JPH06150314A - Production of magnetic recording medium and device for orientating magnetic field - Google Patents

Abstract

PURPOSE:To produce a magnetic recording medium excellent in electromagnetic transducing characteristics by preventing the disordering of orientation of magnetic powder especially after orientation treatment in a magnetic field when a magnetic recording medium is produced by coating. CONSTITUTION:A magnetic coating film is formed on the surface of a substrate by coating the surface with a magnetic coating material contg. magnetic powder while transferring the substrate and a magnetic field in a direction parallel to the surface of the magnetic coating film is applied by means of magnets 1 for orientation in a magnetic field arranged so that parts having the same polarity confront each other. An AC magnetic field in a direction perpendicular to the surface of the coating film is then applied to produce the objective magnetic recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a magnetic recording medium having excellent electromagnetic conversion characteristics, and a magnetic field orientation apparatus for the same.

[0002]

2. Description of the Related Art The mainstream of magnetic recording media is a coating type coated with a magnetic paint. The coating type magnetic recording medium is produced by coating a base material with a coating material prepared by mixing and dispersing magnetic powder in a binder, and then subjecting it to magnetic field orientation, drying and surface treatment. Of these, the magnetic field orientation step is, for example, 2
The permanent magnets are placed facing each other with the polarities facing each other with the magnetic coating applied, and a magnetic field is applied horizontally to the magnetic coating film surface to orient the easy axis of magnetization of the magnetic powder in the longitudinal direction of the substrate. Let The degree of orientation is determined by measuring the magnetic property of the magnetic recording medium by the ratio (Br / B) of the residual magnetization Br and the saturation magnetization Bm.
m = squareness ratio) and the degree of orientation in which the squareness ratio in the longitudinal direction of the tape is divided by the squareness ratio in the width direction of the tape. The larger this value, the greater the electromagnetic conversion characteristics such as sensitivity and output of the magnetic recording medium. Excellent results are obtained.

In recent years, with the increase in recording signal density, the magnetic powder used has become finer particles, higher in Hc and higher in σs. Therefore, the viscosity of the magnetic paint becomes high, and a sufficient squareness ratio cannot be obtained by the conventional magnetic field orientation method.For example, in order to enhance the effect of magnetic field orientation, it is necessary to strengthen the magnetic field generated by the homopolar opposing magnets. ing. However, if the strength of the applied magnetic field is increased for magnetic field orientation, the degree of magnetization of the applied magnetic powder also rises, and the repulsion between the magnetic powders after magnetic field orientation treatment causes a large degree of disorder in the orientation and the surface of the coating film becomes rough. However, there is a drawback that the high-frequency sensitivity becomes poor.

In order to prevent the disorder of the orientation of the magnetic powder after the orientation treatment, it is sufficient to prevent the deviation of the magnetic powder due to the repulsion between the magnetic powders until the magnetic powder is fixed after the orientation treatment, for example, by drying the magnetic paint. For example, it is conceivable to install a solenoid that covers the substrate after applying the magnetic paint and continue to apply a constant static magnetic field in the longitudinal direction until the magnetic powder is fixed.
However, such a method requires a large size of equipment and requires a large amount of electric power for operation. Therefore, it is required to develop an effective method for preventing the disorder of the orientation of the magnetic powder after the magnetic field orientation treatment.

[0005]

SUMMARY OF THE INVENTION A main object of the present invention is to provide an apparatus for preventing disturbance of the orientation of magnetic powder, especially after magnetic field orientation treatment, when manufacturing a coating type magnetic recording medium. It is to manufacture a magnetic recording medium having excellent conversion characteristics.

[0006]

Such an object is achieved by the following constitutions (1) to (9). (1) While the substrate is being transported, a magnetic coating material containing magnetic powder is applied to the surface of the substrate to form a magnetic coating film, and then a magnetic field in the horizontal direction of the magnetic coating film surface is applied by a homopolar opposing magnet for magnetic field orientation. Then, a method of manufacturing a magnetic recording medium, in which an alternating magnetic field is applied to the film surface. (2) The method for manufacturing a magnetic recording medium according to (1), wherein the applied AC magnetic field is in a direction perpendicular to the film surface. (3) The applied AC magnetic field strength is 20 to 500 G, and the value obtained by dividing the AC magnetic field strength (G) by the frequency (Hz) of the AC magnetic field is 1/2 or less (1) or (2). Manufacturing method of magnetic recording medium of. (4) The value obtained by dividing the frequency (Hz) of the AC magnetic field by the substrate transfer speed (m / min) is 1 to 20 (1) to
The method for manufacturing a magnetic recording medium according to any one of (3). (5) The AC magnetic field is applied by an AC electromagnet,
The method for manufacturing a magnetic recording medium according to any one of (2) to (4) above. (6) A magnetic field orientation apparatus for a magnetic recording medium, which has homopolar facing magnets for magnetic field orientation, which are arranged with a substrate transfer path sandwiched between them, and an AC electromagnet for applying an AC magnetic field in the subsequent stage. (7) The magnetic recording according to the above (6), wherein the applied AC magnetic field is 20 to 500 G, and the AC magnetic field strength (G) is divided by the frequency (Hz) of the AC magnetic field to have a value equal to or less than 1/2. Magnetic field orientation device for media. (8) The magnetic field orientation device for a magnetic recording medium according to (6) or (7), which has an AC electromagnet in which the applied AC magnetic field is in a direction perpendicular to the film surface. (9) The magnetic field orientation device for a magnetic recording medium according to any one of the above (6) to (8), wherein an AC electromagnet that applies the AC magnetic field is arranged to face the film surface.

[0007]

According to the present invention, an AC electromagnet for applying an AC magnetic field to the surface of the magnetic paint film is installed in the subsequent stage of the homopolar facing magnet for magnetic field orientation. The magnetic powder in the magnetic paint applied on the substrate is subjected to magnetic field orientation treatment by the homopolar opposing magnets in the wet state, but since it is also magnetized at the same time, the magnetic powders become magnetic when separated from the magnetic field for magnetic field orientation. The repulsion causes disorder of orientation. In order to prevent this, an alternating magnetic field is generated by the alternating electromagnet, and the magnetized magnetic powder is allowed to pass through this alternating magnetic field to reduce the degree of magnetization and prevent disorder of orientation. As a result, for example, in a small facility compared to the case where a solenoid or the like is used, with a small electric power, the disorder of the orientation of the magnetic powder after the magnetic field orientation treatment,
That is, it becomes possible to prevent a decrease in the squareness ratio and the degree of orientation.

[0008]

Specific Structure The specific structure of the present invention will be described in detail below.

An example of the configuration of the magnetic field orientation apparatus of the present invention is shown in FIG.
It was shown to. The method for producing a magnetic recording medium of the present invention is such that a magnetic coating material in which magnetic powder is dispersed in a binder is applied onto the base material while the base material is being transported, and then the base material 4 after the magnetic coating material has been applied,
A magnetic field in the horizontal direction of the magnetic paint film surface is applied by the homopolar facing magnet 1 for magnetic field orientation, and then 50 to 50 by the AC electromagnet 2.
An alternating magnetic field of 200 Gauss perpendicular to the surface of the magnetic paint film is applied, and further drying and surface processing are performed.

The substrate used for the magnetic recording medium of the present invention is not particularly limited, and a material selected from various flexible materials and various rigid materials according to the purpose is used in a predetermined shape and size such as a tape according to various standards. And it is sufficient. For example, examples of the flexible material include various resins such as polyester such as polyethylene terephthalate.

The magnetic coating material for the magnetic recording medium used in the present invention contains magnetic powder, a binder, and a solvent. As the magnetic powder, γ-Fe ₂ O ₃ and Co-containing γ-Fe ₂ O are used.
₃ , Fe ₃ O ₄ , Co-containing Fe ₃ O ₄ , CrO ₂ , barium ferrite, strontium ferrite and other oxide fine powder, Fe, Co, Ni and other metals or their alloy fine powder, iron carbide, etc. It can be used.

The coercive force Hc of the magnetic powder used here is usually about 300 to 2000 Oe. Also, the saturation magnetization σs
Is usually about 50 to 170 emu / g.

The magnetic powder is 75 to 90% of the total magnetic layer.
About wt% is contained.

As the binder, any known binders of various resins can be used. The solvent to be used is not particularly limited, and various solvents such as a ketone system such as cyclohexanone, methyl ethyl ketone and methyl isobutyl ketone, an aromatic system such as toluene and the like may be selected according to the purpose. The magnetic paint may contain various additives such as inorganic fine particles and lubricants, if necessary.

Such a magnetic coating material is coated on a substrate, but the coating method is not particularly limited, and is generally used such as a knife blade coating method with a doctor blade, a reverse roll coating method, a gravure roll coating method or an extrusion coating method. Any of the above methods may be used. Further, the magnetic coating film to be applied is not limited to a single layer film, and may have a multilayer film structure of two or more layers. Furthermore, a non-magnetic coating film layer, a back coat film layer,
An undercoat layer or the like for improving the adhesiveness between the substrate surface and the magnetic coating film may be provided, and it may be determined depending on the performance required for the magnetic recording medium to be manufactured, the application, and the like.

The dry film thickness of the magnetic layer thus provided is preferably about 0.15 to 5 μm. Generally, the coercive force Hc of the magnetic layer is about 300 to 2000 Oe, and the residual magnetic flux density Br is about 1200 to 4000 Gauss. However, for Hc, Br, etc., the set values are different depending on the application, It may be off. Further, the squareness ratio and the degree of orientation are preferably as high as possible, but cannot be limited because they differ depending on the magnetic material used, but generally, a squareness ratio of 0.75 or more and an orientation ratio of 1.5 or more can be obtained. . Various pretreatments can be performed before the base material 4 coated with the magnetic coating material is conveyed to the magnetic field orientation device. For example, an external magnetic field is applied so that the magnetic field is inverted several times or more, and then the base material 4 is applied onto the base material. It is also possible to perform a kind of preliminary orientation, defoaming treatment, or the like by shaking the magnetic powder, and to appropriately perform treatment such as improving the squareness ratio and reducing the porosity inside the magnetic paint film in advance.

Next, the substrate 4 after the magnetic coating is applied is shown in FIG.
The magnetic powder is conveyed between the opposite magnets 1 having the same polarity as shown in (1) and a magnetic field is applied in the horizontal direction to the surface of the magnetic paint film to orient the easy axis of magnetization of the magnetic powder in the longitudinal direction of the substrate. In this case, the orientation magnetic field strength to the magnetic paint film is about 2000 to 10000 gauss, preferably about 3000 to 8000 gauss. Orientation If the magnetic field strength is too high, the degree of orientation of the magnetic powder will increase, but since the magnetic powder in the magnetic paint will be magnetized more strongly, there will be more disorder in the orientation before the magnetic powder is fixed by drying, etc. However, the squareness ratio and the degree of orientation are reduced. On the other hand, if it is too small, the magnetic powder in the magnetic paint, which has become highly viscous as the recording signal becomes denser, cannot be oriented, and the squareness ratio and the degree of orientation are also reduced.

As the homopolar facing magnet 1 used here, any magnet such as its shape and material can be used as long as it can apply the magnetic field required in the present invention to the surface of the magnetic paint film. The magnetic field strength, the width of the substrate, the structure of the device used, and the like satisfying the requirement of 1) may be appropriately selected. Further, any configuration may be used as long as it satisfies the required magnetic field orientation performance, and it may be determined depending on the device to be used, for example, a configuration in which a plurality of homopolar opposed magnets 1 are installed in series in the support passage.

Next, the AC electromagnet 2 is arranged, for example, as shown in FIG. 1 after the magnetic field orientation step of the substrate transfer path, and the AC power is loaded by the AC electromagnet power supply 3 to generate the AC magnetic field. In this case, the relative positions of the homopolar facing magnet 1 for magnetic field orientation and the AC electromagnet 2 are within a range in which the applied magnetic paint is in a wet state and maintains fluidity, and the magnetic field of the AC electromagnet 2 and the magnetic field. It may be separated so as not to interfere with the magnetic field of the homopolar facing magnet 1 for orientation. However, it is possible to install the magnets 1 and 2 adjacent to each other by installing, for example, an appropriate magnetic shield device that cancels the interference between the magnets 1 and 2.

The direction of application of the alternating magnetic field to the magnetic paint film is preferably such that the lines of magnetic force are substantially perpendicular to the film surface, but the direction may be oblique or horizontal. However, when the AC electromagnet 2 having the structure as shown in FIG. 1 is used, the efficiency of the AC electromagnet 2 is lowered because the magnetic flux density applied to the magnetic paint film surface is lowered in the oblique direction or the horizontal direction. Therefore, the magnetic force line from the AC electromagnet 2 is ± 10 with respect to the direction perpendicular to the film surface.
It is preferable to arrange them so as to form an angle within °. Further, although the AC magnetic field is applied from the back side of the magnetic paint film surface in FIG. 1, the AC magnetic field may be applied from the magnetic paint film surface side. However, when an AC magnetic field is applied from the magnetic paint film surface, the magnetic paint film comes close to the undried magnetic paint film surface, and the magnetic paint scatters and adheres to the AC electromagnet 2.

Further, in the present invention, the AC electromagnet 2 is installed in the latter stage of the homopolar opposite magnet 1, but unlike this, when it is installed only in the front stage of the homopolar opposed magnet 1, an AC magnetic field is applied by the AC electromagnet 2. The magnetic powder in the magnetic paint film, which is magnetized at the same time as being magnetized by the homopolar opposing magnet 1 after being magnetized, causes magnetic repulsion between the magnetic powders when the magnetic powder is separated from the magnetic field of magnetic field orientation, resulting in disordered orientation. Therefore, the effect of the present invention cannot be obtained.

The strength of the AC magnetic field applied to the surface of the magnetic paint film by the AC electromagnet 2 is preferably about 20 to 500 Gauss, more preferably about 50 to 200 Gauss. Whether the magnetic field strength is larger or smaller than this range, Experimentally, the disorder of the orientation after the magnetic field orientation is recognized, and the effect of applying the alternating magnetic field by the method of the present invention decreases.

Further, in the present invention, the effect of the present invention is realized by an action similar to so-called AC degaussing. However, even if the magnetic field strength or frequency of the AC magnetic field is increased beyond a proper range, the effect does not increase, and rather, If it is too high, the disorder of the orientation is experimentally observed, which is considered to be different from the effect of the usual AC demagnetization. However, it can be said that the effect is recognized by making the magnetic field applied to each magnetic powder in the magnetic coating film stronger and stronger while reversing the polarity of the applied magnetic field, and then gradually weakening. Therefore, the inversion period of the applied AC magnetic field is represented by a frequency Hz, and the frequency of the applied AC magnetic field and the transport speed of the magnetic paint film are specified as follows. When a certain transport speed is xm / min and the frequency of the applied magnetic field is aHz, the range obtained from the value obtained by dividing the frequency range of the applied magnetic field by the transport speed, a / x, is preferably about 1 to 20. Further, it is more preferably about 2 to 10. If this value is too small, the transport speed (m / min) is too fast for the frequency (Hz), so the polarity reversal of the magnetic field applied to each magnetic powder will be small and the effect will not be obtained. To be On the other hand, if it is too large, the required frequency of the applied AC magnetic field is very high at the transport speed of the magnetic paint film within the range of maintaining normal production efficiency, which causes problems in equipment such as power supply. Therefore, both cases are not preferable.

In the present invention, the disturbance of the orientation is experimentally recognized even when the AC magnetic field strength is too high with respect to the frequency of the applied AC magnetic field. When this relationship is obtained by dividing the AC magnetic field strength (G) by the frequency of the AC magnetic field (Hz), experimentally,
It has been confirmed that the disorder of the orientation becomes particularly large when it exceeds 1/2 (G / Hz). The lower limit of this value is generally 1
It is about 0 ^-4 .

The structure and materials of the AC electromagnet 2 and the AC electromagnet power source 3 used in the present invention are not particularly limited as long as they satisfy the requirements required in the present invention, and the width of the substrate,
It may be determined based on the used frequency, generated magnetic field strength, power consumption, and the like.

[0026]

EXAMPLES Next, the present invention will be described in more detail by showing specific examples of the present invention.

<Example 1> An S-S pole facing magnet 1 and an AC electromagnet 2 were arranged as shown in FIG. The interval between the S-S pole facing magnet 1 and the AC electromagnet 2 was 1 cm. The magnetic paint film surface of the base is the upper side. The magnetic field generated by the S-S pole facing magnet 1 was 4500 gauss, and the AC electromagnet 2 was a coil wound around an iron core, which generated a magnetic field of 230 gauss per 1 A of current. Further, the AC electromagnet power source 3 is of a type that can change the current value and the frequency.

Next, a magnetic paint having the following composition was prepared, and the thickness was 1
After being coated on a polyester film having a thickness of 2 .mu.m by changing the substrate conveying speed to 50 to 200 m / min according to a conventional method, it was passed through the magnetic field orientation apparatus of the present invention. In passing, the current value and frequency were changed by adjusting the AC electromagnet power source 3. In this way, the magnetic powder is oriented in the coating direction, dried, and then calendered to give 0.3
An audio tape was obtained by cutting into 8 cm.

Magnetic coating composition amount Magnetic powder 100 parts by weight Vinyl chloride-vinyl acetate copolymer 10 parts by weight Polyurethane resin 10 parts by weight α-Al ₂ O ₃ 5 parts by weight Stearic acid 2 parts by weight Methyl ethyl ketone 80 parts by weight Methyl isobutyl ketone 80 parts by weight Part Toluene 40 parts by weight

<Comparative Example 1> An audio tape was obtained by the same manufacturing method as in Example except that the orienting device was only the S-S pole facing magnet 1.

The squareness ratio of each of the obtained tapes was measured using a vibrating sample magnetometer manufactured by Toei Industry. The squareness ratio in the table is the squareness ratio in the longitudinal direction of the tape. The degree of orientation is
It is a value obtained by dividing the squareness ratio in the longitudinal direction of the tape by the squareness ratio in the width direction of the tape. The above results are shown in Table 1.

[0032]

[Table 1]

As can be seen from Table 1, the magnetic recording medium of the present invention has better squareness ratio and better degree of orientation than Comparative Example 1 (K).

[0034]

By using the method and apparatus of the present invention, good squareness ratio and degree of orientation can be obtained. That is, in the production of the coating type magnetic recording medium, the magnetic recording medium excellent in electromagnetic conversion characteristics can be effectively prevented by using the method and apparatus of the present invention to prevent the disorder of the orientation of the magnetic powder after the orientation treatment. Can be manufactured.

[Brief description of drawings]

FIG. 1 is a front view showing the configuration of a magnetic field orientation apparatus of the present invention.

[Explanation of symbols]

 1 Opposite magnets of the same pole 2 AC electromagnet 3 AC electromagnet power supply 4 Substrate after applying magnetic paint

Claims (9)

[Claims] 1. A magnetic paint film containing magnetic powder is applied to the surface of a base material while transporting the base material to form a magnetic paint film, and a magnetic field in the horizontal direction of the magnetic paint film surface is then formed by homopolar facing magnets for magnetic field orientation. And then applying an alternating magnetic field to the film surface. 2. The method of manufacturing a magnetic recording medium according to claim 1, wherein the applied AC magnetic field is in a direction perpendicular to the film surface. 3. The applied AC magnetic field strength is 20 to 5
The value obtained by dividing the AC magnetic field strength (G) by the frequency (Hz) of the AC magnetic field is equal to or less than 1/2, which is 00G.
Manufacturing method of magnetic recording medium of. 4. The method of manufacturing a magnetic recording medium according to claim 1, wherein a value obtained by dividing the frequency (Hz) of the AC magnetic field by the substrate transfer speed (m / min) is 1 to 20. 5. The method of manufacturing a magnetic recording medium according to claim 2, wherein the AC magnetic field is applied by an AC electromagnet. 6. A magnetic field orientation apparatus for a magnetic recording medium, comprising homopolar opposing magnets for magnetic field orientation, which are arranged with a substrate transfer path sandwiched between them, and an AC electromagnet for applying an AC magnetic field in the subsequent stage. 7. The applied AC magnetic field is 20 to 500 G
7. An AC electromagnet having a value obtained by dividing the AC magnetic field strength (G) by the frequency (Hz) of the AC magnetic field is 1/2 or less.
Magnetic field orienting device for magnetic recording media. 8. The magnetic field orientation device for a magnetic recording medium according to claim 6, further comprising an AC electromagnet in which the applied AC magnetic field is in a direction perpendicular to the film surface. 9. An AC electromagnet for applying the AC magnetic field,
The magnetic field orientation device for a magnetic recording medium according to any one of claims 6 to 8, which is disposed so as to face the film surface.