JP3533718B2 - Magnetic recording media - Google Patents

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.

[0002]

BACKGROUND OF THE INVENTION A magnetic recording medium is known in which a magnetic coating in which magnetic powder or a binder resin is dispersed in an organic solvent is applied on a non-magnetic support such as a polyester resin and dried. As magnetic powders used in such magnetic recording media, oxide-based acicular magnetic powders such as Fe ₂ O _3, tabular magnetic powders such as barium ferrite, or acicular metal magnetic powders are known. At present, acicular metal magnetic powder is mainly used. That is, since the acicular metal magnetic powder has a higher coercive force Hc and a larger saturation magnetization σs than the oxide-based magnetic powder, the residual magnetic flux density Br is high and Hc is high.
This is because the magnetic energy determined by × Br is high.

In order to perform high density recording, it is necessary to reduce the particle size of magnetic powder. Because the signal / noise (S / N) is proportional to (1 / Vp) ^1/2 (Vp is the volume of the particle). Therefore, when trying to obtain a high S / N,
It is necessary to reduce the size of the magnetic powder. When performing high density recording such that the recording wavelength is 0.5 μm or less, the particle size of the magnetic powder is 0.2 μm or less, particularly 0.12 μm.
It is said that the following is preferable.

By the way, the particle size of the magnetic metal powder is 0.12 μm.
When it becomes small such as m or less, the saturation magnetization σs becomes 1
It becomes 10 emu / g or less. Therefore, it becomes difficult to deal with high density. In addition, there is a problem that the degree of orientation does not increase as the miniaturization progresses. Even if oriented, if the magnetic head is of the helical scan type, the needle-shaped magnetic powder is oriented in the longitudinal direction, so a gap is created in the scanning direction and the magnetization direction of the magnetic head, and Effective recording / reproducing is not performed for the packing density.

[0005]

DISCLOSURE OF THE INVENTION It is an object of the present invention to provide a high performance magnetic recording medium which has an excellent S / N, enables high density recording from a low range to a high range. An object of the present invention is a magnetic recording medium in which two magnetic layers are provided on a support, and the lower magnetic layer of the magnetic layer is plate-shaped,
An upper layer of the magnetic layer includes a magnetic metal powder having an axis of easy magnetization in a plate-like surface, and the plate-like surface of the metal magnetic powder is oriented in a direction along the support surface. Of the magnetic layer contains a plate-shaped magnetic metal powder whose easy axis of magnetization lies within the plate-shaped surface, and the plate-shaped surface of the metal magnetic powder is oriented in a direction upright with respect to the support surface. It is achieved by a magnetic recording medium characterized by being oriented.

The magnetic layer of the present invention is formed by dispersing magnetic metal powder in a binder resin. This metal magnetic powder is a plate-shaped magnetic powder whose easy axis of magnetization lies within the plate-shaped surface. Then, in the lower magnetic layer, the plate-like surface of the metal magnetic powder is oriented so that it is in the direction along the support surface, and in the upper magnetic layer, the plate-like surface of the metal magnetic powder is oriented. Are oriented in an upright direction with respect to the support surface.

As a specific example of such a metal magnetic powder, a hexagonal plate-shaped metal magnetic powder containing iron as a main component can be mentioned. And, such magnetic powder has a hexagonal plate shape of δ-F.
Obtained by firing with eOOH as a seed and reducing. In particular, hexagonal plate-shaped δ-F with a sintering inhibitor on the surface
Obtained by firing with eOOH as a seed and reducing. In addition, as a sintering inhibitor, Si, Al, Cr, R
Specific examples include oxides of elements selected from the group consisting of u, Ca, Zr, P, Mo, Ti, and Mn (eg, SiO ₂ and Al ₂ O ₃ ).

In addition to the above-mentioned metal magnetic powder, a metal magnetic powder obtained by reducing hexagonal plate-shaped ferrite magnetic powder can also be mentioned. In particular, a metal magnetic powder obtained by reducing a hexagonal plate-shaped ferrite magnetic powder having a sintering inhibitor on its surface can be mentioned. The hexagonal plate-shaped ferrite magnetic powder is BaO.6Fe ₂ O ₃ (provided that some of Ba and Fe are other metals (for example, Ti, C
r, Co, Zn, In, Mn, Cu, Ge, Nb or the like) may be substituted). Further, examples of the sintering inhibitor include those mentioned above.

The hexagonal plate-shaped metal magnetic powder obtained as described above has a thickness of about 0.003 to 0.1 μm.
Diameter is about 0.03-0.5μm, plate ratio (diameter / thickness)
Is preferably about 3 to 20. The coercive force is about 800 to 1900 Oe and the saturation magnetization σs is 110 to 110.
It is preferably about 160 emu / g. Further, such magnetic powder has a large size due to its plate-like shape and has a high saturation magnetization σ even when compared with needle-shaped magnetic powder of the same length.
s can be expected. Moreover, since it is plate-shaped, it can be expected that the packing density is high, the number of effective magnetic powders per unit volume is large, and the S / N is high. As a result, a high-performance magnetic recording medium having excellent reproduction characteristics is obtained. Further, the axis of easy magnetization of the hexagonal ferrite magnetic powder is in the direction perpendicular to the plate surface, whereas the one according to the present invention is in the plane, so that the conventional ring-type magnetic head is used. Excellent recording and playback characteristics. Even if it is used in a helical scan system, it tends to be magnetized in the scanning direction of the head and has a high S
/ N is obtained.

A metal magnetic powder having a plate-like shape and an axis of easy magnetization in the plate-like surface can be obtained as follows. For example, a hexagonal plate-shaped metal magnetic powder containing iron as a main component can be obtained as follows. Ferrous sulfate (a part of Fe is Co,
(Although it may be substituted with Ni, Zn, Sn, etc.) While adding an equivalent amount or more of caustic soda to the aqueous solution, the solution is made alkaline. This causes iron hydroxide to precipitate. After this,
Hydrogen peroxide solution is added with stirring to forcefully oxidize. This rapid oxidation produces hexagonal plate-shaped δ-FeOOH. Then water glass and aluminum chloride are added and the pH is brought to below 6 (pH 4-6) with acetic acid. Then, the mixture is filtered, washed with water, and after being washed with water, fired in the air at a temperature of 650 ° C. After firing, reduction with hydrogen gas is performed at a temperature of 420 ° C. to obtain hexagonal plate-shaped metallic magnetic powder containing iron as a main component. The hexagonal plate-shaped metal magnetic powder thus obtained has a thickness of about 0.003 to 0.1 μm and a diameter of about 0.03 to 0.5 μm.
m, and the plate ratio (diameter / thickness) is preferably about 3 to 20. Also, its coercive force is about 800-1900O.
e, those having a saturation magnetization σs of about 110 to 160 emu / g are preferable.

The magnetic powder of the present invention can also be obtained by reducing hexagonal plate-shaped ferrite magnetic powder. First, barium ferrite magnetic powder (hexagonal ferrite magnetic powder)
Can be obtained by a solid phase reaction method, a coprecipitation-heating reaction method, a hydrothermal synthesis method, an oxide flux method, a molten salt method, a glass crystallization method, or the like. Above all, a barium ferrite component is mixed with a glass-forming substance typified by B ₂ O ₃ , melted at a temperature of 1300 ° C. or higher, and rapidly cooled to obtain a glass (amorphous body). A substance obtained by a glass crystallization method in which it is obtained by heating to a temperature of 700 ° C. or higher for crystallization, dissolving an excess glass substance, an acid, etc. with warm water, washing with water, and drying is preferable.
Also, α-FeOOH or Fe (OH) ₃ and NaOH
And Ba (OH) ₂ etc. in an autoclave
The thing obtained by the autoclave method of heating at 300 degreeC for 5 to 10 hours is also preferable.

The hexagonal ferrite magnetic powder as described above, especially Si, Al, Cr, Ru, Ca, Zr,
A hexagonal ferrite magnetic powder having an oxide (for example, SiO ₂ or Al ₂ O ₃ ) selected from the group consisting of P, Mo, Mn, and Ti as a sintering inhibitor is heated. , Hexagonal plate-shaped metal magnetic powder is obtained by reduction with hydrogen gas.

In the present invention, the magnetic powder as described above is mainly used. For example, Co, Ni, Fe-C are used.
o, Fe-Ni, Fe-Al, Fe-Ni-Al, Co
-Ni, Fe-Co-Ni, Fe-Ni-Al-Zn,
A ferromagnetic metal powder such as Fe-Al-Si can also be used together. In the present invention, the magnetic layer is composed of two or more layers.
In the lower magnetic layer of the magnetic layer (hereinafter also referred to as the first magnetic layer), the plate-shaped surface of the hexagonal plate-shaped metal magnetic powder is oriented so as to be along the support surface, and In the upper magnetic layer of the layer (hereinafter also referred to as the second magnetic layer), the plate-shaped surface of the above-mentioned hexagonal plate-shaped metal magnetic powder is oriented so as to be in an upright direction with respect to the support surface. That is, the easy axis of the first magnetic layer is horizontal (longitudinal)
And the easy axis of magnetization of the second magnetic layer is in the vertical direction. Therefore, a high S / N can be obtained in a wide range from the low range to the high range. The thickness of such a first magnetic layer is preferably 0.5 to 5 μm. The second magnetic layer has a thickness of 0.1 to 3 μm, and is preferably thinner than the first magnetic layer. That is, when the thickness of the first magnetic layer is less than 0.5 μm, characteristics such as S / N cannot be obtained, and it is not necessary to make the thickness more than 5 μm. If it becomes too thick, the overall thickness becomes too thick, which causes various problems. Therefore, the thickness of the first magnetic layer is preferably 0.5 to 5 μm. or,
When the thickness of the second magnetic layer is smaller than 0.1 μm, the thickness of the second magnetic layer is 0.1 because the meaning of providing the second magnetic layer is small.
It was set to μm or more. On the other hand, when the thickness is increased, the meaning of the lower first magnetic layer is lowered, and the meaning of having a plurality of magnetic layers is lowered, so the thickness is set to 3 μm or less. Further, from the viewpoint of harmonization between the recording / reproducing characteristics from the first magnetic layer and the recording / reproducing characteristics from the second magnetic layer, it is preferable that the thickness of the second magnetic layer is thinner than that of the first magnetic layer. It was

The magnetic layer (first magnetic layer or second magnetic layer) of the magnetic recording medium.
As the binder for forming the magnetic layer, a thermoplastic resin, a thermosetting resin, a reactive resin, or a mixture thereof can be used together. For example, urethane resin, especially sulfonic acid group, sulfonic acid metal base, sulfobetaine group,
Urethane resin having polar groups such as carbobetaine group, amino group, hydroxyl group, epoxy group, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-vinyl chloride-acrylonitrile copolymer, etc. Resins, particularly vinyl chloride resins having polar groups such as sulfonic acid groups, metal sulfonate groups, amino groups, butadiene-acrylonitrile copolymers, polyamide resins, polyvinyl butyral, ceruce derivatives, styrene-butadiene copolymers, polyester resins , Phenol resin, phenol-formalin-novolak resin, phenol-formalin-resole resin, urea resin, melamine resin, unsaturated polyester resin, terminal isocyanate polyester moisture curable resin, terminal isocyanate polyether moisture curable resin Polyisocyanate prepolymers, and the like. These binder resin components are used in an amount of about 3 to 100 parts by weight, preferably 10 to 30 parts by weight, based on 100 parts by weight of the magnetic powder.

As other components added to the magnetic layer of the magnetic recording medium, a dispersant, a lubricant, an abrasive, an antistatic agent, a rust preventive, a fungicide and the like may be used. As such additives, for example, those described in JP-A-5-298651 and JP-A-5-73883 can be used. Examples of the solvent used for producing the magnetic paint used for forming the magnetic layer by coating include, for example, Japanese Patent Laid-Open No.
Those described in, for example, JP-A-298651 and JP-A-5-73883 can be used.

Magnetic powder, binder, etc. are kneaded to form a magnetic coating material. In the case of kneading, for example, Japanese Patent Application Laid-Open No. Hei 5 (1999) -5200 is used.
The techniques described in JP-A-298651 and JP-A-5-73883 can be used. As a support used for a magnetic recording medium, particularly a non-magnetic support, for example, JP-A-5-298651 and JP-A-5-295651 are available.
Those described in Japanese Patent No. 73883 can be used. Of course, it is not limited to these.

Then, a magnetic paint prepared by kneading and dispersing the above-mentioned magnetic powder, binder and various additives in a solvent is applied to a support so as to have a thickness of 0.5 to 5 .mu.m. Before the magnetic layer is solidified, it is oriented by the solenoid method so that the plate-like surface of the metal magnetic powder in the first magnetic layer is in the direction along the support surface, and then the magnetic powder, binder, and various additives are used as a solvent. The kneaded and dispersed magnetic coating material is applied on a support so as to have a thickness of 0.1 to 3 μm, and a permanent magnet is used to solidify the metal magnetic powder in the second magnetic layer before the applied second magnetic layer is solidified. Orient the plate-like surface in an upright direction with respect to the support surface. If necessary, surface smoothing treatment is performed or cutting into a desired shape is performed.

[0018]

【Example】

Example 1 A 5% ferrous sulfate aqueous solution was placed in a container equipped with a stirrer, and 10% caustic soda aqueous solution was added little by little while operating the stirrer to adjust the pH to 10. This causes white iron hydroxide to precipitate. Then, a 20 wt% hydrogen peroxide aqueous solution was added until it became dark black.
As a result, iron hydroxide is forcibly oxidized to form hexagonal plate-shaped δ-FeOOH. And it filters using a filter press and wash | cleans with water. Then, deionized water is added and sufficiently dispersed, and water glass is added to this in an amount of 1 wt% relative to Fe, and aluminum chloride is added to 1 wt% relative to Fe.
% Was added. Then, acetic acid is added to adjust the pH to 4, and the mixture is filtered using a filter press and washed with water. After this, the precipitate is removed in a muffle furnace in air at 65
It was calcined at 0 ° C. for 2 hours. Then, it was reduced with hydrogen gas at 450 ° C. using a batch kiln. After that, the temperature was lowered to room temperature, air was passed little by little, and the inside of the kiln was replaced with air over 40 hours. After this, the metal powder was taken out.

Examination of the metal powder thus obtained revealed that it had a hexagonal plate shape, a thickness of 0.0125 μm, a diameter of 0.1 μm, and a plate ratio of 8. The coercive force Hc was 1530 Oe, the saturation magnetization σs was 116 emu / g, and the easy axis of magnetization was in the in-plane direction of the hexagonal plate. Next, 246 parts by weight of the metal magnetic powder, 19 parts by weight of vinyl chloride resin, 28 parts by weight of polyurethane resin, 7 parts by weight of polyisocyanate, 30 parts by weight of alumina having a particle diameter of 0.15 μm,
A magnetic paint was prepared using 8 parts by weight of fatty acid ester, 298 parts by weight of toluene, 298 parts by weight of methyl ethyl ketone, and 66 parts by weight of cyclohexanone.

Then, the magnetic paint was dried by the direct gravure method so that the thickness after drying was 10 μm.
Thick polyethylene terephthalate (PET) film 1
Applied on top. After that, it is subsequently placed in an external magnetic field (solenoid) and oriented so that the plate surface (the easy axis of magnetization) of the hexagonal plate-shaped magnetic iron powder in the magnetic coating film before drying becomes parallel to the film 1 surface. To do. Then, after the orientation treatment, it was dried to form the first magnetic layer 2.

Next, the same magnetic coating material as that used for forming the first magnetic layer 2 was coated on the first magnetic layer 2 by the direct gravure method so that the thickness after drying was 0.5 μm. After that, it is subsequently placed in an external magnetic field by permanent magnets arranged opposite to each other, and the plate surface (the easy axis of magnetization) of the hexagonal plate-shaped magnetic iron powder in the magnetic coating film before drying is perpendicular to the film 1 surface. Orientation treatment is performed so that Then, after the orientation treatment, it was dried to form the second magnetic layer 3.

After that, the first magnetic layer 2 of the PET film 1 is formed.
A coating containing carbon black was applied to the surface on the opposite side to a thickness of 0.5 μm after drying to form a back coat layer 4. Then, it was slit into a width of 8 mm to obtain a magnetic tape. [Example 2] In Example 1, the temperature at the time of reoxidation was 50 ° C, and the thickness was 0.02 µm, the diameter was 0.2 µm, the plate ratio was 10, the coercive force was Hc1350Oe, and the saturation magnetization was s12.
Hexagonal plate-shaped magnetic iron powder having 9 emu / g and an axis of easy magnetization in the in-plane direction of the hexagonal plate was obtained.

Then, this magnetic coating material was used in the same manner as in Example 1 to obtain an 8 mm VTR magnetic tape. Example 3 Thickness is 0.01 μm and diameter is 0.12 μm
A hexagonal barium ferrite magnetic powder (produced by an autoclave method) having a plate ratio of 12, a coercive force Hc of 1460 Oe and a saturation magnetization σs of 56 emu / g (produced by an autoclave method) was reduced with hydrogen gas at 450 ° C. using a batch kiln. It was After that, the temperature was lowered to room temperature, air was passed little by little, and the inside of the kiln was replaced with air over 40 hours. Then, the metal powder was taken out.

Examination of the metal powder thus obtained revealed that it had a hexagonal plate shape, a thickness of 0.01 μm, a diameter of 0.09 μm and a plate ratio of 9. Also, coercive force Hc
Was 1600 Oe, the saturation magnetization σs was 125 emu / g, and the easy axis of magnetization was in the in-plane direction of the hexagonal plate. And
This metal magnetic powder is used in the same manner as in Example 1 to obtain 8 mm
A magnetic tape for VTR was obtained.

Comparative Example 1 In Example 1, instead of the magnetic powder used to form the second magnetic layer 3, the average major axis length was 0.1 μm, the needle ratio was 8, the coercive force was Hc1550Oe, and the saturation magnetization was σs115emu. A magnetic tape for 8 mm VTR was obtained in the same manner as above, except that the magnetic powder of needle-like metal magnetic powder of / g was used.

[Comparative Example 2] In Example 1, a diameter of 0.3 was used in place of the magnetic powder used for forming the second magnetic layer 3.
μm, plate ratio 5, coercive force Hc1830Oe, saturation magnetization σ
A magnetic tape for 8 mm VTR was obtained in the same manner except that hexagonal barium ferrite magnetic powder of s50 emu / g was used.

COMPARATIVE EXAMPLE 3 In Example 1, the thickness of the first magnetic layer 2 is 2.5 μm, and the thickness of the second magnetic layer 3 is 0 μm.
A magnetic tape for 8 mm VTR was obtained in the same manner except that the thickness was changed to μm. Comparative Example 4 A magnetic tape for 8 mm VTR was obtained in the same manner as in Example 1, except that the thickness of the first magnetic layer 2 was 0 μm and the thickness of the second magnetic layer 3 was 2.5 μm.

[Characteristics] The magnetic tape obtained in each of the above examples is 8 m
It was loaded into an m-cassette case, and the device was modified from a commercially available 8 mm VTR equipped with a ring-type magnetic head.
The luminance output at 5 MHz, 5 MHz, 10 MHz, and 15 MHz was measured, and compared with a commercially available 8 mm VTR magnetic tape as a reference (0 dB). Further, the coercive force Hc and the saturation magnetic flux density were measured by VSM, and the results are also shown in Table-1.

Table-1 Magnetic properties Brightness Output longitudinal direction Vertical direction Saturation magnetic flux 1MHz 5MHz 10MHz 15MHz Hc Hc Density Example 1 1670Oe 2200Oe 3300G +1.8 +2.9 +4.5 +6.1 Example 2 1500Oe 2080Oe 3600G +1.5 + 2.5 +4.3 +6.0 Example 3 1620Oe 2250Oe 3300G +1.7 +2.6 +4.9 +6.2 Comparative Example 1 1480Oe 1830Oe 3000G +0.8 +1.4 +2.4 +3.1 Comparative Example 2 1340Oe 1650Oe 2130G 0 +0.3 +1.2 +1.4 Comparative Example 3 1640Oe 1200Oe 3200G +1.5 +1.1 0 -0.3 Comparative Example 4 1320Oe 1980Oe 3100G 0 +0.1 +0.8 +1.1 From this, it can be seen that the present invention has a high luminance output from the low range to the high range. On the other hand, in the comparative example, when the luminance output is high in the low range, the luminance output is low in the high range, and conversely, when the luminance output is relatively high in the high range, the luminance output is low in the low range. You have to sacrifice the bandwidth of.

[0030]

[Effect] It has a feature that the luminance output is high from the low range to the high range.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a magnetic recording medium.

[Explanation of symbols]

1 Polyethylene terephthalate film 2 First magnetic layer 3 Second magnetic layer 4 Back coat layer

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hirohide Mizunoya 2606 Akabane, Kai-cho, Haga-gun, Tochigi Prefecture Kao Corporation Information Science Research Institute (72) Inventor Shigemi Wakabayashi 2606 Akabane, Kai-cho, Haga-gun, Tochigi Prefecture Kao Corporation Information (56) References JP-A-3-219422 (JP, A) JP-A-4-134620 (JP, A) JP-A-62-41717 (JP, A) JP-A-61-266310 (JP, A) JP-A-6-195685 (JP, A) JP-A-2-270125 (JP, A) JP-A-57-195329 (JP, A) JP-A-59-129935 (JP, A) JP-A-61 -196427 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 5/62 G11B 5/78

Claims (4)

(57) [Claims] 1. A magnetic tape recording medium comprising two magnetic layers provided on a support, wherein the lower magnetic layer and the upper magnetic layer of the magnetic layer are of the same kind.
The metal magnetic powder is in the form of a plate, and its easy axis of magnetization is in the plate-like plane.
Has a thickness of 0.003 to 0.1 μm and a diameter of
0.03 ~ 0.5μm, diameter / thickness 3 ~ 20
Yes, the holding power is 800 to 1,900 Oe, and
Saturation magnetization is 110 to 160 emu / g, and the lower magnetic layer is formed by orienting the plate-like surface of the metal magnetic powder in a direction along the surface of the support, and the upper layer.
The magnetic tape recording medium is characterized in that the magnetic layer has a plate-like surface of magnetic metal powder oriented in an upright direction with respect to the support surface. 2. The lower magnetic layer formed by orienting the plate-like surface of the magnetic metal powder in the direction along the support surface has a thickness of 0.5 to 5 μm. A magnetic tape recording medium according to item 1. 3. The upper magnetic layer formed by orienting the plate-like surface of the metal magnetic powder in a direction upright with respect to the support surface has a thickness of 0.1 to 3 μm. 3. The magnetic recording tape medium according to claim 1, wherein the plate-shaped surface of the magnetic recording medium is thinner than the lower magnetic layer formed by orienting the plate-shaped surface in the direction along the support surface. 4. The magnetic tape recording medium according to claim 1, wherein the metal magnetic powder is a metal magnetic powder containing hexagonal plate-shaped iron as a main component.