JPH08102035A - Magnetic recording medium, its production and device therefor - Google Patents

Abstract

PURPOSE: To obtain a magnetic recording medium having satisfactory durability, capable of high density recording, having especially high magnetic flux density and advantageous to recording at short wavelength by orienting hexagonal platy iron powder in a magnetic layer on a substrate in a direction perpendicular to the surface of the substrate. CONSTITUTION: A substrate is coated with a magnetic coating material and hexagonal platy iron powder is oriented with an external magnetic field. In this case, the iron powder is oriented in a direction perpendicular to the surface of the substrate by passing through a magnetic field perpendicular to the surface of the substrate. The N and S poles of orienting magnets 21a, 21b are arranged in a direction perpendicular to the surface of the substrate and the hexagonal platy iron powder 23 is oriented in a direction perpendicular to the surface of the substrate 22 by passing the substrate 22 through the space between the magnets 21a, 21b.

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, and more particularly to a coating type magnetic recording medium having a high magnetic flux density and advantageous for recording at a short wavelength.

[0002]

2. Description of the Related Art A coating type magnetic recording medium is obtained by coating a magnetic coating material obtained by dispersing magnetic powder in a binder and an organic solvent on a substrate such as polyester and drying it. There is an increasing demand for higher density recording such as high quality video tapes and large capacity floppy disks.

Ferromagnetic metal powders composed mainly of iron are most often used as magnetic powders for achieving this purpose. Ferromagnetic metal powder composed mainly of iron has high saturation magnetization and coercive force, and has excellent output characteristics. However, since it is chemically unstable and easily rusts (is easily oxidized), the saturation magnetization is lowered by oxidation, and the noise characteristic is not always sufficient, and generally the noise level is higher than that of the oxide magnetic powder. Further, the ferromagnetic metal powder mainly composed of iron has a high cost and has some drawbacks in practical use.

A perpendicular magnetic recording method has been proposed as a method for realizing high-density recording, and hexagonal plate-shaped barium ferrite is used as a magnetic powder particularly suitable for this method. However, since barium ferrite has a low saturation magnetization, when used as a magnetic tape or a magnetic disk, the residual magnetic flux density becomes low and the output in the low range becomes insufficient.

[0005]

Although it is considered that the perpendicular magnetic recording method is advantageous in order to further increase the recording density in the future, as described above, the hexagonal plate barium ferrite has a low residual magnetic flux density. Therefore, a sufficiently satisfactory magnetic recording medium cannot be obtained.

Accordingly, it is an object of the present invention to provide a coating type magnetic recording medium which achieves high density recording and has an improved magnetic flux density.

[0007]

Means for Solving the Problems As a result of earnest research by the present inventor, the above object can be achieved by using hexagonal plate-shaped iron powder as a magnetic material and orienting it in a direction perpendicular to the substrate surface. Finding that a magnetic recording medium can be obtained,
The present invention has been completed.

That is, the present invention provides a magnetic recording medium having a base material and a magnetic layer comprising a hexagonal plate-shaped iron powder formed on the surface of the base material and a binder. (EN) Provided are a magnetic recording medium characterized by being oriented in a direction perpendicular to the longitudinal direction of a material, and an apparatus and method for manufacturing the magnetic recording medium.

(I) Magnetic Recording Medium of the Present Invention [Magnetic Layer] The magnetic layer of the magnetic recording medium of the present invention will be described. Hexagonal plate-shaped iron powder is used for the magnetic layer of the magnetic recording medium of the present invention. Such hexagonal plate-shaped iron powder is produced, for example, by the following method.

<Method for producing hexagonal plate-shaped iron powder> An aqueous ferrous sulfate solution is stirred, and an equivalent amount or more of sodium hydroxide is added thereto to make it alkaline. This causes iron hydroxide to precipitate. Hydrogen peroxide is added to the solution containing the precipitate little by little with stirring. When hydrogen peroxide is added to iron hydroxide,
It is rapidly oxidized to form hexagonal plate-shaped δ-FeOOH.

Next, water glass and aluminum chloride are added, and the pH is adjusted to 4 to 6 using acetic acid or the like. Then, it is filtered, the residue is washed with water, and then baked in air at 650 ° C. Next, it is reduced with hydrogen gas at 420 ° C. and cooled to room temperature to obtain hexagonal plate-shaped iron powder.

[0012] Here, it is preferable that after the reduction and cooling, a small amount of air or oxygen is aerated to oxidize the surface.

Hexagonal plate-shaped iron powder contains M in addition to Co.
A small amount of n, Cr, Ni, Zn, Sn, etc. may be added.

The coercive force of the hexagonal plate-shaped iron powder used in the present invention is not limited, but is generally about 800 to 1900 (Oe).

The hexagonal plate-shaped iron powder used in the present invention is not particularly limited in the diagonal length or plate ratio, but the diagonal length of 0.
It is about 03-0.5 μm and the plate ratio is about 3-20.

The magnetic layer is composed of the above-mentioned magnetic coating mainly composed of cobalt-coated iron oxide powder, metal powder and binder.
It is formed by coating on the base material, but the thickness of the magnetic layer is 0.1 ~
3 μm is preferred.

Since the hexagonal plate-like iron powder as described above is in-plane magnetized, unlike a needle-shaped metal powder, even a magnetic head for spiral scanning is magnetized in the scanning direction of the head. Further, even if the major axis length of the acicular metal powder and the diagonal length of the hexagonal plate-shaped iron powder are the same, since the volume of the hexagonal plate-shaped iron powder is larger, a higher saturation magnetization amount can be obtained. Furthermore, the number of effective magnetic powders per unit volume is greater when the hexagonal plate-shaped iron powder is filled, so a high S / N is obtained.

The magnetic recording medium of the present invention is characterized in that the hexagonal plate-shaped iron powder in the magnetic layer is oriented in the direction perpendicular to the surface of the base material. The situation is shown in FIG. In Figure 1,
Reference numeral 1 is hexagonal plate-shaped iron powder, 2 is an inorganic lubricant blended in a magnetic paint, 3 is a magnetic layer, 4 is a base material, and 5 is a back coat layer.

In the magnetic recording medium of the present invention, the hexagonal plate-shaped iron powder is oriented at the position shown in FIG. 1, and as a result, magnetic recording having the advantages of both the perpendicular magnetic recording system and the longitudinal magnetic recording system. It becomes a medium.

[Binder] The binder used in the present invention is a urethane resin, particularly a polar group such as a sulfonic acid group, a metal sulfonate group, a sulfobetaine group, a carbobetaine group, an amino group, a hydroxyl group, an epoxy group. A vinyl chloride copolymer such as a polyurethane resin containing vinyl chloride, a vinyl chloride-vinyl acetate copolymer, a vinyl chloride-vinylidene chloride copolymer, a vinyl chloride-acrylonitrile copolymer, particularly a sulfonic acid group or a sulfonic acid group. Vinyl chloride copolymers containing polar groups such as metal bases and amino groups, butadiene-acrylonitrile copolymers, polyamide resins, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose propionate, nitrocellulose, etc.), styrene -Butadiene copolymer, polyester resin, various synthesis System, phenol resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicon resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low Examples include a mixture of molecular weight glycol / high molecular weight diol / isocyanate, and a mixture thereof, and the same materials can be used for the magnetic layer and the intermediate layer. Usually, the binder is mixed in the magnetic paint in an amount of about 10 to 30% by weight.

[Organic Solvent] As the organic solvent constituting the magnetic coating material, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, benzene, toluene, xylene, dimethyl sulfoxide, tetrahydrofuran, dioxane, etc. are used as binder resins. Solvents suitable for dissolving are not particularly limited and may be used alone or in combination of two or more. Usually, the organic solvent is mixed in the magnetic coating material in an amount of about 20 to 80% by weight.

In the magnetic coating composition, various commonly used additives such as dispersants, abrasives and lubricants may be appropriately added and used. As the dispersant, lecithin,
Nonionic surfactants, anionic surfactants, cationic surfactants and the like can be used. As an abrasive, α-
Fine powders having an average particle size of 0.05 to 1 μm, such as alumina, fused alumina, chromium oxide (Cr ₂ O ₃ ), iron oxide, silicon carbide, corundum, and diamond can be used, and usually 100 parts by weight of the binder as described above are used. 0.5 to 100 parts by weight is added. Examples of lubricants include silicone oils such as various polysiloxanes, graphite, inorganic powders such as molybdenum disulfide, fine plastic powders such as polyethylene and polytetrafluoroethylene, higher fatty acids, higher alcohols, higher fatty acid esters, and fluorocarbons. And the like are added in a ratio of 0.1 to 50 parts by weight with respect to 100 parts by weight of the binder.

The substrate used in the magnetic recording medium of the present invention includes synthetic resins (for example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamides, polyolefins, cellulose derivatives), non-magnetic metals, glass, ceramics and papers. Etc., and the form thereof is used in films, tapes, sheets, cards, disks and the like.

(II) Production Method of the Present Invention Further, in the present invention, a magnetic coating material containing hexagonal plate-shaped iron powder and a binder is applied to a base material, and then the base material is applied to the surface of the base material. Of hexagonal plate-shaped iron powder in the magnetic paint applied to the base material in a direction perpendicular to the surface of the base material by passing it through a magnetic field perpendicular to the base material. It provides a method. The hexagonal plate-like iron powder, binder, magnetic paint, base material and the like used in this method are as described above for the magnetic recording medium.

In the present invention, the method of applying the magnetic coating material containing the hexagonal plate-shaped iron powder is not particularly limited, and it may be die coating,
This is based on the usual method for producing a magnetic recording medium of coating type such as gravure roll coating.

After the magnetic paint is applied to the base material, the hexagonal plate-shaped iron powder is oriented by an external magnetic field. In the present invention, the hexagonal plate-shaped iron powder is passed through a magnetic field perpendicular to the surface of the base material. The powder is oriented perpendicular to the substrate surface. FIG. 2 is a schematic diagram showing the image. In FIG. 2, 21a, 21
Reference numeral b is an oriented magnet, in which the N pole and the S pole are arranged perpendicularly to the surface of the base material. By passing the base material 22 between them, the hexagonal plate-shaped iron powder 23 is oriented in the direction perpendicular to the surface of the base material.

The thickness of the magnetic layer formed by the present invention is
The thickness is 0.05 to 9 μm, preferably 0.1 to 5 μm.

In the manufacturing method of the present invention, the steps other than the step of orienting after coating the magnetic layer are carried out in accordance with the usual coating type manufacturing method, such as drying, surface treatment, curing, cutting, inspection,
A process such as assembling a cassette may be performed.

(III) Manufacturing Apparatus of the Present Invention The present invention also applies a magnetic coating material containing hexagonal plate-shaped iron powder onto the base material along the base material transfer means and the transfer path of the base material. A magnetic recording medium in which the means, the means for orienting the hexagonal plate-shaped iron powder in the magnetic coating material applied to the base material, and the means for drying the magnetic coating material applied to the base material are arranged in this order. In the manufacturing apparatus, the means for orienting the hexagonal plate-shaped iron powder causes a magnetic field to be generated in a direction perpendicular to the surface of the base material.

The substrate conveying means in the manufacturing apparatus of the present invention is a feed roller, an unwinding roll, a winding roll, etc., and those known in the manufacturing apparatus can be applied. Further, the magnetic coating material may be applied by a known manufacturing apparatus such as a gravure roll coater, a knife coater, a reverse roll coater. Further, as a drying means for the magnetic paint, a known manufacturing apparatus can be applied.

The manufacturing apparatus of the present invention is used for manufacturing a magnetic recording medium using a magnetic coating material containing hexagonal plate-shaped iron powder, and is characterized by a means for orienting the hexagonal plate-shaped iron powder. This is to generate a magnetic field in the direction perpendicular to the surface of the base material.

FIG. 3 is a schematic view showing an example of the manufacturing apparatus of the present invention. In FIG. 3, 30 is a chamber, 31a and 31b are oriented magnets, 32 is an unwinding roll, 33 is an electrostatic dust remover, 34 is a gravure roll coater, 35 is a smoother, 36 is a first drying chamber, and 37 is a first drying chamber. Two drying chambers, 38 is a third drying chamber, 39 is a winding roll, 40 is a base material, and 41 is a dryer.

The base material 40 is removed from the unwinding roll 32 by an electrostatic dust remover.
It is conveyed to the gravure roll coater 34 via 33, and the magnetic coating material A containing the hexagonal plate-shaped iron powder is applied by the gravure roll coater 34. After that, the base material 40 passes through the smoother, and the magnetic coating material applied to the base material passes between the orientation magnets 31a and 31b in a sufficiently fluid state. The orienting magnet is arranged as shown in FIG. 2 so as to generate a magnetic field in the direction perpendicular to the surface of the base material, whereby the hexagonal plate-shaped iron powder is oriented in the state as shown in FIG. The oriented base material is first preliminarily dried by the dryer 41, the first drying chamber 36,
After passing through the second drying chamber 37 and the third drying chamber 38 to complete the drying, the film is taken up by the take-up roll 39.

In the manufacturing apparatus of the present invention, the oriented magnet may be a permanent magnet or an electromagnet, and other means for generating a magnetic field can be applied, but the magnetic field is arranged so as to be perpendicular to the substrate surface. is necessary.

[0035]

According to the present invention, it is possible to obtain a magnetic recording medium which has good durability and enables high density recording, has a particularly high magnetic flux density, and is advantageous for recording at a short wavelength.

[0036]

The present invention will be further described in the following examples, but the present invention is not limited to these examples.

Production Example 1 A 5% ferrous sulfate aqueous solution is placed in a stirring reaction vessel equipped with blades.
Then add 10% sodium hydroxide aqueous solution little by little,
Adjust pH to 10. At this time, white iron hydroxide precipitates. Then, 20% aqueous hydrogen peroxide solution is added until all the precipitate in the solution becomes dark brown (or dark brown). The brown-colored precipitate formed here is a hexagonal plate-like δ-
FeOOH. Subsequently, washing with water and filtration were performed using a filter press.

Then, pure water was added to the same stirred reaction tank to disperse the filtration residue well, and 1% by weight of water glass and 1% by weight of aluminum chloride were added to the iron in the ferrous sulfate aqueous solution initially charged. The pH is adjusted to 4 by adding acetic acid. Subsequently, washing with water and filtration were performed using a filter press. The precipitate is then 650 in air using a muffle furnace.
Bake at 2 ° C. for 2 hours. Then, it is reduced with hydrogen gas using a batch kiln at 450 ° C.

Next, the temperature of the reaction system is lowered to room temperature and a small amount of air is aerated, and all the gas is replaced with air for 40 hours to oxidize and stabilize the surface of the metal powder.

Here, the obtained metal powder is hexagonal plate-shaped iron powder, the plate ratio is 1: 8, Hc is 1530 (Oe), σs
Was 128 (emu / g). This hexagonal plate-shaped iron powder was used as powder A and used in Example 1 below.

Example 1 (1) Preparation of magnetic coating A powder obtained above and the following components were dispersed in a sand mill to prepare a magnetic coating for a magnetic layer. <Magnetic paint components> ・ A powder 24.6% by weight ・ Vinyl chloride resin 1.9% by weight ・ Polyurethane resin 2.8% by weight ・ Isocyanate 0.7% by weight ・ Al ₂ O ₃ (particle size 0.15 μm) 3.0% by weight ・ Fatty acid ester 0.8% by weight % Toluene 29.8% by weight Methyl ethyl ketone 29.8% by weight Cyclohexanone 6.6% by weight.

(2) Manufacture of magnetic recording medium A magnetic recording medium was manufactured by applying a magnetic layer using the apparatus shown in FIG. That is, the above magnetic paint was coated with a direct gravure method to a thickness of 10 μm so that the thickness after drying was 2.5 μm.
Apply on PET film. Immediately thereafter, the magnetic paint is oriented by the oriented magnet while having sufficient fluidity. At this time, the in-plane easy axis of magnetization (plate surface) of the hexagonal plate-shaped iron powder in the magnetic paint changes its direction parallel to the direction of the magnetic field, and is oriented in the magnetic paint in a direction perpendicular to the substrate ( 1 and 2).

Further, a coating material containing carbon black as a main component was applied to the back surface of the film on which the magnetic layer was formed so that the thickness after drying was 0.5 μm and dried.

This film was cut into a tape having a width of 8 mm, placed in an 8 mm cassette case, and put into a commercially available high band 8
The mmVTR device is connected to the noise meter, and YS / N, CS /
N (AM, PM) was measured (recording wavelength 0.7 μm) and compared with a commercially available reference tape (manufactured by Sony Corporation), and displayed in dB. As the magnetic properties of the 8 mm tape, coercive force (Hc ₁ : longitudinal coercive force, Hc ₂ : perpendicular coercive force) and residual magnetic flux density (Br) were measured using VSM. The results are shown in Table 1.

Production Example 2 A 5% ferrous sulfate aqueous solution is placed in a stirring reaction vessel equipped with blades.
Then add 10% sodium hydroxide aqueous solution little by little,
Adjust pH to 10. At this time, white iron hydroxide precipitates. Then, 20% aqueous hydrogen peroxide solution is added until all the precipitate in the solution becomes dark brown (or dark brown). The brown-colored precipitate formed here is a hexagonal plate-like δ-
FeOOH. Subsequently, washing with water and filtration were performed using a filter press.

Next, pure water was added to the same stirring reaction tank to thoroughly disperse the filtration residue, and 5% by weight of cobalt nitrate was added to the iron in the initially prepared ferrous sulfate aqueous solution. Further, 1% by weight of water glass and 1% by weight of aluminum chloride are added to iron in the ferrous sulfate aqueous solution initially charged, and acetic acid is added to adjust the pH to 4. Subsequently, washing with water and filtration were performed using a filter press. The precipitate is then calcined in air in a muffle furnace at 650 ° C for 2 hours. Then reduce with hydrogen gas using a batch kiln at 450 ℃,
Reoxidation was carried out at 250 ° C for 30 minutes.

Here, as a result of scientific analysis of the obtained metal powder, it was found to be Co-γ-Fe ₂ O ₃ , and as a result of observing the shape with TEM, it was confirmed to be a hexagonal plate shape. .
The coercive force of this powder is 600 (Oe), the plate ratio is 1: 8, and σs
Was 75 (emu / g). This hexagonal plate-shaped iron powder was designated as B powder and used in Example 2 below.

Example 2 The powder B obtained in the above Production Example 2 was used in place of the powder A of Example 1 to prepare a magnetic coating material, an 8 mm tape was prepared in the same manner as in Example 1, and the same test was conducted. went. The results are shown in Table 1.

Comparative Example 1 In the magnetic coating material of Example 1, coercive force 5 was used instead of powder A.
90 (Oe), σ s 73 (emu / g), average major axis length 0.2 μm, average minor axis length 0.04 μm of needle-like Co-γ-Fe ₂ O ₃ was used, and otherwise 8 mm as in Example 1. A tape was prepared and the same test was conducted. The results are shown in Table 1.

FIG. 4 is a schematic sectional view showing the structure of the tape obtained in this example. In Fig. 4, needle-shaped Co-γ-
The Fe ₂ O ₃ powder 41 is oriented so as to be oriented in a direction perpendicular to the surface of the base material 42.

Comparative Example 2 An 8 mm tape was prepared in the same manner as in Example 1 except that the conventional device shown in FIG. 5 (device for performing the orientation by the solenoid method) was used in place of the device shown in FIG. 3 in Example 1. A similar test was conducted. 5 is the same as the device of FIG. 3 except for the solenoid 52. A schematic sectional view showing the structure of the tape obtained in this example is shown in FIG. In Fig. 5, hexagonal plate-shaped iron powder
61 is oriented parallel to the surface of the substrate 62.

[0052]

[Table 1]

* Criteria: Commercially available 8 mm reference tape (manufactured by Sony Corporation)

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of the structure of a magnetic recording medium of the present invention.

FIG. 2 is a schematic diagram showing a method for orienting hexagonal plate-shaped iron powder.

FIG. 3 is a schematic view showing an example of an apparatus for manufacturing a magnetic recording medium of the present invention.

4 is a schematic diagram showing the structure of a magnetic recording medium obtained in Comparative Example 1. FIG.

FIG. 5 is a schematic view showing an example of a conventional magnetic recording medium manufacturing apparatus.

6 is a schematic diagram showing the structure of a magnetic recording medium obtained in Comparative Example 2. FIG.

[Explanation of symbols]

 1 Hexagonal plate-shaped iron powder 4 Base material 21a, 21b Oriented magnet 31a, 31b Oriented magnet

Front page continuation (72) Inventor Shigemi Wakabayashi 2606 Akabane, Kai-cho, Haga-gun, Tochigi Prefecture Kao Corporation Information Science Laboratory (72) Inventor Hirohide Mizunoya 2606 Akabane, Kai-cho, Haga-gun, Tochigi Prefecture Kao Corporation Information Science Laboratory

Claims (3)

[Claims] 1. A magnetic recording medium comprising a base material and a magnetic layer comprising a hexagonal plate-shaped iron powder formed on the surface of the base material and a binder, wherein the hexagonal plate-shaped iron powder is formed on the surface of the base material. A magnetic recording medium characterized in that it is vertically oriented. 2. A base material is coated with a magnetic coating material containing hexagonal plate-shaped iron powder and a binder, and then the base material is passed through a magnetic field perpendicular to the surface of the base material. ,
A method for producing a magnetic recording medium, characterized in that hexagonal plate-shaped iron powder in a magnetic coating material applied to a base material is oriented in a direction perpendicular to the surface of the base material. 3. A base material conveying means, a means for applying a magnetic coating material containing hexagonal plate-shaped iron powder onto the base material along a base material conveying path, and a magnetic coating material applied to the base material. In the apparatus for manufacturing a magnetic recording medium, wherein the means for orienting the hexagonal plate-shaped iron powder and the means for drying the magnetic paint applied to the base material are arranged in this order, the hexagonal plate-shaped iron powder is oriented. An apparatus for producing a magnetic recording medium, characterized in that the means for producing generate a magnetic field in a direction perpendicular to the surface of the base material.