JPH01227221A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the squareness ratio in a perpendicular direction by executing a random orientation treatment prior to a perpendicular orientation treatment. CONSTITUTION:An AC random orientation device 2 provided in such a manner that the axis of easy magnetization of the magnetic powder of a tape 1 to be made into the recording medium 1 when a magnetic coating compd. contg. the magnetic powder is coated on a nonmagnetic base can be oriented at about the same degree in the direction X and the direction Y and a perpendicular orientation device 3 provided in such a manner that the magnetic powder can be perpendicularly oriented are provided. The tap 1 is run between magnets 4, 5 of the device 3 and AC magnetic fields are impressed to the respective magnets, by which the magnetic field of the magnetic coated film coated on the tape 1 is oriented in the direction perpendicular to the coated film plane.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Application Field The present invention relates to a method for manufacturing a magnetic recording medium used in a perpendicular magnetic recording system, and in particular to an improvement in perpendicular alignment technology for coated magnetic recording media. It is related to.

B9 Summary of the Invention The present invention attempts to improve the squareness ratio in the vertical direction by performing a random alignment process before the vertical alignment process when manufacturing a coated magnetic recording medium.

C0 Prior Art Conventionally, in a magnetic recording medium used as an information storage medium of a computer or the like or a recording medium of an audio tape recorder, a video tape recorder, etc., a magnetic recording layer is deposited on a substrate. Magnetization in the horizontal direction (in-plane direction magnetization) is performed for recording.

However, recording using in-plane magnetization has the disadvantage that as the recording density increases, the demagnetizing field within the medium increases, the residual magnetic density attenuates, and the reproduction output decreases.

Therefore, a perpendicular magnetic recording method has been proposed in which recording is performed by magnetization in the thickness direction of the recording layer of a magnetic recording medium. According to this perpendicular magnetic recording method, the demagnetizing field becomes smaller as the recording density becomes higher, so it is known that it is superior to the above-mentioned recording using in-plane direction magnetization, especially in high-density recording and short wavelength recording. It is being

Incidentally, a characteristic necessary for the magnetic recording medium used in this perpendicular 6ffi recording system is that it has magnetic anisotropy in the direction perpendicular to the surface of the magnetic recording layer.

Therefore, in order to make the axis of easy magnetization extend in the perpendicular direction, a recording layer that uses a thin film manufactured by depositing a ferromagnetic metal such as a Co-Cr alloy by sputtering or vapor deposition is usually considered. ing.

However, manufacturing perpendicular magnetic recording media using the sputtering method or the trick method has limitations in the manufacturing process, increases manufacturing costs, which is undesirable, and has problems with durability, runnability, etc. There are also many problems in terms of practical characteristics.

On the other hand, in a coated magnetic recording medium, in order to align the axis of easy magnetization perpendicular to the magnetic coating surface, for example, I Fe2
In the case of magnetic powder such as acicular magnetic powder such as O2, which generates coercive force Hc due to shape magnetic anisotropy, the magnetic powder must be aligned perpendicularly to the film surface, and barium In the case of magnetic powder, such as ferrite, which generates the coercive force Hc not by its shape but by its magnetocrystalline anisotropy, the anisotropy must be oriented perpendicularly to the surface of the magnetic coating.

To do this, it is necessary to perform some kind of magnetic field orientation treatment on the surface of the magnetic coating before the magnetic coating is completely cured. If the magnetic powder is oriented perpendicularly by applying a DC magnetic field that is sufficiently larger than the coercive force of the magnetic powder, the orientation may be disturbed by the demagnetizing field during the drying process of the coating film, or the coating surface may be distorted due to magnetic aggregation. A phenomenon occurs in which the magnetic field increases in the direction of the applied magnetic field, and the surface of the recording medium tends to become rough, resulting in surface-like deterioration. When such surface properties deteriorate, the spacing between the magnetic head and the magnetic head varies, which greatly affects the reproduction output, and this is especially a big problem for perpendicular magnetic recording media used in short wavelength ranges.

Therefore, the applicant of the present application previously proposed in Japanese Patent Application Laid-Open No. 61-50217 a method for manufacturing a magnetic recording medium characterized in that orientation treatment is performed by applying a rotating alternating magnetic field in a direction perpendicular to the orientation direction. . It has been found that a magnetic recording medium with improved surface properties and orientation can be obtained by applying a rotating alternating magnetic field in a direction perpendicular to the orientation method of the magnetic powder.

However, the method of applying a rotating alternating magnetic field as described above is not only difficult to apply to tape-shaped media, but also is not sufficient to meet the current demands for higher density recording. However, further improvement is desired.

D9 Problems to be Solved by the Invention The present invention was proposed in view of the above circumstances, and an object of the present invention is to propose a method for manufacturing a magnetic recording medium in which it is easy to improve the vertical alignment. The object of the present invention is to make it possible to manufacture a magnetic recording medium having perpendicular magnetic characteristics compatible with a perpendicular magnetic recording system in which the recording wavelength extends to an extremely short wavelength region.

89 Means for Solving the Problems The present invention has been proposed to achieve the above object, and comprises applying a magnetic coating film on a non-magnetic support and subjecting the magnetic coating film to a random orientation treatment. It is characterized by forming a perpendicular magnetic recording layer by performing a perpendicular alignment treatment after the magnetic recording medium is applied, and before performing the orientation treatment of the magnetic recording medium, a random orientation treatment is performed to improve the surface properties and orientation. The objective is to obtain a magnetic recording medium with excellent performance.

The method for producing a magnetic recording medium according to the present invention can be applied to any coated media, and can be applied to any type of coated media. The powder is not limited in any way,
Any magnetic powder used in ordinary coated magnetic recording media can be used. Examples of magnetic powders that can be used include IF etos, Fe30a,
Iron oxide with an oxidation state intermediate between T Fezos and Fe1o4, Co-containing 1-FezO,+, I Fezes
Cro! is an iron oxide containing Co and has an oxidation state intermediate between that of Fe5Oa and Fe5Oa. .

CrO□ with one or more metal elements 2 such as Te,
Oxides containing Sb, Fe, Bi, etc., hexagonal barium ferrite (e.g. barium ferrite), Fe,
Metals such as Co and Ni, Fe-Co, Fe-Ni, Fe-
Co-Ni, Fe-C.

-B, Fe-Co-Cr-B, Mn-B1. Mn-Af
Examples include alloys such as fi-Fe-Co-V, iron nitride, and the like.

After applying a magnetic paint containing magnetic powder as described above onto a non-magnetic support according to a conventional method, a random orientation treatment is first performed while the paint film is not yet dry and can flow. Perform vertical alignment treatment.

The random orientation treatment is a method in which the easy axis of magnetization of the magnetic powder is oriented approximately uniformly in the in-plane direction (for example, the longitudinal direction, which is the X direction, and the width direction, which is the Y direction) on the nonmagnetic support. Any of these may be used, such as a solenoid that generates an alternating magnetic field or an N pole.

Permanent magnets with alternating south poles may be used, or a combination of the above-mentioned solenoids and permanent magnets may be used.

The above-mentioned vertical alignment process may be performed as long as it applies a magnetic field in the vertical direction of the magnetic recording medium (so-called AC vertical alignment process, DC vertical alignment process, etc. can be employed. For example, a magnet is arranged with an S pole facing the upper surface of the medium and an N pole facing the lower surface so as to generate a magnetic field perpendicular to the magnetic surface of the magnetic recording medium, or Magnets with rotation axes in orthogonal directions are arranged on both sides of the above 6. For example, the magnets are arranged perpendicularly to each other and rotated at the same speed.Furthermore, the magnets are fixed and the magnetic recording medium is rotated to generate a magnetic field in the perpendicular direction of the magnetic recording medium. Note that even though it is called a vertical direction, a certain degree of direction deviation is allowed in practice, and all such directions should be understood to be included in the vertical direction here. Needless to say.

F0 Effect According to the present invention, since the random orientation treatment is performed before the vertical orientation treatment, the orientation of the magnetic powder in the thickness direction of the magnetic coating surface is performed smoothly.

G. Examples Hereinafter, specific examples of a method for manufacturing a magnetic recording medium to which the present invention is applied will be described with reference to the drawings. In this embodiment, the present invention is applied to a tape-shaped magnetic recording medium.

(Example 1) This example is an example in which AC random orientation and AC vertical orientation are combined.

First, the configuration of the magnetic recording medium manufacturing apparatus used in this example will be explained.

As shown in Figure 1, in this device, a magnetic tape (1), which is a magnetic recording medium in which a magnetic paint containing magnetic powder is coated on a non-magnetic support, has an axis of easy magnetization of the magnetic powder aligned with the X direction. It consists of an AC random orientation device (2) provided so that the magnetic powder can be oriented to the same degree as the Y direction, and a vertical orientation device (3) provided so that the magnetic powder can be oriented perpendicularly.

The AC random orientation device (2) has a coil wound multiple times to form a cylindrical body with a rectangular cross section as a main component, and both ends of the coil are connected to an AC power source (not shown). There is. And the above magnetic tape (1)
is designed to run in the space within this coil.

On the other hand, the vertical alignment device (3) is arranged so that the magnetic tape (1
The main components are a pair of substantially U-shaped magnets (4) and (5) that are placed opposite to each other on both sides with the magnet (4) and (5) in between. These magnets (4) and (5) are
They each have a pair of rod-shaped magnetic poles (4a), (4b) and (5a>, (5b), and their connecting portion (4c)
) and (5c) to form an abbreviated shape. Moreover, each magnetic pole (4a), (4b), (5a) of each magnet (4), (5).

(5b) are each wound with an AC coil (6) to operate as an AC magnet.

A connecting part (4c) of the magnets (4) and (5),
At the center of (5c), each of the magnetic poles (4a) and (4
b) Rotating shafts (7), (8) are provided on the opposite side to the protrusion direction of (5a), (5b), and each magnetic pole (4a), (4b), (5a),
(5b) is rotatable without changing the relative positional relationship.

In addition, the magnets (4) and (5) have magnetic poles (4a)
and magnetic pole (4a), and 6n pole (4b) and (5b)
are arranged to face each other with the magnetic tape (1) in between, and the magnetic pole (4a), the magnetic pole (5a), and the magnetic pole (
An alternating current is supplied to each alternating current coil (6) so that the magnetic pole (5b) and the magnetic pole (5b) have the same polarity. In other words, when the magnetic pole (4a) becomes the N pole, the magnetic pole (5a) also becomes the N pole.
The phases of the alternating currents flowing through these electrodes (4a) and (5a) are aligned so that they form magnetic poles (4b).
) and (5b) so that the phases of the alternating currents flowing in the positions are aligned.

However, when the magnetic pole (4a) becomes the north pole, the magnetic pole (4b) becomes the south pole, and when the magnetic pole (3a) becomes the south pole, the magnetic pole (4b) becomes the north pole. Therefore, the magnetic pole (4a)
An alternating magnetic field is generated between the magnetic pole (4b) and the magnetic pole (5b).
An alternating magnetic field is generated between a) and the magnetic pole (5b). here,
These magnetic poles (4a), (4b), (5a)
, (5b) The alternating magnetic fields generated between are compressed with each other,
magnetic pole (4a) of (4), (5),
In the inner region 1 of (4b), (5Ll), and (5b), the magnetic field is approximately parallel to the magnetic tape (1) surface.

According to the vertical alignment device (3) having such a configuration,
By running the magnetic tape (1) between the magnets (4) and (5) and applying the above-mentioned alternating current magnetic field to these magnets (4) and (5), the magnetic tape (1)
The magnetic coating film applied to the surface is magnetically oriented in a direction perpendicular to the coating surface.

In the magnetic recording medium manufacturing apparatus configured as described above, in this example, a magnetic recording medium was manufactured under the conditions described below, and the squareness ratio Rs-Z in the Z direction was measured.

First, the magnetic powder applied to the tape (1) has a coercive force H
The one with C of 416 oersted was used.

The AC voltage in the AC random orientation device (2) was approximately 20V. This is because when an alternating current voltage is applied to an alternating current random orientation device (2) while running a magnetic tape coated with magnetic paint (1) and the voltage is gradually increased, the easy magnetization axis of the magnetic powder is This is due to the fact that it was found through experiments that the orientation is the same in the in-plane direction of the tape (1), that is, in the X direction and the Y direction in FIG. That is, as shown in FIG. 2, the voltage applied to the AC random orientation device (2) and each direction (X direction, Y direction in the figure)
squareness ratio Rs -X, Rs -Y (direction, Z direction)
.

When the relationship with Rs-Z is plotted, χ
, Y, and Z, the squareness ratio Rs-X in the X direction and the squareness ratio Rs-Y in the Y direction of the magnetic recording medium are approximately 20V in the case of the magnetic tape (1) used in this example. By matching. In this case, the BX direction magnetic field and the syX direction magnetic field in the AC random orientation device (2) are each approximately 5 Gauss, as shown in the figure.

On the other hand, the strength of the alternating current magnetic field applied in the vertical alignment device (3) is determined by the coercive force H of the magnetic powder used in this example.
It may be set appropriately based on the coercive force Hc, and is preferably set to about 30X to 120χ in proportion to the coercive force Hc.

As shown in Fig. 3, when the alternating current magnetic field applied to the vertical alignment device (3) is gradually increased while running the magnetic tape (1), the magnetic field is perpendicular to the in-plane direction of the magnetic tape (1). The highest value of the squareness ratio Rs-Z in the direction of
This is due to the knowledge that this occurs when an alternating current magnetic field of X to 12 oz is applied.

For comparison, a magnetic recording medium was manufactured without using the random orientation device (2), and a vertical orientation device (3) was used.
When the vertical squareness ratio Rs-Z of each magnetic recording medium manufactured by changing the strength of the applied alternating magnetic field was compared, the results shown in FIG. 4 were obtained.

As is clear from FIG. 4, the squareness ratio Rs-Z is better when the AC random alignment treatment is performed before the vertical alignment treatment.
It can be seen that this is about 10% higher.

(Example 2) This example is an example in which AC random orientation and DC vertical orientation are combined.

First, the configuration of the magnetic recording medium manufacturing apparatus used in this example will be explained.

As shown in FIG.
This device has the same configuration as the device described in . ), a vertical alignment device (l) installed so that the magnetic powder is vertically aligned
O).

The vertical alignment device (10) includes a permanent magnet (11) arranged such that its N pole faces the upper surface of the magnetic tape (1).
) and a permanent magnet (12) arranged so that the S poles face each other on the lower surface. Both ends of these magnetometers (11) and (12) are connected by connecting plates (14) and (15), so that the overall shape of this vertical alignment device (10) is a cylindrical body with a square cross section. The magnetic tape (1) is configured to run inside this cylindrical body.

Then, magnetic recording media were manufactured by changing the strength of the direct current oriented magnet by the magnetic recording medium manufacturing apparatus configured as described above, and as a comparative example, a random A magnetic recording medium was manufactured by performing only the vertical alignment process 8'6 using the vertical alignment apparatus (10) described above without performing the alignment process.

Then, the measured value of the squareness ratio Rs-Z in the vertical direction (Bz force direction) of the magnetic powder of each magnetic recording medium manufactured under the above conditions and the magnetic recording medium manufactured according to the comparative example, that is, before performing the vertical alignment treatment. The measured value of the squareness ratio Rs-Z of a magnetic recording medium manufactured without random orientation treatment as in this example was compared.As a result of the sheep, values as shown in FIG. 6 could be obtained.

As is clear from FIG. 6, even in the case of direct current vertical alignment, if random alignment treatment is performed before performing vertical alignment treatment, the squareness ratio Rs-Z in the vertical direction can be improved by about 10%. Recognize.

Effects of the H8 Invention As is clear from the results of the above examples, in the present invention, random alignment treatment is performed before vertical alignment treatment, so compared to the conventional case where only vertical alignment treatment is applied. The magnetic coating film can be vertically aligned at a higher ratio, and the squareness ratio in the vertical direction of the obtained magnetic recording can be greatly improved.

Therefore, it is possible to manufacture a magnetic recording medium having perpendicular magnetic characteristics compatible with a perpendicular magnetic recording system in which the recording wavelength extends to an extremely short wavelength range.

[Brief explanation of the drawing]

FIG. 1 is a schematic external perspective view showing an example of a magnetic recording medium manufacturing apparatus used in carrying out the present invention, and FIG. 2 shows the squareness ratio depending on the magnitude of the voltage applied to the AC random orientation device. Figure 3 is a characteristic diagram showing the change in squareness ratio due to the strength of the AC magnetic field applied to the AC vertical alignment device. Figure 4 is a characteristic diagram showing the change in squareness ratio due to the strength of the AC magnetic field applied to the AC vertical alignment device. FIG. 3 is a characteristic diagram showing the dependence of the squareness ratio Rs-Z on an alternating current magnetic field in an example in comparison with a case where only vertical alignment treatment is performed. FIG. 5 is a schematic external perspective view showing another example of a magnetic recording medium manufacturing apparatus used in carrying out the present invention, and FIG. 6 is an embodiment in which AC random alignment processing and DC vertical alignment processing are combined. FIG. 3 is a characteristic diagram showing the AC magnetic field dependence of the squareness ratio R and s-Z in comparison with the case where only vertical alignment treatment is performed. 1...Magnetic tape 2...AC random alignment device 3.10...Vertical alignment device Patent Applicant: Sony Corporation Agent
Patent Attorney Koike Mimi Ei Kuchizai - Masaru Sato Slighter v'7@pressure (V) Figure 2 Figure 3 Figure 4 Rs-Z ('10)

Claims (1)

[Claims] Manufacture of a magnetic recording medium characterized in that a magnetic coating film is coated on a non-magnetic support, a random orientation treatment is performed on the magnetic coating film, and then a perpendicular orientation treatment is performed to form a perpendicular magnetic recording layer. Method.