JPH0668451A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide the magnetic recording medium having excellent traveling durability and excellent recording characteristics in a wide range of wavelength region by enhancing the dispersibility and orientability of magnetic powders into the magnetic layer of the magnetic recording medium constituted by mixing plural kinds of the magnetic powders and applying the magnetic powder mixture together with a binder on a nonmagnetic base body, thereby improving the surface smoothness. CONSTITUTION:The kinds of the magnetic powders are so selected that at least a pair of the magnetic powders selected from plural kinds of the magnetic powders have a difference of 3.0 to 9.0 isoelectric points of the high-density magnetic recording medium contg. such superfine magnetic powders as Ba ferrite and metallic powders as the magnetic powders. When the above- mentioned difference in the isoelectric points exist between the magnetic powder particles, the electrostatic interaction between the particles is enhanced and the primary particle formation is accelerated. The dispersibility is thereby improved. The value of the isoelectric points of the magnetic powders is easily changed by a surface treatment using an adequate metallic compd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a high recording density and excellent recording characteristics in a wide wavelength range from a short wavelength range to a long wavelength range.

[0002]

2. Description of the Related Art Conventionally, a coating type magnetic recording medium has been obtained by coating a substrate such as a polyester film with magnetic powder such as γ-ferrite or iron powder together with a resin binder. This resin binder is added to secure the dispersibility of the magnetic powder and the running property of the medium, and the addition amount is usually required to be 10 parts by weight or more per 100 parts by weight of the magnetic powder.

By the way, as one of the methods for meeting the recent demand for higher density of magnetic recording media, it has been attempted to reduce the particle size of magnetic powder and increase its coercive force Hc. At present, hexagonal powders such as barium ferrite and metallic powders having a particle size of 0.3 μm or less are suitable as magnetic powders for magnetic recording media that are compatible with higher recording densities due to such finer particles. This is because the medium in which these magnetic powders are applied smoothly at a high filling rate allows the high-density recording because the magnetic powders are fine particles and are not easily affected by the demagnetizing effect.

In order to fully exert the high density recording characteristics in such a coating type magnetic recording medium, the magnetic powder is dispersed to a state close to that of primary particles, whereby the orientation ratio is improved and the surface of the magnetic layer is improved. It is necessary to make the roughness as small as possible.

Further, in order to improve the recording / reproducing output of the medium, it is necessary to increase the volume ratio of the magnetic powder particles in the resin binder, that is, to increase the filling rate of the magnetic powder particles in the resin binder as much as possible. Is required.

[0006]

However, in general,
It is very difficult to highly disperse ultrafine particle powder in a dispersion medium. Therefore, there are great difficulties in dispersing the ultrafine magnetic powder in the resin binder. Then, in a magnetic recording medium prepared by applying a magnetic coating material obtained by dispersing such magnetic powder in a resin binder onto a non-magnetic substrate, the filling rate of the magnetic powder tends to be lower than in the conventional case. Also, it is not easy to improve the smoothness of the coating film. Further, if the dispersion state of the magnetic powder in the resin binder is not good, the orientation ratio of the magnetic powder in the magnetic layer obtained in the magnetic field orientation step after coating will be reduced.
As a result, not only the output at the time of recording / reproducing of the manufactured magnetic recording medium is lowered, but also a new problem is caused that noise is increased.

That is, at present, it cannot be said that the technique for dispersing the ultrafine magnetic powder used to meet the demand for high density recording has been fully established. Therefore, it is difficult to say that the smoothness of the coating film and the filling rate of the magnetic powder in the magnetic layer are sufficiently improved, and there is a new inconvenience on the recording / reproducing characteristics due to the poor dispersibility of the magnetic powder. Has occurred. as a result,
At present, the short-wavelength recording / reproducing output as expected from the particle size of the magnetic powder has not yet been obtained.

Therefore, the present invention has been made to solve the above-mentioned conventional problems, and in a magnetic recording medium for high density recording using ultrafine magnetic powder, dispersibility of the magnetic powder in a magnetic layer. By improving the filling rate of the magnetic powder in the magnetic layer and the smoothness of the magnetic layer surface by improving the orientation and orientation, the running characteristics are excellent and the recording characteristics in a wide wavelength range are excellent, especially in the short wavelength range. It is an object of the present invention to provide a magnetic recording medium having improved recording / reproducing characteristics.

[0009]

The magnetic recording medium of the present invention is a magnetic recording medium in which a plurality of types of magnetic powders are mixed and coated with a resin binder on a non-magnetic substrate. At least one pair of magnetic powders selected from the above has a difference in isoelectric points of 3.0 to 9.0.

Examples of the magnetic powder that can be used in the magnetic layer of the present invention include metal powder mainly containing iron, hexagonal ferrite powder, Co-modified ferrite powder and Co-modified magnetite powder. Examples of the metal powder mainly containing iron include Fe-Al metal powder and Fe-N.
i metal powder, Fe-Al-P metal powder, Fe-Ni-S
i-Al metal powder, Fe-Si-Al-Mn metal powder,
Fe-Mn-Zn metal powder, Fe-Co-Ni metal powder, Fe-Co-Ni-Cr metal powder, Fe-Co-N
An i-P metal powder etc. can be mentioned.

Hexagonal ferrite powder is particularly suitable for the purpose of the present invention, and is M-type (Magnetoplumbite type) or W-type hexagonal Ba ferrite, Sr ferrite,
Lead ferrite, Ca ferrite, a solid solution thereof, or an ion-substituted compound represented by the following formula can be used.

MaO.n {Fe _1-x Mb _x } ₂ O ₃ (In the formula, Ma represents any one element of Ba, Sr, Ca and Pb, and Mb represents Co, Zn, Ni, Cu, Mg,
Mn, In, Ti, Sn, Ge, Zr, Hf, V, N
It represents at least two elements selected from the group consisting of b, Sb, Ta, Cr, Mo and W, and n represents a number of 5.4 to 6.0. Among the substitution elements Mb, for example, a divalent metal mainly acts to reduce the coercive force of the hexagonal ferrite powder to an appropriate range, a pentavalent metal Nb acts to increase the saturation magnetization, and a tetravalent metal Sn has the effect of reducing the change in coercive force with temperature, respectively.

Therefore, for example, in the hexagonal ferrite powder used in the present invention, a part of Fe atoms, which are the constituent elements of these uniaxial hexagonal ferrite crystals, are
A divalent metal and a pentavalent metal substituted with Nb, or further substituted with 0.05 to 0.5 Sn atom per one chemical formula are suitable, and the substitution amount x has a coercive force of 500. The amount should be adjusted within the range of ~ 3,000 Oe.
Note that Ti having the same valence may be used instead of Sn described above.

In the hexagonal ferrite used in the present invention, the proper substitution amount of divalent metal and pentavalent metal is 2
2 depending on the combination of valent metal and pentavalent metal,
The substitution amount of a valent metal per chemical formula is about 0.05 to 1.
There are two.

The average particle size of the magnetic powder used in the present invention is
In the case of acicular metal powder or oxide powder, the range is preferably 0.05 to 0.2 μm, and in the case of hexagonal powder, the range is preferably 0.01 to 0.1 μm.
The definition of particle size depends on the type of magnetic powder, but here we define the shape and size of each particle by the length of the longest part, for example, for needle-shaped powder, the size in the longitudinal direction of the needle, and hexagonal crystal. The system powder is defined by the dimension connecting the opposite angles of the hexagonal faces. The lower limit of the particle size is determined from the fact that stable magnetic properties cannot be secured when the particle size is smaller than that of each magnetic powder, and the upper limit of the particle size is aimed at by the present invention when the particle size is larger than this. It is decided from the point that it becomes difficult to reduce the noise in short wavelength recording and secure the output.

The coercive force of the acicular metal powder, oxide powder or hexagonal crystal powder according to the present invention is preferably in the range of 500 to 3,000 Oe. When the coercive force is less than 500 Oe, the recording signal on the recording medium does not remain stably, and when it exceeds 3,000 Oe, it becomes difficult to read and write the signal by a general recording / playback head.

In the present invention, it is important to properly select two or more kinds of magnetic powders having different isoelectric points from the above-mentioned magnetic powders, and mix and use them.

Examples of the combination of magnetic powders having different isoelectric points include hexagonal powder / hexagonal powder, needle powder / needle powder having different aspect ratios, and hexagonal powder / acicular powder. It is possible to select a combination of powders, a combination of magnetic powders having the same crystalline state but different particle diameters, or a combination of two or more kinds of these magnetic powders.

When selecting the types of magnetic powders to be combined and mixed, the difference between the isoelectric points of 3.0 to 9.0 in at least one pair of magnetic powders among a plurality of types of magnetic powders is the standard. More preferably, it has a difference in isoelectric points of 4.0 to 9.0. When the difference between the isoelectric points is less than 3.0, the intended effect of improving the dispersibility cannot be seen. If the difference between the isoelectric points is 9.0 or more,
There is less room for selection as a combination of magnetic powders having a desired difference in isoelectric point.

Among the plural kinds of magnetic powders mentioned above, 3.0 to 9.
The ratio of each of the at least one pair of magnetic powders having an isoelectric point difference of 0 to 100 parts by weight of the total magnetic powder is preferably 5 parts by weight or more. More preferably 10
It is in the range of more than weight part. This is because if it is less than 5 parts by weight, the effect of improving the dispersibility becomes small.

The isoelectric point of the magnetic powder can be expressed as the hydrogen ion concentration (pH) of the solution when the potential of the electric double layer produced by dispersing the magnetic powder in water becomes zero. This is a value peculiar to each magnetic powder. Therefore, in the present invention, the desired effect can be obtained by appropriately selecting the type of magnetic powder so that at least one pair of magnetic powders has a predetermined difference in isoelectric point.

As described above, the value of the isoelectric point of the magnetic powder is unique to each magnetic powder, but when the surface condition of the magnetic powder changes due to surface treatment or the like, the value changes. Therefore, when the surface of the magnetic powder is treated with a metal compound or the like, the value of the isoelectric point can be easily changed by appropriately selecting the type of metal. Therefore, even if a suitable magnetic powder having a desired value of the isoelectric point is not found, the value of the isoelectric point is changed by performing the surface treatment, and the isoelectric point of the desired value is changed. It is possible to easily obtain a magnetic powder having

In the present invention, as the resin binder,
Vinyl chloride / vinyl acetate copolymer having a hydroxyl group, a carboxyl group, a phosphoric acid group, a sulfone group, a sulfobetaine group or a metal base thereof, or a polar group such as an amino group, an alkylamino group and an ammonium group, a polyester resin, and a polyester. Ter resins, polyurethane resins, polyacrylic resins and the like are suitable, and those having a metal base of sulfonic acid or sulfobetaine are particularly suitable as the resin of the present invention. The reason is probably that these resins are well adsorbed on the magnetic powder and assist the dispersion. These polar groups do not have to exist alone in the resin molecule, and a plurality of types of polar groups may coexist in the same molecule. The number of these polar groups in the resin binder is important and for the purposes of the present invention is in the range of at least 0.01-4.0 mmol / g, more preferably 0.05-2.
It is in the range of 0 mmol / g.

In the present invention, the resin binder having a molecular weight of 1,000 to 60,000 can be used. However, in order to increase the filling rate of the magnetic powder, it is preferable that the molecular weight (Mw) of the resin binder is relatively small within the above range. If the molecular weight is less than 1,000, the effect as a binder is small, and if it exceeds 30,000, the required amount of the resin binder increases and it becomes difficult to achieve a desired high filling rate. Therefore, in the present invention, the molecular weight of the resin binder is more preferably in the range of 1,000 to 30,000.

By the way, among the polar groups of the resin binder according to the present invention, the metal sulfonate base is introduced as follows. First, when the resin binder containing a metal sulfonate group is a resin obtained by vinyl polymerization, it is usually obtained by copolymerizing a vinyl monomer containing these polar groups with an ordinary vinyl monomer. Further, when the resin binder containing the polar group is a polyester resin or a polyurethane resin, a polyvalent basic acid or polyvalent alcohol which is a component thereof and a polyvalent basic acid into which the polar group is introduced, or It is obtained by mixing polyhydric alcohol and conducting a condensation reaction. Examples of monomers, polybasic acids or polyalcohols used for producing a resin containing a metal sulfonate base include, for example, vinyl sulfonic acid, vinyl benzene sulfonic acid and 2-acrylamide.
2-Methylpropanesulfonic acid metal salt, or a compound represented by the following chemical formula, (Ph is an aromatic ring, M is H or an alkali metal) and the like.

Various resin binders can be used together for the purpose of improving the mechanical strength and running property of the coating film. Resins that can be used in combination include polyurethane resins, polyester resins, polycarbonate resins,
Polyacrylic resin, polyamide resin, epoxy resin, phenol resin, polyether resin, phenoxy resin, melamine resin, vinyl butyral resin, furan resin, vinyl chloride resin, vinyl acetate resin, vinyl alcohol resin or a mixture thereof. Alternatively, a copolymer may be used.
The compounding amount of these combined resin binders is appropriately set within 80% by weight with respect to the total resin binder.

In the present invention, the resin binder is magnetic powder 10
It is added in an amount of 5 to 20 parts by weight, preferably 8 to 15 parts by weight, based on 0 parts by weight. The reason why a medium whose durability is ensured can be obtained with such a small addition amount as compared with the addition amount of the resin binder used for the magnetic layer of the ordinary magnetic recording medium is that the resin binder is a metal sulfonate base or sulfobetaine. It is considered that this is because a magnetic layer having a highly adsorptive polar group such as a group is used and the dispersibility is improved by using a mixed magnetic powder having a different isoelectric point, so that a magnetic layer having a high packing rate can be obtained. In order to increase mechanical strength and durability, polyamine-based or polyisocyanate-based paint is used.
G-based curing agents can be added.

The resin binder in the present invention is defined as the total amount of the resin binder added during dispersion and the curing agent added prior to coating.

In producing the magnetic recording medium of the present invention, first, the above-mentioned mixed magnetic powder and resin binder are mixed with an organic solvent and, if desired, additives such as a dispersant, a lubricant and an abrasive, and then kneaded. The kneaded material is further dispersed with a ball mill or a sand grinder to prepare a magnetic coating material. Then, after passing through the magnetic filter after the dispersion step, the filter for filtration,
A curing agent such as polyisocyanate is added. Then, it is coated on the substrate by a usual coating method using a reverse coater, a gravure coater, an applicator coater, a slot die coater or the like.

Examples of the organic solvent that can be used for the above magnetic coating material include toluene, xylene, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, nitropropane, butyl acetate, and the like, and these can be used as a mixture.

As the dispersant for dispersing the magnetic powder in the resin binder, any of anionic surfactants, cationic surfactants and nonionic surfactants is effective. Nonionic phosphoric acid ester surfactants and lecithin which are ionic surfactants are effective. The dispersibility can be improved by adding a silane coupling agent or a titanium coupling agent in addition to such a dispersant in the step of kneading the magnetic powder and the resin binder.

It is desirable to add a lubricant to the magnetic paint. Preferred lubricants include fatty acids having 12 or more carbon atoms or fatty acid esters, fatty acid amides, silicone oils, fluorinated hydrocarbon oils, and the like.

If desired, a conductive powder such as carbon black, titanium oxide or tin oxide may be added to the magnetic coating material of the present invention.

As the non-magnetic substrate according to the present invention, a polyester film, a polycarbonate film, a polyimide film, a polysulfonate film or the like can be used. Further, it is desirable that a back layer containing a conductive powder such as carbon black is formed on the surface of the surface of the substrate on which the magnetic layer is not formed. The back layer plays a very important role in preventing generation of static electricity on the surface of the substrate, improving running property, and preventing blocking with the magnetic layer. for that reason,
This back layer is usually made to have a surface resistance of 10 ⁶ ohms or less. Further, the surface property of the back layer is also very important, and the surface roughness measured by a stylus type surface roughness meter is preferably prepared so that the 10-point average roughness Rz is 0.05 or less. .

After the above-mentioned coating step and coating step, the magnetic recording medium of the present invention is obtained through steps such as magnetic field orientation treatment and calendar treatment according to a conventional method.

In the magnetic recording medium of the present invention,
In order to enhance the adhesive strength of the magnetic layer and thereby enhance the durability of the medium, plasma treatment of the substrate surface or an underlayer containing carbon black coated on the substrate surface is extremely effective.

[0037]

The interaction of the magnetic powder particles and the isoelectric point thereof, which is the focus of the present invention, will be described in detail below.

In producing a magnetic recording medium, the magnetic powder particles are dispersed in an organic solvent together with various additives to form a coating as described above. It can be said that the dispersed state depends on the charged state of the particles. Therefore, the dispersed state can be known by examining the charged state of the magnetic powder particles in the magnetic paint. Further, in order to improve the dispersibility of the magnetic powder in the formed magnetic layer, it is necessary that the magnetic powder particles are already sufficiently dispersed in the solvent in a state close to the primary particles at the stage of being made into a paint. It can be said that it is necessary. Therefore, by studying the charged state of the magnetic powder particles in the magnetic coating material, it is possible to obtain knowledge about the dispersibility of the magnetic powder in the formed magnetic layer.

However, the charged state of particles such as magnetic powder in a solvent is a state brought about by the interaction between each magnetic powder particle and the solvent, and the charged amount as a quantity capable of expressing the state. Is a relative value. Therefore, it has been difficult to use such a relative value as a universal standard for capturing the charged state of the magnetic powder particles, and it has been very difficult to use it as an index indicating the dispersion state.

Therefore, for the purpose of improving the dispersibility of the magnetic powder in the magnetic layer, and for obtaining an index representing the dispersion state of the magnetic powder in the magnetic coating material, various magnetic coating films were tried to be produced. Then, when trying to prepare a coating film by mixing various magnetic powders that have undergone surface modification, some findings suggest that the metal in the metal compound on the magnetic powder surface can be approximated as a metal ion. Was obtained.

On the other hand, it has been reported by Koguchi that the charge amount of a metal ion correlates with its electronegativity, and the electronegativity of a metal ion correlates with its isoelectric point (surface, Vol. .23, 320-330 (1985)). Therefore, if the metal in the metal compound on the surface of the magnetic powder particles can be regarded as a metal ion, the isoelectric point of the magnetic powder particles can be treated as a criterion for capturing the charged state of the magnetic powder particles instead of the charge amount.

As described above, the isoelectric point of the magnetic powder is expressed as the hydrogen ion concentration (pH) of the solution when the potential of the electric double layer produced by dispersing the magnetic powder in water becomes zero. can do. Since this is a value peculiar to each magnetic powder, it can be used as a reference for capturing the charged state of the magnetic powder particles. Further, as described above, if the metal in the metal compound on the surface of the magnetic powder particles is regarded as a metal ion, the isoelectric point is generally closely related to the electronegativity of the metal ion. When the metal ion in the metal compound on the surface of the magnetic powder particles is a metal ion having high electronegativity, the isoelectric point of the magnetic powder becomes small. On the contrary, when the metal ion in the metal compound on the surface of the magnetic powder particles is a metal ion having a low electronegativity, the isoelectric point of the magnetic powder increases. Therefore, by surface-treating the magnetic powder with a metal compound in which the type of metal is appropriately selected,
The isoelectric point of the magnetic powder can be controlled to a desired value.

For example, SiO ₂ , TiO ₂ , ZrO ₂ ,
The isoelectric point of the magnetic powder whose surface is treated with a compound such as Ta ₂ O ₅ , V ₂ O ₅ , Nb ₂ O ₅ , and WO ₃ having a large atomic number of constituent metals is small. On the other hand, CaO, ZnO, Mg
The isoelectric point of the magnetic powder whose surface is treated with a compound such as O or Al ₂ O ₃ having a small atomic value is large.

In the above surface treatment, magnetic powder may be immersed in an aqueous solution of chloride or sulfide containing these metals to change the pH of the aqueous solution. By such an operation, the metal oxide is easily deposited on the surface of the magnetic powder.

As described above, the isoelectric point is regarded as an index representing the charged state of the magnetic powder, and various magnetic powders are selected and combined from this point of view to manufacture a magnetic recording medium. It was put out. That is, when different types of magnetic powders are simply mixed and used, the dispersibility of the magnetic powders in the resin binder and the improvement of the filling rate of the magnetic powders in the coating film are rather hindered. However, it has been found that when a combination of magnetic powders having different isoelectric points of at least 3.0 or more is included, the dispersibility is remarkably improved. As a result of the markedly improved dispersibility of the magnetic powder, it has been found that a coating film having a high filling rate of the magnetic powder and a magnetic field orientation rate can be produced.

Although the reason why the dispersibility of the magnetic powder is improved by the constitution of the present invention has not been completely clarified yet, it is presumed that there is a difference in isoelectric point between the ultrafine magnetic powder particles. It is considered that this is because the electrostatic interaction between the particles is in a strengthened state, and this strengthened electrostatic interaction effectively works to make the magnetic powder into primary particles.

In the present invention, when each of at least one pair of magnetic powders having an isoelectric point difference of 3.0 or more is contained in an amount of 5 parts by weight or more based on 100 parts by weight of the total magnetic powder, the magnetic property is The effect of improving the dispersibility of the powder is obtained. This means that when only a small amount of magnetic powder having a different isoelectric point is contained, this significantly promotes dispersion of other magnetic powder.

The effect of improving the dispersibility of the magnetic powder obtained by the present invention is surprisingly effective even when the shape of the magnetic powder to be mixed is changed. For example, a combination of acicular powder and hexagonal powder. Also in the above, a highly oriented coating film can be obtained with a higher filling rate than when these are used alone.

[0049]

EXAMPLES Specific examples of the present invention will be described below.

Example 1 The following material compositions were weighed in a kneader and kneaded for about 30 minutes.

[Magnetic coating composition] Co, Ti, Nb-substituted Ba ferrite powder (Hc 1000 Oe,
Number average particle size 0.05 μm, specific surface area 38 m ² / g, isoelectric point 8.0,
Aspect ratio 3.0) 90 parts by weight Co-modified magnetite powder (Hc 900 Oe, number average particle size 0.02
μm, specific surface area 40 m ² / g, isoelectric point 4.0) 10 parts by weight Sulfonated urethane resin (molecular weight 15,000, Na sulfonate content 0.2 mmol / g) 8 parts by weight Stearic acid 2 parts by weight Alumina 4 parts by weight Part cyclohexanone / methyl ethyl ketone (1/1 mixed solvent) 25 parts by weight Then, 170 parts by weight of the above mixed solvent was added, diluted with a dissolver, and further dispersed with a sand grinder. After passing the obtained dispersion through a filter with a pore size of 0.3 μm,
2.0 parts by weight of Coronet L (trade name: Tolylene diisocyanate-based curing agent 50% diluted) was added and mixed to obtain a magnetic paint.

The magnetic coating material thus obtained was applied to a polyester film while being supplied to a slot die coater, and introduced into a Sonorade generating a magnetic field strength of 6 kOe before the coating film was dried, and the organic coating was applied. The solvent was stripped off. The thickness of the dried coating film was 1.5 μm. The raw fabric thus obtained was slit into a width of 8 mm to produce a tape-shaped magnetic recording medium that was an example of the present invention.

Example 2 The Co-modified magnetite powder used in Example 1 was replaced with Fe-N.
A magnetic coating film was formed in the same manner as in Example 1 except that the i-type metal powder (particle size: 0.15 μm, specific surface area: 50 m ² / g, isoelectric point: 3.0) was used to prepare a magnetic recording medium. did.

Example 3 The Co-modified magnetite powder in Example 1 was used as in Example 1.
A magnetic recording medium was prepared by forming a magnetic coating film in the same manner as in Example except that the surface of the Ba ferrite powder was changed to that of the Ba ferrite powder (isoelectric point 3.5) by adhering corrodyl silica to the Ba ferrite powder. did.

Example 4 As the magnetic powder, the Ba ferrite powder (isoelectric point 7.5, aspect ratio 3.0) obtained in Example 1 was treated with alumina to obtain Ba ferrite powder (isoelectric point 10.0, aspect ratio). Ratio 3.0) 50 parts by weight, and B in Example 1 as well.
Ba obtained by treating a ferrite powder with silica-alumina
Ferrite powder (isoelectric point 4.0, aspect ratio 3.0) 5
A magnetic coating film was formed in the same manner as in Example 1 except that 0 part by weight was used to prepare a magnetic recording medium.

Example 5 The Ba ferrite powder (isoelectric point 7.5, aspect ratio 3.0) in Example 1 was converted into Ba ferrite powder (isoelectric point 8.
No. 0, aspect ratio 4.5), and treated with silica-alumina to obtain Ba ferrite powder (isoelectric point 4.5,
Aspect ratio 4.5) was used instead of the silica-alumina-treated Ba ferrite powder (isoelectric point 4.5, aspect ratio 3.0) in Example 4, and the magnetic coating film was formed in the same manner as in Example 4. To form a magnetic recording medium.

Example 6 Except that the compounding amounts of the two kinds of Ba ferrite powders in Example 5 were each 40 parts by weight and 20 parts by weight of the metal powder used in Example 2 was added and used as a magnetic powder. A magnetic film was formed in the same manner as in Example 1 to manufacture a magnetic recording medium.

Further, in order to examine the effect of the present invention, the following magnetic recording medium was manufactured as a comparative example.

Comparative Example 1 A magnetic recording medium was prepared by forming a magnetic coating film in the same manner as in Example 1 except that 100 parts by weight of Ba ferrite powder in Example 1 was used as the magnetic powder.

Comparative Example 2 A magnetic coating film was formed in the same manner as in Example 1 except that only 100 parts by weight of the metal powder used in Example 2 was used as the magnetic powder, to prepare a magnetic recording medium.

COMPARATIVE EXAMPLE 3 As a magnetic powder, 100 parts by weight of only the silica-alumina-treated Ba ferrite powder (isoelectric point 4.5, aspect ratio 4.5) used in Example 5 was used. 1
A magnetic coating film was formed in the same manner as in 1. to prepare a magnetic recording medium.

The in-plane orientation ratio, the saturation magnetization amount, the recording / reproducing output, and the still durability characteristics of the thus obtained coated strip tape sample were evaluated. The evaluation results are shown in Table 1. When measuring the recording / reproducing output,
The mmVTR deck was used.

[0063]

[Table 1]

[0064]

As described above, according to the present invention, since the combination of magnetic powders having excellent dispersibility can be appropriately selected, the dispersibility and orientation of the magnetic powders in the magnetic layer can be improved. This makes it possible to improve the smoothness of the magnetic layer surface and the packing density of the magnetic powder. As a result, it is possible to obtain a magnetic recording medium having excellent running durability and excellent recording characteristics in a wide wavelength range, and particularly improved recording / reproducing characteristics in a short wavelength range.

[0065]

Claims (6)

[Claims] 1. A magnetic recording medium in which a plurality of types of magnetic powders are mixed and coated with a resin binder on a non-magnetic substrate, wherein at least one pair of magnetic powders selected from the plurality of types of magnetic powders comprises: A magnetic recording medium having an isoelectric point difference of 3.0 to 9.0. 2. Each of the pair of magnetic powders is a total magnetic powder 1.
The magnetic recording medium according to claim 1, wherein the content is 5 parts by weight or more with respect to 00 parts by weight. 3. The resin binder according to claim 1, wherein the resin binder is a resin binder having a metal sulfonate group or a sulfobetaine group.
The magnetic recording medium described. 4. The magnetic powder of at least one of the pair of magnetic powders has a coercive force Hc of 500 to 3,000 Oe and a particle size of 0.05 to 0.2 μm.
The magnetic recording medium according to claim 1, 2 or 3, which is a metal powder mainly composed of iron. 5. The magnetic powder of at least one of the pair of magnetic powders has a coercive force Hc of 500 to 3,000 Oe and a particle size of 0.01 to 0.1 μm.
The magnetic recording medium according to claim 1, 2 or 3, wherein the magnetic recording medium is the hexagonal ferrite powder. 6. The magnetic powder of at least one of the pair of magnetic powders is Si, Ti, Zr, Ta, V, Nb, W, C.
6. A magnetic powder having a surface coated with at least one metal selected from a, Zn, Mg, and Al, The claim 1, 2, 3, 4, or 5. Magnetic recording medium.