JPS6341134B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic field orientation device used in manufacturing perpendicular magnetic recording media, and particularly to a magnetic field orientation device for manufacturing perpendicular magnetic recording media that is capable of manufacturing recording media with a high orientation rate and a smooth surface. Regarding. Magnetic recording generally relies on a method that uses magnetization in the in-plane longitudinal direction of a recording medium. However, in a recording method that uses magnetization in the in-plane longitudinal direction,
If an attempt is made to increase the recording density, the demagnetizing field within the recording medium will increase, so the recording density cannot be improved that much. Therefore, in order to eliminate such problems,
In recent years, perpendicular magnetic recording methods have been proposed that use magnetization in a direction perpendicular to the surface of a recording medium. In this perpendicular magnetic recording method, the demagnetizing field in the recording medium decreases as the recording density increases, so it can be said to be a recording method essentially suitable for high-density recording. However, in order to employ such a perpendicular magnetic recording method, a magnetic recording medium having an axis of easy magnetization in a direction perpendicular to the surface is required. Conventionally, as a recording medium that satisfies these demands, the recording film was made of Co-Cr.
There have been proposed methods in which the recording film is formed from a sputtered film and a recording film formed from a coating layer of magnetic fine particles. By the way, in the case where the recording film is formed of a coating layer of magnetic fine particles, the following manufacturing method can be considered. That is, as magnetic fine particles, for example
A hexagonal ferrite such as BaFe ₁₂ O ₁₉ is used. The reason for using hexagonal ferrite is that this ferrite has a flat plate shape and the axis of easy magnetization is perpendicular to the plate surface, so it can be easily vertically aligned by magnetic field alignment treatment or mechanical treatment. It is. After mixing such magnetic fine particles of hexagonal ferrite and a binder and coating the mixture on the surface of a non-magnetic tape, this coated layer is placed in a magnetic field so that the surface is perpendicular to the direction of the magnetic field. By arranging the easy axis of magnetization of each magnetic fine particle to match the direction of the magnetic field, and then drying the paint, a recording medium suitable for perpendicular magnetic recording can be obtained. However, when manufacturing a perpendicular magnetic recording medium by the above-mentioned so-called coating method, the following points need to be taken into consideration. In other words, in order to clarify the advantages of perpendicular magnetic recording compared to conventional longitudinal magnetic recording, it is necessary to make the minimum recording unit on the order of submicrons. It is necessary to use it. Such small-sized magnetic particles have a single domain structure,
In other words, since they become minute magnets, they are easily magnetically coupled to each other. Therefore, care must be taken to ensure uniform distribution within the binder. Furthermore, even if a desired magnetic paint with uniform dispersion is obtained, the following phenomenon may occur when such a magnetic paint is applied onto a substrate and vertically aligned using a magnetic field orientator. It often happens. In other words, when a substrate coated with magnetic paint is placed between the magnetic poles of a magnetic field orientator with NS poles facing each other, and its surface is placed perpendicular to the magnetic field, the axis of easy magnetization of the magnetic fine particles in the paint coincides with the direction of the magnetic field. Rotate and orient as shown. After oriented in this way, when the application of the magnetic field is stopped or the substrate is taken out of the magnetic field, the magnetic poles remaining on both sides of the coating cause the magnetic field to move in the opposite direction to the direction of the magnetic field of the above-mentioned orienting magnetic field. A magnetic field is generated, and the magnetic fine particles forming an angle with the direction of the magnetic field of this demagnetizing field are subjected to a torque in the in-plane direction, and as a result, the vertical orientation obtained by the magnetic field orientator is significantly inhibited.
The recording characteristics of perpendicular magnetic recording media are closely related to the ratio (orientation rate) in which the easy magnetization axes of the magnetic particles in the coating are perpendicular to the substrate surface; the higher the orientation rate, the higher the reproduction rate. This enables output and high-density recording. Therefore, it is necessary to take some means to prevent the orientation ratio from decreasing due to the demagnetizing field. In addition, the orientation rate is also affected by the angle between the orientation magnetic field and the surface of the substrate.In order to vertically align magnetic fine particles with a high orientation rate, the angle of the substrate surface to the magnetic field direction must be adjusted.
It is necessary to set it within the range of 90°±15°. This not only requires some means to strictly control the inclination angle of the substrate placed in the magnetic field, but also requires some means to prevent the substrate placed in the magnetic field from bending, twisting, etc.
It is necessary to prevent vibration. Furthermore, depending on the viscosity or composition of the paint, it takes several milliseconds to several hundred milliseconds for the magnetic fine particles to rotate in a magnetic field and complete their orientation. If the above-mentioned perpendicular magnetic field continues to be applied, magnetic fine particles will magnetically aggregate, resulting in unevenness on the coating surface. In this way, when unevenness occurs, recording density characteristics and reproduction output characteristics are impaired even when the orientation rate is high. Therefore, it is necessary to prevent the occurrence of magnetic aggregation by some means. For this reason, during the alignment process,
The reality is that there is a strong desire for a magnetic field orientation device that can provide a high orientation rate and smooth the coating surface. The present invention has been made in view of these circumstances, and its purpose is to provide a magnetic field orientation apparatus for manufacturing perpendicular magnetic recording media that can satisfy all of the above-mentioned demands. Hereinafter, details of the present invention will be explained with reference to illustrated embodiments. In FIG. 1, reference numeral 1 is an orientation magnet, and this magnet 1 has a magnetic core 2 formed in such a shape that both end faces face each other with a predetermined interval, and a winding around the outer periphery of the magnetic core 2. The solenoids 3a and 3b are connected to a DC power source (not shown) so that the directions of the generated magnetic fields are the same. In the vicinity of the magnet 1, a tape-shaped base 5 made of a non-magnetic material whose upper surface is covered with an undried coating layer 4 containing magnetic fine particles is placed on the magnetic pole face 2a of the magnetic core 2,
A running mechanism including a pinch roller 7, a capstan 8, a guide roller 9, etc., is provided to run between the rollers 2b and 2b at a constant speed and under constant tension in the direction indicated by an arrow 6 in the figure. Four guide rollers 10a, 10b, 10c, and 10d are rotatably provided along the traveling path of the tape-shaped substrate 5 and on both sides of the magnetic core 2.
10b, 10c, and 10d, a portion of which is in close contact with the lower surface of the tape-shaped substrate 5 passing between the magnetic pole faces 2a and 2b, and directs the surface of the tape-shaped substrate 5 located within the magnetic field in the direction of the magnetic field. An endless belt 11 is stretched so as to be orthogonal to the position of the belt. The rotating shaft of the guide roller 10b is connected to a rotational drive device 12, and the portion of the endless belt 11 that is in contact with the tape-shaped base 5 receives rotational force from the rotational drive device 12 in the direction of the strike of the base. It is arranged to move cyclically in the same direction as the base body and in a state where the relative speed difference between the base body and the base body is almost zero. Further, electric heaters 13a and 13 are provided between each of the magnetic pole surfaces 2a and 2b and a portion of the endless belt 11 that crosses between the magnetic pole surfaces 2a and 2b.
b are arranged along the running direction of the belt. Similarly, the guide roller 10b and the pinch roller 7
Electric heaters 14a and 14b are also disposed between them in a non-contact manner to sandwich the base body traveling in this section. And the electric heaters 13a, 13b
The amount of heat generated by the coating layer 4 is determined by the amount of heat generated by the coating layer 4 moving between the magnetic pole surfaces 2a and 2b until the coating layer 4 finishes passing through the gap.
The value is set to such a value that the coating layer 4 can be dried to a viscosity at which the magnetic fine particles therein cannot be rotated again. On the other hand, the amount of heat generated by the electric heaters 14a and 14b is set to a value that allows the coating layer 4 to be completely dried before the coating layer 4 finishes passing between them. With such a configuration, the solenoids 3a, 3
b, electric heaters 13a, 13b, 14a, 14b
is energized and the rotational drive device 12 and traveling mechanism are operated, the tape-shaped substrate 5 whose upper surface is covered with the undried coating layer 4 containing magnetic fine particles is moved in the direction indicated by the arrow 6 in the figure. When you run it to
The magnetic fine particles in the undried coating layer 4 are formed on the magnetic pole surface 2.
While moving between the pole faces 2a and 2b, the axis of easy magnetization is oriented perpendicular to the base surface by the magnetic field between the magnetic pole faces 2a and 2b, and then the electric heater 1
After being fixed in the oriented state as described above by the drying of the paint accompanying the heat supply from 3a and 13b, it moves out of the magnetic field. Thus, the undried coating layer 4 is finally connected to the electric heater 14a.
and 14b, it is completely dried,
A perpendicular magnetic recording medium is formed here. In this case, a portion of the endless belt 11 is used as a holding member that maintains the relationship between the substrate surface and the direction of the magnetic field, and the portion is moved in the same direction as the running direction of the tape-shaped substrate 5 so that the difference in relative linkage is almost zero. Since the tape-shaped substrate 5 is run in such a manner that the frictional resistance between the tape-shaped substrate 5 and the part of the endless belt 11 that comes into contact with the tape-shaped substrate 5 can be reduced to almost zero. Therefore, it is possible to prevent the occurrence of waving, vibration, and twisting of the base due to friction between the tape-like base 5 and the holding member and static electricity generated thereby, and to prevent the tape-like base 5 from being attached to the endless belt 11. Therefore, it is possible to stably travel along a designated path, and as a result, the magnetic fine particles in the coating layer 4 can be oriented at a high orientation rate. Furthermore, in the magnetic field, the coating layer 4 is dried to a viscosity that makes it impossible for the magnetic fine particles to rotate again, thereby fixing the orientation state of the magnetic fine particles.
Even if an agglomeration phenomenon occurs during the application of a magnetic field, or even if a demagnetizing field is generated when the coating layer 4 is moved out of the magnetic field, the magnetic fine particles do not rotate, so the orientation rate decreases. Also, unevenness does not occur on the surface of the coating layer 4. Therefore, by using this orientation apparatus, a perpendicular magnetic recording medium with a high orientation rate and a smooth surface can be manufactured. In addition, in order to dry the coating layer in a magnetic field,
Depending on the application speed, the distance of the magnetic field must be increased. However, increasing the length of the drying magnetic field not only increases the space and weight but is also economically disadvantageous. Therefore, as shown in FIG. 2, the roll 10a is formed to be able to be heated and cooled according to the coating speed.
The length of the magnetic field can be shortened when applying at high speed by increasing the temperature of the magnetic field or by using a pre-dryer 21 that dries the material to some extent before entering the magnetic field, or both. You may also do so. In this case, conversely, when coating at a low speed, the pre-dryer 21 is stopped and the roll 10a is cooled, or the electric heaters 13a, 13 in the magnetic field are
By adjusting the calorific value of b, drying can be carried out under optimal conditions. Next, an example in which a perpendicular magnetic recording medium was actually manufactured using the above-mentioned orientation apparatus will be described. First, an alkali was dropped into an aqueous solution containing a barium salt, an iron salt, a cobalt salt, and a titanium salt to obtain a coprecipitate, and then the alkali was removed and heated to obtain hexagonal barium ferrite fine particles. These have a crystal grain size of 0.1 μm or less and plate-like properties, and the magnetic properties of this powder are a saturation magnetization of 60 emu/g and a coercive force of 1000.
It was (Oe). Next, a magnetic paint having the composition shown in Table 1 was prepared using the magnetic fine particles.

[Table] (In addition to the ones shown in Table 1, two types of paints were prepared, one in which only the acicular crystal γ ferrite was replaced with hexagonal Ba ferrite.) The film after drying the above two types of paints. It was coated on a tape-shaped substrate 5 made of polyethylene terephthalate to a thickness of approximately 3 μm, oriented and dried using the apparatus shown in FIG. The length of the magnetic field at this time was 60 cm, and the coating speed was 20 m/min.
3a and 13b were adjusted so that the temperature of the tape-shaped substrate 5 was about 100°C. As a result, all paints appeared to be dry approximately 40 cm after entering the magnetic field. Further, at this time, the circulation speed of the endless belt 11 was made the same as the coating speed. Next, orientation drying was carried out in the same manner using the apparatus shown in FIG. That is, the drying zone of the pre-dryer 21 is set to 2 m, the temperature is adjusted so that this section is approximately 70°C, and the
Coating speed 60m/with a maintained at approximately 80°C.
It was applied at min. The length of the magnetic field at this time is 1m,
The temperature in the magnetic field was controlled by adjusting the heat generation amount of the electric heaters 13a and 13b so that the tape-shaped substrate 5 reached about 120°C. As a result, approximately
It was almost dry at 80 cm, and it was completely dried outside the magnetic field. This also applies to the case of low-speed coating. In addition, the endless belt 11 at this time
The speed was 55m/min and 60m/min, but
In all cases, the tape-like substrate 5 maintained its flatness and had extremely good running safety. In addition, in the case of acicular crystal γ-ferrite paint, two permanent magnets are used as the magnets shown in Figures 1 and 2, and the N
Everything was done in the same way except that the poles were used opposite each other. The orientation ratio of the recording medium thus obtained is as shown in Table 2.

[Table] As described above, according to the apparatus of the present invention, an alignment apparatus capable of producing a perpendicular magnetic recording medium with a high orientation rate and a smooth surface can be obtained. Note that the drying means is not particularly limited, and any method can be used, such as hot air, electric heater, steam, high frequency, etc., as long as the solvent of the paint can be evaporated.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of a magnetic field orientation device according to one embodiment of the present invention, and FIG. 2 is a schematic side view of a magnetic field orientation device according to another embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Magnet, 2a, 2b... Magnetic pole surface, 4... Coating film layer, 5... Tape-shaped substrate, 7... Pinch roller, 8... Capstan, 11... Endless belt, 13a, 13b... Electricity heater.

Claims (1)

[Scope of Claims] 1. An alignment magnet with both magnetic pole faces facing each other, and a tape whose one surface is covered with an undried coating layer containing magnetic fine particles so as to pass between the magnetic pole faces of this magnet. means for running a tape-shaped substrate; an endless belt that partially contacts the tape-shaped substrate passing between the magnetic pole faces to constantize the angle formed between the surface of the tape-shaped substrate and the direction of the magnetic field; a driving means for circulating the endless belt so that the relative speed difference with the tape-shaped substrate becomes almost zero; and a drive means for circulating the endless belt until the coating layer on the substrate finishes passing between the magnetic pole faces. A magnetic field orientation apparatus for manufacturing a perpendicular magnetic recording medium, comprising means for drying the coating layer to a viscosity such that the magnetic fine particles in the coating layer cannot rotate again. 2. The manufacturing of a perpendicular magnetic recording medium according to claim 1, wherein the drying means also includes means for pre-drying the coating layer before it enters between the magnetic pole faces. magnetic field orientation device.