JPH06162488A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium which simultaneously attain a lower noise and higher reproduced output and is lowered in modulation noise. CONSTITUTION:A magnetic layer having a two-layered structure is formed by successively laminating the magnetic layer of the upper layer and the magnetic layer of the lower layer on a nonmagnetic base. Magnetic metallic powder having a large specific surface area is used for the magnetic layer on the upper layer side to suppress bias noise. On the other hand, magnetic metallic powder having a small specific surface area is used for the magnetic layer on the lower layer side to adjust the residual magnetic flux density so as to increase the density. The coercive force Hc of the magnetic layer on the upper layer side is specified to 1400 to 15900e and the coercive force Hc of the magnetic layer on the lower layer side to 1050 to 1200Oe. The surface roughness Ra of the magnetic layer is specified to <=0.009mum so as to lower the modulation noise.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating type magnetic recording medium using metallic magnetic powder as magnetic powder, and more particularly to a magnetic recording medium having a two-layer magnetic layer structure.

[0002]

2. Description of the Related Art Conventionally, in the field of magnetic recording, a nonmagnetic support made of polyester, polyethylene terephthalate (PET) or the like has a main component containing magnetic oxides such as ferrite and chromium oxide, Fe, Co and Ni. A so-called coating type magnetic recording medium in which a magnetic layer is formed by coating a magnetic coating material in which powder of a magnetic alloy or the like is dispersed in a binder made of an organic polymer material is widely used.

In this coating type magnetic recording medium, when the magnetic layer is a single layer, the coercive force and the residual magnetic flux density are improved for the purpose of reducing the noise and increasing the output.
However, when the coercive force and the residual magnetic flux density are increased, the reproduction output is improved, but the bias noise is increased. Therefore, if a magnetic powder having a large specific surface area (SSA) is used to improve the bias noise, the magnetization energy of the magnetic powder is reduced, so that a sufficient residual magnetic flux density cannot be secured and the reproduction output is reduced. To do. Therefore, it is very difficult to obtain a good reproduction output while reducing noise.

To solve this problem, a method has been proposed in which the magnetic layer has a multilayer structure. For example, in a magnetic recording medium having a structure in which a first magnetic layer and a second magnetic layer are laminated on a non-magnetic support, the magnetic powder used for the first magnetic layer and the second magnetic layer is Good electromagnetic conversion characteristics can be obtained by changing the specific surface area or changing the coercive force, residual magnetic flux density, film thickness, etc. of each magnetic layer.

However, in such a magnetic recording medium,
Especially in the manufacturing process, although it is expected that the electromagnetic conversion characteristics will be slightly improved, it is extremely difficult to achieve both low noise and high output, and in order to ensure satisfactory characteristics, the magnetic powder used and each It is necessary to more strictly select the conditions of the magnetic layer.

Modulation noise, which hinders good sound quality, is also one of the problems of magnetic recording media. This modulation noise is greatly related to the surface roughness of the magnetic layer, and in order to improve it, it is required to reduce the unevenness of the magnetic layer as much as possible. In the magnetic tape currently on the market, the surface roughness Ra of this magnetic layer is 0.011.
The modulation noise of the magnetic tape is still inadequate in order to obtain a magnetic recording medium with good sound quality. Therefore, it is necessary to reduce the surface roughness by using a base film having a surface roughness superior to the conventional one and improving the dispersibility of the magnetic layer.

[0007]

Therefore, the present invention has been proposed in view of the above-mentioned conventional circumstances, and it is possible to realize low noise and high reproduction output at the same time, and to reduce modulation noise. Another object of the present invention is to provide a magnetic recording medium.

[0008]

Means for Solving the Problems As a result of intensive investigations by the present inventors, the characteristics of the magnetic layer having a two-layer structure are strictly regulated and the surface roughness of the magnetic layer is reduced. The inventors have found that a magnetic recording medium exhibiting excellent electromagnetic conversion characteristics can be obtained by controlling the magnetic field, and have completed the present invention.

That is, according to the present invention, in a magnetic recording medium comprising a non-magnetic support and a magnetic layer mainly composed of magnetic metal powder and a binder, the magnetic layer has a two-layer structure of a lower layer and an upper layer. In addition, the lower magnetic layer has a specific surface area of 33
˜40 m ² / g of metal magnetic powder, coercive force H _C of 1050 to 1200 Oe, and the upper magnetic layer contains metal magnetic powder of specific surface area of 55 to 65 m ² / g. , The coercive force H _C is 1400 to 1590 Oe, and the surface roughness Ra of the magnetic layer is 0.009.
It is characterized in that it is not more than μm.

In the magnetic recording medium of the present invention, the magnetic layer has a two-layer structure in which a first magnetic layer (lower layer) and a second magnetic layer (upper layer) are sequentially laminated on a non-magnetic support. As the metal magnetic powder used in the first magnetic layer and the second magnetic layer, any of conventionally known metal powders can be used. For example, Fe, Co, Ni and Fe-C can be used.
o, Fe-Ni, Fe-Co-Ni, Co-Ni, Fe
-Co-B, Fe-Co-Cr-B, Mn-Bi, Mn
-Al, Fe-Co-V, etc., and for the purpose of improving these various characteristics, Al, Si, Ti, Cr, Mn,
An element such as Cu, Zn, Mg or P may be added.

The specific surface area of such magnetic metal powder is 33 to 40 m ² / g in the first magnetic layer, and
The magnetic layer has a thickness of 55 to 65 m ² / g. In this way, by using the metal magnetic powder having a different specific surface area for each magnetic layer, the bias noise can be suppressed and
A large residual magnetic flux density can be obtained, and the reproduction output can be improved.

[0012] Incidentally, the coercive force H _C of the first magnetic layer which is the lower layer is a 1050～1200Oe, coercive force H _C of the second magnetic layer which is the upper layer is a 1400～1590Oe. By thus defining the coercive force of each magnetic layer, both the bias noise and the reproduction output can be satisfactorily adjusted.

In general, it is desirable that the residual magnetic flux density B _r and the squareness ratio Rs of the magnetic layer are increased in order to improve the low-range molar characteristic and the high-range molar characteristic. However, when the residual magnetic flux density B _r is too high, the bias noise is reduced. Therefore, in order to secure good bias noise while improving the low-range mole characteristic and the high-range mole characteristic, the residual magnetic flux density B _r of the first magnetic layer is 3900 to 4850.
Gauss and the residual magnetic flux density B of the second magnetic layer
It is preferable that _r is 2300 to 3100 Gauss. The squareness ratio Rs is preferably 85% or more for both magnetic layers.

If the residual magnetic flux density B _r and the squareness ratio Rs of the first magnetic layer as the lower layer and the second magnetic layer as the upper layer are out of the above ranges, the balance between the bias noise and the reproduction output is disturbed, which is good. Can not be obtained.

Further, the larger the film thickness of each magnetic layer is, the larger the reproduction output can be obtained, but the transfer characteristics and the frequency characteristics are deteriorated. Therefore, it is necessary to select the optimum value. From this, the film thickness of the lower first magnetic layer is 2.0 to
3.0 μm, the thickness of the upper second magnetic layer is 1.0 to
The thickness is preferably 2.5 μm. When the film thickness of each magnetic layer deviates from the above range, it becomes impossible to sufficiently secure both the bias noise characteristic and the reproduction output characteristic, and the transfer characteristic deteriorates.

In the present invention, the non-magnetic support used is polyethylene terephthalate (PET), polyethylene naphthalate (PEN), aramid (ST).
It may be any of F). However, the surface roughness Ra of the magnetic layer must be suppressed to 0.009 μm or less, and for that purpose, the surface roughness of the base film is naturally defined. Therefore, the surface roughness Ra of the base film is
Can be said to be preferably about 0.007 μm.

If too large, the surface roughness R of the magnetic layer is
It becomes difficult to secure a to 0.009 μm or less,
On the other hand, if it is too small, the friction coefficient becomes large and the problem of running durability tends to occur. In the present invention,
The surface roughness is represented by the center line average roughness Ra.

In the magnetic recording medium of the present invention, the magnetic metal powder is dissolved in a predetermined organic solvent together with a binder to obtain a magnetic paint. Then, by applying these magnetic paints to the surface of the non-magnetic support, the coating film is formed as a magnetic layer. As the above-mentioned binder, any binder that is usually used as a binder for a magnetic recording medium may be used, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinyl acetate-vinyl alcohol copolymer, vinyl chloride-vinyl acetate. -Maleic acid copolymer, vinyl chloride-vinyl acetate-acrylic acid copolymer, vinyl chloride-vinyl acetate-maleic acid-acrylic acid copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer , Ethylene-vinyl acetate copolymer, cellulose derivatives such as nitrocellulose resin, acrylic resin, polyvinyl acetal resin, polyvinyl butyral resin, epoxy resin, phenoxy resin, polyurethane resin, polycarbonate polyurethane resin and the like can all be used.

If desired, a dispersant, a lubricant, an antistatic agent, an anticorrosive agent, etc. may be added to the magnetic paint. As the dispersant, the lubricant, the antistatic agent, the rust preventive and the former non-magnetic support, any conventionally known materials can be used, and the materials are not limited at all.

[0020]

In general, the low-range molar characteristic, which is an index of the reproduction output in the long wavelength range, is expressed by the following formula.

[0021]

[Equation 1]

As shown in the above equation (1), in order to improve the reproduction output in the long wavelength region, it is necessary to increase the residual magnetic flux density B _r and decrease the coercive force H _C. On the other hand, the high-range molar characteristic, which is an index of the reproduction output in the short wavelength range, is
It is expressed by the following formula.

[0023]

[Equation 2]

From the above equation (2), it is understood that the residual magnetic flux density B _r and the coercive force H _C may be increased in order to improve the reproduction output in the short wavelength region. From this, in order to obtain a magnetic recording medium having an excellent dynamic range, it is rational to make the magnetic layer have a two-layer structure.

Therefore, in the lower first magnetic layer, a metal magnetic powder having a small specific surface area and excellent dispersibility is used in order to improve the molar characteristics from the long wavelength region to the medium wavelength region. As a result, the residual magnetic flux density B _r becomes large and a good reproduction output can be obtained. At the same time, by setting the coercive force H _C of the first magnetic layer to be smaller than that of the second magnetic layer, the reproduction output from the long wavelength region to the medium wavelength region is improved and the bias noise is reduced. It can be suppressed.

The noise characteristic is expressed by the following equation.

[0027]

[Equation 3]

As shown in the above equation (3), good noise characteristics
In order to increase the number of magnetic powders filled in the magnetic layer.
Therefore, it is sufficient to add fine metal magnetic powder, that is, a comparison table.
It is required to use metal magnetic powder having a large area.
Therefore, the second magnetic layer has a large specific surface area.
Good noise characteristics can be obtained by using metal magnetic powder.
can get. Also, the coercive force H of the second magnetic layer _CIs the first
By setting it larger than that of the magnetic layer of
The reproduction output in the wavelength range is improved.

By thus laminating the first magnetic layer and the second magnetic layer having different characteristics, the noise characteristic and the reproduction output characteristic are simultaneously improved.

Furthermore, in the present invention, the range of the surface roughness Ra of the magnetic layer is defined and the unevenness of the magnetic layer is eliminated, whereby the spacing loss can be suppressed and the modulation noise can be reduced.

[0031]

EXAMPLES The present invention will be described below based on specific experimental results. First, two types of magnetic paints A and B were prepared according to the following basic composition.

Composition of Magnetic Paint A Metal magnetic powder 105 parts by weight Vinyl chloride-vinyl acetate copolymer 9 parts by weight Thermoplastic polyester / polyurethane resin 6 parts by weight Stearic acid 1.2 parts by weight Myristic acid 0.3 parts by weight

Methyl ethyl ketone, toluene and cyclohexanone were used as the solvent, and the above materials were kneaded with a kneader, and then sand mill mixed. The final solid content was set to 36%. Finally, as a curing agent, Nippon Polyurethane Co., Ltd. trade name Coronate L-
3 parts by weight of 50EBT was added to obtain a magnetic paint A.

Composition of Magnetic Paint B Metal magnetic powder 102 parts by weight Polyester / polyurethane resin 17 parts by weight Silane coupling agent (trade name A-1100 gamma, aminopropyl, triethoxy, silane) 2 parts by weight Carbon 1 part by weight Alumina 3 0.5 parts by weight Cr ₂ O ₃ 1 part by weight Stearic acid ester 1.2 parts by weight Myristic acid 0.3 parts by weight

Methyl ethyl ketone, toluene and cyclohexanone were used as a solvent, and the above materials were kneaded with a kneader, and then sand mill mixed. The final solid content was set to 36%. Finally, as a curing agent, Nippon Polyurethane Co., Ltd. trade name Coronate L-
Add 1.7 parts by weight of 50EBT, and add this to magnetic paint B.
And

Then, the magnetic coating material A was applied to one surface of the nonmagnetic support having a thickness of 11.7 μm and calendering was performed. Then, it preserve | saved at 60 degreeC for 20 hours, and produced the 1st magnetic layer. Subsequently, the magnetic coating material B was applied onto the first magnetic layer and calendered to prepare a second magnetic layer.

After that, a 1/8 inch width was cut to prepare a magnetic tape. The surface roughness Ra of the non-magnetic support is 0.02517 μm, and the magnetic field orientation treatment is 4
It was performed in a magnetic field of kOe.

Experiment 1 First, regarding the magnetic tape obtained as described above,
The relationship between the specific surface area of the metal magnetic powder used and the electromagnetic conversion characteristics of the produced magnetic tape was investigated. The specific surface area of the metal magnetic powder used for the second magnetic layer is 56.4 m ² / g, and the specific surface area of the metal magnetic powder used for the first magnetic layer is 30 to
The noise characteristics, the low-range molar characteristics, the transfer characteristics, and the erasing characteristics of the sample tapes manufactured by changing the range of 50 m ² / g were examined.

The results are shown in FIGS. 1 and 2. In these magnetic tapes, the thickness of the first magnetic layer is 2 μm.
m, and the film thickness of the second magnetic layer is 2 μm. FIG. 1 shows the relationship between the specific surface area of the metallic magnetic powder used for the first magnetic layer and the noise characteristics and low-range molar characteristics, and FIG. 2 shows the specific surface area of the metallic magnetic powder and the transfer characteristics and erasing characteristics. Represents the relationship.

From FIG. 1, it was found that when the specific surface area of the metal magnetic powder used for the first magnetic layer was 35 to 47 m ² / g, the bias noise had a substantially constant value and was sufficiently suppressed. Further, the low-range molar characteristics became better as the specific surface area of the metal magnetic powder was smaller. Therefore, the reproduction output in the low wavelength region can be improved as the specific surface area of the metal magnetic powder is reduced and the residual magnetic flux density is increased.

The transfer characteristic is desired to be 52 dB or more, but as shown in FIG. 2, the specific surface area is 35 m ² /
It was found that good transfer characteristics were exhibited when a metal magnetic powder of g or less was used. Further, the erasing property is desired to be 65 dB or more, and therefore, in the range of 30 to 50 m ² / g, satisfactory results were obtained. From these results, it was found that good characteristics were obtained when the specific surface area of the metal magnetic powder used in the first magnetic layer was around 35 m ² / g.

Therefore, by using the metal magnetic powder having a specific surface area of 35 m ² / g for the first magnetic layer, the relationship between the specific surface area of the metal magnetic powder used for the second magnetic layer and the above-mentioned characteristics is shown. Examined. The results are shown in FIGS. 3 and 4. FIG. 3 shows the second
4 shows the relationship between the specific surface area of the metal magnetic powder used for the magnetic layer, the noise characteristic and the low range molar characteristic, and FIG. 4 shows the relationship between the specific surface area of the metal magnetic powder and the transfer characteristic and the erasing characteristic.

From FIG. 3, in the range where the specific surface area of the metal magnetic powder used for the second magnetic layer exceeds 56 m ² / g, the bias noise did not change so much and good characteristics were obtained. Further, the low-range molar characteristic is that the smaller the specific surface area of the metal magnetic powder, that is, the larger the residual magnetic flux density,
It turned out to improve.

Further, from FIG. 4, it is preferable that the specific surface area is at least 56 m ² / g or less in order to obtain the transfer characteristic of 52 dB or more. Further, regarding the erasing property, satisfactory results were obtained when the specific surface area was 65 m ² / g or less.
From these results, it is judged that the best characteristics are obtained when the specific surface area of the metal magnetic powder used for the second magnetic layer is 56 m ² / g.

Experiment 2 Next, the electromagnetic conversion characteristics of the magnetic tape prepared by changing the base film used were examined. Here, as the material of the magnetic tape, a coercive force Hc1180Oe and a metal magnetic powder having a specific surface area of 35 m ² / g are used for the lower layer, and the coercive force H
A metal magnetic powder having c1426Oe and a specific surface area of 56.4 m ² / g was used for the upper layer. Table 1 shows the magnetic characteristics of the first magnetic layer (lower layer) formed of this material, the magnetic characteristics of the second magnetic layer (upper layer), and the magnetic characteristics of the two-layer magnetic tape. .

[0046]

[Table 1]

Then, the sample tape of Comparative Example 1 in which the two magnetic layers having the above-mentioned magnetic characteristics are formed on the conventional base film having the surface roughness Ra of 0.02517, or the surface roughness Ra is 0. The sample tape of Example 1 in which the two magnetic layers having the above-mentioned magnetic characteristics were formed on the base film of 0.00735 was prepared, and the electromagnetic conversion characteristics were compared. The results are shown in Table 2.

[0048]

[Table 2]

From this, it is understood that the magnetic tape using the base film having good surface roughness is inferior in bias noise, but is superior in high-range sensitivity output and high-range molar characteristic. Regarding the modulation noise, the total component is improved by 30.3%, and the AM component is 29.3%.
It turned out to have been improved.

Comparing the total components of the modulation noise with the output at a position 2 kHz away from the original signal, the output of the tape of Example 1 is -69 dB and the output of the tape of Comparative Example 1 is -60 dB. Magnetic tape with good roughness is 9
It became lower by dB.

The electromagnetic conversion characteristics shown in Table 2 are shown as relative values with respect to a conventionally commercially available metal master (manufactured by Sony Corporation, trade name CS-421) as a reference tape. It is a thing.

Here, in order to compare the difference in sound quality between the above-mentioned two magnetic tapes, the same music was recorded on both tapes, played back and compared. As a result, the magnetic tape using the base film having a good surface roughness was evaluated to be superior, such as "the sound is clear and the band extends and feels wide".

From these results, it was found that the tape using the base film having a good surface roughness is superior in the high frequency characteristic and the modulation noise characteristic is also greatly improved, so that the sound quality of the tape is also improved.

Experiment 3 Next, proper coercive forces of the first magnetic layer and the second magnetic layer were examined. Base film with good surface roughness (Ra = 0.00
735) and the specific surface area of the first magnetic layer is 56 m.
² / g of metal magnetic powder was used, and the second magnetic layer was made of metal magnetic powder having a specific surface area of 35 m ² / g.

The magnetic tape used here was prepared in the same manner as the above-mentioned magnetic tape except that the magnitude of the orientation magnetic field was changed to 10 kOe after the magnetic coating material was applied. The first
The magnetic layer of was prepared to have a thickness of 2.5 μm, and the second magnetic layer was prepared to have a thickness of 2.0 μm.

Electromagnetic conversion characteristics were investigated when the coercive force Hc of the first magnetic layer (lower layer) was kept constant and the coercive force Hc of the second magnetic layer (upper layer) was varied. FIGS. 5 to 8 show changes in the low-range molar characteristic, high-range molar characteristic, erasing characteristic, and transfer characteristic with respect to the upper layer coercive force when the coercive force of the lower layer is 1020 Oe, respectively. It is a thing.

From the figure, satisfactory results were obtained for all of the low-range molar characteristics required to be 0 dB or more. Similarly, it is desired that the high-range molar characteristics be 0 dB or more, but in order to satisfy this, the coercive force H of the upper layer is required.
It can be seen that c must be 1510 Oe or more. The erasing property is desired to be 65 dB or more, and therefore satisfactory results are obtained in the entire range.
On the other hand, the transfer characteristic is desired to be 52 dB or more, and it is understood that the coercive force Hc of the upper layer is required to be 1555 Oe or more for this purpose.

9 to 12 show the coercive force of the lower layer of 1055.
When Oe is set, the change in each of the above characteristics with respect to the coercive force of the upper layer is shown. From the figure, satisfactory results were obtained in all of the low-range molar characteristic, the high-range molar characteristic, and the erasing characteristic. Regarding the transfer characteristics, it can be seen that the coercive force Hc of the upper layer must be 1485 Oe or more in order to achieve 52 dB or more.

13 to 16 show that the coercive force of the lower layer is 109.
At 6 Oe, the change in each of the above characteristics with respect to the coercive force of the upper layer is shown. From the figure, satisfactory results were obtained in all of the low-range molar characteristic, the high-range molar characteristic, and the erasing characteristic. Regarding the transfer characteristics, it can be seen that the coercive force Hc of the upper layer must be 1555 Oe or more in order to achieve 52 dB or more.

17 to 20, the lower layer has a coercive force of 112.
At 4 Oe, the change in each of the above characteristics with respect to the coercive force of the upper layer is shown. From the figure, satisfactory results were obtained in all of the low-range molar characteristic, the high-range molar characteristic, and the erasing characteristic. Regarding the transfer characteristics, it can be seen that the coercive force Hc of the upper layer must be 1450 Oe or more in order to achieve 52 dB or more.

21 to 24, the coercive force of the lower layer is 115
At 0 Oe, the change in each of the above characteristics with respect to the coercive force of the upper layer is shown. From the figure, satisfactory results were obtained in all of the low-range molar characteristic, the high-range molar characteristic, the erasing characteristic, and the transfer characteristic.

25 to 28, the coercive force of the lower layer is 119.
At 5 Oe, the change in each of the above characteristics with respect to the coercive force of the upper layer is shown. From the figure, satisfactory results were obtained in all of the low-range molar characteristic, the high-range molar characteristic, the erasing characteristic, and the transfer characteristic.

From the above results, the coercive force H of the first magnetic layer
It was found that satisfactory results can be obtained by setting c in the range of 1055 to 1195 Oe.

Experiment 4 Experiment 1 showed that the electromagnetic conversion characteristics of the magnetic tape using the base film having a good surface roughness were significantly improved. Here, the change of the modulation noise with the surface roughness was investigated. It was The coercive force Hc of the first magnetic layer is 1124 O
e, the coercive force Hc of the second magnetic layer was 1500 Oe, and the magnetic tape was produced in the same manner as described above except that polyethylene terephthalate having a surface roughness Ra of 0.00735 μm was used as the base film.

However, in order to control the surface roughness of the magnetic layer, the mixing time by a sand mill, which is a mixer for magnetic paint, is usually 3.5 hours, but 1.0-
It adjusted in the range of 7.0 hours. Also, regarding the calendering temperature, the temperature which is usually 100 ° C. is 60 ° C.
The temperature was adjusted in the range of 100 ° C.

The surface roughness Ra and the modulation noise (total component, AM component) of the magnetic tape manufactured as described above were measured, and the results are shown in FIGS. Surface roughness R
a is a surface roughness meter manufactured by Kosaka Laboratory, trade name SE-3O
Using H 2, the magnification was 50,000 times, the measurement length was 2 mm, and the cutoff value was 0.8 mm.

As a result, as the surface roughness deteriorates,
It was found that both the total component of the modulation noise and the AM component were deteriorated. Since the total component of modulation noise is 4300 or less and the AM component is 3400 or less,
It was found that the surface roughness Ra of the magnetic layer needs to be set to 0.009 μm or less in order to satisfy these requirements.

Experiment 5 Based on the above experimental results, a magnetic tape was produced under appropriate conditions, and its magnetic characteristics and electromagnetic conversion characteristics were investigated. Metal magnetic powders having the coercive force and specific surface area shown in Table 3 were used for the first magnetic layer and the second magnetic layer, and the magnetic characteristics of the magnetic layers using the same are also shown in Table 3.

[0069]

[Table 3]

The magnetic characteristics and electromagnetic conversion characteristics of the sample tape of Example 2 having the magnetic layer having the above characteristics are as shown in Table 4. A metal master (manufactured by Sony Corporation, trade name CS-421) was used as Comparative Example 2, and each output characteristic was shown as a relative value based on this.

[0071]

[Table 4]

From this, it can be seen that in the sample tape of Example 2 to which the present invention was applied, good reproduction output characteristics were obtained and the modulation noise was suppressed to an extremely small level. In particular, in terms of electromagnetic conversion characteristics, the low-range molar characteristics are improved by +1.4 dB, and the high-range molar characteristics are also improved by +1.4 dB as compared with the tape of Comparative Example 2 which has been commercially available. . The bias noise is suppressed to a value of -0.1 dB even though a base film having a low surface roughness is used.

The modulation noise characteristics are improved by 32.3% for the total component and 44.5% for the AM component. The total component of modulation noise is 2 kHz from the original signal
Comparing the outputs at the positions apart from each other by z, the output of the sample tape of Example 2 to which the present invention was applied is -69 dB, which is improved by 10 dB from the value of -59 dB of Comparative Example 2 (Table In the column of "Output" in the modulation noise characteristics.).

[0074]

As is apparent from the above description, in the present invention, since the magnetic layer has a two-layer structure and the coercive force H _C of each magnetic layer is set separately, it is considered as the lower layer. It is possible to secure good high range molar characteristics in the upper second magnetic layer while improving the low range molar characteristics in the first magnetic layer.

Further, since the magnetic metal powder having a large specific surface area is used in the second magnetic layer, the noise characteristic is not largely deteriorated even though the base film having a small surface roughness is used. In addition, since the magnetic layer has a good surface roughness, it has excellent modulation noise characteristics. As a result, by applying the present invention, it is possible to provide a magnetic recording medium having excellent electromagnetic conversion characteristics and good tape sound quality.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a specific surface area of a metal magnetic powder used for a first magnetic layer, a noise characteristic, and a low range molar characteristic.

FIG. 2 is a characteristic diagram showing the relationship between the specific surface area of the metal magnetic powder used in the first magnetic layer and the transfer characteristics and erasing characteristics.

FIG. 3 is a characteristic diagram showing the relationship between the specific surface area of the metallic magnetic powder used in the second magnetic layer and the noise characteristics and low-range molar characteristics.

FIG. 4 is a characteristic diagram showing a relationship between a specific surface area of a metal magnetic powder used for a second magnetic layer and transfer characteristics and erasing characteristics.

FIG. 5 is a characteristic diagram showing a relationship between coercive force and low range molar characteristics.

FIG. 6 is a characteristic diagram showing a relationship between coercive force and high-range molar characteristic.

FIG. 7 is a characteristic diagram showing a relationship between coercive force and erasing characteristics.

FIG. 8 is a characteristic diagram showing a relationship between coercive force and transfer characteristics.

FIG. 9 is a characteristic diagram showing the relationship between coercive force and low range molar characteristics.

FIG. 10 is a characteristic diagram showing a relationship between coercive force and high range molar characteristics.

FIG. 11 is a characteristic diagram showing the relationship between coercive force and erasing characteristics.

FIG. 12 is a characteristic diagram showing the relationship between coercive force and transfer characteristics.

FIG. 13 is a characteristic diagram showing a relationship between a coercive force and a low range molar characteristic.

FIG. 14 is a characteristic diagram showing a relationship between coercive force and high-range molar characteristic.

FIG. 15 is a characteristic diagram showing the relationship between coercive force and erasing characteristics.

FIG. 16 is a characteristic diagram showing the relationship between coercive force and transfer characteristics.

FIG. 17 is a characteristic diagram showing the relationship between coercive force and low range molar characteristics.

FIG. 18 is a characteristic diagram showing a relationship between coercive force and high-range molar characteristic.

FIG. 19 is a characteristic diagram showing the relationship between coercive force and erasing characteristics.

FIG. 20 is a characteristic diagram showing the relationship between coercive force and transfer characteristics.

FIG. 21 is a characteristic diagram showing the relationship between coercive force and low range molar characteristics.

FIG. 22 is a characteristic diagram showing a relationship between coercive force and high range molar characteristics.

FIG. 23 is a characteristic diagram showing the relationship between coercive force and erasing characteristics.

FIG. 24 is a characteristic diagram showing the relationship between coercive force and transfer characteristics.

FIG. 25 is a characteristic diagram showing the relationship between coercive force and low-range molar characteristics.

FIG. 26 is a characteristic diagram showing the relationship between coercive force and high-range molar characteristic.

FIG. 27 is a characteristic diagram showing a relationship between coercive force and erasing characteristics.

FIG. 28 is a characteristic diagram showing the relationship between coercive force and transfer characteristics.

FIG. 29 is a characteristic diagram showing the relationship between the surface roughness and the total component of modulated noise.

FIG. 30 is a characteristic diagram showing the relationship between the surface roughness and the modulation noise AM component.

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Miyoko Ujiie 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation

Claims (1)

[Claims] 1. A magnetic recording medium comprising a non-magnetic support and a magnetic layer mainly composed of metallic magnetic powder and a binder, wherein the magnetic layer has a two-layer structure including a lower layer and an upper layer. The lower magnetic layer contains metal magnetic powder having a specific surface area of 33 to 40 m ² / g and has a coercive force H _C of 1050 to 50
1,200 Oe, the upper magnetic layer contains a metal magnetic powder having a specific surface area of 55 to 65 m ² / g, and has a coercive force H _C of 1400 to
The magnetic recording medium is characterized in that the magnetic layer has a surface roughness Ra of 0.009 μm or less.