieved is not necessarily clear, but is considered as follows. That is, due to the synergistic effect of the high magnetic anisotropy of the Fe ₁₆ N ₂ phase and the surface magnetic anisotropy by micronization, it exhibits unique performance not found in conventional magnetic powders, and also rare earth elements, silicon, aluminum The presence of a compound containing C on the surface of the magnetic powder improves dispersibility, and these elements bring about the effect of maintaining the shape of the magnetic powder at the time of reduction. This is thought to be based on factors.

In the iron nitride magnetic powder of the present invention, rare earth elements, silicon, and aluminum may be present inside the magnetic powder, but in order to obtain high dispersibility and excellent shape retention, the magnetic powder is used as an inner layer. As the multilayer structure with the outer layer, it is desirable that the outer layer part contains at least one element selected from rare earth elements and / or silicon and aluminum, and the inner layer part contains at least an Fe ₁₆ N ₂ phase.

Here, it is not necessary for the inner phase to be all Fe ₁₆ N ₂ phase, and it may be a mixed phase of Fe ₁₆ N ₂ phase and α-Fe phase. Rather, by adjusting the ratio of the Fe ₁₆ N ₂ phase and the α-Fe phase, there is an advantage that the desired coercive force can be easily set, so that the design as a magnetic recording medium can be widened.

Examples of rare earth elements include yttrium, ytterbium, cesium, praseodymium, lanthanum, europium, and neodymium. Of these, yttrium, samarium, or neodymium is particularly effective in maintaining the particle shape during reduction, and therefore it is desirable to selectively use at least one of these elements.

In addition to silicon and aluminum, boron or phosphorus may be included as necessary. Furthermore, carbon, calcium, magnesium, zirconium, barium, strontium, and the like may be included as effective elements. By using these other elements in combination with rare earth elements and / or silicon and aluminum, it is possible to obtain higher shape maintainability and dispersion performance.

A method for producing the iron nitride magnetic powder of the present invention will be described.

An iron-based oxide or hydroxide is used as a starting material. Examples include hematite, magnetite, and goethite. The average particle size is not particularly limited, but is usually 5 to 80 nm, preferably 5 to 50 nm, more preferably 5 to 30 nm. If the particle size is too small, inter-particle sintering is likely to occur during the reduction treatment, and if it is too large, the reduction treatment tends to be heterogeneous, making it difficult to control the particle size and magnetic properties.

Rare earth elements can be deposited on this starting material.

In this case, usually, a starting material is dispersed in an aqueous solution of an alkali or acid, a salt of a rare earth element is dissolved therein, and a hydroxide or hydrate containing a rare earth element in the starting material powder is obtained by a neutralization reaction or the like. May be precipitated.

In addition, silicon and aluminum, and if necessary, a compound composed of elements such as boron and phosphorus are dissolved, and the raw material powder is immersed in this to deposit silicon, aluminum, etc. on the raw material powder. Good. In order to perform these deposition processes efficiently, additives such as a reducing agent, a pH buffering agent, and a particle size controlling agent may be mixed.

As these deposition treatments, a rare earth element and silicon, aluminum or the like may be deposited simultaneously or alternately.

Such a raw material is heated and reduced in a hydrogen stream. The reducing gas is not particularly limited, and a reducing gas such as carbon monoxide gas may be used in addition to 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. When the reduction temperature exceeds 600 ° C., powder particles are likely to be sintered, which is not preferable.

By performing nitriding after such heat reduction treatment, the magnetic powder of the present invention comprising at least one element selected from rare earth elements and / or silicon and aluminum, and iron and nitrogen as constituent elements is obtained. It is done.

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. If it is too high, nitriding will be promoted excessively, the proportion of Fe ₄ N, Fe ₃ N phase, etc. will increase, the coercive force will rather decrease, and it will tend to cause an excessive decrease in saturation magnetization.

In such nitriding treatment, it is desirable to select the nitriding treatment conditions so that the nitrogen content with respect to iron in the obtained magnetic powder is 1.0 to 20.0 atomic%. If the amount of nitrogen is too small, the amount of Fe ₁₆ N ₂ produced is small and the effect of improving the coercive force is reduced. If the amount of nitrogen is too large, an Fe ₄ N or Fe ₃ N phase or the like is likely to be formed, the coercive force is rather lowered, and the saturation magnetization is likely to be excessively lowered.

Unlike the conventional acicular magnetic powder based only on the shape magnetic anisotropy, the iron nitride magnetic powder in the present invention has a large magnetocrystalline anisotropy, and has an essentially spherical or elliptical shape. Even in this case, it is considered that a large coercive force is developed in one direction.

When this magnetic material is a fine particle having an average particle size of 5 to 50 nm, particularly 5 to 30 nm, it exhibits a high coercive force and an appropriate saturation magnetization within the range that can be recorded and erased by a magnetic head. As a coating type magnetic recording medium, it provides excellent electromagnetic conversion characteristics with high output and low noise. As described above, the magnetic powder of the present invention is essentially suitable for obtaining a thin magnetic layer in terms of saturation magnetization, coercive force, particle size, and particle shape.

In the present invention, a thin magnetic layer (for example, a thickness of 300 nm or less) is formed by using the above-mentioned specific magnetic powder, thereby obtaining good recording / reproducing characteristics. However, the particle size is extremely small. In addition, although it is essentially a spherical or elliptical magnetic powder, it has been found that the material has not only high crystal magnetic anisotropy, that is, high coercive force and appropriate saturation magnetization, but also high dispersibility. This is an epoch-making thing that breaks the common sense of the material technology of coating type magnetic recording media.

The magnetic recording medium of the present invention is produced by applying a magnetic coating material in which the above-described iron nitride magnetic powder and binder are dispersed and mixed in a solvent to a nonmagnetic support and drying to form a magnetic layer. it can. 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 apply a back coat paint on the side opposite to the magnetic layer forming surface of the nonmagnetic support and dry it to form a (f) back coat layer, This layer will also be described.

Further, in the production of the magnetic recording medium, (g) the solvent used in the magnetic paint, the undercoat paint, the back coat paint, (h) the dispersion and application method of each paint, and (li) the LRT treatment method of the magnetic layer. explain.

(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, etc. is usually 2 to 15 μm, especially 2 to 7 μm. The 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. If it exceeds 7 μm, the total thickness of the tape is increased, and the storage capacity per tape roll 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 nonmagnetic 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 nonmagnetic support is MD and the Young's modulus in the width direction is TD, the ratio (MD / TD) of both is preferably in the range of 0.60 to 0.80 in the helical scan system. . 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, the magnetic powder has an average particle size of 5 to 50 nm, particularly 5 to 30 nm, and is very fine, essentially spherical or elliptical. Therefore, an extremely thin magnetic layer thickness almost impossible with conventional acicular magnetic powders. It will also be possible.

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 to 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 is usually 0.6 to 0.9, and particularly preferably 0.8 to 0.9.

Furthermore, the product of the saturation magnetic flux density in the longitudinal direction and the thickness 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 10 to 10. When the 20th convex amount is 30 nm and (P1 -P20) is 5 nm or less, when the MR head is used, the contact with the MR head is improved and the MR head is used. This is preferable because the reproduction output is high.

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.

The content of carbon black is preferably 0.2 to 5% by weight and more preferably 0.5 to 4% by weight with respect to the magnetic powder. 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 preferably 35 to 83% by weight, and 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. If the average particle size is smaller than the above, uniform dispersion becomes difficult, and if larger than the above, irregularities at the interface between the undercoat layer and the magnetic layer tend 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, and 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 content of carbon black varies depending on the particle size of 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 There is a 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.

These binders preferably have a functional group in order to improve the dispersibility of magnetic powder or the like and to increase the filling property.

As functional groups, 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, and the like.

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 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 solid powder such as magnetic powder and nonmagnetic powder. Particularly, 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 with respect to 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, the magnetic layer and the magnetic head can easily exude and transfer to the surface of the magnetic layer at the time of high-speed sliding contact, 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.

Further, 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 between 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 with SUS (μMsus) 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, more preferably 0.8 to 1.2. As a result, tracking deviation (off-track) due to meandering of the magnetic tape is reduced.

In addition, each said friction coefficient is a value measured by the method as described in ECMA-319 standard.

(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 preferably 60 to 98% by weight, 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 it is too large, it will be necessary to add a large amount of carbon black. In either case, the surface will become rough and cause embossing to the magnetic layer. It is easy to become.

When carbon black having a large particle size of 5 to 15% by weight of the carbon black having a small particle size and an average particle size of 300 to 400 nm is used, the surface is not roughened, and the effect of improving running performance is increased. .

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 size 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. If the thickness is less than 0.05 μm, the effect of improving the strength is reduced. If the thickness exceeds 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 the amount 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 more 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. 70 to 110 parts by weight are more preferable. If the amount is too small, the strength of the backcoat layer becomes insufficient. If the amount is too large, the friction coefficient tends to increase.

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 backcoat layer, it is desirable to use a crosslinking agent in order to cure the binder.

As the cross-linking 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 is too small, the coating strength of the backcoat layer tends to be weak, and if the amount 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 Tissue (for example, 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 the rotating rod on the back coat layer and magnetic layer surface, respectively. Perform a cleaning process.

Hereinafter, while describing "Examples 1 to 9" of the present invention, "Comparative Examples 1 to 5" for comparison with these Examples are also described in more detail. In the following, “parts” means parts by weight.

(A1) Manufacture of iron nitride-based magnetic powder 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, 2.5 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. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, 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 in which the yttrium hydroxide was deposited on the surface of the magnetite particles in this manner was heated and reduced at 450 ° C. for 2 hours in a hydrogen stream to obtain an yttrium-iron magnetic powder.

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 temperature was lowered from 150 ° C. to 90 ° C. with ammonia gas flowing, and at 90 ° C., the ammonia gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours.

Next, with the mixed gas flowing, the temperature was lowered from 90 ° C. to 40 ° C., held at 40 ° C. for about 10 hours, and then taken out into the air.

The yttrium-iron nitride-based magnetic powder thus obtained was measured for the yttrium and nitrogen contents by fluorescent X-ray to be 5.3 atomic% and 10.8 atomic%, respectively, with respect to Fe. It was.

Further, from the X-ray diffraction pattern to obtain a profile indicating a Fe ₁₆ N ₂ phase.
FIG. 1 shows an X-ray diffraction pattern of this yttrium-iron nitride magnetic powder. A diffraction peak based on Fe ₁₆ N ₂ and a diffraction peak based on α-Fe are observed. This yttrium-iron nitride is observed. It was found that the system magnetic powder was composed of a mixed phase of Fe ₁₆ N ₂ phase and α-Fe 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 22 nm. FIG. 2 shows a transmission electron micrograph (magnification: 200,000 times) of this magnetic powder. The specific surface area determined by the BET method was 53.2 m ² / g.

Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) was 135.2 Am ² / kg (135.2 emu / g), and the coercive force was 226.9 kA / m (2 , 850 Oersted).

(B1) Preparation of magnetic tape After kneading the following undercoat paint components with a kneader, dispersion treatment was performed with a sand mill with a residence time of 60 minutes, and 6 parts of polyisocyanate was added thereto, followed by stirring and filtration to obtain an undercoat paint. Prepared.

Separately, after kneading the following magnetic coating component (1) with a kneader, dispersing with a sand mill with a residence time of 45 minutes, adding the following magnetic coating component (2), mixing, A magnetic paint was prepared.

<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 yttrium-iron nitride magnetic powder produced in (A1) above

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

Dry the above-mentioned undercoating paint into a 6 μm thick polyethylene naphthalate film (105 ° C., 30 minutes thermal shrinkage ratio of 0.8% in the vertical direction and 0.6% in the horizontal direction) as a nonmagnetic support. The undercoat layer after the calendering is applied so that the thickness is 2 μm, and the magnetic coating is further applied thereon so that the magnetic layer after the magnetic field orientation treatment, drying and calendering has a thickness of 120 nm. It was applied to.

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 is 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.

(B2) Production of magnetic tape Magnetic tape was produced in the same manner as in Example 1 except that the thickness of the magnetic layer after the magnetic field orientation treatment, drying and calendar treatment was changed to 50 nm in the production of the magnetic tape of Example 1. This was assembled into a cartridge and used as a computer tape.

(A3) Production of iron nitride magnetic powder In the production of the iron nitride magnetic powder of Example 1, after depositing and depositing yttrium hydroxide, 0.007 mol of boric acid was dissolved in 30 cc of water. After redispersing in an aqueous solution and filtering this dispersion, the powder was dried at 60 ° C. for 4 hours to remove water, thereby obtaining a powder on which yttrium containing boron was deposited.

This powder was subjected to hydrogen reduction, nitriding treatment in ammonia and stabilization treatment in the same manner as in Example 1 to produce an yttrium-iron nitride-boron magnetic powder.

The yttrium-iron nitride-boron magnetic powder thus obtained was measured by fluorescent X-ray for the contents of yttrium and nitrogen, and 4.0 atomic% and 9.0 atomic% with respect to Fe, respectively. Met. The boron content was 3.0 atomic%.

From the X-ray diffraction pattern, a profile showing an Fe ₁₆ N ₂ phase was obtained. 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 specific surface area determined by the BET method was 56.1 m ² / g.

For this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) was 105.7 Am ² / kg (105.7 emu / g), and the coercive force was 213.4 kA / m (2,680). Oersted).

(B3) Production of magnetic tape In production of the magnetic tape of Example 1, instead of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1), 100 parts of the yttrium-iron nitride-boron magnetic powder described above. A magnetic tape was produced in the same manner as in Example 1 except that was used, and this was incorporated into a cartridge to obtain a computer tape.

(B4) Production of magnetic tape In production of the magnetic tape of Example 3, a magnetic tape was produced in the same manner as in Example 3 except that the thickness of the magnetic layer after drying and calendering was changed to 30 nm. This was incorporated into a cartridge and used as a computer tape.

(A5) Manufacture of iron nitride-based magnetic powder 10 g of magnetite particles having an average particle size of approximately 18 nm and a substantially spherical shape were dispersed in 500 cc of water for 30 minutes using an ultrasonic disperser. To this dispersion, 0.5 g of yttrium nitrate was added and dissolved, followed by stirring for 30 minutes. Separately, 0.16 g of sodium hydroxide was dissolved in 100 cc of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, the mixture was further stirred for 1 hour.

Next, 1.13 g of sodium silicate was added to the dispersion and dissolved, and stirred for 30 minutes. A solution obtained by diluting 0.6 g of nitric acid 10 times was added dropwise to the dispersion in which sodium silicate was dissolved over 30 minutes.

By this treatment, hydroxides of yttrium and silicon were 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 hydroxides of yttrium and silicon were deposited on the surface of magnetite particles.

Thus, the powder which adhered and formed the hydroxide of the yttrium and the silicon on the surface of the magnetite particle | grain was heat-reduced for 2 hours at 430 degreeC in hydrogen stream, and the yttrium-silicon-iron type magnetic powder was obtained.

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 temperature was lowered from 150 ° C. to 90 ° C. with ammonia gas flowing, and at 90 ° C., the ammonia gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours.

Next, with the mixed gas flowing, the temperature was lowered from 90 ° C. to 40 ° C., held at 40 ° C. for about 10 hours, and then taken out into the air.

The yttrium-silicon-iron nitride magnetic powder thus obtained was measured for the contents of yttrium, silicon, and nitrogen by fluorescent X-ray. As a result, 1.1 atomic% and 2.8% with respect to Fe, respectively. Atomic% and 10.3 atomic%. Further, a profile having an Fe ₁₆ N ₂ phase as a main phase was obtained from the X-ray diffraction pattern.

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 15 nm. The specific surface area determined by the BET method was 90.1 m ² / g.

Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 102.8 Am ² / kg (102.8 emu / g), and the coercive force is 215.8 kA / m (2 , 710 Oersted).

(B5) Production of magnetic tape In production of the magnetic tape of Example 1, instead of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1), 100 parts of the above yttrium-silicon-iron nitride magnetic powder. And a magnetic tape was prepared in the same manner as in Example 1 except that the thickness of the magnetic layer after magnetic field orientation treatment, drying and calendar treatment was 50 nm, and this was incorporated into a cartridge, It was set as the tape for computers.

(A6) Manufacture of iron nitride-based magnetic powder In the manufacture of iron nitride-based magnetic powder of Example 5, the amount of sodium silicate added from 1.13 g to 2.03 g without addition of yttrium nitrate and addition of nitric acid A silicon hydroxide was deposited on the surface of the magnetite particles in the same manner as in Example 5 except that the amount was changed from 0.6 g to 1.08 g. This was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which silicon hydroxide was deposited on the surface of magnetite particles.

The powder in which the silicon hydroxide was deposited on the surface of the magnetite particles was heated and reduced in a hydrogen stream in the same manner as in Example 5 to obtain a silicon-iron-based magnetic powder. Next, this silicon-iron-based magnetic powder was subjected to nitriding treatment in the same manner as in Example 5, and further subjected to stabilization treatment in the same manner as in Example 5 and taken out into the air.

The silicon-iron nitride magnetic powder thus obtained was 4.7 atomic% and 11.2 atomic% of Fe, respectively, when the silicon and nitrogen contents were measured by fluorescent X-ray. . A profile having an Fe ₁₆ N ₂ phase as a main phase was obtained from the X-ray diffraction pattern.

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 14 nm. The specific surface area determined by the BET method was 92.3 m ² / g.

Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) was 98.1 Am ² / kg (98.1 emu / g), and the coercive force was 214.1 kA / m (2 , 690 Oersted).

(B6) Production of magnetic tape In production of the magnetic tape of Example 1, 100 parts of the above-mentioned silicon-iron nitride magnetic powder was used instead of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1). In addition, a magnetic tape was produced in the same manner as in Example 1 except that the thickness of the magnetic layer after magnetic field orientation treatment, drying and calendar treatment was 50 nm, and this was incorporated into a cartridge for use in a computer. Tape.

(A7) Manufacture of iron nitride-based magnetic powder 10 g of magnetite particles having an average particle size of approximately 18 nm and a substantially spherical shape were dispersed in 500 cc of water for 30 minutes using an ultrasonic disperser. To this dispersion, 0.5 g of yttrium nitrate was added and dissolved, followed by stirring for 30 minutes. Separately, 0.16 g of sodium hydroxide was dissolved in 100 cc of water. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, the mixture was further stirred for 1 hour.

Next, 0.68 g of sodium aluminate was added to the dispersion and dissolved, and the mixture was stirred for 30 minutes. To this dispersion in which sodium aluminate was dissolved, 0.6 g of nitric acid diluted 10-fold was added dropwise over 30 minutes.

By this treatment, hydroxides of yttrium and aluminum were 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 hydroxides of yttrium and aluminum were deposited on the surface of the magnetite particles.

Thus, the powder which adhered and formed the hydroxide of the yttrium and the aluminum on the surface of the magnetite particle | grain was heat-reduced for 2 hours at 430 degreeC in hydrogen stream, and the yttrium-aluminum-iron type magnetic powder was obtained.

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 temperature was lowered from 150 ° C. to 90 ° C. in a state of flowing ammonia gas, and the ammonia gas was changed to a mixed gas of oxygen and nitrogen at 90 ° C., and a stabilization treatment was performed for 2 hours.

Next, with the mixed gas flowing, the temperature was lowered from 90 ° C. to 40 ° C., held at 40 ° C. for about 10 hours, and then taken out into the air.

The yttrium-aluminum-iron nitride magnetic powder thus obtained was measured for the contents of yttrium, aluminum and nitrogen by fluorescent X-ray. Atomic% and 9.8 atomic%. Further, a profile having an Fe ₁₆ N ₂ phase as a main phase was obtained from the X-ray diffraction pattern.

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 15 nm. The specific surface area determined by the BET method was 93.3 m ² / g.

Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) was 103.1 Am ² / kg (103.1 emu / g), and the coercive force was 211.7 kA / m (2 , 660 Oersted).

(B7) Production of magnetic tape In production of the magnetic tape of Example 1, 100 parts of the yttrium-aluminum-iron nitride magnetic powder described above was used instead of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1). And a magnetic tape was prepared in the same manner as in Example 1 except that the thickness of the magnetic layer after magnetic field orientation treatment, drying and calendar treatment was 50 nm, and this was incorporated into a cartridge, It was set as the tape for computers.

(A8) Manufacture of iron nitride-based magnetic powder In the manufacture of iron nitride-based magnetic powder of Example 7, the amount of sodium aluminate added was changed from 0.68 g to 1.0 g without adding yttrium nitrate. Aluminum hydroxide was deposited on the surface of the magnetite particles in the same manner as in Example 7 except that the addition amount was changed from 0.6 g to 0.9 g. This was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which an aluminum hydroxide was deposited on the surface of magnetite particles.

The powder in which the hydroxide of aluminum was deposited on the surface of the magnetite particles in this manner was heated and reduced in a hydrogen stream in the same manner as in Example 5 to obtain an aluminum-iron-based magnetic powder. Next, this magnetic powder was subjected to nitriding treatment in the same manner as in Example 5, and further subjected to stabilization treatment in the same manner as in Example 5 and taken out into the air.

The aluminum-iron nitride magnetic powder thus obtained was 4.6 atomic percent and 10.0 atomic percent, respectively, based on Fe, when the aluminum and nitrogen contents were measured by fluorescent X-ray. It was. Further, a profile having an Fe ₁₆ N ₂ phase as a main phase was obtained from the X-ray diffraction pattern.

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 15 nm. The specific surface area determined by the BET method was 90.5 m ² / g.

Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) was 95.6 Am ² / kg (95.6 emu / g), and the coercive force was 214.1 kA / m (2 , 690 Oersted).

(B8) Production of magnetic tape In production of the magnetic tape of Example 1, 100 parts of the above-described aluminum-iron nitride magnetic powder was used instead of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1). In addition, a magnetic tape was produced in the same manner as in Example 1 except that the thickness of the magnetic layer after magnetic field orientation treatment, drying and calendar treatment was 50 nm, and this was incorporated into a cartridge for use in a computer. Tape.

(A9) Manufacture of iron nitride-based magnetic powder Example 5 except that magnetite particles having an average particle size of nearly 11 nm in shape were used as magnetite particles in the manufacture of the iron nitride-based magnetic powder of Example 5. In the same manner as above, a powder in which a hydroxide of yttrium and silicon was formed on the surface of magnetite particles was obtained.

A powder obtained by depositing yttrium and silicon hydroxide on the surface of the magnetite particles was heated and reduced at 400 ° C. for 2 hours in a hydrogen stream to obtain an yttrium-silicon-iron-based magnetic powder.

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 temperature was lowered from 150 ° C. to 90 ° C. in a state of flowing ammonia gas, and the ammonia gas was changed to a mixed gas of oxygen and nitrogen at 90 ° C., and a stabilization treatment was performed for 2 hours.

Next, with the mixed gas flowing, the temperature was lowered from 90 ° C. to 40 ° C., held at 40 ° C. for about 10 hours, and then taken out into the air.

The yttrium-silicon-iron nitride magnetic powder thus obtained was measured for the contents of yttrium, silicon, and nitrogen by fluorescent X-ray. Atomic% and 9.3 atomic%. Further, a profile having an Fe ₁₆ N ₂ phase as a main phase was obtained from the X-ray diffraction pattern.

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 9 nm. The specific surface area determined by the BET method was 153.3 m ² / g.

Further, with respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) was 81.1 Am ² / kg (81.1 emu / g), and the coercive force was 200.6 kA / m (2 , 520 Oersted).

(B9) Production of magnetic tape In production of the magnetic tape of Example 1, in place of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1), 100 parts of the yttrium-silicon-iron nitride magnetic powder described above. And a magnetic tape was prepared in the same manner as in Example 1 except that the thickness of the magnetic layer after magnetic field orientation treatment, drying and calendar treatment was 50 nm, and this was incorporated into a cartridge, It was set as the tape for computers.

Comparative Example 1
(C1) Production of magnetic powder In the production of the iron nitride magnetic powder of Example 1, 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 85 nm. In the same manner as in No. 1, hydrogen reduction, nitriding treatment in ammonia and stabilization treatment were performed to produce an yttrium-iron nitride magnetic powder.

The yttrium-iron nitride magnetic powder thus obtained was measured for the yttrium and nitrogen contents by fluorescent X-ray, and was found to be 5.0 atomic% and 12.5 atomic%, respectively, with respect to Fe. It was. 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 60 nm. The specific surface area determined by the BET method was 8.3 m ² / g.

With respect to this magnetic powder, the saturation magnetization measured by applying a magnetic field of 1,270 kA / m (16 kOe) is 194.2 Am ² / kg (194.2 emu / g), and the coercive force is 183.9 kA / m (2,310). Oersted).

(D1) Production of magnetic tape In production of the magnetic tape of Example 1, 100 parts of the yttrium-iron nitride magnetic powder was used instead of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1). Except for the above, a magnetic tape was produced in the same manner as in Example 1, and this was incorporated into a cartridge to obtain a computer tape.

Comparative Example 2
(D2) Production of magnetic tape In production of the magnetic tape of Comparative Example 1, a magnetic tape was produced in the same manner as in Comparative Example 1, except that the thickness of the magnetic layer after drying and calendering was changed to 90 nm. This was incorporated into a cartridge and used as a computer tape.

Comparative Example 3
(D3) Production of magnetic tape In the production of the magnetic tape of Example 1, in place of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1), acicular Fe-Co alloy magnetic powder [Co / Fe: 24.6% by weight, specific surface area: 55.3 m ² / g, coercive force: 183.1 kA / m (2,300 Oe), saturation magnetization: 135.0 Am ² / kg (135.0 emu / g), average major axis Diameter: 80 nm, axial ratio: 3] A magnetic tape was produced in the same manner as in Example 1 except that 100 parts were used, and this was incorporated into a cartridge to obtain a computer tape.

Comparative Example 4
(C4) Production of magnetic powder 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, 2.5 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. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, 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 in which the yttrium hydroxide was deposited on the surface of the magnetite particles in this manner was heated and reduced at 450 ° C. for 2 hours in a hydrogen stream to obtain an yttrium-iron magnetic powder.

Next, the temperature was lowered to 90 ° C., and at 90 ° C., the hydrogen gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours.

Further, the temperature was lowered from 90 ° C. to 40 ° C. in the state of flowing the mixed gas, and the mixture was held at 40 ° C. for about 10 hours and then taken out into the air.

Thus, yttrium-iron-based magnetic powder was obtained without performing nitriding treatment.

The yttrium content of this magnetic powder was 5.4 atomic% with respect to Fe. Moreover, the diffraction peak based on (alpha) -Fe was observed from the X-ray diffraction pattern. 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 22 nm. The specific surface area was 55.1 m ² / g.

As for the magnetic powder, 1,270 kA / m saturation magnetization 137.7m ² /kg(137.7emu/g measured by applying a magnetic field (16 kOe)), the coercive force is 156,0kA / m (1 , 960 Oersted).

(D4) Production of Magnetic Tape In production of the magnetic tape of Example 1, 100 parts of the yttrium-iron-based magnetic powder was used instead of 100 parts of the yttrium-iron nitride-based magnetic powder in the magnetic coating component (1). Except for the above, a magnetic tape was produced in the same manner as in Example 1, and this was incorporated into a cartridge to obtain a computer tape.

Comparative Example 5
(C5) Production of magnetic powder 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, 2.5 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. This aqueous sodium hydroxide solution was added dropwise to the above dispersion over about 30 minutes, and after completion of the addition, the mixture was further stirred for 1 hour.

By this treatment, yttrium hydroxide was deposited on the surface of the magnetite particles. Furthermore, it is re-dispersed in an aqueous solution in which 0.007 mol of boric acid is dissolved in 30 cc of water, and this dispersion is filtered and dried at 60 ° C. for 4 hours to remove the water, thereby removing yttrium containing boron. Was obtained.

This was washed with water, filtered, and dried at 90 ° C. to obtain a powder in which yttrium hydroxide and boron were deposited on the surface of magnetite particles.

The powder in which the yttrium hydroxide was deposited on the surface of the magnetite particles in this manner was heated and reduced at 450 ° C. for 2 hours in a hydrogen stream to obtain an yttrium-boron-iron-based magnetic powder.

Next, the temperature was lowered to 90 ° C., and at 90 ° C., the hydrogen gas was switched to a mixed gas of oxygen and nitrogen, and a stabilization treatment was performed for 2 hours.

Further, the temperature was lowered from 90 ° C. to 40 ° C. in the state of flowing the mixed gas, and the mixture was held at 40 ° C. for about 10 hours and then taken out into the air.

Thus, yttrium-boron-iron-based magnetic powder was obtained without performing nitriding treatment.

As a result of measuring the content of yttrium and boron by fluorescent X-ray, the magnetic powder was 4.0 atomic% and 3.1 atomic%, respectively, with respect to Fe. Moreover, the diffraction peak based on (alpha) -Fe was observed from the X-ray diffraction pattern. 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 22 nm. The specific surface area was 54.3 m ² / g.

As for the magnetic powder, 1,270 kA / m (16 kOe) saturation magnetization is 133.9m ² /kg(133.9emu/g measured by applying a magnetic field), the coercive force is 172,7kA / m (2 , 170 oersted).

(D5) Production of magnetic tape In the production of the magnetic tape of Example 1, instead of 100 parts of the yttrium-iron nitride magnetic powder in the magnetic coating component (1), 100 parts of the yttrium-boron-iron magnetic powder was used. A magnetic tape was produced in the same manner as in Example 1 except that it was used, and this was incorporated into a cartridge to obtain a computer tape.

About each magnetic tape of said Examples 1-9 and Comparative Examples 1-5, the product of longitudinal coercive force, squareness ratio, saturation magnetic flux density, and magnetic layer thickness was measured as a magnetic characteristic, and the following procedure Then, the electromagnetic conversion characteristics were measured.

These results were as shown in Tables 1 and 2. In the table, for reference, the average particle size and magnetic layer thickness of the magnetic powder used in 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 output (dB) is obtained as a relative value with the value of Comparative Example 2 as the reference (0), and the relative value with the value of Comparative Example 2 as the reference (0) is used as a noise index. / N ratio (dB) was determined.

As is clear from the results in Tables 1 and 2 above, each of the magnetic tapes of Examples 1 to 9 showed high output and low noise, and the thickness of the magnetic layer was 50 nm (Examples 2 to 9). ) And 30 nm (Example 4), it can be seen that there is almost no deterioration in characteristics, and excellent high-density recording characteristics with high output and low noise.

On the other hand, in the case of using a spherical magnetic powder having a large particle size like the magnetic tapes of Comparative Examples 1 and 2, the smoothness of the surface is lowered, and the output when the film is thinned is greatly deteriorated. . Also, the magnetic tape using the needle-like magnetic powder as in the magnetic tape of Comparative Example 3 does not achieve high output as described above.

Further, as in the magnetic tapes of Comparative Examples 4 and 5, the magnetic powder that is small in particle size but not subjected to nitriding treatment as in the present invention is used, compared with the iron nitride magnetic powder in the present invention. Since a large coercive force cannot be obtained, the output is lower than that of the present invention, and the influence of the coercive force appears in the noise characteristics, which is inferior to that of the present invention.

3 is a characteristic diagram showing an X-ray analysis pattern of yttrium-iron nitride magnetic powder used in Example 1. FIG. 2 is a transmission electron micrograph (magnification: 200,000 times) of the yttrium-iron nitride magnetic powder used in Example 1. FIG.

Claims (3)

A magnetic layer containing a magnetic powder and a binder on a nonmagnetic support, and having at least one undercoat layer between the magnetic layer and the nonmagnetic support, and the magnetic layer of the nonmagnetic support In a magnetic recording medium having a backcoat layer on the side opposite to the formation surface, the magnetic powder has a multilayer structure of an inner layer and an outer layer, and includes at least a rare earth element in the outer layer portion, and at least Fe ₁₆ N _{2 in the} inner layer portion. the phases observed including, axial ratio contains a magnetic powder is (major axis diameter / minor axis diameter) of 1 to 2, the thickness of the magnetic layer has a 300nm or less, and the longitudinal direction of the coercive force (Hc) The magnetic recording medium is characterized by being 79.6 to 318.4 kA / m (1,000 to 4,000 Oe).

A magnetic layer containing a magnetic powder and a binder on a nonmagnetic support, and having at least one undercoat layer between the magnetic layer and the nonmagnetic support, and the magnetic layer of the nonmagnetic support In a magnetic recording medium having a back coat layer on the side opposite to the formation surface, the magnetic powder has a multilayer structure of an inner layer and an outer layer, and the outer layer portion includes at least a rare earth element, and the inner layer portion includes at least Fe ₁₆ N _2. the phases observed including, axial ratio (major axis diameter / minor axis diameter) is contains a magnetic powder is 1 to 2, the thickness of the magnetic layer has a 300nm or less, and the longitudinal direction of the saturation magnetic flux density and magnetic A magnetic recording medium having a product (Bm · t) with a layer thickness of 0.001 to 0.1 μTm.

3. The magnetic recording medium according to claim 1, wherein in the magnetic powder having a multilayer structure of an inner layer and an outer layer, the outer layer portion includes at least one element selected from silicon and aluminum together with a rare earth element.

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