JPS6319933B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a magnetic field orientation apparatus used when manufacturing perpendicular magnetic recording media, and particularly to a magnetic field orientation apparatus for manufacturing perpendicular magnetic recording media that can manufacture recording media with a high orientation rate. 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 coated layer of magnetic fine particles. By the way, if the recording film is to be formed from 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 being oriented in this way, if you stop applying the magnetic field or try to take the substrate out of the magnetic field, the magnetic poles remaining on both sides of the coating will cause the magnetic field to move in the opposite direction to the direction of the oriented magnetic field. A demagnetizing field is generated, and the magnetic 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) of the easy magnetization axes of the magnetic particles in the coating film that are perpendicular to the substrate surface.
The higher the orientation rate, the higher the reproduction output and the higher density recording possible. For these reasons, the reality is that there is a strong desire for a magnetic field orientation device that can obtain a high orientation rate during the orientation process. The present invention has been made in view of the above circumstances, and its purpose is to provide a magnetic field orientation apparatus for manufacturing perpendicular magnetic recording media that can manufacture recording media with a high orientation rate. . Hereinafter, details of the present invention will be explained with reference to illustrated embodiments. In the figure, reference numeral 1 is a main magnet for orientation consisting of a permanent magnet (an electromagnet is also possible) with its NS poles facing each other. Travel guide mechanisms 5, 6, and 7 are provided for causing a tape-shaped substrate 3 whose surface is covered with an undried coating layer 2 containing magnetic fine particles to travel in the direction indicated by arrow 4 in the figure at a constant speed under constant tension. It is being The traveling guide mechanisms 5, 6, and 7 are configured to cause the tape-shaped substrate 3 to travel in such a manner that the surface of the tape-shaped substrate 3 is perpendicular to the direction of the magnetic field between the magnetic pole faces 1a and 1b. However,
At a position close to the magnet 1 between the magnet 1 and the guide mechanism 5, there is a direction parallel to the surface of the coating layer 2 before entering between the magnetic pole faces 1a and 1b of the magnet 1. An auxiliary magnet 8 is provided to apply an alternating magnetic field of . This auxiliary magnet 8 is connected to the tape-shaped base 3
It consists of a magnetic core 9 arranged so that both end faces of the magnetic core 9 are held non-contact by both magnetic pole faces, and a solenoid (not shown) wound around the outer periphery of this magnetic core 9, and both ends of the solenoid are not shown. Connected to AC power. On the other hand, between the main magnet 1 and the traveling guide mechanism 7,
A blowing nozzle 11 is provided that blows hot air toward the surface of the coating layer 2 passing between the magnetic pole surfaces 1a and 1b to dry the paint within the layer. Connected to a wind source. In addition, in the figure, 12 indicates a regulating plate made of a heat insulating material that regulates the range to which hot air is blown. With such a configuration, the tape-shaped substrate 3 whose one surface is covered with the undried film layer 2 containing the magnetic fine particles P
When the is run as shown in the figure by the running guide mechanisms 5, 6, and 7, the magnetic fine particles P in the undried coating layer 2 are
When passing through the alternating current magnetic field generated by the auxiliary magnet 8, the magnetic field violently rotates in a direction parallel to the base surface. This rotation aligns the axes of easy magnetization of each magnetic fine particle P, and the rotation temporarily increases the fluidity of the paint. When the paint enters between the magnetic pole faces 1a and 1b of the main magnet 1 with its fluidity increased in this way, most of the magnetic fine particles P in the paint layer 2 orient their easy magnetization axes in the direction of the magnetic field, so-called Orient. When the vehicle further travels in this state, the magnetic fine particles P in the coating layer 2
is fixed in an oriented state by the drying of the paint by heating with hot air from the spray nozzle 11, and a perpendicular magnetic recording medium is manufactured here. In this case, an auxiliary magnet 8 applies an alternating magnetic field to the coating layer 2 before it enters the magnetic field of the main magnet 1 for orientation, thereby temporarily increasing the fluidity of the coating layer 2. Therefore, when entering the magnetic field of the main magnet 1, the easy axis of magnetization of almost all of the magnetic fine particles P can be oriented in the same direction as the direction of the magnetic field between the magnetic pole faces 1a and 1b. Also,
Since the coating layer 2 is dried before passing between the magnetic pole faces 1a and 1b of the main magnet 1, the magnetic fine particles P are oriented in a direction perpendicular to the base surface.
is fixed in the above-mentioned orientation state, and even if it moves out of the magnetic field, the orientation state will not change due to the influence of the demagnetizing field. Therefore, by using this magnetic field orientation device, it is possible to manufacture a perpendicular magnetic recording medium with an extremely high orientation rate. Next, an experimental example in which a perpendicular magnetic recording medium was manufactured using such an apparatus of the present invention will be described. First, an alkali is added dropwise to an aqueous solution containing barium salt, iron salt, cobalt salt, and titanium salt to obtain a coprecipitate, which is then heated to remove the alkali and Co-Ti
Substituted barium ferrite fine particles were obtained. These have a crystal grain size of 0.1 μm or less and plate-like properties, and the magnetic properties of this powder are saturation magnetization of 60 (em u/g) and coercive force.
It was 1000 (Oe). Next, a magnetic paint having the composition shown in Table 1 was prepared and applied to a 15 μm thick polyethylene terephthalate film.

[Table] The film coated with magnetic paint was passed through the apparatus shown in the figure to obtain a perpendicular magnetic recording medium. Note that the magnitude of the orientation magnetic field at this time is the alternating magnetic field.
600Oe, 1000Oe, DC magnetic field 1000Oe, 2000Oe,
3000Oe and 4000Oe. For each sample obtained as above,
When VSM measurement was performed and the vertical squareness ratio was determined,
The results shown in Table 2 were obtained.

[Table] In addition, Comparative Example 1 in Table 2 uses the paint shown in Table 1 and uses the device shown in the figure to operate the auxiliary magnet 8.
Comparative Example 2 shows the results when no alternating magnetic field was applied, and Comparative Example 2 similarly shows the results when the coating layer 2 was dried outside the magnetic field of the main magnet 1. It is. As is clear from Table 2, although the degree of vertical orientation of the medium obtained by the apparatus of the present invention is dependent on the magnetic field strength, the degree of orientation is significantly improved compared to Comparative Examples 1 and 2. I understand that.

[Brief explanation of the drawing]

The figure is a schematic side view of a magnetic field orientation device according to an embodiment of the present invention. 1...Main magnet, 8...Auxiliary magnet.

Claims (1)

[Claims] 1. A main magnet for alignment that is provided with both magnetic pole faces facing each other and generates a DC magnetic field between the two magnetic pole faces, and an undried coating layer on one surface of which contains magnetic fine particles between the magnetic pole faces of this main magnet. a guide mechanism that guides the base covered with the base so that the surface of the base is perpendicular to the direction of the magnetic field between the magnetic pole faces; and a guide mechanism that is provided near the main magnet and enters between the magnetic pole faces of the main magnet. an auxiliary magnet for applying an alternating magnetic field in a direction parallel to the surface of the coating layer to the previous coating layer; and means for drying the coating layer on the substrate that passes between the magnetic pole faces of the main magnet. 1. A magnetic field orientation apparatus for manufacturing perpendicular magnetic recording media, comprising: