JPH0896349A - Magnetic recording medium - Google Patents

Abstract

PURPOSE: To provide a magnetic recording medium having satisfactory durability, excellent in S/N, capable of high density recording and having high performance. CONSTITUTION: Two or more magnetic layers 2, 3 are formed on a substrate 1 to obtain the objective magnetic recording medium. The lower magnetic layer 2 is a metallic thin film type magnetic layer and the upper magnetic layer 3 is a coating film type magnetic layer contg. platy metallic magnetic powder having its axis of easy magnetization in the plate surface.

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 the magnetic energy determined by Hc × Br is high. Because.

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 smaller than m, the saturation magnetization σs becomes 110e.
mu / 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 size is reduced. 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 be highly durable and
An object of the present invention is to provide a high-performance magnetic recording medium having excellent S / N, capable of high-density recording. An object of the present invention is a magnetic recording medium in which two or more magnetic layers are provided on a support, wherein the lower magnetic layer of the magnetic layer is composed of a metal thin film type magnetic layer, and The magnetic layer is composed of a coating type magnetic layer, and the coating type magnetic layer is plate-shaped and contains a magnetic metal powder having an easy axis of magnetization in a plate-shaped surface. Achieved by

In the present invention, a metal thin film type magnetic layer (also referred to as a lower magnetic layer or a first magnetic layer) is provided on a support by a dry plating means such as vapor deposition or sputtering. Examples of the material of the magnetic particles forming the metal thin film type magnetic layer include Co, in addition to metals such as Fe, Co, and Ni.
-Ni alloy, Co-Pt alloy, Co-Ni-Pt alloy,
Fe-Co alloy, Fe-Ni alloy, Fe-Co-Ni alloy, Fe-Co-B alloy, Co-Ni-Fe-B alloy,
Co-Cr alloys or Al, Ta, Pt,
Au, Ti, V, Cr, Mn, Cu, Mg, Zn, N
i, W, La, Ce, Pr, Nd, Pm, Sm, Eu,
Li, Si, B, Ca, As, Y, Zr, Nb, Mo,
Examples thereof include magnetic alloys containing one or more elements selected from the group consisting of Ru, Rh, Ag, Sb and Hf.

This metal thin film type magnetic layer preferably does not have diagonal columns formed by means such as oblique vapor deposition. That is, it is difficult to obtain a material having a high saturation magnetic flux density when it is configured by means such as oblique vapor deposition. The saturation magnetic flux density Bs ₁ is 4000 to 10
About 000G is preferable. From this meaning, it can be said that the metal thin film type magnetic layer is a high magnetic permeability layer.

The thickness of the metal thin film type magnetic layer is preferably 0.05 to 1 μm, more preferably 0.1 to 0.3 μm. That is, if this metal thin film type magnetic layer is too thin, the characteristics due to Bs with a high bending angle will not be exhibited, and the effect will be reduced, and conversely, if it is too thick, it will become hard and cupping will be severe, and the contact between the tape and the head will be poor. This is because a defect will occur. Moreover, even if the thickness is increased, there is no merit due to this.

It should be noted that an oxidizing gas or the like may be provided when the metal thin film type magnetic layer is formed, and an oxide film, a nitride film, a carbide film or the like may be formed on the surface of the metal magnetic layer. A coating type magnetic layer (also referred to as an upper magnetic layer or a second magnetic layer) is provided on the metal thin film type magnetic layer. This coating type magnetic layer is formed by dispersing magnetic metal powder in a binder resin. This metallic magnetic powder
It is a metal magnetic powder which is plate-shaped and whose easy axis of magnetization lies within the plate-shaped surface.

A specific example of such a metal magnetic powder is a metal magnetic powder containing hexagonal plate-shaped iron as a main component. 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, 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.

The saturation magnetic flux density Bs _{2 of} such a coating type magnetic layer is preferably about 2000 to 8000G. In particular, Bs ₁ > Bs ₂ is preferable. or,
Its thickness is 0.1-3 μm, preferably 0.3-2.5
It is preferably μm. That is, if the thickness of the coating type magnetic layer is less than 0.1 μm, it is difficult to obtain a sufficient output, and the thickness is set to 0.1 μm or more. On the contrary, if the thickness is increased, the meaning of providing the lower metal thin film type magnetic layer is lowered, so the thickness is set to 3 μm or less. That is, from the viewpoint of harmony between the lower magnetic layer (metal thin film type magnetic layer) and the upper magnetic layer (coating type magnetic layer), the upper magnetic layer has a thickness of 0.
It was set to 1 to 3 μm.

Further, since the upper magnetic layer is a coating type magnetic layer, a lubricant or the like can be contained in the coating type magnetic layer, and the metal thin film type magnetic layer faces the magnetic head. It excels in running and is more durable than when The metal magnetic powder which is plate-shaped and whose easy axis of magnetization is within the plate-shaped 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 (F
(Part of e may be replaced with Co, Ni, Zn, Sn, etc.) While adding an equivalent amount or more of caustic soda to the aqueous solution with stirring, the solution is made alkaline. This causes iron hydroxide to precipitate. Then, hydrogen peroxide solution is added with stirring to forcefully oxidize. Due to this rapid oxidation, hexagonal plate-like δ
-FeOOH is produced. Then, water glass and aluminum chloride are added, and the pH is adjusted to 6 or less (p
H4-6). Then, the mixture is filtered, washed with water, and after being washed with water, fired in the air at a temperature of 650 ° C. 42 after firing
By reducing with hydrogen gas at a temperature of 0 ° C., a hexagonal plate-shaped metallic magnetic powder containing iron as a main component is obtained.
The hexagonal plate-shaped metal magnetic powder thus obtained is
The thickness is about 0.003 to 0.1 μm and the diameter is about 0.0.
Those having a size of 3 to 0.5 μm and a plate ratio (diameter / thickness) of about 3 to 20 are preferable. Also, its coercive force is about 800 ~
1900 Oe, saturation magnetization σs 110 to 160 emu /
It is preferably about g.

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).
Was obtained again by heating this glass to a temperature of 700 ° C. or higher for crystallization, dissolving excess glass substances, acids, etc. with warm water, etc., and washing and drying to obtain the glass. Those are preferable. Also, α
-FeOOH or Fe (OH) ₃ and NaOH and Ba
(OH) ₂ etc. put in an autoclave and 200-300
The thing obtained by the autoclave method of heating at 5 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 binder resin used to form the coating type magnetic layer is a thermoplastic resin,
A thermosetting resin or a reactive resin or a mixture thereof can be used together. For example, urethane resin, particularly urethane resin having a polar group such as sulfonic acid group, metal sulfonate group, sulfobetaine group, carbobetaine group, amino group, hydroxyl group, epoxy group, vinyl chloride-vinyl acetate copolymer, vinyl chloride. -Vinyl chloride resins such as vinylidene chloride copolymers and vinyl chloride-acrylonitrile copolymers, especially vinyl chloride resins having polar groups such as sulfonic acid groups, metal sulfonate groups, amino groups, butadiene-
Acrylonitrile copolymer, polyamide resin, polyvinyl butyral, ceruce derivative, styrene-butadiene copolymer, polyester resin, phenol resin, phenol-formalin-novolak resin, phenol-formalin-resole resin, urea resin, melamine resin, unsaturated polyester Examples thereof include resins, terminal isocyanate polyester moisture curable resins, terminal isocyanate polyether moisture curable resins, and polyisocyanate prepolymers. The content of the binder resin is preferably 3 to 100 parts by weight, more preferably 10 to 30 parts by weight, based on 100 parts by weight of the magnetic powder.

The coating type magnetic layer preferably contains non-magnetic particles. For example, carbon black, α-alumina, γ-alumina, α-γ-alumina,
Fused alumina, silicon carbide, chromium oxide, titanium oxide, cerium oxide, corundum, artificial diamond, α-iron oxide, garnet, emery, garnet, silica, silicon nitride, boron nitride, tungsten carbide, titanium carbide,
One or more selected from the group consisting of quartz, tripoli, diatomaceous earth, dolomite and the like are used. If the size of these non-magnetic particles is too large, the surface property is deteriorated. On the contrary, if they are too small, it is meaningless to include them, so that the average particle size is preferably 0.01 to 2 μm. . Further, the content thereof is preferably 0.5 to 30 parts by weight, particularly 3 to 20 parts by weight, based on 100 parts by weight of the magnetic powder.

Further, it is preferable that the coating type magnetic layer contains a lubricant. For example, silicone oil such as dialkyl polysiloxane, dialkoxy polysiloxane and monoalkyl monoalkoxy polysiloxane, conductive fine powder such as graphite, inorganic fine powder such as molybdenum disulfide and tungsten disulfide, and plastic fine powder such as polyethylene and polypropylene. Powder, fatty acid esters, etc. are mentioned. In addition, a fatty acid having 12 to 18 carbon atoms, a metal soap composed of an alkali metal or an alkaline earth metal of the above fatty acid, an amide of the above fatty acid, a polyalkylene oxide alkyl phosphate ester, lecithin, a trialkyl polyolefin oxy group. Tetraammonium salt,
There are also higher alcohols having 12 or more carbon atoms, sulfuric acid esters and the like. The content thereof is preferably 0.1 to 30 parts by weight, particularly 0.5 to 15 parts by weight, based on 100 parts by weight of the magnetic powder.

As the other component added to the coating type magnetic layer, a dispersant, an antistatic agent, a rust preventive, a fungicide or the like may be used. As the solvent used in the production of the magnetic paint used for forming the magnetic layer by coating, those described in, for example, JP-A-5-73883 and JP-A-5-298651 can be used.

Magnetic powder, binder resin, etc. are kneaded to form a magnetic coating material. In the case of kneading, the techniques described in, for example, JP-A-5-73883 and JP-A-5-298651. Can be used. Examples of the support (which may be either a magnetic support or a non-magnetic support, generally a non-magnetic support) used for a magnetic recording medium are disclosed in, for example, JP-A-5-73883 and 5-2.
Those described in Japanese Patent Publication No. 98651 can be used. Of course, it is not limited to these.

Then, a metal thin film type magnetic layer having a thickness of 0.05 to 1 μm is provided on the support by vapor deposition means or the like, and then hexagonal plate-shaped metal magnetic powder containing iron as a main component,
A magnetic paint prepared by kneading and dispersing a binder and various additives in a solvent is applied to a thickness of 0.1 to 3 μm (dry thickness),
Before the coated magnetic layer is solidified, it is oriented by the solenoid method so that the plate-shaped surface of the metal magnetic powder is in the direction along the support surface, or the plate-shaped metal magnetic powder is passed through between the opposing permanent magnets. Orient the surface so that it is in an upright orientation with respect to the support surface. That is, particularly for long-wavelength recording, orientation treatment is performed so that the plate-like surface of the metal magnetic powder is in the direction along the support surface, and for short-wavelength recording, the plate-like surface of the metal magnetic powder is on the support surface. Orient it so that it stands in the opposite direction. If necessary, surface smoothing treatment is performed or cutting into a desired shape is performed.

[0024]

【Example】

Example 1 [First magnetic layer] Co-Ni (80-2) was formed on a polyethylene terephthalate (PET) film 1 having a thickness of 10 μm.
0) A magnetic alloy was deposited to a thickness of 0.15 μm using a vacuum vapor deposition device to provide a metal thin film type magnetic layer (first magnetic layer) 2. The Bs ₁ of the first magnetic layer 2 was 8000G.

[Second magnetic layer] A 5% ferrous sulfate aqueous solution was placed in a vessel 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
Adjusted to. 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 dispersed sufficiently, and water glass is added to this in an amount of 1 wt% with respect to Fe, and aluminum chloride is added to Fe.
To 1 wt%. 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 was calcined in air at 650 ° C. for 2 hours using a muffle furnace. 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 115 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 became 0.5 μm.
It was coated on the magnetic layer 2. 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 second magnetic layer 3.

The Bs ₂ of the second magnetic layer 3 is 3600G.
Met. [Backcoat Layer] The backcoat layer 4 is formed by applying a coating containing carbon black to the surface of the PET film 1 opposite to the second magnetic layer 3 so that the thickness after drying is 0.5 μm. did.

Then, slit to a width of 8 mm, and
A magnetic tape for TR was obtained. [Embodiment 2] In Embodiment 1, the orientation treatment of the second magnetic layer 3 is performed by the opposing permanent magnets, and the plate surface of the hexagonal plate-shaped magnetic iron powder in the magnetic coating film before drying (direction of easy magnetization axis). Was subjected to the same process except that the film was oriented so that it was perpendicular to the surface of the film 1 to obtain an 8 mm VTR magnetic tape.

[Embodiment 3] In Embodiment 1, the temperature at the time of reoxidation is 50 ° C., the thickness is 0.02 μm, the diameter is 0.2 μm, the plate ratio is 10, the coercive force is Hc1350Oe, and the saturation magnetization is ss129 emu / g. A hexagonal plate-shaped magnetic iron powder having an easy axis of magnetization in the in-plane direction of the hexagonal plate was obtained. Then, using this hexagonal plate-shaped magnetic iron powder, the same procedure as in Example 1 was performed, and 8 mm
A magnetic tape for VTR was obtained.

[Embodiment 4] In Embodiment 1, the thickness of the first magnetic layer 2 is 0.3 μm and the thickness of the second magnetic layer 3 is 0.6 μm.
A magnetic tape for 8 mm VTR was obtained in the same manner except that the thickness was changed to μm. Example 5 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 0.1 μm and the thickness of the second magnetic layer 3 was 2.5 μm. .

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 acicular ratio was 8, the specific surface area was 53 m ² / g, A magnetic tape for 8 mm VTR was obtained in the same manner except that acicular metal magnetic powder having a coercive force Hc1550 Oe and a saturation magnetization σs115 emu / g was used.

[Comparative Example 2] A diameter of 0.3 is used instead of the magnetic powder used for forming the second magnetic layer 3 in Example 2.
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.

[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.
Measure the luminance output at MHz, 5MHz, 10MHz, 15MHz, and use commercially available Hi8 magnetic tape as a reference (0
It was shown as a relative value as 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 Magnetism Characteristics Brightness Output Longitudinal direction Vertical direction Saturation magnetic flux 1MHz 5MHz 10MHz 15MHz Hc Hc Density Example 1 1650Oe 2050Oe 4800G +3.2 +2.8 +3.7 +6.2 Example 2 1180Oe 2450Oe 4600G +1.0 + 2.5 +4.6 +7.3 Example 3 1390Oe 1790Oe 5000G +4.4 +2.5 +1.8 +1.3 Example 4 1560Oe 1920Oe 5100G +5.1 +4.0 +3.2 +2.8 Example 5 1590Oe 1730Oe 3900G +5.3 +3.8 +3.1 +2.5 Comparative Example 1 1260Oe 1900Oe 4300G +1.0 +1.5 -1.0 -1.9 Comparative Example 2 1060Oe 2210Oe 2800G -6.2 -5.1 -2.4 -0.3 According to 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. The output of any of the comparative examples is lower than that of the present example.

[0036]

[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 front page (72) Inventor Hirohide Mizunoya 2606 Akabane, Kai-cho, Haga-gun, Tochigi Prefecture Kao Co., Ltd.Institute of Information Science Research Institute (72) Inventor Shigemi Wakabayashi 2606 Akabane, Kai-cho, Haga-gun, Tochigi Kao Co., Ltd. Company Information Science Laboratory

Claims (6)

[Claims] 1. A magnetic recording medium comprising two or more magnetic layers provided on a support, wherein the lower magnetic layer of the magnetic layer is composed of a metal thin film type magnetic layer and the upper magnetic layer. Is a coating type magnetic layer, and the coating type magnetic layer contains a plate-shaped magnetic magnetic powder having an easy axis of magnetization in a plate-shaped surface. 2. The metal thin film type magnetic layer has a thickness of 0.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of 05 to 1 μm. 3. The coating type magnetic layer has a thickness of 0.1 to 10.
The magnetic recording medium according to claim 1, wherein the magnetic recording medium has a thickness of 3 μm and is thicker than the metal thin film type magnetic layer. 4. A saturation magnetic flux density Bs _{1 of a} metal thin film type magnetic layer.
Is higher than the saturation magnetic flux density Bs ₂ of the coating type magnetic layer. 5. The magnetic recording medium according to claim 1, wherein the plate-shaped surface of the metal magnetic powder in the coating type magnetic layer is oriented in a direction upright with respect to the support surface. 6. The magnetic recording medium according to claim 1, wherein the plate-shaped surface of the metal magnetic powder in the coating type magnetic layer is in a direction along the support surface.