JPH09251633A - Magnetic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve high-density recording and simultaneously to obtain high durability by specifying the surface roughness on the magnetic layer side of a magnetic recording medium to a prescribed value or above and the residual magnetic flux density and coercive force thereof respectively to prescribed values or above. SOLUTION: This magnetic recording medium has the magnetic layer 2. The surface roughness Ra of the magnetic layer 2 side thereof is Ra>=12nm, the residual magnetic flux density Br is Br>=300mT and the coercive force Hc is Ha>=160kA/m. Particularly magnetic metallic powder is used as the magnetic powder to be incorporated into the magnetic layer 2, by which the residual magnetic flux density Br of the medium is made to attain >=300mT and the coercive force Hc is made to attain >=160kA/m. The magnetic recording medium is so constituted that the surface roughness of the medium attains Ra>=12nm. As a result, the magnetic recording medium having large output at a high recording density and excellent durability is obtd.

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 used for audio tapes, video tapes, data storage tapes and the like.

[0002]

2. Description of the Related Art As a recording medium used in an audio device, a video device, a computer device, and the like, a magnetic paint prepared by dispersing and kneading a magnetic powder, a binder and various additives in an organic solvent is used as a non-magnetic support. A so-called coating type magnetic recording medium, in which a magnetic layer is formed by coating and drying on a body, occupies the mainstream because of its excellent productivity and versatility.

In the various magnetic recording / reproducing apparatuses described above, in recent years, miniaturization and weight reduction, high image quality, and long time have been advanced, and along with this, high output has been achieved even for the above-mentioned coating type magnetic recording medium. There is a strong demand for higher density and higher density recording.

In order to improve the characteristics of the above-mentioned coating type magnetic recording medium, selection of magnetic powder is important first. That is, as the magnetic powder, the saturation magnetic flux density is large, the coercive force is high,
It is required to be fine particles, have a uniform particle shape, and have excellent oxidative stability.

In recent years, since the saturation magnetic flux density is particularly high, a metallic magnetic powder mainly containing iron is used as the magnetic powder to be contained in the magnetic layer, instead of the iron oxide type magnetic powder which has been conventionally used. It is like this.

The magnetic metal powder is obtained by heating and reducing needle-like iron oxyhydroxide or iron oxide mainly composed of iron in a reducing gas, and then forming a thin oxide film on the particle surface in order to secure oxidative stability. It is generated by the above, and has a higher saturation magnetic flux density and a higher coercive force than those of the iron oxide-based magnetic powder.

At present, the saturation magnetic flux density, the coercive force, and the oxidation stability are remarkably improved by adding cobalt or the like to the metal magnetic powder or surface-treating it with a shape-retaining agent.

Further, in the magnetic recording medium, since the head and the medium come into contact with each other to perform recording / reproducing, running durability becomes a problem in addition to the above magnetic characteristics. In the past, in order to improve the running durability, the running durability has been improved by mixing an abrasive in the coating film or adding a lubricant to the surface or inside of the coating film.

However, no satisfactory magnetic recording medium has been obtained in which the magnetic characteristics and the electromagnetic conversion characteristics are well balanced with the running durability.

[0010]

As described above, various studies have been made so far on the magnetic recording medium using the metal magnetic powder, but as a magnetic recording medium having excellent high density and high durability. The reality is that nothing is satisfactory.

The present invention has been made in view of such a conventional situation, and an object thereof is to provide a magnetic recording medium which is excellent in high density recording and has high durability.

[0012]

That is, according to the present invention, in a magnetic recording medium having a magnetic layer, the surface roughness (Ra) on the magnetic layer side is Ra ≧ 12 nm, and the residual magnetic flux density B is
The present invention relates to a magnetic recording medium having r ≧ 300 mT and coercive force Hc ≧ 160 kA / m.

According to the present invention, the residual magnetic flux density (Br) of the medium is 300 mT or more and the coercive force (H) is high by using the metal magnetic powder as the magnetic powder contained in the magnetic layer.
c) is 160 kA / m or more, and the magnetic recording medium is configured such that the surface roughness of the medium is Ra ≧ 12 nm.
As a result, a magnetic recording medium having high recording density, high output, and excellent durability can be obtained.

The reason why such an excellent effect occurs is that the contact area between the medium and the head is reduced by specifying the surface roughness Ra ≧ 12 nm. As a result, friction when the recording medium is run is reduced, and durability is improved. However, with this alone, the spacing between the recording medium and the head increases, and the output decreases. Therefore, by using a magnetic powder having a high residual magnetic flux density and a high coercive force satisfying the above conditions, it is possible to obtain a magnetic recording medium that suppresses a decrease in output and has both high durability and high output.

In order to obtain these effects more sufficiently, the above-mentioned residual magnetic flux density (Br) of the medium is 320 mT or more and 450 mT or less, coercive force (Hc) is 170 kA / m or more and 200 kA / m or less, and surface roughness ( Ra) is preferably 13 nm or more and 20 nm or less.

The magnetic metal powder used in the magnetic recording medium of the present invention has an average major axis length of 0.05 to 0.2 μm,
The average axial ratio is 3 to 10, and needle-shaped, columnar, spindle-shaped or rod-shaped ones are preferable. Further, although iron is usually used for the metal portion, it may be an alloy of iron with cobalt, nickel or the like, and aluminum, silicon, zirconia, a rare earth metal or the like exists near the oxide layer on the surface. Good.

Specific examples of the metal magnetic powder usable in the present invention include ferromagnetic metal materials such as Fe, Co and Ni, Fe-Co, Fe-Ni and Fe-Co-N.
i, Co-Ni, Fe-Mn-Zn, Fe-Ni-Z
n, Fe-Co-Ni-Cr, Fe-Co-Ni-P,
Fe-Co-B, Fe-Co-Cr-B, Fe-Co-
Examples thereof include ferromagnetic metal fine particles made of various ferromagnetic alloy materials containing Fe, Co, Ni as main components such as V, and further, Al, Si, for the purpose of improving these various characteristics.
A metal component such as Zr, Ti, Cr, Mn, Cu, Zn, or P may be added.

Examples of the method for producing such a ferromagnetic metal powder include iron hydrates such as α-FeOOH and γ-FeOOH, α-Fe ₂ O ₃ , γ-Fe ₂ O ₃ and Fe ₃ O _4.
There is a method of reducing iron oxides such as H ₂ with H ₂ or the like at high temperature.
For example, ferrous salt compounds (eg FeSO ₄ , FeCl 2
₂ etc.) is reacted with an alkaline component (for example, NaOH etc.) to produce α-FeOOH.
Is reduced at high temperature, for example with H ₂ , or α-Fe
After converting OOH to α-Fe ₂ O ₃ , it is heated at a high temperature, for example, H
Reduce by ₂ .

As the other constituent elements constituting the magnetic recording medium of the present invention, any of those used in a usual coating type magnetic recording medium can be used.

For example, as the binder that can be used in the magnetic layer, a modified or non-modified vinyl chloride resin, a vinyl copolymer such as a vinyl acetate copolymer, a polyurethane resin such as a polyester polyurethane resin or a polycarbonate polyurethane resin. Alternatively, a polyester resin may be used or mixed, and further, a fibrin resin such as nitrocellulose, a phenoxy resin, or a thermoplastic resin having a specific usage system, a thermosetting resin, a reactive resin, an electron beam irradiation curing You may use mold resin etc. together.

The groups introduced for the above modification include --SO ₃ M and --OSO which can improve the dispersibility of the magnetic powder.
₃ M, -COOM, -PO (OM ') ₂ or the like (M is an alkali metal atom such as Na, and M' is the same alkali metal atom or alkyl group).

As usable fibrin resin, cellulose ether, cellulose inorganic acid ester, cellulose organic acid ester and the like can be used. Phenoxy resin has advantages such as high mechanical strength, excellent dimensional stability, good heat resistance, water resistance, chemical resistance, and good adhesiveness.

Further, it is preferable to add a curing agent to such a binder in order to further improve durability. As this curing agent, polyfunctional isocyanates can be used, especially tolylene diisocyanate (TD
The I) system is preferred. The addition amount of the curing agent is preferably 5 to 30% by weight based on the total amount of the binder.

In addition to the magnetic powder and the binder, additives such as a lubricant, an abrasive and an antistatic agent may be added to the magnetic layer, if necessary. These additives include:
Any conventionally known materials can be used, and there is no particular limitation.

Lubricants usable in the magnetic layer include monobasic fatty acids having 10 to 24 carbon atoms (unsaturated bonds or branched ones) or monobasic fatty acids having 10 to 24 carbon atoms are used. An ester, a mixed ester, a difatty acid ester, or a trifatty acid ester with any one of monohydric to hexahydric alcohol having 2 to 12 carbon atoms can be used.

Specific examples of usable lubricants include lauric acid, myristic acid, palmitic acid, stearic acid,
Examples include behenic acid, oleic acid, linoleic acid, linolenic acid, elaidic acid, butyl stearate, pentyl stearate, heptyl stearate, octyl stearate, isooctyl stearate, and octyl myristate.

If desired, a dispersant such as lecithin, an antistatic agent such as carbon black, an abrasive such as alumina, and a rust preventive may be added to the magnetic layer. As these dispersants, antistatic agents, abrasives and rust inhibitors,
Any conventionally known materials can be used, and there is no particular limitation.

The magnetic layer is usually formed on a non-magnetic support, and usable non-magnetic supports include polyesters such as polyethylene terephthalate and polyethylene-2,6-naphthalate, polyethylene, polypropylene and the like. Polyolefins, cellulose derivatives such as cellulose triacetate, cellulose diacetate and cellulose butyrate, vinyl resins such as polyvinyl chloride and polyvinylidene chloride, and plastics such as polyamide, polyamide imide and polycarbonate.

Other examples include light metals such as aluminum alloys and titanium alloys, and ceramics such as alumina glass. When a rigid substrate such as an Al alloy plate or a glass plate is used as the non-magnetic support, an oxide film such as an alumite treatment or a Ni-P film is formed on the substrate surface to harden the surface. You may

To form a magnetic layer on a non-magnetic support,
It can be realized by using the above-mentioned metal magnetic powder as a magnetic coating material together with a binder, a lubricant, an organic solvent, and various additives, and coating this magnetic coating material on a non-magnetic support. The dry film thickness of the magnetic layer is preferably 0.5 to 4.5 μm, more preferably 2 to 4 μm.

Surface roughness R of the magnetic recording medium according to the present invention
The adjustment of a is performed by changing the shape and size of the abrasive or magnetic powder used, the roughness of the non-magnetic support to be applied and the preparation conditions, and the binder.

An intermediate layer or an undercoat layer may be provided on the surface of the non-magnetic support in order to improve the adhesiveness of the magnetic layer. Further, an overcoat layer may be provided on the surface of the magnetic layer.

Further, on the surface of the non-magnetic support opposite to the magnetic layer, a non-magnetic powder (eg silica, carbon black) and a binder (similar to those described above) are used to improve the running property of the medium. Back coat layer consisting of
It can be provided in a thickness of 0.4 to 0.8 μm.

FIG. 1 shows an example (magnetic tape for video) of the magnetic recording medium of the present invention. That is, the magnetic layer 2 containing metal magnetic powder, a binder and the like is provided on one surface of the non-magnetic support 1. Further, the other surface may have a back coat layer 3 mainly composed of a non-magnetic powder and a binder as indicated by a chain line.

[0035]

EXAMPLES The present invention will now be described in more detail with reference to examples, but the present invention is not limited to the following examples.

Example 1 Using a magnetic metal powder (Fe type) having an average major axis length of 0.15 μm, a saturation magnetization (σs) of 152 Am ² / kg, and a coercive force (Hc) of 183 kA / m, the following composition was used. A magnetic paint was prepared by measuring, kneading and dispersing each composition for the magnetic paint.

<Magnetic coating composition> 100 parts by weight of magnetic metal powder (Fe-based) Binder: 10 parts by weight of polyester-based polyurethane resin (weight average molecular weight = 50,000, containing polar group sulfonic acid sodium salt 0.16 mmol / g) Vinyl chloride Polymer 10 parts by weight (polymerization degree 300, polar group sulfonic acid potassium salt 0.07 mmol / g contained) Abrasive: α-alumina (Al ₂ O ₃ ) (average particle size 0.2 to 0.5 μm) 3 parts by weight Solvent: methyl ethyl ketone 100 Parts by weight toluene 100 parts by weight cyclohexanone 50 parts by weight

Then, 4 parts by weight of a curing agent (Coronate L manufactured by Nippon Polyurethane Industry Co., Ltd.) was added to the magnetic coating, and the coating was dried on a polyethylene terephthalate (PET) base film to form a magnetic layer having a predetermined width. A sample tape was produced by cutting into pieces.

The residual magnetic flux density (Br) of this tape is 370
mT, coercive force (Hc) is 184 kA / m, surface roughness (Ra) is R
It was a = 14.2 nm. Here, the surface roughness of the tape was adjusted by appropriately setting the above process conditions (abrasive size, base film roughness, etc.).

Example 2 As the magnetic metal powder, the average major axis length was 0.10 μm and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that one having a 145 Am ² / kg and a coercive force (Hc) of 185 kA / m was used.

The residual magnetic flux density (Br) of this tape is 341
mT, coercive force (Hc) is 187 kA / m, surface roughness (Ra) is R
It was a = 13.8 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Example 3 As magnetic metal powder, the average major axis length was 0.06 μm, and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that one having 140 Am ² / kg and coercive force (Hc) of 190 kA / m was used.

The residual magnetic flux density (Br) of this tape is 320
mT, coercive force (Hc) is 191 kA / m, surface roughness (Ra) is R
It was a = 13.6 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Example 4 As magnetic metal powder, the average major axis length was 0.10 μm, and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that one having a coercive force (Hc) of 195 kA / m and a resistance of 135 Am ² / kg was used.

The residual magnetic flux density (Br) of this tape is 300
mT, coercive force (Hc) is 196 kA / m, surface roughness (Ra) is R
It was a = 13.8 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Example 5 As magnetic metal powder, the average major axis length was 0.06 μm, and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that one having 140 Am ² / kg and coercive force (Hc) of 190 kA / m was used.

The residual magnetic flux density (Br) of this tape is 320
mT, coercive force (Hc) is 191 kA / m, surface roughness (Ra) is R
It was a = 12.0 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 1 As magnetic metal powder, the average major axis length was 0.15 μm and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that the one having 123 Am ² / kg and the coercive force (Hc) of 134 kA / m was used.

The residual magnetic flux density (Br) of this tape is 280
mT, coercive force (Hc) is 136 kA / m, surface roughness (Ra) is R
It was a = 11.7 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 2 As the magnetic metal powder, the average major axis length was 0.10 μm and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that a material having a coercive force (Hc) of 142 kA / m and a magnetic force of 119 Am ² / kg was used.

The residual magnetic flux density (Br) of this tape is 262
mT, coercive force (Hc) is 145 kA / m, surface roughness (Ra) is R
It was a = 11.7 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 3 As the magnetic metal powder, the average major axis length was 0.06 μm and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that the one having 117 Am ² / kg and the coercive force (Hc) of 150 kA / m was used.

The residual magnetic flux density (Br) of this tape is 250
mT, coercive force (Hc) 151kA / m, surface roughness (Ra) R
a = 11.5 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 4 As the magnetic metal powder, the average major axis length was 0.15 μm and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that the one having a coercive force (Hc) of 183 kA / m and a coercive force (Hc) of 152 Am ² / kg was used.

The residual magnetic flux density (Br) of this tape is 372
mT, coercive force (Hc) is 182 kA / m, surface roughness (Ra) is R
It was a = 11.6 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 5 As the magnetic metal powder, the average major axis length was 0.10 μm and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that one having a 145 Am ² / kg and a coercive force (Hc) of 185 kA / m was used.

The residual magnetic flux density (Br) of this tape is 342
mT, coercive force (Hc) is 183 kA / m, surface roughness (Ra) is R
It was a = 11.7 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 6 As the magnetic metal powder, the average major axis length was 0.06 μm and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that one having 140 Am ² / kg and coercive force (Hc) of 190 kA / m was used.

The residual magnetic flux density (Br) of this tape is 323
mT, coercive force (Hc) is 189 kA / m, surface roughness (Ra) is R
It was a = 11.7 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 7 As the magnetic metal powder, the average major axis length was 0.15 μm, and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that the one having 123 Am ² / kg and the coercive force (Hc) of 134 kA / m was used.

The residual magnetic flux density (Br) of this tape is 279
mT, coercive force (Hc) is 134 kA / m, surface roughness (Ra) is R
It was a = 14.3 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 8 As the metal magnetic powder, the average major axis length was 0.10 μm and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that a material having a coercive force (Hc) of 142 kA / m and a magnetic force of 119 Am ² / kg was used.

The residual magnetic flux density (Br) of this tape is 260
mT, coercive force (Hc) is 143 kA / m, surface roughness (Ra) is R
It was a = 13.7 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

Comparative Example 9 As the metal magnetic powder, the average major axis length was 0.06 μm, and the saturation magnetization (σ
s) A sample tape was prepared in the same manner as in Example 1 except that the one having 117 Am ² / kg and the coercive force (Hc) of 150 kA / m was used.

The residual magnetic flux density (Br) of this tape is 247
mT, coercive force (Hc) is 149 kA / m, surface roughness (Ra) is R
It was a = 13.8 nm. Here, the surface roughness of the tape was adjusted in the same manner as in Example 1.

The above Examples 1 to 5 and Comparative Examples 1 to 1
Coercive force (Hc) and saturation magnetization (σ of the magnetic powder of Comparative Example 9)
s), tape coercive force (Hc) and residual magnetic flux density (Br) were measured using a sample vibrating magnetometer (manufactured by Toei Industry Co., Ltd.).
The surface roughness (Ra) of the tape was measured using a non-contact three-dimensional roughness meter of Kosaka Laboratory.

Further, Examples 1 to 5 and Comparative Examples 1 to 1
The electromagnetic conversion characteristics of the sample tape of Comparative Example 9 were evaluated.
For the electromagnetic conversion characteristics, the output (OUT) and the noise ratio (C / N) at 7 MHz were measured.

The durability was evaluated by incorporating the tape in an 8 mm cassette and deteriorating the electromagnetic conversion characteristics in a still state on an 8 mm video deck.

Conditions of the metal magnetic powders and sample tapes of Examples 1 to 5 and Comparative Examples 1 to 9, and the output (OUT) and noise ratio (C / C) measured by the above method.
N) and the results of durability are shown in Table 1 below.

[0070]

[0071]

[0072]

From these results, the electromagnetic conversion characteristics of Comparative Examples 4 to 6 are similar to those of the Examples, but the durability is poor and not practical. Further, the durability of Comparative Examples 7 to 9 is at a practical level like the Examples, but the electromagnetic conversion characteristics are low values. In Comparative Examples 1 to 3, all performances are poor.

That is, as in Examples 1 to 5, the surface roughness is Ra ≧ 12 nm, Br ≧ 300 mT, and Hc ≧ 160 kA /
A magnetic recording medium having a relationship of m 2 has both excellent electromagnetic conversion characteristics and durability and is practically excellent.

[0075]

As described above, according to the present invention, the residual magnetic flux density (Br) is 300 mT or more, the coercive force (Hc) is 160 kA / m or more, and the surface roughness is Ra ≧ 12 nm. Since the magnetic recording medium is constructed in the above, a magnetic recording medium having a high recording density, a large output and excellent durability can be obtained.

That is, since the surface roughness is specified to be Ra ≧ 12 nm, the contact area between the medium and the head is reduced, so that the friction when the recording medium is run is reduced and the durability is improved. . However, with this alone, the spacing between the recording medium and the head increases, and the output decreases, so using a magnetic powder with a high residual magnetic flux density and a high coercive force that satisfies the above conditions will reduce the output. Thus, it is possible to obtain a magnetic recording medium which suppresses both high durability and high output.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing one structural example of a magnetic tape to which the present invention is applied.

[Explanation of symbols]

 1 ... Non-magnetic support, 2 ... Magnetic layer

Claims (3)

[Claims] 1. A magnetic recording medium having a magnetic layer,
The surface roughness (Ra) on the magnetic layer side is Ra ≧ 12 nm,
Moreover, the residual magnetic flux density Br ≧ 300 mT, the coercive force Hc ≧ 160 kA /
A magnetic recording medium that is m. 2. The magnetic recording medium according to claim 1, wherein a metal magnetic powder is used as the magnetic powder contained in the magnetic layer. 3. The magnetic recording medium according to claim 1, wherein the magnetic layer is a coating type magnetic layer mainly containing magnetic powder and a binder.