JPH0419815A - Multi-frequency superposed magnetic recording system - Google Patents

Abstract

PURPOSE:To satisfactorily record and reproduce the magnetic recording signals of both short and long wave areas superposed on each other by using a 1st magnetic layer (lower layer) containing the needle-shaped ferromagnetic powder and a 2nd magnetic layer (upper layer) containing the hexagonal ferromagnetic powder to form a magnetic recording medium and at the same time specifying the thickness of the 2nd magnetic layer. CONSTITUTION:A magnetic recording medium consists of a 1st magnetic layer containing the needle-shaped ferromagnetic powder and a 2nd magnetic layer containing the hexagonal ferromagnetic powder. The thickness of the upper layer (2nd magnetic layer) is set under the magnetization penetrating thickness 1/2lambdamin which the maximum output is secured for at least a high frequency signal especially a short wave length signal lambdamin. As a result, the magnetization penetration is surely attained with the lower layer (1st magnetic layer) that is easily magnetized within a surface for a low frequency signal superposed on a high frequency signal. Thus both high and low frequency signals are obtained at high output levels.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention is a multi-frequency recording device capable of high-density recording that provides high reproduction output in a wide range of wavelength ranges from short wavelength ranges to long wavelength ranges. Related to superposition magnetic recording method.

(Prior Art) In recent years, magnetic recording media have come into widespread use as recording media for recording large amounts of information in various fields such as audio, video, and computer applications.

Therefore, in such magnetic recording, attention is being paid to a method in which a plurality of low frequency signals such as color signals and audio signals are superimposed and recorded on a high frequency signal related to brightness and darkness such as a video signal.

In such a superimposed recording method of high-frequency signals and low-frequency signals, magnetic Generally used as a recording medium. However, when formed using hexagonal ferromagnetic powder, high reproduction output can be obtained in the short wavelength region where the recording wavelength is about 1μ or less, but on the other hand, the signal in the long wavelength region is recorded by superimposing it on the short wavelength signal. In some cases, it has been found that the long wavelength signal has a characteristic that a high reproduction output cannot be obtained. For this reason, when recording and reproducing signals in a long wavelength range such as audio signals or color signals on a video signal in a short wavelength range, such as on a VTR tape, it becomes difficult to record enough information. There was a problem.

On the other hand, when it is formed using acicular ferromagnetic powder, it is good for superimposed recording and reproduction of long wavelength range signals such as audio signals and color signals, but high playback output cannot be obtained in short wavelength ranges such as video signals. The problem is that there isn't one.

One way to compensate for these drawbacks is to form two magnetic layers made of acicular ferromagnetic powder, such as metal magnetic powder or oxide magnetic powder, and use the upper layer for recording short wavelength signals such as those for video. Attempts have been made to use a magnetic recording medium whose lower layer can be used for audio and for superimposed recording and reproduction of long-wavelength signals. However, the effectiveness of this case and fault is currently not clear.

(Problems to be Solved by the Invention) The present inventors have developed a method for recording a plurality of low frequency signals by superimposing them on a high frequency signal.
A magnetic recording medium with a two-layer structure comprising a magnetic layer and a second magnetic layer mainly composed of hexagonal ferromagnetic powder is applied, and S
It was confirmed that when the thickness of the magnetic layer No. 2 was selected and set within a certain range, excellent recording and reproducing characteristics could be achieved.

Based on such findings, the present invention aims to provide a magnetic recording system that can easily and reliably achieve excellent recording and reproducing characteristics in a short wavelength region and a long wavelength region recorded superimposed thereon.

[Structure of the Invention] (Means for Solving the Problems) The magnetic recording method of the present invention is a magnetic recording method in which multi-frequency superimposed recording is performed on a magnetic recording medium via a magnetic head, wherein the magnetic recording medium is an acicular ferromagnetic material. A first magnetic layer (lower layer) formed by applying powder together with a binder component; and a second magnetic layer formed by applying hexagonal ferromagnetic powder formed on the first magnetic layer together with a binder component. (upper layer), and the thickness δ4 of the second magnetic layer is R≦δ≦λ, /2 a A 1nn (where R is the center line average roughness, λ, is the shortest recording a
It is characterized by using a magnetic recording medium within the range of 1lIn wavelength).

In addition, "center line average roughness R" is a roughness display method specified in JIS BO601, and the surface roughness is expressed on a chart using a measuring instrument with a stylus tip radius of 2 μm, and the roughness is 3 times or more of the cutoff value. If we set a center line over which the upper and lower areas are equal over the measurement length, and express the roughness curve as f (x) with this center line as the X axis, then It is expressed as

(Sakukawa) In the magnetic recording system according to the present invention, a first magnetic layer whose magnetic powder is made of acicular ferromagnetic powder and a second magnetic layer whose magnetic powder is hexagonal ferromagnetic powder are used. A magnetic recording medium having the following configuration is used.

Therefore, the thickness of the upper layer (second magnetic layer) is set to at least the magnetization penetration thickness 1/2λ to obtain the maximum output of the high frequency signal, that is, the shortest wavelength signal λ, as follows.
n, the lower layer (first magnetic layer) that can easily be magnetized in-plane ensures the magnetization penetration of the low-frequency signal superimposed on the high-frequency signal.
Therefore, high outputs can be obtained for both high-frequency signal output and low-frequency signal output. If the high frequency signal output is magnetized in the very surface or perpendicular direction, the semicircular magnetization moat that obtains the maximum output will be maintained, so high output will be maintained.

If the lower limit of δA is the center line average roughness R, there is no fear that the magnetization mode will be disturbed.

(Example) The present invention will be described in detail below. Prior to explaining specific examples, the structure of a magnetic recording medium used in the magnetic recording method according to the present invention will be explained.

In the magnetic recording medium according to the present invention, the acicular ferromagnetic powder used for forming the first magnetic recording layer may be an oxide ferromagnetic powder having an acicular structure, such as γ-Fe203 or Co-7-Fe2O3. Magnetic powder, CrO2, Do-Fe
A metal ferromagnetic powder having an acicular structure such as an alloy is exemplified. Further, the particle size of these acicular ferromagnetic powders is generally expressed by the major axis diameter, and is preferably 0.1 μm to 1 μm.

On the other hand, the hexagonal ferromagnetic powder used in the composition of the second magnetic recording layer has uniaxial anisotropy in which the axis of easy magnetization is perpendicular to the plate-like surface of the particle, and for example, the coercive force is 200
Examples include ultrafine ferrite powders of about 0e to 20,000e, such as M-type or W-type Ba ferrite, sr ferrite, ca-mitzerite, pb ferrite, solid solutions thereof, or ion-substituted products represented by the following general formula.

General formula: AO-n(re, 1M, ) 20 m(
In the formula, A is one of Ba5Sr-Ca5Pb, and H is ZnSCo, Ti5Nj, Mn5InS
Cu, Ge5Nb.

5nSZrSHfs ^(, etc., width is 0 to 2, and n is a number of 5.4 to 6.0. If it is an element, X has an average valence of 3, 2
It is a combination of more than one species of elements. ) These hexagonal ferromagnetic powders have a hexagonal plate-like crystal structure, and have an average particle size of 0.03 μm to 0.
．． A diameter in the range of 1 μm is suitable for recording and reproducing in the short wavelength range. Further, the ratio of the diagonal length of the hexagonal plate surface to the thickness, 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, acicular ferromagnetic powder and a binder are dispersed or dissolved in a solvent, and thoroughly mixed and dispersed using a ball mill, sand mill, etc. to prepare a magnetic paint.

Dispersants, lubricants, etc. may be added to this magnetic coating material as desired, and appropriate amounts of various additives such as antistatic agents such as graphite powder and carbon black may also be added.

Next, the magnetic paint is applied onto the substrate, subjected to in-plane orientation treatment, and then dried to produce a first magnetic layer.

As the binder component for producing the above-mentioned magnetic paint, it is possible to use various conventionally known binder components, such as polyurethane resin, polyester resin, polycarbonate resin, polyacrylic resin, Examples include epoxy resins, phenol resins, vinyl chloride resins, vinyl acetate resins, and mixtures or copolymers thereof. Examples of lubricants include lauric acid, palmitic acid, and stearic acid, and examples of dispersants include lecithin and various surfactants.

Preferably, the first magnetic layer is adjusted to have an internal distribution ratio of about 0.6 or more, and its thickness is about 1 μm to 5 μm. In other words, in normal superimposition recording, the recording current of the long-wavelength signal to be superimposed or the recording current of the short-wavelength signal is set to less than a fraction of the recording current, so the thickness of the first magnetic layer should normally be 1μ or more. It is enough.

Next, a second magnetic layer is formed on the first magnetic layer formed above. To form this second magnetic layer, as in the case of forming the first magnetic layer, first, hexagonal ferromagnetic powder is uniformly dispersed in the various binder components described above to prepare a magnetic paint. . The magnetic paint for the second magnetic layer contains abrasives such as TiO2, Cr203,
An inorganic powder having a Mohs hardness of 5 or more and an average particle size of about 0.1 μm to 2.0 μm, such as 0E, SIC, ZrO2, is added in an amount of 0.5 to 10 parts by weight per 100 parts by weight of the magnetic powder.

After that, the prepared magnetic coating for the second sulfur layer was applied,
It is applied onto the first magnetic layer formed above, subjected to a necessary orientation treatment, for example, a vertical orientation treatment, dried, and then the surface is smoothed by a calender treatment or the like. By this surface smoothing treatment, the abrasive particles contained in the second magnetic layer are embedded in the first magnetic recording layer, are sufficiently retained by the binder component, and are prevented from detaching.

The film thickness δ9 of the second magnetic layer is R≦δ ≦λ /2 a A IIIn (where R is the center line average roughness, λ is a
min, the shortest recording wavelength). In other words, it is necessary to maintain the short wavelength recording characteristics while not degrading the long wavelength characteristics.
A level of µ is suitable.

Additionally, a small amount of antistatic agent may be added to the second magnetic layer, but as long as the conductivity of the first magnetic layer is ensured, charging can be achieved even if almost no conductive powder is added. This makes it possible to increase the filling rate of the magnetic powder in the second magnetic layer and improve the recording and reproducing output. Note that this conductivity can also be ensured by the base.

Specific Example First, the following composition was thoroughly mixed and then dispersed for an additional hour using a sand grinder to prepare a magnetic paint for the first magnetic layer.

(Coating component for first magnetic layer) Co adhesion γ ~ Ferrite powder (coercive force He 6350
e.

Average particle size: 0.5μ) 100 parts by weight Carbon black 4 1/Lecithin 3 Polyurethane resin 12//PVC monoacetate copolymer resin 8 ・Methyl ethyl ketone
801/cyclohexane 8
0〃Toluene 801〆Next, the obtained magnetic paint for the first magnetic layer was coated to a thickness of 50 μm.
The film thickness after drying is 2.2μ on a polyester film of
After applying it in a cluster and performing an in-plane orientation treatment, it was dried to form a first magnetic layer.

Next, the following composition was thoroughly mixed and then dispersed for another 2 hours using a sand grinder to prepare a magnetic paint for a second magnetic layer.

[Magnetic paint component for second magnetic layer] Ba-ferrite powder (coercive force 620 to Ei 250e
.

Average particle size 0.05μ, plate ratio 3) 100 parts by weight Aβ203 powder 4 //(
Average particle size: 0.5 μl (1 l) Lecithin 3 // Stearic acid 2 // Polyurethane resin 8 / Vinyl mechloride-acetic acid copolymer resin g // Methyl ethyl ketone 80 / Mediclohexane 80 / l Toluene
80I/After adding 3 parts by weight of an isocyanate compound as a curing agent to the above-prepared magnetic paint for the second magnetic layer and kneading it, a film with a dry film thickness of 0.80I/3.80I/3 parts by weight was added to the above-prepared magnetic paint for the second magnetic layer and kneaded. 05μm (sample 1), 0,
12 μl (sample 2), 0.20 μm (sample 3) or 0
．． 42 μm (sample 4), and then perpendicular to the surface of the magnetic layer and dried.
A second magnetic layer was prepared by performing calendering to smooth the surface. The properties of this magnetic recording medium are shown in Table 1.
and shown in Table-2.

Comparative Example 1.2 In the magnetic paint for the first magnetic layer in the above example, Co-coated γ-ferrite powder (average particle size 0.5μ
A magnetic recording medium (Comparative Example 1) having a magnetic layer with a layer thickness of 4.3 .mu.m was produced under the same conditions except that a magnetic material with a coercive force of He 8500e was used. In addition, the layer thickness was determined under the same conditions except that Ba-ferrite powder (coercive force 6600e, average particle size 0.05 μm, plate ratio 3) was used for the magnetic paint for the second magnetic layer in the example. A magnetic recording medium (Comparative Example 2) including a 3.2 μm magnetic layer was produced. Tables 1 and 2 show the properties of these magnetic recording media.
It is also shown in .

(Leaving space below) Table 1 Table 2 Using each of the magnetic recording media with the above configurations, the superimposition recording characteristics were measured under the following conditions using a measurement system with the configuration shown schematically in Figure 1. That is, 5VHS type V
At the same running speed as the TR, V-5.8 m/sec, the color signal C (frequency 630 KHz, λ-9, 2 μm) was superimposed on the video signal Y (frequency 7 MHz, λ-0, 83 μm), and the ferrite head ( A one-loop tester evaluation was performed using an effective gap length g-0, 3 μm added, track width w=35 μm, and number of windings n-LOT). In Figure 1,
1 is a polyester film, 2 is a first magnetic layer, 3 is a second magnetic layer, 4 is a magnetic head, 5 is a recording circuit, and 6 is a reproduction circuit.

In the case of magnetic recording methods using the magnetic recording media of Samples 1 to 4 according to the present invention, all exhibited better recording/output characteristics than Comparative Example 1 in the video and color regions. In other words, high frequency and low frequency superimposed recording signals are output and S/
I was able to record and play back with high N.

FIG. 2 shows the results of the output evaluation on various magnetic recording media including the magnetic recording media of Samples 1 to 4. The video signal output (curve A)
This value is higher than that of the conventional example (Comparative Example 1) regardless of the magnetic layer thickness δH.

On the other hand, the color signal output (curve B) varies depending on the second magnetic layer thickness δ
It can be seen that there is a sharp increase from around 172 or less of the H video signal wavelength 0.83μ button. In the case of Sample 1, the video signal output (curve A) and the color signal output (curve B) either slightly decreased or maintained high outputs sufficient for practical use. The slight decrease in the output in sample 1 is due to the surface roughness approaching the second magnetic layer thickness δa, which indicates the necessity of maintaining 6M>Ra.

In addition, although the example in which the coercive force of the first magnetic layer and the second magnetic layer are approximately the same is shown above, the coercive force of the first magnetic layer is greater than the coercive force of the second magnetic layer. It may be made slightly smaller.

[Effects of the Invention] As is clear from the above embodiments, according to the multifrequency magnetic recording method according to the present invention, magnetic recording signals in which short wavelength regions and long wavelength regions are superimposed can be easily and reliably output. It is also possible to record and reproduce data at all times with a high S/N ratio. Of course, the long wavelength component to be superimposed is not limited to one type of color signal, but similar effects can be obtained for multiple frequency bands such as FM audio signals and tracking pilot signals.

Thus, it can be said that the multifrequency superimposed magnetic recording method according to the present invention brings many practical advantages.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an embodiment of the magnetic recording method according to the present invention, and FIG. 2 is a superimposition recording with respect to the thickness of the second magnetic layer (upper layer) of the magnetic recording medium used in the magnetic recording method according to the present invention. FIG. 3 is a characteristic diagram showing dependence of signal output. 1... Magnetic layer support base 2... First magnetic layer 3... Second magnetic layer 4... Magnetic head 5... Recording circuit 6 - Reproducing circuit

Claims (2)

[Claims] (1) In a multi-frequency superimposed magnetic recording method in which multi-frequency superimposed recording is performed on a magnetic recording medium via a magnetic head, a first magnetic layer ( (lower layer) and a second magnetic layer (upper layer) formed by coating hexagonal ferromagnetic powder together with a binder component on the first magnetic layer, and the thickness δ_A of the second magnetic layer is A multi-frequency superposition magnetic recording method characterized by using a magnetic recording medium within the range of R_a≦δ_A≦λ_m_i_n/2 (where R_a is center line average roughness and λ_m_i_n is the shortest recording wavelength). (2) The multi-frequency superimposed magnetic recording system according to claim 1, wherein the coercive forces of the first magnetic layer and the second magnetic layer are set to be approximately equal.