JPH11185243A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic recording medium of a double layer coating type which is prevented of the disturbance at the boundary between layers and is improved in electromagnetic conversion characteristics. SOLUTION: This magnetic recording medium is constituted by providing the surface of a nonmagnetic base 2 with an intermediate layer 3 contg. inorg. powder of Mohs hardness below 6 and a binder and a magnetic layer 4 formed by dispersing ferromagnetic powder into binder in this order. In such a case, the ferromagnetic powder and the inorg. powder are formed to satisfy the equation 1.5L1>=L2 and the equation 1/2A1<=A2<=1.5A1 when the grain size of the ferromagnetic powder is defined as L1, the axial ratio thereof as A1 and the grain size of the inorg. powder is defined as L2, the axial ratio thereof as A2. The thicknesses of the magnetic layer 4 and the intermediate 3 are respectively specified to <=0.6 μm and 0.2 to 2.5 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer coating type magnetic recording medium suitable for high-density recording, and more particularly to a magnetic recording medium in which disturbance at an interface between layers is prevented and electromagnetic conversion characteristics are improved. .

[0002]

2. Description of the Related Art In a multilayer coating type magnetic recording medium, there is a conventional technique relating to a technique for preventing the occurrence of disturbance at an interface between upper and lower layers and improving electromagnetic conversion characteristics, for example, as disclosed in Japanese Patent Application Laid-Open (JP-A) no. 2566126
And those described in Japanese Patent No. 2607356 are known.

[0003] The prior art described in these patent specifications will be described.
Wherein the dry thickness of the upper magnetic layer is 1 μm or less, and the ratio of the longest axis length to the shortest axis length of the nonmagnetic powder contained in the lower nonmagnetic layer is 2.5 or more and less than 20. A recording medium is described. In the paragraph [0008] of the same specification, a needle-shaped non-magnetic powder is used for the lower non-magnetic layer to form a strong coating film even when the lower non-magnetic layer is in an undried state. It describes that even if the ferromagnetic powder is rotated by the magnetic field orientation treatment, no mixing occurs at the interface.

Japanese Patent No. 2607356 discloses that the upper magnetic layer has a dry thickness of 1 μm or less, the ferromagnetic powder contained in the upper recording layer has a crystallite size of 100 to 450 °, and the primary non-recording layer has an average primary particle size of less than 100 μm. A magnetic recording medium characterized by containing a nonmagnetic inorganic powder having a particle diameter of 0.08 μm or less is described.

However, the prior arts described in these patent specifications all attempt to prevent disturbance at the interface between the upper and lower layers by defining the particle size or the axial ratio of the nonmagnetic powder contained in the lower layer. However, since the relative relationship between the shape and type of the magnetic powder mixed in the upper layer is not taken into account, it cannot be said that the disturbance of the interface between the upper and lower layers can be completely prevented. In particular, in recent years, as the recording density of magnetic recording media has become even higher and the thickness of the upper magnetic layer has been further reduced, the disorder of the interface between the upper and lower layers has been significantly affecting the surface properties of the magnetic layer. Therefore, there is an urgent need to prevent the occurrence of the disturbance and improve the electromagnetic conversion characteristics of the magnetic recording medium.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a multilayer coating type magnetic recording medium in which disturbance at an interface between layers is prevented and electromagnetic conversion characteristics are improved. Also,
An object of the present invention is to provide a multilayer coating type magnetic recording medium suitable for high-density recording.

[0007]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the shape of the specific inorganic powder to be blended in the lower layer is similar to the shape of the ferromagnetic powder to be blended in the upper layer. It has been found that by setting the thickness of the magnetic recording medium to a specific range, a magnetic recording medium that can achieve the above object can be obtained.

[0008] The present invention has been made based on the above findings, and comprises an intermediate layer containing an inorganic powder having a Mohs hardness of 6 or less and a binder, and a magnetic layer in which ferromagnetic powder is dispersed in the binder. In a magnetic recording medium provided on a non-magnetic support in this order, the particle diameter of the ferromagnetic powder contained in the magnetic layer is L1, the axial ratio is A1, and the inorganic powder contained in the intermediate layer is When the particle size of L2 is A2 and the axial ratio is A2, the ferromagnetic powder contained in the magnetic layer and the inorganic powder contained in the intermediate layer satisfy the following formulas (1) and (2): And the thicknesses of the magnetic layer and the intermediate layer are 0.6 μm or less and 0.2 to
The above object has been achieved by providing a magnetic recording medium characterized by having a thickness of 2.5 μm.

[0009] 1.5L1 ≧ L2 (1) 0.5A1 ≦ A2 ≦ 1.5A1 (2)

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a magnetic recording medium of the present invention will be described.
The preferred embodiment will be described with reference to the drawings. Here, FIG. 1 is a schematic diagram showing the configuration of one embodiment of the magnetic recording medium of the present invention.

In the magnetic recording medium 1 of the embodiment shown in FIG. 1, an intermediate layer 3 is provided on a support 2 and a magnetic layer 4 as an uppermost layer is provided adjacent to the intermediate layer 3. . Further, the back coat layer 5 is provided on the other surface of the support 2.

The magnetic layer 4 is formed by applying a magnetic paint containing a binder and a ferromagnetic powder, while the intermediate layer 3 is made of an intermediate paint containing a binder and an inorganic powder having a Mohs hardness of 6 or less. Is formed. Various powders can be used as the inorganic powder having a Mohs hardness of 6 or less. For example, when the intermediate layer 3 is a magnetic layer, that is, when the magnetic recording medium 1 has a magnetic / magnetic multilayer structure, Magnetic powder and non-magnetic inorganic powder are used as the inorganic powder. On the other hand, when the intermediate layer is a non-magnetic layer, that is, when the magnetic recording medium 1 has a magnetic / non-magnetic multilayer structure. A non-magnetic inorganic powder or the like is used as the inorganic powder, and no magnetic powder is used.

In the magnetic recording medium 1,
The following relationship exists between the shape of the ferromagnetic powder contained in the magnetic layer 4 and the shape of the inorganic powder having a Mohs hardness of 6 or less contained in the intermediate layer 3. That is, in the magnetic recording medium 1, the particle diameter of the ferromagnetic powder contained in the magnetic layer 4 is L1, the axial ratio is A1, the particle diameter of the inorganic powder contained in the intermediate layer 3 is L2, and the axial ratio is A2. With respect to the ferromagnetic powder, the inorganic powder contained in the intermediate layer 3 satisfies the following formulas (1) and (2). 1.5L1 ≧ L2 (1) 0.5A1 ≦ A2 ≦ 1.5A1 (2)

When the ferromagnetic powder contained in the magnetic layer 4 and the inorganic powder contained in the intermediate layer 3 satisfy the relations of the above formulas (1) and (2), the ferromagnetic powder and the inorganic powder The shape of the powder is similar to that of the powder, and the particle diameter of the inorganic powder contained in the intermediate layer 3 is about the same as or smaller than that of the ferromagnetic powder contained in the magnetic layer 4. When forming the intermediate layer 3 and the magnetic layer 4 by applying each of the above magnetic paints, it is possible to effectively prevent the mixing of both paints at the interface, and to prevent the occurrence of disturbance at the interface between both layers. Can be prevented. As a result, the unevenness and surface properties of the magnetic layer 4 and the orientation of the ferromagnetic powder are improved, and the electromagnetic conversion characteristics of the magnetic recording medium 1 are improved. This phenomenon becomes more remarkable when the diameter of the ferromagnetic powder in the magnetic layer 4 is reduced, as described later. Furthermore,
Together with the thickness of the magnetic layer 4 being 0.6 μm or less and the thickness of the intermediate layer 3 being 0.2 to 2.5 μm, it is possible to make the magnetic recording medium 1 suitable for high-density recording. it can.

The ferromagnetic powder contained in the magnetic layer 4 and the intermediate layer 3
The above inorganic powder preferably satisfies the following formulas (1 ′) and (2 ′), and more preferably satisfies the following formulas (1 ″) and (2 ″).

1.3L1 ≧ L2 (1 ′) 0.7A1 ≦ A2 ≦ 1.3A1 (2 ′)

0.9L1 ≧ L2 (1 ″) 0.8A1 ≦ A2 ≦ 1.1A1 (2 ″)

In the present specification, the “particle size L1” of the ferromagnetic powder contained in the magnetic layer 4 and the “particle size L2” of the above-mentioned inorganic powder contained in the intermediate layer 3, respectively, have the dimensions of these powders. The length of the largest part. For example, when these powders are acicular or spindle-shaped powders,
The length of the portion having the largest dimension in the longitudinal axis (major axis), that is, the major axis length. In this case, the “axial ratio A1” and the “axial ratio A2” respectively refer to the ratio of the major axis length to the length (minor axis length) of the portion having the largest dimension in the direction orthogonal to the major axis. . Therefore, when the powder is acicular or spindle-shaped powder, the axial ratios A1 and A2 are:
It corresponds to the needle ratio. On the other hand, when the ferromagnetic powder contained in the magnetic layer 4 and the inorganic powder contained in the intermediate layer 3 are plate-like, the “particle size L1” and “particle size L2” respectively refer to the dimensions on the plate surface. Means the length of the largest part, that is, the plate diameter. In this case, the "axial ratio A1" and "axial ratio A2" refer to the ratio between the plate diameter and the length (plate thickness) in the direction perpendicular to the plate surface, respectively. Therefore, when the powder is plate-like, the axial ratios A1 and A2 correspond to the plate-like ratio.

The major axis length and the plate diameter and the minor axis length and the plate thickness are measured by the following methods. That is, the powder is observed with a transmission electron microscope by a commonly used method, and a 60,000-fold photograph is taken. The length is further doubled, the length is measured with a digital display caliper, and the average value thereof is used as the major axis length and plate diameter and the minor axis length and plate thickness. The measurement is performed on 200 to 500 powders.

As described above, the inorganic powder having a Mohs hardness of 6 or less contained in the intermediate layer 3 includes various inorganic powders. And for all of these inorganic powders,
It is preferable that L2 and A2 satisfy the above formulas (1) and (2) in relation to L1 and A1 of the ferromagnetic powder, but the inorganic powder that does not satisfy the formulas (1) and (2) is intermediate. Even if a small amount is inevitably mixed into the layer 3, the effect of the present invention is not impaired.

In the present invention, when the L2 or the average particle size of each powder contained in the intermediate layer 3 is measured, the powder contained in the intermediate layer 3 (this powder includes the above-mentioned inorganic powders) It is preferable that the L2 or the average particle size of the powder of 70% by weight or more with respect to the total weight of (1) is 1.5 times or less the L1 of the ferromagnetic powder contained in the magnetic layer 4. If this value is 70% by weight or more, the powder resembling the shape of the ferromagnetic powder contained in the magnetic layer 4 occupies most of the total powder contained in the intermediate layer 3. In addition, it is possible to sufficiently prevent the occurrence of disturbance at the interface between the two layers when the intermediate layer 3 is formed. This value is more preferably at least 85% by weight, even more preferably at least 90% by weight. In the present specification, the “average particle size” refers to a case where the powder is spherical or a particle morphology of the powder cannot be specified.
It means the average value of the length of the portion having the largest dimension of the powder in a case where 2 and A2 cannot be measured.

The above-mentioned inorganic powder contained in the intermediate layer 3 will be further described. The magnetic powder used as the inorganic powder includes a ferromagnetic powder and the like. Are preferably used. By blending the magnetic powder in the intermediate layer 3, a high output can be obtained in a wide frequency band from a high band to a low band. Thereby, excellent block error characteristics can be obtained.

Examples of the hard magnetic powder include a ferromagnetic hexagonal ferrite powder which is a plate-like magnetic powder, a ferromagnetic metal powder mainly composed of iron which is a needle-like or spindle-like magnetic powder, and a ferromagnetic oxide. Iron-based powders and the like. Among them, it is particularly preferable to use ferromagnetic hexagonal ferrite powder which is a plate-like magnetic powder.

As the ferromagnetic hexagonal ferrite powder, barium ferrite and strontium ferrite in the form of fine flat plate, and a part of their Fe atoms are Ti, C
Magnetic powders substituted with atoms such as o, Ni, Zn, V, and the like. L of the ferromagnetic hexagonal ferrite powder
2 and A2 are selected so as to be similar to the shape of the ferromagnetic powder included in the magnetic layer 4, and are preferably selected so as to satisfy the above equations (1) and (2). Specifically, L2 is preferably from 10 to 100 nm, particularly preferably from 20 to 60 nm, and A2 is preferably from 2 to 10, particularly preferably from 3 to 8. The ferromagnetic hexagonal ferrite powder preferably has a BET specific surface area of 30 to 60 m ² / g.

The coercive force of the ferromagnetic hexagonal ferrite powder is 120 to 220 kA / m, particularly 130 to 200 kA.
/ M. Within the above range, the RF output in all wavelength regions can be obtained without excess and deficiency, and the overwrite characteristics are also good. The saturation magnetization of the ferromagnetic hexagonal ferrite powder is preferably from 30 to 70 Am ² / kg, and more preferably from 45 to 70 Am ² / kg. Within the above range, a sufficient reproduction output can be obtained.

The above ferromagnetic metal powder has a metal content of 5
0% by weight or more, and a ferromagnetic metal powder in which 60% or more of the metal content is iron. Specific examples of the ferromagnetic metal powder include Fe-Co, Fe-Ni, Fe-Al,
Fe-Ni-Al, Fe-Co-Ni, Fe-Ni-A
Examples include l-Zn and Fe-Al-Si. on the other hand,
Examples of the ferromagnetic iron oxide powder include γ-Fe ₂ O ₃ , C
o-coated γ-Fe ₂ O ₃ , Co-coated FeOx (4/3 ≦ x
And <1.5). L2 and A2 of the ferromagnetic metal powder and the ferromagnetic iron oxide-based powder are selected so as to be similar to the shape of the ferromagnetic powder included in the magnetic layer 4, and satisfy the above-described formulas (1) and (2). Is preferably selected. Specifically, L2 is 30 to 200 nm,
Particularly, it is preferably 45 to 150 nm, and A2 is 3
It is preferably from 10 to 10, especially from 4 to 9. Further, the ferromagnetic metal powder and the ferromagnetic iron oxide-based powder are
The specific surface area is preferably 30 to 60 m ² / g.

The coercive force of the ferromagnetic metal powder and the ferromagnetic iron oxide powder is 120 to 220 kA / m, particularly 130 to 2 kA / m, as in the case of the ferromagnetic hexagonal ferrite powder.
It is preferably 00 kA / m. The ferromagnetic metal powder and the ferromagnetic iron oxide-based powder have a saturation magnetization of 100 to 100.
180Am ² / kg, in particular 110~160Am ² / kg
It is preferred that

The above various magnetic powders may contain a rare earth element or a transition metal element as required.
Further, in order to improve the dispersibility and the like of these magnetic powders, a surface treatment of coating the surface thereof with an inorganic oxide described in, for example, column 4, lines 9 to 25 of JP-A-9-35246 is used. May be applied.

When the intermediate layer 3 is a magnetic layer, a magnetic powder having a Mohs hardness of 6 or less and a magnetic powder having a Mohs hardness of more than 6 may be used in combination as the magnetic powder.

Next, the nonmagnetic inorganic powder used as the inorganic powder having a Moh's hardness of 6 or less contained in the intermediate layer 3 will be described. As the inorganic powder, a nonmagnetic inorganic powder having a filling action for the intermediate layer 3 is used. Powder (hereinafter, referred to as “filler”).

Examples of the filler include non-magnetic iron oxide (α-Fe ₂ O ₃ , red iron oxide), barium sulfate,
Zinc sulfide, magnesium carbonate, calcium carbonate, calcium oxide, magnesium oxide, magnesium dioxide, tungsten disulfide, molybdenum disulfide, boron nitride, silicon carbide, cerium oxide, silica, silicon nitride, molybdenum carbide, boron carbide, tungsten carbide, Examples include titanium carbide, diatomaceous earth, dolomite, and resinous powder. Among these, nonmagnetic iron oxide (α-Fe ₂ O ₃ , red iron oxide), which is a nonmagnetic powder in the form of a needle or a spindle,
Boron nitride or the like is preferably used. These fillers may be used alone or in combination of two or more. These fillers may be subjected to the same treatment as the surface treatment applied to the magnetic powder, if necessary. As the filler, needle-like α-Fe ₂ O whose surface is treated with La
_The use of ₃ is preferred because it has excellent anti-fusing properties when reduced, has a uniform particle size distribution, and has excellent dispersibility and dispersion stability when formed into a paint. Particularly preferably, the filler is surface-treated with La and Al. In this case, the amount of La is preferably 2/3 or less of the amount of Al, from the viewpoint of preventing fusion, obtaining a sharp particle size distribution, and dispersibility and dispersion stability.

The shape of the filler is selected so as to be two-dimensionally similar to the shape of the ferromagnetic powder contained in the magnetic layer 4. The particle size and the axial ratio are determined by the above equations (1) and (2). Selected to be satisfied. "Similar in two dimensions"
The term “shape” refers to the shape of a particle in which the major axis length and the minor axis length are simultaneously projected because the particle diameter (eg, major axis length) and the particle diameter / axis ratio (eg, minor axis length) are similar. Means similar. For example, needle-like α-Fe ₂ O is used as the filler.
_When a needle-shaped or spindle-shaped non-magnetic inorganic powder such as ₃ is used, its L2 is 25 to 150 nm, particularly 3 nm.
It is preferably 0 to 100 nm, and A2 is 2 to 1
It is preferably 0, particularly preferably 3 to 8.

When the filler is used in combination with the magnetic powder (ie, when the intermediate layer 3 is a magnetic layer), it is preferably 10 to 100 parts by weight based on 100 parts by weight of the magnetic powder.
0 parts by weight, more preferably 80 to 500 parts by weight. In this case, when the Mohs hardness of the magnetic powder is 6 or less, it is sufficient that the total amount of the magnetic powder and the filler is 70% by weight or more of the total weight of the powder contained in the intermediate layer 3. It is preferable because high film rigidity can be obtained. When the Mohs hardness of the magnetic powder is greater than 6,
It is preferable that the ratio of the filler is 50% by weight or more and 70% by weight or less based on the total weight of the powder contained in the intermediate layer 3 for the same reason. On the other hand, when the magnetic powder is not used (that is, when the intermediate layer 3 is a non-magnetic layer), the ratio of the filler is 7% of the total weight of the powder contained in the intermediate layer 3.
It is preferably 0% by weight or more for the same reason.

In particular, when a plate-like hexagonal ferrite powder is used as the magnetic powder and a needle-like α-Fe ₂ O ₃ is used as the filler, the hexagonal ferrite powder is made of α-Fe ₂ 30 to 100 parts by weight of O ₃
70 parts by weight, particularly 40 to 60 parts by weight,
It is preferable because a sufficient filling action is obtained and the film rigidity is increased. It is also preferable to use an appropriate amount of magnetic powder because RF output in all wavelength regions can be obtained without excess or deficiency. In this case, the plate diameter of the hexagonal ferrite powder is 2/3 or less of the major axis length of α-Fe ₂ O ₃ , particularly 1
/ 2 or less is preferable in that the filling action can be more sufficiently obtained.

In addition to the inorganic powder, the powder contained in the intermediate layer 3 includes abrasive particles used to increase the film strength of the intermediate layer 3 and carbon powder used as an antistatic agent or a solid lubricant for a magnetic recording medium. There are powders and the like.

In the present invention, the abrasive particles include, for example, Al ₂ O ₃ , SiO ₂ , ZrO ₂ , Sn
O ₂ , Sb ₂ O ₃ , ZnO and the like are preferably used. The shape of these abrasive particles is preferably selected so as to be similar to the shape of the ferromagnetic powder contained in the magnetic layer 4, but in such a case, the original function of the abrasive particles cannot be exhibited. There is. Therefore, in consideration of these balances, the abrasive particles have an average particle diameter of 50 to 350 n.
m, particularly preferably 100 to 300 nm. Further, the compounding amount is adjusted to 100 parts by weight (when the intermediate layer 3 is a magnetic layer) or 100 parts by weight (when the intermediate layer 3 is a non-magnetic layer) of the magnetic powder and the filler. Is preferably 1 to 25 parts by weight, particularly preferably 2 to 20 parts by weight.

It is preferable to use carbon black as the carbon powder. The shape of the carbon powder is preferably selected so as to be similar to the shape of the ferromagnetic powder included in the magnetic layer 4, as in the case of the abrasive particles described above. May not be exhibited. Therefore, considering these balances, the carbon powder has an average particle size of 20%.
250 nm, especially 25-100 nm, and the compounding amount thereof is 100 parts by weight (when the intermediate layer 3 is a magnetic layer) or 100 parts by weight of the filler (intermediate layer 3). 0.1 to 10 parts by weight, especially 0.1 to 10 parts by weight,
It is preferable to set it to 5 parts by weight.

The particle size of each of the various powders contained in the intermediate layer 3 is as described above. When viewed as a whole of these powders, at least 70% by weight of the powder has an L2 of 5 to 100 nm. Preferably, there is.
When L2 is within this range, the ratio of the powder similar to the shape of the ferromagnetic powder included in the magnetic layer 4 among the powders included in the intermediate layer 3 becomes sufficiently high, and the ratio of the magnetic layer 4 and the intermediate layer 3 is increased. This is preferable because disturbance at the interface between the two layers can be further prevented during formation. A more preferred range of L2 is 10 to 1
00 nm, and a more preferable range is 20 to 90 nm.

Next, components contained in the intermediate layer 3 other than the above-mentioned various powders will be described. As described above, the intermediate layer 3 contains a binder, and the various powders are dispersed in the binder. Further, the intermediate layer 3 may contain a lubricant, a curing agent, and the like.

As the above binder, for example, JP-A-9-3
No. 5,246, column 4, lines 25 to 32 can be used, and any one used for a magnetic recording medium can be used without limitation. The binder preferably has a number average molecular weight of 2,000 to 200,000. Further, in order to improve the dispersibility of magnetic powder and the like, a hydroxyl group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a nitro group or a nitrate ester group, an acetyl group, Contains polarizable functional groups (so-called polar groups) such as sulfate groups or their salts, epoxy groups, nitrile groups, carbonyl groups, amino groups, alkylamino groups, alkylammonium bases, betaine structures such as sulfobetaine and carbobetaine. May be. The binder is used in an amount of 100 parts by weight (when the intermediate layer 3 is a magnetic layer) or 100 parts by weight (when the intermediate layer 3 is a nonmagnetic layer) of the total amount of the magnetic powder and the filler. , Preferably 1 to 50 parts by weight, more preferably 5 to 35 parts by weight.

Fatty acids and fatty acid esters are generally used as the lubricant. As fatty acids, total carbon number 8
Up to 30 linear or branched fatty acids can be used, for example, myristic acid, palmitic acid, stearic acid, isostearic acid, linolenic acid, oleic acid and the like. On the other hand, examples of the fatty acid ester include, for example, alkyl esters of the above fatty acids, and those having a total carbon number of 12 to 36 are preferable. The lubricant is used in a total amount of 100 parts by weight of the magnetic powder and the filler (when the intermediate layer 3 is a magnetic layer) or 100 parts by weight of the filler (when the intermediate layer 3 is a nonmagnetic layer). , Preferably 0.5 to 5 parts by weight, more preferably 1 to 3 parts by weight.

As the above-mentioned curing agent, an isocyanate-based curing agent and an amine-based curing agent represented by Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd. are generally used. The curing agent is used in an amount of 100 parts by weight (when the intermediate layer 3 is a magnetic layer) or 100 parts by weight (when the intermediate layer 3 is a non-magnetic layer) of the total amount of the magnetic powder and the filler. , Preferably 5 parts by weight or less, more preferably 3 parts by weight or less.

In the intermediate layer 3, in addition to the above-mentioned components, additives such as a dispersant, an antistatic agent, a rust inhibitor, a fungicide, and an effective fungicide, which are used in ordinary magnetic recording media, may be added as required. Can be added.

The intermediate layer 3 is formed by applying an intermediate layer paint containing the above-mentioned components and a solvent on the support 2. Examples of the solvent include ketone solvents, ester solvents, ether solvents, aromatic hydrocarbon solvents, and chlorinated hydrocarbon solvents. The amount of the solvent used is
The total amount of the magnetic powder and the filler is 100 parts by weight (when the intermediate layer 3 is a magnetic layer) or the filler 100
Parts by weight (when the intermediate layer 3 is a non-magnetic layer)
It is preferably 80 to 500 parts by weight, particularly 100
It is preferable to set it to 350 parts by weight.

When the intermediate layer 3 composed of the above components is a magnetic layer, its coercive force is 50
２５０250 kA / m, particularly preferably 100-230 kA / m, and the saturation magnetic flux density is 0.01-0.5 T;
Particularly, it is preferably 0.05 to 0.2T. If the coercive force and the saturation magnetic flux density are within the above ranges, a magnetic recording medium having sufficient magnetic properties corresponding to high-density recording can be obtained.

Next, the magnetic layer 4 will be described. As the ferromagnetic powder contained in the magnetic layer 4, the same ones as those listed as the hard magnetic powder contained in the intermediate layer 3 can be used, and in particular, a magnetic powder having a needle-like shape is used.
Ferromagnetic metal powders and ferromagnetic iron oxide powders are preferably used. In particular, the saturation magnetization and coercive force are large,
Further, ferromagnetic metal powder is preferably used because it has conductivity. One or more kinds of the ferromagnetic powders can be used. It is preferable that all of the ferromagnetic powder contained in the magnetic layer 4 satisfy the above (1) and (2) in relation to the above inorganic powder contained in the intermediate layer 3; The effect of the present invention is not impaired even if a small amount of a ferromagnetic powder that does not satisfy the conditions (2) and (2) inevitably enters the magnetic layer 4.

These ferromagnetic powders have a particle size L1 of 20 to 150 nm, particularly 20 to 150 nm, in order to cope with high-density recording.
It is preferably 100 nm, especially 20 to 80 nm. Further, the axial ratio A2 is preferably 3 to 10, particularly preferably 4 to 9. The crystallite size is 5-20n
m, especially 8 to 18 nm, is preferable from the viewpoint that the filling property and the dispersibility are excellent, so that high output can be achieved in short wavelength recording. Further, the ferromagnetic powder can contain a rare earth element or a transition metal element, if necessary, similarly to the magnetic powder contained in the intermediate layer 3. A similar surface treatment may be performed. It should be noted that, in addition to the above, for the points not described with respect to these magnetic powders, the detailed description regarding the intermediate layer 3 is appropriately applied. When a ferromagnetic powder having a fine particle diameter of 100 nm or less is used, the interface with the intermediate layer is likely to be disturbed. Thus, high-density recording with high output and low noise can be performed.

The magnetic layer 4 is formed by dispersing the ferromagnetic powder in a binder. As the binder, those similar to the binder used for the intermediate layer 3 can be used, and the details thereof are not particularly described, but the detailed description regarding the intermediate layer 3 is appropriately applied. The binder is preferably blended in an amount of 5 to 30 parts by weight, especially 8 to 25 parts by weight, based on 100 parts by weight of the ferromagnetic powder.

The magnetic layer 4 preferably contains abrasive particles, carbon powder, a lubricant, a curing agent, and the like, in addition to the components described above. Although the details of these components are not particularly described, the detailed description of the intermediate layer 3 is appropriately applied. Preferred amounts of these components in the magnetic layer 4 are as follows with respect to 100 parts by weight of the ferromagnetic powder. Abrasive particles: 0.5 to 20 parts by weight, especially 2 to 10 parts by weightCarbon powder: 0 to 10 parts by weight, particularly 0.1 to 5 parts by weightLubricant: 0.5 to 10 parts by weight, especially 1 to 5 parts by weight Curing agent: 5 parts by weight or less, especially 4 parts by weight or less

The magnetic layer 4 may contain the same additives as those contained in the intermediate layer 3 if necessary.

The magnetic layer 4 is formed by applying a magnetic paint containing the above components and a solvent on the intermediate layer 3. As the solvent, those similar to the solvents contained in the intermediate layer paint used for forming the intermediate layer 3 are used. The amount of the solvent used is 80 to 50 parts by weight based on 100 parts by weight of the ferromagnetic powder.
It is preferably 0 parts by weight, more preferably 100 to 350 parts by weight.

Regarding the magnetic characteristics of the magnetic layer 4, the coercive force is 1
It is preferably 20 to 220 kA / m, particularly preferably 130 to 200 kA / m, and the saturation magnetic flux density is 0.2 to 0.6.
T, particularly preferably 0.3 to 0.45T. If the coercive force and the saturation magnetic flux density are within the above ranges, a magnetic recording medium having sufficient magnetic properties corresponding to high-density recording can be obtained.

As described above, the thicknesses of the magnetic layer 4 and the intermediate layer 3 are 0.6 μm or less and 0.2 to 2.5 μm, respectively. That is, the magnetic recording medium of the present invention is a magnetic recording medium having a thin magnetic layer. By having such a thin magnetic layer, the magnetic recording medium of the present invention is compatible with high-density recording. As described in the related art section above, when the magnetic layer is thin, the disturbance of the interface between the magnetic layer and the intermediate layer affects the surface properties of the magnetic layer and adversely affects the electromagnetic conversion characteristics. In the magnetic recording medium of the present invention, the shape of the inorganic powder contained in the intermediate layer 3 is selected so as to be similar to the shape of the ferromagnetic powder contained in the magnetic layer 4, and L2 and A2 of the inorganic powder are set as By selecting such that the above equations (1) and (2) are satisfied in relation to L1 and A1 of the ferromagnetic powder, such interface disturbance is effectively prevented, and the thickness of the magnetic layer 4 is reduced. The magnetic recording medium is improved in unevenness, surface properties, and orientation of the ferromagnetic powder, and thus has improved electromagnetic conversion characteristics. The preferable range of the thickness of the magnetic layer 4 is 0.05 to 0.3 μm, particularly 0.05 to 0.2 μm.
μm, and the preferable thickness range of the intermediate layer 3 is 0.2 to
It is 1.5 μm, especially 0.2 to 1.0 μm.

Next, the back coat layer 5 will be described. The back coat layer 5 is mainly composed of a binder and carbon black. As the binder and carbon black, those similar to those used in the magnetic layer 4 and the intermediate layer 3 can be used. The compounding amount of carbon black is 5 to 150 parts by weight, particularly 2 to 100 parts by weight of the total binder contained in the back coat layer 5.
It is preferably from 0 to 120 parts by weight. Further, the thickness of the back coat layer is 0.05 to 1.0 μm, particularly 0.1 μm.
It is preferably about 0.7 μm.

Next, the support 2 will be described. As a material for forming the support 2, for example, JP-A-9-35
No. 246, column 2, lines 30 to 42 can be used. The support composed of these materials includes:
If necessary, a uniaxial or biaxial stretching treatment, a corona discharge treatment, or the like may be performed. Further, a thin adhesive layer (easily adhesive layer) may be provided on the surface of these materials.

The thickness of the support 2 is not particularly limited and can be appropriately selected depending on the use and form of the magnetic recording medium. For example, when used in the form of a disk, the thickness is preferably 2 to 1000 μm, more preferably 2 to 300 μm. More preferred. When used in the form of a tape, the thickness is preferably 1 to 10 μm, particularly preferably 1 to 6 μm, particularly preferably 1 to 5 μm.

As a preferred method of manufacturing the magnetic recording medium 1 shown in FIG. 1, for example, the method described in JP-A-9-35246, column 11, line 5 to column 12, line 7 can be mentioned. As described above, in the present invention, the shape of the inorganic powder contained in the intermediate layer 3 is selected so as to be similar to the shape of the ferromagnetic powder contained in the magnetic layer 4, and the L of the inorganic powder is selected.
2 and A2 are selected so as to satisfy the above formulas (1) and (2) in relation to L1 and A1 of the ferromagnetic powder, so that the magnetic layer 4 and the intermediate layer in the manufacture of a magnetic recording medium are selected. In the formation of 3, it is possible to effectively prevent the occurrence of disturbance at the interface between both layers.

Although the magnetic recording medium of the present invention has been described based on the preferred embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. . For example, in the magnetic recording medium 1 of the embodiment shown in FIG. 1, a primer layer is further provided between the support 2 and the intermediate layer 3 or the back coat layer 5, or a hard system using a long wavelength signal is provided. Correspondingly, another magnetic layer and another layer for recording a servo signal or the like may be provided. Further, the magnetic recording medium of the present invention has a DV
It is suitable as a magnetic tape such as a tape for image / audio recording such as C tape, 8 mm video tape and DAT tape, a DDS tape, a 1/4 inch data cartridge tape, and a data recording tape such as 8 mm data tape. The present invention can be applied to other magnetic recording media such as a magnetic disk.

[0059]

The present invention will be described in more detail with reference to the following examples and the effectiveness thereof will be illustrated. However, the scope of the present invention is not limited to such an embodiment.
In the following examples, "parts" and "%" mean "parts by weight" and "% by weight", respectively, unless otherwise specified.

Example 1 The following components (excluding the curing agent) were kneaded in a kneader, dispersed by a stirrer, finely dispersed by a sand mill, and filtered by a 1 μm filter. A hardening agent was added last to prepare a magnetic paint, an intermediate layer paint and a back coat paint having the following compositions, respectively.

<Mixing of magnetic paint> 100 parts of acicular ferromagnetic powder mainly composed of iron [Coercive force: 175 kA / m, saturation magnetization: 143 Am ² / kg, L1: 100 nm, A1: 5, crystallite size] : 20 nm) ・ Abrasive particles 7 parts (α-alumina, average particle size: 200 nm, shape: irregular) ・ Carbon black 2 parts (average particle size: 30 nm, shape: irregular) ・ Binder (vinyl chloride type) Polymer 10 parts [MR104 (trade name) manufactured by Zeon Corporation] Binder (sulfonate group-containing polyurethane resin) 10 parts [UR8300 (trade name) manufactured by Toyobo Co., Ltd., solid content concentration 30 % Product] ・ Lubricant (butyl myristylate) 2 parts ・ Solvent (methyl ethyl ketone / cyclohexanone = 3/1) 290 parts

<Formulation of Intermediate Layer Coating> 45 parts of needle-like α-Fe ₂ O ₃ (Bengara) (L2: 75 nm, A2: 5, crystallite size: 15 nm, surface treatment with La2% and Al4%, Mohs) Hardness: 5) 55 plate-shaped hexagonal barium ferrites (coercive force: 155 kA / m, saturation magnetization: 60 Am ² / kg, L2: 35 nm, A2: 4, Mohs hardness: 4, crystallite size: 17)・ Abrasive particles 5 parts (α-alumina, average particle size: 200 nm, shape: irregular, Mohs hardness: 9) ・ Carbon black 2 parts (average particle size: 30 nm, Mohs hardness: 3 or less, shape: (Amorphous) ・ Binder (vinyl chloride copolymer) 10 parts [MR104 (trade name) manufactured by Zeon Corporation] ・ Binder (sulfonic acid group-containing polyurethane resin) 10 parts [Toyobo Co., Ltd. UR 8300 (trade name), solid content concentration 30% product]-5 parts of lubricant (butyl myristate)-4 parts of curing agent (isocyanate-based curing agent) [Coronate L (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.] 170 parts of solvent (methyl ethyl ketone / cyclohexanone = 3/1)

<Blending of Back Coating Paint> 40 parts of carbon black (average particle size of primary particles: 18 nm) 1.5 parts of carbon black (average particle size of primary particles: 75 nm) Binder (polyurethane resin) 50 Part (solid content) [Nipporan 2301 (trade name) manufactured by Nippon Polyurethane Industry Co., Ltd.]-Binder (nitrocellulose) 30 parts (solid content) [Celnova BTH 1/2 (trade name) manufactured by Asahi Chemical Industry Co., Ltd. 4 parts of hardener (polyisocyanate) (solid content) [D-250N (trade name) manufactured by Takeda Pharmaceutical Co., Ltd.] 5 parts of copper phthalocyanine 1 part of lubricant (stearic acid) 1 part of solvent (methyl ethyl ketone) 140 parts ・ Solvent (toluene) 140 parts ・ Solvent (cyclohexanone) 140 parts

A thickness of 4.5 μm subjected to corona discharge treatment
The intermediate layer paint and the magnetic paint were coated on the polyamide support of
m and 0.2 μm, simultaneous multi-layer coating was performed with a die coater to form respective coating films. Then
These coating films were subjected to a magnetic field orientation treatment using a 0.5 T permanent magnet and a 0.5 T solenoid magnet, and subsequently subjected to an orientation fixation treatment using 30 ° C. hot air. Further, in a drying oven, 80
The coating film was dried by blowing warm air of 10 ° C. at a speed of 10 m / min. After drying, the coating film was calendered to form an upper layer and an intermediate layer. Subsequently, the backcoat paint was applied on the surface on the opposite side of the support so as to have a dry thickness of 0.7 μm, and dried at 90 ° C. to form a backcoat layer. Finally, the magnetic tape was slit to a width of 3.81 mm to produce a magnetic tape having the structure shown in FIG.

[Examples 2 to 7 and Comparative Examples 1 to 4] L2, A2 and crystallite size shown in Table 1 were changed in place of α-Fe ₂ O ₃ and barium ferrite in the intermediate layer paint used in Example 1. A magnetic tape was obtained in the same manner as in Example 1 except that a magnetic tape having L1 and A1 shown in Table 1 was used instead of the ferromagnetic powder in the magnetic paint.
However, in Example 3, the thickness of the intermediate layer was 1.0 μm, in Example 7, the amount of alumina mixed in the intermediate layer was 35 parts by weight, and in Comparative Example 1, spherical particles were used instead of α-Fe ₂ O _3. T
iO ₂ (average particle size 35 μm, Mohs hardness 6.5) was blended in the intermediate layer, and in Comparative Example 2, the thickness of the magnetic layer was 0.8 μm.

In order to evaluate the performance of the magnetic tapes obtained in Examples and Comparative Examples, the center line average roughness Ra and the squareness ratio Sq of the magnetic layer were measured by the following method, and the reproduction output of the magnetic recording medium and Block error rate (BER)
Was measured. Table 1 shows the results.

<Measurement of Center Line Average Roughness Ra> Laser Interferometric Microscope Maxim 3D Model manufactured by Zygo
It was measured under the following conditions using 5700. -Filter: Fixed-Remove: Cylinder-Filter Freg: 4.0 (1 / mm)-Filter Wavelength: 0.250 (mm)-Trim: 0-Trim Move: All-Lens: Fizeau x 40

<Measurement of squareness ratio Sq> Only the magnetic layer was peeled off from the magnetic tape and punched to a predetermined size, and VS made by Riken Denshi was used.
The measurement was performed with an external magnetic field of 796 kA / m using M-BHV.

<Measurement of Reproduction Output> Using a drum tester type evaluator, a tape speed of 1.2 m / s and a recording wavelength of 0.33
The reproduction output was measured under the conditions of μm (high band) and 1.32 μm (low band). In Table 1, the reproduction output was represented as a relative value with Comparative Example 1 being 0 dB.

<Measurement of Block Error Rate (BER)> Measurement was performed using a DDS drive manufactured by Hewlett-Packard Company.

[0071]

[Table 1]

As is apparent from the results shown in Table 1, the inorganic powder having a Mohs hardness of 6 or less blended in the intermediate layer and the ferromagnetic powder blended in the magnetic layer were expressed by the above formulas (1) and (2).
And the thicknesses of the magnetic layer and the intermediate layer are within a specified range (the present invention product)
Indicates that the surface properties of the magnetic layer are better, the reproduction output is higher, and the block error rate is lower than that of the magnetic tape of the comparative example.

[0073]

As described in detail above, according to the present invention,
The occurrence of disturbance at the interface between the layers is prevented, and a multilayer coating type magnetic recording medium with improved electromagnetic conversion characteristics is obtained. Further, according to the present invention, a multilayer coating type magnetic recording medium suitable for high-density recording can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an embodiment of a magnetic recording medium according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic recording medium 2 Nonmagnetic support 3 Intermediate layer 4 Magnetic layer 5 Back coat layer

Claims (7)

[Claims] 1. An intermediate layer containing an inorganic powder having a Mohs hardness of 6 or less and a binder, and a magnetic layer in which a ferromagnetic powder is dispersed in a binder are formed on a nonmagnetic support in this order. In the magnetic recording medium provided, the particle size of the ferromagnetic powder contained in the magnetic layer is L1, the axial ratio is A1, the particle size of the inorganic powder contained in the intermediate layer is L2, and the axial ratio is A2. Where the ferromagnetic powder contained in the magnetic layer and the inorganic powder contained in the intermediate layer satisfy the following formulas (1) and (2), and the thickness of the magnetic layer and the intermediate layer Each 0.6
A magnetic recording medium having a thickness of 0.2 μm or less and 0.2 to 2.5 μm. 1.5L1 ≧ L2 (1) 0.5A1 ≦ A2 ≦ 1.5A1 (2) 2. The inorganic powder contained in the intermediate layer,
2. The magnetic recording medium according to claim 1, comprising a needle-like or spindle-like powder. 3. The inorganic powder contained in the intermediate layer,
3. The magnetic recording medium according to claim 1, further comprising a magnetic powder. 4. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder contained in the magnetic layer is an acicular ferromagnetic powder. 5. The L2 or average particle size of 70% by weight or more of the powder based on the total weight of the powder contained in the intermediate layer is 1.5 times the L1 of the ferromagnetic powder contained in the magnetic layer. The magnetic recording medium according to claim 1, wherein: 6. The magnetic recording medium according to claim 1, wherein L1 of the ferromagnetic powder contained in the magnetic layer is from 20 to 150 nm. 7. The inorganic powder contained in the intermediate layer contains α-Fe ₂ O ₃ whose surface has been treated with La.
The magnetic recording medium according to any one of the above.