JP2664713B2 - Magnetic recording media - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a magnetic recording medium having a high recording density and excellent short-wavelength recording characteristics.

(Prior art) A coating type magnetic recording medium is obtained by applying a magnetic powder such as γ-Fe ₂ O ₃ , CrO ₂ CO-γ-Fe ₂ O ₃ or iron powder together with a resin binder onto a base such as a polyester film. Has been obtained.

In recent years, higher recording densities have been required for magnetic recording media, and attempts have been made to reduce the particle size of magnetic powder as a solution to this problem. On the other hand, as a magnetic powder suitable for this purpose, a part of Fe is replaced with Co, Ti, etc., so that the coercive force can be recorded and reproduced by a normal recording and reproducing head.
It has been found that ultrafine hexagonal ferrite powder such as Ba-ferrite having a particle size of 〜2000 Oe and a particle size of 0.2 μm or less is suitable.

That is, ultrafine hexagonal ferrite powder such as Ba-ferrite is a hexagonal plate-like crystal, and provides a high-density perpendicular magnetic recording medium having an easy axis of magnetization in a direction perpendicular to the plate surface.

(Problems to be Solved by the Invention) Meanwhile, in a magnetic recording medium obtained by using such magnetic powder, the surface roughness of the magnetic recording layer must be extremely high in order to obtain excellent recording characteristics for recording short-wavelength signals. And the saturation magnetization (M _S ) must be as large as possible. However, usually used for such purposes, for example Ba
-Ultrafine hexagonal ferrite powder such as ferrite originally has a small saturation magnetization, so there is a limit from the viewpoint of sufficiently extending short wavelength characteristics. One method of increasing the saturation magnetization of the magnetic recording layer is to decrease the ratio of the resin binder. However, when the saturation magnetization is increased by this method, the amount of the resin binder is reduced to 14 parts by weight or less with respect to 100 parts by weight of the magnetic powder. Then, there is a problem that the saturation magnetization hardly increases any more and only the surface roughness increases.

The present inventors have conducted various studies to solve such a conventional problem, and as a magnetic powder, a part of Fe is at least Nb.
Surprisingly, when the hexagonal ferrite powder having an average particle size of 0.01 to 0.2 μm substituted by is used, even if the compounding amount of the resin binder is set to 14 parts by weight or less with respect to 100 parts by weight of the magnetic powder, It was found that the saturation magnetization increased.

The present invention has been made based on this finding, the amount of the resin binder, 14 parts by weight of the magnetic powder, 14 parts
It is an object of the present invention to provide a high-density magnetic recording medium having a short-wavelength recording characteristic in which the saturation magnetization is further increased to less than part by weight.

[Constitution of the Invention] (Means for Solving the Problems) That is, the magnetic recording medium of the present invention has an average particle diameter of 0.01 to 0.2 in which at least a part of Fe is substituted by Nb on a substrate.
μm hexagonal ferrite powder in a magnetic recording medium having a magnetic recording layer coated with a resin binder, wherein the ratio of the hexagonal ferrite powder to the resin binder is 100: 5
100100: 14 (weight ratio).

As the hexagonal ferrite powder used in the present invention, for example, an M type (Magnetop lumbite tip) represented by the following general formula:
e), W-type hexagonal Ba ferrite, Sr ferrite, lead ferrite, Ca ferrite, or a solid solution or ion-substituted material thereof.

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, Z
At least two elements selected from the group consisting of r, Hf, V, Nb, Sb, Ta, Cr, Mo, and W, one of which is Nb. n represents the number of 5.4-6.0. More specifically, the hexagonal ferrite powder used in the present invention includes a part of Fe atoms, which are constituent elements of these uniaxially anisotropic hexagonal ferrite crystals, with a divalent metal and
Those substituted with Nb, which is a valent metal, or 1
Those substituted with 0.05 to 0.5 Sn atoms per chemical formula are suitable, and the substitution amount is such that the coercive force becomes 200 to 2000 Oe.

Among the substitution elements, divalent metals mainly reduce the coercive force of hexagonal ferrite powder to an appropriate range, and
Nb of the valent metal acts to increase the saturation magnetization, and Sn of the tetravalent metal acts to reduce the change in the temperature characteristic of the coercive force.

As the divalent metal, an element such as Co, Zn, Ni, Mn, Cu, and Mg which is relatively well substituted for Fe atoms in ferrite is selected.

In the hexagonal ferrite used in the present invention, the appropriate substitution amount of the divalent metal (M _II ) and the pentavalent metal (M _V ) is M _II
Substitution amount per chemical formula and M _V differ by combining M _II of is generally 0.5 to 1.2 pieces.

As for the relationship between the substitution amounts of these substitution elements, for example, regarding magnet plumbite type Ba ferrite, the chemical formula of the substitution product is BaFe _{12- (x + y (+ z))} M _{II x} M _Vy (M _{IV z} ) represented by O _19. Here x, y, z is the substitution amount of ferrite per chemical formula of M _II, M _V and M _IV elements. M _II , M _V and M _IV are divalent, pentavalent and tetravalent, respectively, and the substituted Fe atom is trivalent.
= (X−z) / 2 holds. That substitution of M _V is uniquely determined from the amount of substitution substitution amount and M _IV of M _II.

In the magnetic powder of the present invention, when using Sn as M _IV element, a proper range of the amount of substitution is from 0.05 to 0.5 or the range of per formula of the hexagonal ferrite.

Note that Ti having the same valence may be used in place of Sn.

Further, the average particle size of the hexagonal ferrite powder is 0.01 to 0.2 μm.
When the diameter is less than 0.01 μm, the magnetization and the coercive force are reduced, and the reproduction output of the magnetic recording medium is reduced. When the diameter exceeds 0.2 μm, the coercive force is reduced and the high density recording is performed. This is because the noise at the time of reproduction becomes remarkable. If the coercive force is less than 200 Oe, the recording signal on the recording medium does not remain sufficiently. If the coercive force exceeds 2000 Oe, it becomes difficult to write a signal with a normal recording / reproducing head.

When the ferrite powder is applied on a support such as a polyester film, it is mixed with a solvent and a binder to prepare a paint.

As the resin binder, polyurethane resin, polyester resin, polycarbonate resin, polyacryl 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, cellulose derivative, epoxy resin, or a mixture or copolymer thereof Use things.

When these resins are applied on a support together with ferrite powder, it is desirable to add a polyamine or polyisocyanate-based curing agent to increase the mechanical strength of the obtained coating film and increase the durability.

The weight ratio of the resin binder including the curing agent to 100 parts by weight of the hexagonal ferrite powder is selected in the range of 100: 5 to 100: 14. If the amount of the resin binder is less than 5 parts by weight per 100 parts by weight of the hexagonal ferrite, it is difficult to maintain the mechanical strength of the coating, and if it is more than 14 parts by weight, the saturation magnetization of the coating decreases. Therefore, it is difficult to obtain a sufficiently short wavelength output.

If desired, a lubricant, a dispersant, an abrasive, or a conductivity-imparting agent such as carbon black may be added to the components of the magnetic coating film.

As the lubricant, fatty acid or fatty acid alkyl ester type, silicone type, fluorinated hydrocarbon type, or a mixture or compound thereof can be used. In addition, as the dispersant, an anionic surfactant, a cationic surfactant, and a nonionic surfactant can be used. In particular, a surfactant having a phosphate group, a silane coupling agent, and a titanium cup. Ring agents are effective. further,
As the abrasive, an inorganic powder having a Moh's hardness of 5 or more, such as TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , SiC, and ZrO ₂ , is suitable.

It is desirable that the amount of these additives is as small as possible, based on 100 parts by weight of hexagonal ferrite.
For example, it is preferable that the lubricant and the dispersant are each in a range of 4 parts by weight or less, the abrasive is 5 parts by weight or less, and the carbon black is 3 parts by weight or less.

The magnetic recording medium of the present invention is prepared by thoroughly mixing a hexagonal ferrite powder, a resin binder, and various additives as necessary with a solvent, and further adding a crosslinking agent such as a polyisocyanate compound to the substrate, if necessary. , And then subjected to an orientation treatment and a drying treatment, and the resulting coating film is subjected to a smoothing treatment by a calendar. If necessary, a conductive primer layer may be formed on the substrate, and the magnetic recording layer may be formed on the primer layer.

Thus, the obtained magnetic recording medium has a squareness ratio.
It has excellent magnetic recording characteristics of 0.5 or more.

(Operation) In the magnetic recording layer of the present invention, the saturation magnetization of the coating film can be increased even if the resin binder is reduced to 14 parts by weight or less based on 100 parts by weight of the magnetic powder. This effect is considered to be due to an increase in the saturation magnetization (δ _S ) of the magnetic powder due to the substitution of a part of the Fe atoms of the hexagonal ferrite powder with Nb, but the actual saturation magnetization (M _S ) The increase corresponds to a magnitude two to three times the value expected from the saturation magnetization (δ _S ) of the magnetic powder. Therefore, the effect of the present invention is not only attributable to the increase in the saturation magnetization (δ _S ) of the Nb-substituted hexagonal ferrite powder, but is also obtained by superimposing some action for improving the packing of the hexagonal ferrite powder due to the Nb content. It is thought that it is possible.

The increase in the saturation magnetization (M _s ) is effective for making the surface denser, thereby improving the contact with the recording / reproducing head, and remarkably improving the recording / reproducing output especially in the short wavelength region.

(Example) Next, an example of the present invention is described.

The amounts of the resin binders shown in the following examples are all
It is the amount as 100% solids.

Example 1 Co, Ti, Nb-substituted Ba-100 parts by weight Ferrite powder * Nitrocellulose 5 parts by weight MAU-53006 Loose 5 parts by weight (polyurethane resin trade name, manufactured by Dainichi Seika Co.) Toluene / cyclohexanone = 1/2 mixture Solution 180 parts by weight Lecithin 3 parts by weight Alumina (average particle size 0.3 μm) 3 parts by weight Stearic acid 2 parts by weight *: Nb substitution amount y = 0.45 (average particle size: 0.05 μm Plate ratio: 4: 1,
Hc600Oe) After mixing the above materials, they were further dispersed by a sand grinder for 2 hours. After filtration, 2 parts by weight of Coronate L (polyisocyanate trade name: manufactured by Nippon Polyurethane) was added to the obtained magnetic paint, which was then applied on a polyester film by a reverse coater.

The resulting coating film was cured at 40 ° C. for 3 days, cut into a 1/2 inch width to prepare a magnetic tape, and used for measurement.

Example 2 In place of nitrocellulose and MAU-5300 of Example 1, VAGH (vinyl chloride-vinyl acetate copolymer resin) was used.
A magnetic paint was prepared in the same manner as in Example 1 except that 3 parts by weight of Union Carbide Co., Ltd. and 3 parts by weight of TA-107 (polyurethane resin trade name: Nippon Polyurethane Co., Ltd.) were used. It was created.

Example 3 After the magnetic paint was applied on the polyester film in Example 2, the coating was dried while passing through a magnetic field perpendicular to the film surface while the coating surface was not dried.
A magnetic tape was prepared in the same manner as described above.

Example 4 10 parts by weight of carbon black (Ketjen Black EC) 10 parts by weight TA-107 10 parts by weight Toluene / cyclohexanone = 1/2 mixed solution 80 parts by weight were mixed and further subjected to a dispersion treatment by a sand grinder. To 100 parts by weight of the obtained magnetic paint, 3 parts by weight of coronate 3041 was added and applied to a polyester film, followed by curing treatment to obtain a polyester film having a conductive primer layer.

A magnetic paint was applied on the film according to Example 3 to prepare a magnetic tape.

Comparative Example 1 In the same manner as in Example 1 except that Co- and Ti-substituted Ba-ferrite powder containing no Nb (average particle size: 0.05 μm, plate ratio: 4: 1, Hc: 600 Oe) was used. To make a magnetic tape.

Comparative Example 2 A coating film and a magnetic tape were produced in the same manner as in Example 2 except that the vinyl chloride-vinyl acetate copolymer resin in Example 2 was reduced to 2 parts by weight and TA-107 to 2 parts by weight.

The surface properties, saturation magnetization (M _S ) of the magnetic tapes obtained in the above Examples and Comparative Examples, and the relative speed of the magnetic tapes
The following table shows the results of measuring the Y signal output and still endurance time when recording / reproducing at 5.8 m and a frequency of 7 MHz.

[Effects of the Invention] As is clear from the above embodiments, the magnetic recording medium of the present invention has a large saturation magnetization and is extremely excellent in short-wavelength recording characteristics.

Claims (1)

(57) [Claims] 1. A magnetic recording medium having a magnetic recording layer obtained by applying a hexagonal ferrite powder having an average particle size of 0.01 to 0.2 μm in which at least a part of Fe is replaced by Nb together with a resin binder on a substrate, A magnetic recording medium, wherein the ratio between the hexagonal ferrite powder and the resin binder is in the range of 100: 5 to 100: 14 (weight ratio).