JP2744114B2 - Multi-frequency superimposed magnetic recording method and magnetic recording medium for multi-frequency superimposed magnetic head recording - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a multi-frequency capable of high-density recording capable of obtaining a high reproduction output in a wide wavelength range from a short wavelength range to a long wavelength range. The present invention relates to a superposition magnetic recording system.

(Prior Art) In recent years, magnetic recording media have been widely used as recording media for recording a large amount of information in various fields such as audio, video, and computer fields. In such magnetic recording, attention has been paid to a method of superposing a plurality of low-frequency signals, such as color and audio, on a high-frequency signal relating to light and dark, such as video, for example, for recording.

In such a superposition recording method of a high frequency signal and a low frequency signal, for example, a magnetic material obtained by using an ultrafine hexagonal ferromagnetic powder or a needle-shaped ferromagnetic powder such as a metal magnetic powder or an oxide magnetic powder is used. Recording media are commonly used. However, when formed using hexagonal ferromagnetic powder, when a recording wavelength is about 1 μm or less, a high reproduction output can be obtained in a short wavelength range, while a signal in a long wavelength range is superimposed on a short wavelength signal for recording. , It has been found that such a long wavelength signal has a characteristic that a high reproduction output cannot be obtained. For this reason, when recording and reproducing a signal in a long wavelength range such as an audio signal or a color signal, such as a VTR tape, on a video signal in a short wavelength range, sufficient recording becomes difficult. There was a problem.

On the other hand, when formed using acicular ferromagnetic powder, it is good for superposition recording and reproduction of long wavelength band signals such as audio signals and color signals, but high reproduction output is obtained in short wavelength bands such as video signals. There is no problem.

As a means for compensating for such a defect, two magnetic layers made of acicular ferromagnetic powder such as metal magnetic powder and oxide magnetic powder are formed, and the upper layer is used for recording short wavelength signals such as for video. Attempts have been made to use a magnetic recording medium that can be used selectively for reproduction, and for the lower layer for superimposed recording and reproduction of long wavelength signals such as for audio. However, in this case, the effectiveness of the two-layer structure with respect to the recording / reproducing characteristics has not yet been clarified.

(Problems to be Solved by the Invention) The present inventors have proposed a method of superimposing a plurality of low frequency signals on a high frequency signal and recording the first magnetic layer mainly composed of the acicular ferromagnetic powder and a hexagonal magnetic layer. When a magnetic recording medium having a two-layer structure including a second magnetic layer mainly composed of crystalline ferromagnetic powder is applied and the thickness of the second magnetic layer is selected and set within a certain range, excellent results are obtained. It has been confirmed that the recording / reproducing characteristics can be achieved.

An object of the present invention is to provide a magnetic recording system capable of easily and reliably achieving excellent recording / reproducing characteristics in a short wavelength region and a long wavelength region superimposed thereon based on such knowledge.

[Structure of the Invention] (Means for Solving the Problems) The magnetic recording system of the present invention is a magnetic recording system in which multi-frequency superposition recording is performed on a magnetic recording medium via a magnetic head. A first magnetic layer (lower layer) formed by applying powder with a binder component and a second magnetic layer formed by applying hexagonal ferromagnetic powder formed on the first magnetic layer with a binder component (Upper layer), and the thickness δ of the second magnetic layer
_A is characterized by the use of a magnetic recording medium which is within the range of R _a ≦ [delta] _{A =} 0.05 to 0.2 [mu] m (wherein R _a represents a center line average roughness). Further, the magnetic recording medium for recording a multi-frequency superimposed magnetic head according to the present invention has a first magnetic layer (lower layer) formed by applying acicular ferromagnetic powder together with a binder component and a hexagonal crystal on the first magnetic layer. A second magnetic layer (upper layer) formed by applying a base ferromagnetic powder together with a binder component;
Wherein the thickness δ _A of the magnetic layer is within the range of _Ra ≦ δ _A = 0.05 to 0.2 μm (where _Ra indicates the center line average roughness).

The “center line average roughness _Ra ” is a stylus tip radius of 2 μm in the roughness display method defined in JIS B0601.
The surface roughness is represented on a chart by a measuring device of No. 3, and a center line is provided in which the upper and lower areas are equal over a measurement length 1 which is three times or more the cutoff value, and the center line is defined as an X axis, and a roughness curve is represented by f ( When represented by x), it is represented by _Ra = 1 / l1 / | f (x) | dx.

(Operation) In the magnetic recording system according to the present invention, the first magnetic layer made of magnetic powder of acicular ferromagnetic powder and the second magnetic layer made of magnetic powder of hexagonal ferromagnetic powder are used. The magnetic recording medium having the provided configuration is used. By setting the thickness of the upper layer (the second magnetic layer) to at least a high-frequency signal, which is also equal to or less than the magnetization penetration thickness λ _min / 2 for obtaining the maximum output of the shortest wavelength signal λ _min , The low-frequency signal superimposed on the magnetic layer can be surely realized in the lower layer (the first magnetic layer) that is easily magnetized in the plane, so that both high-frequency signal output and low-frequency signal output can obtain high output. If the surface of the high-frequency signal output is magnetized in the vertical direction, the semi-circular magnetization mode for obtaining the maximum output is maintained, so that the high output is maintained. Its δ lower limit of _A is no fear that the magnetization mode is disturbed if the center line average roughness R _a above.

(Example) Hereinafter, an example of the present invention will be described. Prior to the description of a specific example, the configuration of a magnetic recording medium used in the magnetic recording system according to the present invention will be described.

In the magnetic recording medium according to the present invention, examples of the acicular ferromagnetic powder used for the configuration of the first magnetic recording medium layer include acicular ferromagnetic powders such as γ-Fe ₂ O ₃ and Co-γ-Fe ₂ O _3. Examples thereof include an oxide ferromagnetic powder having a structure and a metal ferromagnetic powder having a needle-like structure such as CrO _{2 or} a Co—Fe alloy. The particle size of these acicular ferromagnetic powders is generally represented by the major axis diameter, and is 0.1 μm
１1 μm is preferred.

On the other hand, the hexagonal ferromagnetic powder used for the configuration of the second magnetic recording layer has a uniaxial anisotropy in which the axis of easy magnetization is perpendicular to the particle plate-like surface. 200O
Ultrafine powder of ferrite such as e-2000 Oe, M-type or W-type Ba ferrite, Sr ferrite, Ca ferrite, Pb ferrite or a solid solution thereof, or an ion-substituted product represented by the following general formula is exemplified. .

General formula: AOn (Fe _1-m M _m ) ₂ O ₃ (where A is any one element of Ba, Sr, Ca, and Pb,
M is Zn, Co, Ti, Ni, Mn, In, Cu, Ge, Nb, Sn, Zr, H
f represents at least one element selected from Al and the like, m represents a number of 0 to 2, and n represents a number of 5.4 to 6.0. However,
When M is a divalent or tetravalent or higher valent element,
M is a combination of two or more elements having an average valence of 3. These hexagonal ferromagnetic powders have a hexagonal plate-like crystal structure, and those having an average particle size in the range of 0.03 μm to 0.1 μm when the diagonal length of the plate surface is defined as the particle size are short. It is suitable for recording and reproduction in the wavelength range. Further, the ratio between the length and the thickness of the diagonal line of the hexagonal plate surface, that is, the plate ratio is preferably in the range of 3 to 5.

The magnetic recording medium according to the present invention is generally manufactured as follows.

First, a needle-shaped ferromagnetic powder and a binder are dispersed or dissolved in a solvent and sufficiently mixed and dispersed by a ball mill, a sand mill, or the like to prepare a magnetic paint. If necessary, a dispersant, a lubricant, and the like may be added to the magnetic paint, and various additives such as an antistatic agent such as graphite powder and carbon black may be added in an appropriate amount.

Next, after applying the magnetic coating material on the substrate, the substrate is subjected to an in-plane orientation treatment and then dried to produce a first magnetic layer.

As a binder component of the above-mentioned magnetic paint,
It is possible to use various known materials conventionally used, for example, polyurethane resins, polyester resins, polycarbonate resins, polyacrylic resins, epoxy resins, phenolic resins, vinyl chloride resins, Examples thereof include vinyl acetate resins, and mixtures or copolymers thereof. Examples of the lubricant include lauric acid, palmitic acid, and stearic acid, and examples of the dispersant include lecithin and various surfactants.

The first magnetic layer is preferably adjusted to have an in-plane orientation ratio of about 0.6 or more, and preferably has a thickness of about 1 μm to 5 μm. That is, in normal superposition recording, the recording current of the long wavelength signal to be superimposed is set to be a fraction of the recording current of the short wavelength signal, so that the first magnetic layer thickness is usually 1 μm or more. It is enough.

Next, a second magnetic layer is formed on the formed first magnetic layer. This second magnetic layer is formed by the first magnetic layer.
As in the case of the formation of the magnetic layer, first, the hexagonal ferromagnetic powder is uniformly dispersed in the above-mentioned various binder components to prepare a magnetic paint. In this second magnetic material layer magnetic paint, for example, TiO ₂ , Cr ₂ O ₃ , Al ₂ O ₃ , Si
C, and Mohs hardness of 5 or more, such as ZrO _2, average particle diameter 0.1μm~
About 2.0μm of inorganic powder to 100 parts by weight of magnetic powder
Add about 0.5 to 10 parts by weight.

Thereafter, the prepared magnetic coating material for the second magnetic material layer is applied on the formed first magnetic material layer, subjected to a required orientation treatment, for example, a vertical orientation treatment, dried, and then calendered. To smooth the surface. By this surface smoothing treatment, the abrasive particles contained in the second magnetic material layer enter into the first magnetic recording layer and are sufficiently retained by the binder component to prevent desorption.

The thickness δ _A of the second magnetic layer is selected within a range of _Ra ≦ δ _A ≦ λ _min / 2 (where _Ra is the center line average roughness and λ _min is the shortest recording wavelength). Is set. In other words, it is necessary to maintain the short-wavelength recording characteristics and not to degrade the long-wavelength characteristics, and a thickness of about 0.05 μm to 0.5 μm is generally suitable. Also, a small amount of an antistatic agent may be added to the second magnetic layer, but if the first magnetic layer has sufficient conductivity, the charge can be obtained without adding any conductive powder. This does not occur, and the filling rate of the magnetic powder in the second magnetic layer can be increased accordingly, and the recording / reproducing output can be improved. This conductivity can be ensured by the base.

Specific Example First, after sufficiently mixing the following composition, it was further dispersed for 1 hour using a sand grinder to prepare a first magnetic material layer magnetic coating material.

(Coating component for first magnetic layer) Co-coated γ-ferrite powder (Hc635Oe, average particle size
0.5 μm) 100 parts by weight carbon black 4 〃 lecithin 3 ポ リ ウ レ タ ン polyurethane resin 12 ビ vinyl chloride-vinyl acetate copolymer resin 6 メ チ ル methyl ethyl ketone 80 シ ク ロ cyclohexane 80 〃 toluene 80 〃 Then, the obtained magnetic coating material for the first magnetic layer The thickness
The film thickness after drying on a 50 μm polyester film is 2.2
It was applied to a thickness of μm, subjected to an in-plane orientation treatment, and then dried to form a first magnetic layer.

Next, after sufficiently mixing the following composition, it was further dispersed for 2 hours by using a sand grinder to prepare a second magnetic material layer magnetic coating material.

[Magnetic paint component for second magnetic layer] Ba-ferrite powder (coercivity 620 to 625 Oe, average particle size 0.05
μm, plate-like ratio 3) 100 parts by weight Al ₂ O ₃ powder (average particle size 0.5 μm) 4 〃 lecithin 3 〃 stearic acid 2 ポ リ ウ レ タ ン polyurethane resin 8 ビ ニ ル vinyl chloride-acetic acid copolymer resin 8 メ チ ル methyl ethyl ketone 80 〃 Cyclohexane 80〃Toluene 80〃 3 parts by weight of an isocyanate compound as a curing agent is added to the above-prepared magnetic coating material for the second magnetic material layer, kneaded, and then dried on the first magnetic material layer. 0.05μ thick
m (sample 1), 0.12 μm (sample 2), 0.20 μm (sample 3) or 0.42 μm (sample 4), and then dry the surface of the magnetic layer after performing the vertical processing. Then, the surface was smoothed by calendering to produce a second magnetic layer. Tables 1 and 2 show the properties of the magnetic recording medium.

Comparative Examples 1 and 2 In the first magnetic coating material for the magnetic layer in the above examples, Co-coated γ-ferrite powder (average particle size 0.5 μm,
Except for using coercive force (Hc850Oe), the layer thickness was 4.3
A magnetic recording medium provided with a μm magnetic layer (Comparative Example 1) was manufactured. In addition, except that the Ba-ferrite powder (coercive force: 660 Oe, average particle size: 0.05 μm, plate ratio: 3) was used for the second magnetic material layer magnetic paint in the example, the layer thickness was 3.2 mm. A magnetic recording medium having a μm magnetic layer (Comparative Example 2) was manufactured. The properties of these magnetic recording media are also shown in Tables 1 and 2.

Using each of the magnetic recording media having the above-described configurations, the superposition recording characteristics were measured under the following conditions using a measurement system having a configuration schematically shown in FIG. That is, at the same running speed V = 5.8 m / sec as the SVHS VTR, the video signal Y (frequency 7 MHz, λ
= 0.83μm) and color signal C (frequency 630KHz, λ = 9.2μ)
m) and a ferrite head (effective gap length g _e =
One-loop tester evaluation was performed using 0.3 μm, track width w = 35 μm, and number of windings n = 10 T). In FIG. 1, 1 is a polyester film, 2 is a first magnetic layer, 3
Denotes a second magnetic layer, 4 denotes a magnetic head, 5 denotes a recording circuit, and 6 denotes a reproducing circuit.

In the case of the magnetic recording system using the magnetic recording media of Samples 1 to 4 according to the present invention, all of them exhibited better recording / output characteristics in the video and color regions as compared with Comparative Example 1. That is, high-frequency and low-frequency superimposed recording signals are output and S /
Recording and playback were possible with a high N.

FIG. 2 shows the results of the output evaluations on various magnetic recording media including the magnetic recording media of Samples 1 to 4. The video signal output (curve A) shows a higher value than that of the conventional example (Comparative Example 1) regardless of the second magnetic layer thickness δM. On the other hand, color signal output (curve B)
Means that the second magnetic layer thickness δM is approximately equal to the video signal wavelength 0.83 μm.
It can be seen that it rises sharply from around 1/2 or less. In the case of Sample 1, the video signal output (curve A) and the color signal output (curve B) tended to decrease slightly, but maintained a sufficiently high output for practical use. The slight decrease in the output in Sample 1 is due to the surface roughness approaching the second magnetic layer thickness δM, and indicates the necessity of maintaining δM> Ra.

In the above description, an example is shown in which the first magnetic layer and the second magnetic layer have substantially the same coercive force. However, the coercive force of the first magnetic layer is made smaller than the coercive force of the second magnetic layer. It may be slightly smaller.

[Effects of the Invention] As is clear from the above embodiments, according to the multi-frequency magnetic recording system of the present invention, a magnetic recording signal in which a short wavelength region and a long wavelength region are superimposed can be output easily and reliably. In addition, recording and reproduction can be always performed in a high S / N state. Of course, the long wavelength component to be superimposed is not limited to one type of color signal, and a similar effect can be obtained in a plurality of frequency bands such as an FM audio signal and a tracking pilot signal. Thus, it can be said that the multi-frequency superimposed magnetic recording system according to the present invention provides many practical advantages.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an embodiment of a magnetic recording system according to the present invention, and FIG. 2 is an overlap recording with respect to a thickness of a second magnetic layer (upper layer) of a magnetic recording medium used in the magnetic recording system according to the present invention. FIG. 4 is a characteristic diagram illustrating the dependence of signal output. DESCRIPTION OF SYMBOLS 1 ... Magnetic layer support base 2 ... 1st magnetic layer 3 ... 2nd magnetic layer 4 ... Magnetic head 5 ... Recording circuit 6 ... Reproduction circuit

Claims (4)

(57) [Claims] 1. A multi-frequency superposition recording system for performing multi-frequency superposition recording on a magnetic recording medium via a magnetic head, wherein a first magnetic material layer formed by applying acicular ferromagnetic powder together with a binder component as the magnetic recording medium. (Lower layer) and a second magnetic layer (upper layer) formed by applying hexagonal ferromagnetic powder together with a binder component on the first magnetic layer, and a thickness of the second magnetic layer. _A multi-frequency superposition recording method using a magnetic recording medium in which δ _A is in _{a range of Ra} ≦ δ _A = 0.05 to 0.2 μm (where _Ra indicates a center line average roughness). 2. The multi-frequency superposition recording method according to claim 1, wherein the coercive forces of the first magnetic layer and the second magnetic layer are set substantially equal. 3. A first magnetic layer (lower layer) formed by applying acicular ferromagnetic powder together with a binder component, and a hexagonal ferromagnetic powder formed by applying a binder component on the first magnetic layer. made from the second magnetic layer (upper layer), and the thickness [delta] _a of the second magnetic layer, the R _a ≦ [delta] _{a =} 0.05 to 0.2 [mu] m (wherein R _a center line average roughness A magnetic recording medium for recording a multi-frequency superposed magnetic head. 4. The magnetic recording medium according to claim 3, wherein the coercive forces of the first magnetic layer and the second magnetic layer are set substantially equal.