JPH07102194A - Magnetic coating and production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic coating which comprises ferromagnetic fine powder containing iron as a main component, a binder and THF, thus gives a magnetic recording medium excellent in high-frequency output because the magnetic powder disperses stably and uniformly and gives excellent surface properties to the magnetic layer. CONSTITUTION:The objective coating contains (A) a ferromagnetic metal powder which mainly comprises iron having less than 0.13mum average main axis length, less than 160Angstrom crystal size, over 1850 (Oe) coercive force and more than 130(emu/g) saturation magnetization, (B) a binder such as sulfonic acid group- containing polyurethane resin or sulfonic acid group-containing vinyl chloride copolymer and (C) THF. In usual cases, the component B is added to the coating in an amount of 3 to 10 wt.%. The component C is added in an amount of 20 to 40wt.%.As the component A, is used, for example, iron powder or iron alloys with cobalt, nickel or the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic coating material having a high coercive force and a magnetic powder having a fine particle size uniformly dispersed therein.

The present invention also relates to a method for manufacturing a magnetic recording medium, and more particularly to a method for manufacturing a magnetic recording medium in which the surface properties of a magnetic layer are improved and which is excellent in high frequency output.

[0003]

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.

As the magnetic powder for achieving this purpose, fine particles having high coercive force and high saturation magnetization are preferable. Among them, the most widely used is a ferromagnetic metal powder mainly composed of iron. is there.

With the progress of magnetic heads in recent years, a ferromagnetic metal powder mainly composed of iron, which has higher magnetic properties and is further finely divided, than a conventional ferromagnetic metal powder mainly composed of iron. Have been considered, for example, the average major axis length 0.13
A metal powder having a crystallite size of 160 μm or less, a coercive force of 1850 (Oe) or more, and a saturation magnetization of 130 (emu / g) or more is attracting attention as a magnetic powder suitable for high-density recording.

Further, in the coating type magnetic recording medium, as a paint solvent used when preparing a magnetic paint,
Usually, methyl ethyl ketone, methyl isobutyl ketone,
Ketone-based solvent such as cyclohexanone, ethyl acetate,
An ester solvent such as butyl acetate is used, and these are often used as a mixture of several kinds, and toluene is often mixed as a diluent for cost reasons.

[0007]

However, the finely divided metal powder having the above-mentioned higher magnetic properties has poor dispersibility and the surface smoothness is impaired, so that the magnetic powder originally has such properties. You cannot fully exercise your ability to live.

On the other hand, a solvent having a boiling point of 70 ° C. or higher has been the mainstream of the solvent conventionally used for magnetic paints, which is disadvantageous in terms of heat consumption in a drying furnace. Further, the mixed solvent obtained by mixing the above-mentioned solvents is difficult to collect when it is collected and reused. Further, from the viewpoint of mass productivity, it is said that it is better to apply the magnetic paint at a high speed, but in this case as well, the amount of heat in the drying furnace becomes large. Further, in the case of high-speed coating, it is necessary to increase the drying speed, and as a result, there arises a problem that the surface property of the coating film deteriorates.

[0009]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that by using a fine metal powder with a high coercive force as a magnetic powder and tetrahydrofuran as a solvent in a magnetic paint, The inventors have found that a magnetic recording medium can be obtained in which the powder is stably dispersed and the original performance of the magnetic powder can be sufficiently exhibited, and the present invention has been completed.

That is, the present invention is a ferromagnetic metal powder mainly composed of iron having an average major axis length of 0.13 μm or less, a crystallite size of 160 Å or less, a coercive force of 1850 (Oe) or more, and a saturation magnetization of 130 (emu / g) or more. And a binder, and a magnetic coating material containing tetrahydrofuran.

Further, the present invention is a ferromagnetic metal mainly composed of iron having an average major axis length of 0.13 μm or less, a crystallite size of 160 Å or less, a coercive force of 1850 (Oe) or more, and a saturation magnetization of 130 (emu / g) or more. A powder (hereinafter abbreviated as metal powder of the present invention), a binder,
The present invention provides a method for producing a magnetic recording medium, which comprises coating a non-magnetic support with a magnetic coating material containing tetrahydrofuran (hereinafter abbreviated as THF) to form at least one magnetic layer.

[Magnetic Paint of the Present Invention] First, the magnetic paint of the present invention will be described. The metal powder used in the magnetic coating material of the present invention has an average major axis length of 0.13 μm or less, preferably 0.05.
~ 0.13 μm, crystallite size 160 Å or less, preferably 120
~ 160Å, coercive force 1850 (Oe) or more, preferably 1850 ~ 2000
(Oe), saturation magnetization 130 (emu / g) or more, preferably 130 to 140
It has magnetic properties and particle size of (emu / g). If these magnetic properties and particle diameters deviate from the ranges specified in the present invention, the high frequency properties of the obtained magnetic recording medium deteriorate. Especially, if the saturation magnetization is not more than 130 (emu / g), the saturation magnetic flux density will be low,
If the crystallite size is not 160 Å or less, the axial ratio becomes large and the orientation becomes unfavorable, resulting in a decrease in residual magnetic flux density.

In the present invention, the crystallite size of the metal powder
(D ₁₁₀ ) is calculated by the Scherrer formula shown in the following formula (1) using β [radian] of the half-value width of the peak of the (110) plane measured by an X-ray diffraction measurement device. Define.

[0014]

[Equation 1]

Where λ is the wavelength (Å) of the X-ray and θ is (11
It is the Bragg angle of the 0) plane diffraction line. The definition of the crystallite size used in the present invention is general, and the detailed explanation is described in "X-ray Diffraction Principles" (Karity, Agne Publishing), 91-.
You can refer to the description on page 96.

The composition of the metal powder of the present invention is not limited as long as it has the above-mentioned specific magnetic properties and particle diameters. Iron powder, alloy powder of iron and cobalt, nickel or the like, and further Aluminum, chrome,
Examples thereof include alloy powders containing manganese, silicon, zinc, transition metal elements, rare earth metal elements, and the like.

Surface treatment may be carried out in order to further improve the dispersibility of the metal powder. The surface treatment of such metal powder is described in "Characterization of Powder Surfaces
Academic Press can be referred to, for example, a method of coating the surface of the metal powder with an inorganic oxide can be mentioned. As the inorganic oxide used here, Al ₂ O
₃ , SiO ₂ , TiO ₂ , ZrO ₂ , SnO ₂ , Sb ₂ O ₃ , ZnO and the like can be mentioned. These may be used in combination or may be used alone.

Although THF is used as a solvent in the magnetic paint of the present invention, other organic solvents such as cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone,
Ethyl acetate, butyl acetate, benzene, toluene, xylene, dimethyl sulfoxide, dioxane and the like can be used in combination within a range that does not impair the effects of the present invention.
THF: Other uses = 100: 0 to 50:50. THF
(The total amount of the other organic solvent when used in combination) is mixed in the magnetic coating material in an amount of about 20 to 80% by weight.

The binder used in the present invention is a urethane resin, particularly a polyurethane containing polar groups such as sulfonic acid groups, metal sulfonate groups, sulfobetaine groups, carbobetaine groups, amino groups, hydroxyl groups and epoxy groups. Resins, vinyl chloride-vinyl acetate copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl chloride-acrylonitrile copolymers, and other vinyl chloride-based copolymers, particularly sulfonic acid groups, sulfonic acid metal bases, amino Chloride copolymers containing polar groups such as groups, butadiene-acrylonitrile copolymers, polyamide resins, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose propionate, nitrocellulose, etc.), styrene-butadiene copolymer Coalesced, polyester resin, various synthetic rubber, Nole resin, epoxy resin, urea resin, melamine resin, phenoxy resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, mixture of polyester polyol and polyisocyanate, urea formaldehyde resin, low molecular weight glycol / Examples are high molecular weight diol / isocyanate mixtures, and mixtures thereof. Normally, the binder is 3.0 to 10.0 in the magnetic paint.
It is blended in the amount of about wt%.

In the magnetic coating material of the present invention, various additives usually used in magnetic coating materials, such as a dispersant, an abrasive and a lubricant, may be appropriately added and used. As the dispersant, lecithin, nonionic surfactants, anionic surfactants, cationic surfactants and the like can be used.
As the abrasive, fine powders having an average particle size of 0.05 to 1 μm, such as α-alumina, fused alumina, chromium oxide (Cr ₂ O ₃ ), iron oxide, silicon carbide, corundum, and diamond, can be used. 0.5 to 100 parts by weight of binder
100 parts by weight are added. As the lubricant, silicone oil such as various polysiloxanes, graphite,
Inorganic powders such as molybdenum disulfide, plastic fine powders such as polyethylene and polytetrafluoroethylene, higher fatty acids, higher alcohols, higher fatty acid esters, fluorocarbons, etc. are 0 per 100 parts by weight of the binder.
It is added in a proportion of 1 to 50 parts by weight.

In the present invention, the use of THF as the solvent for the magnetic paint improves the surface properties of the coating film after applying it. The reason for this is not clear, but it is presumed that THF is a good solvent and the binder has good solubility, so that the dispersibility of the metal powder, which was a magnetic powder having poor dispersibility, is improved.

[Manufacturing Method of the Present Invention] Next, a manufacturing method of the magnetic recording medium of the present invention will be described.

The method for producing the magnetic recording medium of the present invention is carried out by coating the nonmagnetic support with the magnetic coating material of the present invention containing the metal powder of the present invention, THF and a binder as described above.

In addition to the magnetic layer formed of the magnetic coating material of the present invention, other magnetic layers and non-magnetic layers may be provided to provide a magnetic recording medium having a multilayer structure. In this case, it is desirable that the magnetic layer formed from the magnetic coating material of the present invention is the uppermost layer (the layer farthest from the base material in the surface of the base material on which the magnetic layer is formed). The non-magnetic layer is an intermediate layer made of suitable non-magnetic particles.

In the present invention, the method of forming (coating) the magnetic layer is not particularly limited, and is in conformity with the usual coating type magnetic recording medium manufacturing methods such as die coating and gravure roll coating.

In the case of a multi-layer structure, a method of simultaneously forming the magnetic layer according to the present invention and another magnetic layer or a non-magnetic layer (multi-layer simultaneous formation method) or a method of sequentially forming one layer at a time ( Either of the sequential forming methods)
When forming one layer at a time, calendering may be performed on each layer.

The thickness of the magnetic layer formed by the magnetic coating material of the present invention is 0.05 to 9 μm, preferably 0.1 to 5 μm.
m. The thickness of other magnetic and non-magnetic layers is 0.1
.About.5 .mu.m, preferably 0.5 to 4 .mu.m.

Further, in the method for producing a magnetic recording medium of the present invention, a coating containing carbon black or other particles is applied to the surface opposite to the surface on which the magnetic layer is formed to form a back coat layer. May be. The thickness of the back coat layer is about 0.3 to 2 μm.

In the manufacturing method of the present invention, the steps other than the step of forming the magnetic layer are carried out in accordance with the usual coating type manufacturing method.
Processes such as orientation, drying, surface treatment, curing, cutting, inspection, and cassette incorporation may be performed.

Examples of the non-magnetic support used in the magnetic recording medium of the present invention include synthetic resins (for example, polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyamides, polyolefins, cellulose derivatives), non-magnetic metals, glass and ceramics. , Paper and the like, and the form thereof is used in films, tapes, sheets, cards, disks and the like. The thickness of the non-magnetic support is 3
It is about 50 μm.

[0031]

According to the present invention, a magnetic coating having a high coercive force and fine magnetic powder uniformly dispersed can be obtained. By coating the magnetic coating on a non-magnetic support, the surface property of the magnetic layer is improved. Moreover, a magnetic recording medium excellent in high frequency output can be obtained.

[0032]

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

Example 1 The following ingredients were dispersed in a sand mill to prepare a magnetic coating material. <Magnetic coating compound> (1) 100 parts by weight of needle-shaped ferromagnetic powder [Fe: Ni: Al: Si = 93: 3: 2: 2 (weight ratio) alloy powder, average major axis length = 0.12 μm, D ₁₁₀ = 155Å, coercive force = 1880 Oe, saturation magnetization = 132 emu / g] (2) 4 parts by weight of alumina (average particle size 0.3 μm and average particle size 0.5 μm were mixed in a weight ratio of 1: 1). (3) Carbon black 2 parts by weight (average particle size = 55 nm, oil absorption = 180 ml / 100 g, specific surface area = 35 m ² / g) (4) Sulfonic acid group-containing vinyl chloride-acrylic acid ester co-weight Combined 7 parts by weight (degree of polymerization = 300, sulfonic acid group concentration = 0.1 meq / g, Tg = 60 ° C) (5) 7 parts by weight of sulfonic acid group-containing polyurethane resin [terephthalic acid, isophthalic acid, ethylene glycol as soft segment MDI-based polyurethane resin, weight average molecular weight 60,000 (based on GPC in terms of polystyrene), sulfonic acid group concentration 0.1 meq / g, Tg = 25 ℃) (6) Myristic acid 1 part by weight (7) Oleic acid 0.5 part by weight (8) 2-Ethylhexyl stearate 2 parts by weight (9) Polyisocyanate 2 parts by weight [D-114N Takeda Made by Yakuhin Kogyo Co., Ltd.) (10) THF 220 parts by weight.

Among the components of the above magnetic paint, (1)-
After mixing (4) using a screw blade type powder mixer, 35 parts by weight of the blending components (5), (6), and (10) were added, and the mixture was further stirred and mixed. Next, this mixture was kneaded by a continuous twin-screw extrusion kneading device, and the rest of (10) was added to dilute. The obtained mixture was dispersed using a continuous sand mill, and then the ingredients (8) and (9) were added to the mixture so that the average pore diameter was 1
It was filtered using a μm filter, and the passing portion was used as a magnetic paint.

The magnetic coating material thus prepared was dried with a gravure roll so that the thickness after drying was 2.5 μm.
The above magnetic paint was applied on a polyethylene terephthalate (PET) film of μm, longitudinally oriented with a magnetic field strength of 5000 G, dried to form a magnetic layer, and further calendered (80 ° C.), then at 50 ° C. Aged for 24 hours.

Subsequently, the backcoat layer coating material prepared by mixing the following components in a sand mill was applied to the surface of the film opposite to the surface provided with the magnetic layer so that the dry thickness would be 0.5 μm, and thereafter, Aged at 50 ° C for 24 hours. <Coating ingredients for back coat layer> ・ Carbon black (average particle size 0.02 μm) 32 parts by weight ・ Carbon black (average particle size 0.06 μm) 8 parts by weight ・ Polyurethane resin 20 parts by weight (Nipporan 2301 manufactured by Nippon Polyurethane Co., Ltd.) ) ・ Nitrocellulose 20 parts by weight (viscosity indication by Hercules Powder CO. Is 1/2 second) ・ Polyisocyanate 4 parts by weight [Coronate HX, curing agent manufactured by Nippon Polyurethane Industry Co., Ltd.] ・ Stearic acid 1 part by weight -320 parts by weight of solvent (methyl ethyl ketone / toluene / cyclohexanone = 1/1/1, weight ratio).

As described above, the film on which the magnetic layer and the back coat layer were formed was cut into a tape having a width of 8 mm, loaded into an 8 mm cassette case, and the recording time was 8/120.
mm video cassette was made.

Comparative Examples 1 to 3 In the formulation of the magnetic coating material of Example 1, the solvent shown in Table 1 was used in place of THF as a solvent, and other conditions were the same as in Example 1 to prepare 8 mm video cassettes.

[Performance Evaluation of Magnetic Recording Medium] Example 1 above
The outputs at 7 MHz and 10 MHz of the 8 mm video cassettes obtained in Comparative Examples 1 to 3 were measured by the following method.・ Measurement method of output at 7 Hz or 10 MHz An 8 mm video cassette was mounted on a device modified from a commercially available Hi8VTR, recorded at 7 MHz or 10 MHz, and the reproduction output was measured. The numerical values in Table 1 are relative values with Comparative Example 2 as a reference (0 dB).

Further, in the above manufacturing process, the magnetic coating was applied onto the PET film, and after drying and calendering, the surface roughness (Ra), coercive force, residual magnetic flux density and squareness ratio were measured. Here, Ra (nm) is measured using an optical interference type surface roughness meter (manufactured by ZYGO). These results are also shown in Table 1.

[0041]

[Table 1]

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Claims (2)

[Claims] 1. A mean major axis length of 0.13 μm or less and a crystallite size of 1.
A magnetic paint containing a ferromagnetic metal powder mainly composed of iron having a coercive force of 1850 (Oe) or more and a saturation magnetization of 130 (emu / g) or more, a binder, and tetrahydrofuran. 2. An average major axis length of 0.13 μm or less and a crystallite size of 1.
Magnetic paint containing 60 Å or less, coercive force of 1850 (Oe) or more and saturation magnetization of 130 (emu / g) or more of iron, a binder, and a magnetic paint containing tetrahydrofuran is applied on a non-magnetic support. And forming at least one magnetic layer.