JPH08329446A - Reproducing method of video image - Google Patents

Abstract

PURPOSE: To reproduce a video image having high video S/N by forming a magnetic layer having >=1270Oe coercive force (Hc) on a nonmagnetic supporting body to produce a video tape, recording image signals in the obtd. tape, and reproducing the image signals by using a metallic magnetic head. CONSTITUTION: A preferable range of the specific surface area is 40-70m<2> /g, preferably 40-65m<2> /g and more preferably 45-65m<2> /g considering the stabilization of a ferromagnetic metal powder and the surface property of a magnetic layer. The saturation magnetization (σs) is required to be in the range of 120 to 160emu/g. The magnetic layer (magnetic recording layer) is formed by dissolving each component in an org. solvent, mixing and dispersing to prepare a coating liquid, applying the coating liquid on a nonmagnetic supporting body, and drying. Mixing and dispersing is performed by using a kneading-dispersing machine such as a ball mill, Atleiter or sand mill.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of reproducing a video image on a video tape using a ferromagnetic metal powder.

[0002]

Ferromagnetic powders that have been conventionally used in magnetic recording media include maghemite, cobalt-doped maghemite, magnetite, cobalt-doped magnetite, maghemite-magnetite beltride compounds, and cobalt-doped maghemite. There were magnetite beltride compounds, chromium dioxide and so on. However, the coercive force (Hc) of these ferromagnetic powders
The magnetic characteristics such as maximum residual magnetic flux immediate density (Br) are not sufficient for use in so-called high density recording, and signals with a short recording wavelength (about 1 μm or less) and narrow track width (about 50 μm or less) are used. It was not very suitable for magnetic recording. Recently, a ferromagnetic powder having characteristics suitable for high-density recording has been actively developed, and a ferromagnetic metal powder is one of the target materials.

The following method is known as a method for producing a ferromagnetic metal powder. (1) A method of thermally decomposing an organic acid salt of a ferromagnetic metal and reducing it with a reducing gas (Japanese Patent Publication No. 48-29280 and Japanese Patent Publication No. 47-38523). (2) A method of reducing needle-shaped oxyhydroxide or one containing these metals, or needle-shaped iron oxide obtained from these oxyhydroxides (iron oxide reduction method;
9-97738, USP 3,607,219, USP 3,702,270). (3) A method of evaporating a ferromagnetic powder in a low-pressure inert gas (low vacuum evaporation method; Japanese Patent Publication Nos. 49-15320 and 49-18160). (4) Method of thermally decomposing a metal carbonyl compound (USP
3,172,776, USP 3,200,007
Specification, USP 3,228,882 specification). (5) A method in which a ferromagnetic metal powder is electrodeposited using a mercury cathode and then separated from mercury (USP 3,156,650 specification, USP 3,262,812 specification). (6) A method of adding a reducing agent to a solution containing a metal salt having ferromagnetism to perform reduction (borohydride method; USP 3,6
69, 643 specification, USP 3,672, 867 specification, USP 3,726, 664 specification). Among these methods, from the viewpoint of characteristics and practicality,
The methods (2), (3), and (6) are general, and the iron oxide reduction method (2) can be said to be the most practical in terms of cost.

[0004]

The ferromagnetic powder has a large coercive force (Hc) and saturation magnetization (σs) as compared with a ferromagnetic substance such as conventional iron oxide and CrO _2, and is particularly high recording density medium. Expected as a magnetic material. Especially for video use, the current VHS is in the direction of downsizing the video tape recorder (VTR) so that it can be integrated with the camera.
The direction of improving the image quality and sound quality of the (registered trademark) / β system (registered trademark) is being studied. However, there are some problems when using ferromagnetic metal powders especially for high recording densities. One is that since the saturation magnetization is large, the particles are likely to aggregate in the coating solution, and it is difficult to obtain a magnetic layer having a good surface property when coated on a non-magnetic support. As a result, there is a problem in that the spacing between the head and the tape becomes large, a sufficient output cannot be obtained, and the noise becomes large, so that the S / N cannot be increased. Various methods have been proposed to solve these problems. However, it is difficult to make the characteristics of the magnetic recording medium compatible with the stability of the ferromagnetic metal powder. For example, a method of gradually oxidizing the powder surface for stabilization has been generally attempted, but when an oxide layer that ensures sufficient stability is formed, a decrease in saturation magnetization (σs) is unavoidable, S /
There arises a problem that a recording medium having a high N cannot be obtained.
The stability problem becomes more pronounced with smaller particles. Further, it is considerably stabilized by kneading with a binder to form a magnetic layer, but it is still not sufficient. A main object of the present invention is to provide a method of reproducing a video image having a high video S / N.

[0005]

As a result of various studies by the present inventor, the object of the present invention is to obtain a specific surface area of 40 to 70 m.
² / g, saturation magnetization (σs) is 120 to 160 emu /
g, and coercive force (Hc) 127 mainly composed of a ferromagnetic metal powder having a metal content of 78 to 95 wt% and a binder
It has been found that a video image reproducing method is characterized in that an image signal recorded on a video tape having a magnetic layer of 0 Oe or more provided on a non-magnetic support is reproduced by a metal magnetic head. .

In the present invention, the specific surface area of the ferromagnetic metal powder is a value obtained by a known BET method for adsorbing N ₂ gas. If its specific surface area is less than 40 m ² / g,
It is easy to obtain a magnetic material having a relatively high saturation magnetization (σs), but the surface property of the magnetic layer is limited, and a sufficient S / N can be obtained especially when a high recording density of a recording wavelength of 1 μm or less is required. Absent. When the specific surface area of the ferromagnetic metal powder exceeds 70 m ² / g, the progress of the oxidation reaction on the surface is remarkable, and even if the ferromagnetic metal powder shows a high saturation magnetization immediately after its production, the saturation magnetization within a relatively short time Deteriorates, and as a result, a high S / N video tape cannot be obtained.

That is, from the viewpoint of the stabilization of the ferromagnetic metal powder and the surface property of the magnetic layer, the inventors found out that the specific surface area has a preferable range in order to achieve the object of the present invention. . The range is 40 to 70 m ² / g
And preferably 40 to 65 m ² / g, particularly preferably 45 to 60 m ² / g. The saturation magnetization ([sigma] s) should be in the range of 120 to 160 emu / g.
If the saturation magnetization is less than 120 emu / g, the saturation magnetic flux density (Bm) of the magnetic layer of the video tape cannot be increased and the output cannot be obtained sufficiently. On the other hand, when it exceeds 160 emu / g, the aggregation of the magnetic powder (ferromagnetic metal powder) in the coating liquid during the production of the magnetic layer becomes remarkable, and it becomes difficult to obtain a magnetic layer having a smooth surface. The saturation magnetization (σs) is more preferably 125 to
150 emu / g, particularly preferably 128-145 em
u / g. Further, when the metal content is less than 78 wt%, it becomes stable, but sufficient saturation magnetization cannot be obtained, and as a result, a video tape having a magnetic layer with high output cannot be obtained. Further, when the metal content exceeds 95 wt%, it becomes unstable. The metal content is preferably 80 to 93 wt%. In the present invention, magnetic properties such as saturation magnetization (σs) and saturation magnetic flux density (Bm) are values measured by a vibrating sample type magnetometer (“VSM-III” manufactured by Toei Industry Co., Ltd.), The metal content in the ferromagnetic metal powder is a value obtained from the result of atomic absorption analysis of the solution after being dissolved in hydrochloric acid.

The ferromagnetic metal powder used in the present invention can be manufactured by any of the methods (1) to (6) described above.
From the viewpoint of practicality, the ferromagnetic metal powder produced by the iron oxide reduction method, the low vacuum evaporation method or the borohydride method is preferable, and the ferromagnetic metal powder produced by the iron oxide reduction method is particularly preferable. The particle size of the ferromagnetic metal powder is
It does not necessarily correspond to the specific surface area. That is, when synthesizing by reducing iron oxide, it is apparent that the particle size becomes porous while retaining the needle-like skeleton of the raw material iron oxide by the dehydration reaction and deoxygenation reaction in the synthetic route. It is considered that this is because the specific surface area does not necessarily correspond to the specific surface area. Further, as a condition of the ferromagnetic metal powder used in the present invention, the specific surface area is more important than the measured particle size for the characteristics such as S / N and stability of the ferromagnetic metal powder which are the objects of the present invention.
It turned out to be better correlated. The particle shape of the ferromagnetic metal powder used in the present invention is needle-like or necklace-like, and the shape layer has a high coercive force (Hc) due to the shape anisotropy.
Is preferable in order to keep

The composition of the ferromagnetic metal powder is not particularly limited and may be Fe or an alloy containing Co and Ni added thereto. In particular, when Ni containing 1 to 15% of Fe is contained, stability for the purpose of the present invention is improved, and in order to maintain Hc above a certain level, Co is more preferably contained. Therefore, as the ferromagnetic metal powder, Fe-
Co-Ni based alloy powder or Fe-Ni based alloy powder is more desirable.

In the video image reproducing method of the present invention, a metal-based head such as sendust or amorphous alloy is used as the magnetic head. That is, a ferrite head has been conventionally used as a magnetic head for reproducing a video image. However, reproduction of video images requires higher frequencies and more severe conditions than high-speed reproduction of audio signals. In addition, the requirements for the head gap and the gap between the running video tape and the magnetic head become strict. For this reason, recently developed Sendust,
The use of an amorphous alloy metal magnetic head as a video magnetic head is also under consideration. However, little research has been made on what characteristics the video tape should have when such a metal-based magnetic head is used as a magnetic head for reproducing a video image.
According to the research by the inventor of the present invention, a ferromagnetic metal powder having the above characteristics is used as a video tape used in combination with a metal magnetic head, and the magnetic layer has a coercive force of 1270 Oersted (Oe) or more. Found that is desirable. The high coercive force as described above can be easily obtained by using a ferromagnetic metal powder having a high coercive force, selecting the constituent material components of the magnetic layer, and adjusting the ratio of each component.

Next, a method of manufacturing the video tape used in the present invention will be described. A conventionally known method can be applied to a method of kneading a ferromagnetic metal powder with a binder and coating the obtained magnetic coating material on a non-magnetic support to obtain a recording medium.
The magnetic coating material contains a ferromagnetic metal powder, a binder and a coating solvent as main components, and may further contain additives such as a dispersant, a lubricant, an abrasive and an antistatic agent. Various methods can be considered for increasing the saturation magnetic flux density (Bm), but the most effective method is to adjust the amount of binder. The volume ratio of the magnetic powder to the binder is preferably 2: 1 to 1: 2. Further, in order to improve the surface property of the magnetic layer, it is important to sufficiently knead and disperse the magnetic material and the binder and to pay attention to the surface formation after coating. If the ferromagnetic metal powder satisfies the conditions of the present invention, the preferred Bm and surface properties of the magnetic layer are relatively easy to obtain.

As the binder (binder) used together with the ferromagnetic metal powder according to the present invention, a conventionally known thermoplastic resin, thermosetting resin or reactive resin, or a mixture thereof is used. For example, a cellulose resin, a polyvinyl chloride copolymer, a polyurethane resin (which may be cured with an isocyanate compound), a butadiene resin, an acrylic copolymer, an epoxy resin, or the like. These binders may be used alone or in combination, and other additives may be added. Usually, the mixing ratio with the ferromagnetic metal powder is 10 to 100 parts by weight of the ferromagnetic metal powder in a binder.
Used in the range of 50 parts by weight. As the lubricant, solid particles of various fatty acids, fatty acid esters, silicone oils, graphite, molybdenum disulfide, etc. are effective. As the abrasive, a commonly used material (particularly particles having a Mohs hardness of 6 or more is preferable), for example, fused alumina, silicon carbide, chromium oxide, corundum, artificial corundum, diamond, artificial diamond, garnet,
There are emery (main components: corundum and magnetite).

The magnetic layer (magnetic recording layer) of the video tape of the present invention is formed by dissolving the components of the above composition in an organic solvent, mixing and dispersing them to form a coating solution, and coating and drying on a nonmagnetic support. It is done by Mixing / dispersion is a ball mill,
It is carried out using a kneading disperser such as an attritor or a sand mill. The coating layer coated on the support is, if necessary, subjected to a treatment for orienting the magnetic powder in the coating layer, and then dried to obtain a target magnetic layer. If necessary, the surface is smoothed or cut into a desired shape to produce the video tape of the present invention. In particular, surface smoothing is an important technique for video tapes using ferromagnetic metal powder.

The form of the non-magnetic support is film, tape,
Any material such as a sheet may be used, and various materials are selected as necessary according to the form. In this case, it is desirable that the surface roughness of the magnetic layer as a video tape for high density magnetic recording be 0.2 μm or less. As the material of the support, polyesters such as polyethylene terephthalate, polyolefins such as polypropylene, cellulose derivatives such as cellulose triacetate and cellulose diacetate, polycarbonate, polyamide, polyimide, polyamideimide and the like are used.

In producing the video tape of the present invention, the fatty acid ester is used in an amount of 1 wt% or more of the ferromagnetic metal powder, particularly 1 to
Particles with 12 wt% and Mohs hardness of 6 or more are used as abrasives.
Addition of more than wt%, especially 1 to 10 wt% further enhances the advantage. That is, when such a composition is used, when the video tape of the present invention is run in a video tape device (VTR), scratches on the magnetic layer surface, stains on the head and guide poles, and still images are to be obtained. The defect of the magnetic layer is remarkably improved. However, if the addition amount is too large, in the case of a fatty acid ester, the running becomes rather difficult, and in the case of abrasive particles, Bm decreases and the output cannot be obtained. The upper limit of each is 12 wt%,
It is desirable to suppress it to 10 wt%. Examples of the fatty acid ester include monobasic fatty acids having 2 to 20 carbon atoms and 3 to 1 carbon atoms.
It is an ester composed of two monohydric alcohols. Butyl stearate, amyl stearate, butoxyethyl stearate and the like are particularly preferable.

The video tape of the present invention has good stability over time and has a high S / N ratio. That is, VHS
-4 MHz output obtained when a 4 MHz carrier is used in a VTR device, and 3 MHz separated by 1 MHz.
Regarding modulation noise C / N at z, compared with VHS standard tape, +8 dB or more at 4 MHz output, 3 MHz C / N
An electromagnetic conversion characteristic of +6 dB or more with N is possible. Further, according to the present invention, the dispersion stability of the particles in the dispersion liquid as the magnetic paint and the temporal stability of the magnetic characteristics of the tape are relatively good. These characteristics of the present invention largely depend on the specific surface area, σs, and metal content of the ferromagnetic metal powder, and it is important that each physical property value is within the above range.

The video image reproducing method of the present invention is characterized in that the above-mentioned video tape is used in a reproducing system using a metallic head such as sendust or amorphous alloy as a magnetic head. The combination of the metal-based magnetic head of the present invention and a video tape having specific characteristics is advantageous for reproducing a signal at a high frequency required for reproducing a video image, and also has a high C / N.

[0018]

The present invention will be described more specifically with reference to the following examples and comparative examples. In the examples and comparative examples, "part" means "part by weight". [Examples 1 to 3] α-FeOOH (goethite) was reduced in a hydrogen stream to obtain various ferromagnetic metal powders shown in Table 1 below.

Table 1 ──────────────────────────────────── Example Coercive force (Hc) Saturation magnetization (Σs) Specific surface area Metal content (Oe) (emu / g) (m ² / g) (wt%) ─────────────────────────── ─────────── 1 1480 133 33 42 84 2 1520 141 151 82 3 1420 128 68 80 ───────────────────────── ─────────────

The magnetic characteristics of the ferromagnetic metal powder and the video tape are all vibrating sample type magnetometer (Vibration Sa).
ple Magnetometer VS manufactured by Toei Kogyo
The magnetic properties of the ferromagnetic metal powder and the video tape are measured by an external magnetic field (H
m) It is a value of 5 kOe, and the specific surface area is determined by the most general BET formula and is a value measured by a counter soap manufactured by Yuasa Denko.

300 g of each of the above ferromagnetic metal powders was kneaded and dispersed in the following composition for 48 hours with a ball mill. Vinyl chloride-vinyl acetate strong polymer containing maleic acid (degree of polymerization: about 400; vinyl chloride: vinyl acetate: maleic acid = (86: 13: 1) 30 parts Polyester type polyurethane (ethylene adipate and 2,4-tolylene diene Reaction product with isocyanate; Polystyrene equivalent weight average molecular weight of about 110,000) 20 parts Palmitic acid 5 parts Butyl stearate 5 parts α-alumina 6 parts Butyl acetate 500 parts Methyl isobutyl ketone 400 parts

After the dispersion operation was completed, 25 parts of a triisocyanate compound [adduct of 3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane (trade name "Desmodur L-75", manufactured by Bayer AG)] 75 wt
% Ethyl acetate solution was added and the mixture was subjected to high speed shear dispersion for 1 hour to obtain a magnetic coating solution.

The coating solution thus obtained was coated on a polyethylene terephthalate film having a thickness of 14 μm, subjected to magnetic field orientation treatment, dried, calendered and slit into a 1/2 inch width to obtain a video tape. The dry film thickness of the magnetic layer was about 3.0 μm.

The magnetic characteristics and the video electromagnetic conversion characteristics of the video tape thus obtained are shown in Table 2 below.

Table 2 ──────────────────────────────────── Example Hc (Oe) (Gauss) Square ratio Demagnetization (%) 4MHz C / N Bm Video output (dB) (dB) ────────────────────────────── ─────── 1 1270 3300 0.76 8 + 9.0 +8.0 2 1300 3800 0.77 8 +10 +9.0 3 1310 2600 0.73 12 +8.5 +7.5 ──── ────────────────────────────────

The magnetic characteristics were measured with a vibrating sample type magnetometer VSM-III ^K manufactured by Toei Industry Co., Ltd.). Demagnetization is 60 ° C, 90% R
It was expressed by the reduction rate of Bm of the video tape when stored in H for 1 week. Video characteristics are VHS system VTR (Matsushita Electric NV "NV")
8200 "). The sendust head has a gap of 0.3 μm and a track width of 30 μm.

The standard tape is a Fuji video cassette T
-120E ^R (manufactured by Fuji Photo Film Co., Ltd.). The C / N ratio is the ratio of the noise level to the carrier signal, and is roughly correlated with the S / N ratio of the television signal. The data shown in Table 2 is the C / N ratio which is the noise level at the position of 3 MHz of the amplitude modulation signal reproduced by recording the carrier signal of 4 MHz.

Comparative Examples 1 to 4 Various ferromagnetic metal powders shown in Table 3 below were produced in the same manner as in the above examples.

Table 3 ──────────────────────────────────── Comparative example Coercive force (Hc) Saturation magnetization (Σs) Specific surface area Metal content (Oe) (emu / g) (m ² / g) (wt%) ─────────────────────────── ─────────── 1 1400 125 125 28 85 2 1380 115 138 81 3 1550 105 105 41 72 4 1600 130 71 71 78 ─────────────────── ─────────────────

Table 4 shows the characteristics of the video tapes obtained by using the above-mentioned various ferromagnetic metal powders in the same manner as in the above-mentioned examples. It can be seen that the video characteristics are lower than those of the video tapes of the examples in Table 2.

Table 4 ──────────────────────────────────── Comparative Example Hc (Oe) (Gauss) Square ratio Demagnetization (%) 4MHz C / N Bm Video output (dB) (dB) ────────────────────────────── ─────── 1 1280 2800 0.77 6 +7.5 +5.5 2 1210 2400 0.79 8 +6.0 +5.0 3 1420 2100 0.76 5 +5.5 +4.5 4 1440 290 00 0.73 9 + 7.0 + 6.0 ──────────────────────────────────────

[0032]

According to the method of reproducing a video image of the present invention, a reproducing system using a metallic head such as sendust or an amorphous alloy as a magnetic head is used, and a ferromagnetic metal powder having a specific condition is used. By using a video tape whose height is also increased, excellent reproduction of a signal at a high frequency required for reproduction of a video image (high video output in a high frequency range) is possible, and C / N is also increased.

Claims (1)

[Claims] 1. A coercive force mainly composed of a ferromagnetic metal powder having a specific surface area of 40 to 70 m ² / g, a saturation magnetization (σs) of 120 to 160 emu / g and a metal content of 78 to 95 wt% and a binder. (Hc) A method of reproducing a video image, wherein an image signal recorded on a video tape having a magnetic layer of 1270 Oe or more provided on a non-magnetic support is reproduced by a metal magnetic head.