JPH01263941A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To make the orientation of ferromagnetic particles into a circumference, and to obtain a disk magnetic recording medium at a excellent recording/ reproducing feature by using a rotary magnet moving with the conveyance of a supporting body. CONSTITUTION:After the coating processing of a non-magnetic supporting body 1, and before dry-setting a direction at >50rpm for the coated surface is applied by rotary magnets 5 and 6 in a relatively still condition with respect to the supporting body 1. Since the magnets 5 and 6 move at the same speed as the conveying speed of the supporting body 1, they are always in the still condition with respect to the supporting body,and the magnetic field to rotate in the circumferential direction can be applied to the supporting body as it is. Thus, the high magnetic recording medium at the same aspect ratio in the circumferential direction in the arbitrary position of the circumferential track can be obtained.

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a disc-shaped magnetic recording medium suitable for high-density recording and a method for manufacturing the same.

[Conventional technology]

In recent years, flexible disk-shaped magnetic recording media have been widely used, such as flexible disks as large-capacity storage media for computers and magnetic sheets (video floppies) for still video cameras. In magnetic recording media, which include not only flexible disks and magnetic sheets but also magnetic tapes, a magnetic head slides over the medium to read and write records.Therefore, the magnetic layer of these magnetic recording media is formed by coating. In this case, it is preferable that the magnetic powder be oriented along the sliding direction of the magnetic head, that is, in the case of magnetic tape, it is preferably oriented in the tape running direction, and in the case of flexible disks and magnetic sheets, it is oriented in the circumferential direction. preferable. Generally, when a flexible magnetic recording medium is manufactured by applying magnetic paint, the base film carrying the magnetic paint passes between two rotating rollers with a gap slightly wider than the thickness of the base film. For this reason, magnetic powder is oriented in the running direction, and this is called mechanical orientation.Generally speaking, the larger the shape anisotropy, that is, the larger the axial ratio of magnetic powder, the easier it is to be mechanically oriented, and as a result of orientation, the larger the square shape. The ratio is obtained. In the case of a magnetic tape, if a magnetic powder with a large axial ratio is applied as described above and then cut into strips, the magnetic tape will be oriented in the running direction of the magnetic head due to mechanical orientation. However, when a flexible disk or magnetic sheet is made by punching this out into a disk shape, the magnetic head slides along the circumference, but due to mechanical orientation, the residual magnetization is larger in the coating direction, so the envelope waveform There was a problem that the output was not constant and the output fluctuated periodically. To solve this problem, several concentric orientation directions have been proposed as shown later, but they have not yet been put to practical use, and currently commercially available floppy disks and video floppies do not have They try to make the envelope as flat as possible by weakening the mechanical orientation during the process or by using magnetic powder with a small axial ratio. However, since the magnetic powder is not oriented in a circumferential manner, the squareness ratio is poor and the residual magnetization is smaller than that of a magnetic tape in which the magnetic powder is oriented. Therefore, in this disc-shaped magnetic recording medium, it is necessary to widen the track width in order to obtain sufficient output, which is an obstacle to increasing the recording density. For example, taking a metal tape as an example, the axial ratio of the metal magnetic powder can be varied from about 5 to about 15, but usually about 10 is used. The squareness ratio of the tape using such long needle-shaped magnetic powder is around 0.55 in the case of no orientation, but due to mechanical orientation, it increases to 0.6 to 0 in the longitudinal direction of the coating line. It will be about .65. In addition,
As disclosed in No. 536, if magnetic field orientation is applied using a device in which a magnetic paint coated sheet before solidification passes between two plate magnets with the same magnetic poles facing each other, the square ratio can be improved. increases to about 0.8 to 0.85. On the other hand, the squareness ratio in the circumferential direction of a metal video floppy whose magnetic field orientation is suppressed is essentially the same as that of a non-oriented tape, 0.55 to 0.
When compared with a tape to which magnetic field orientation is applied at about 65, the output decreases by about 3 dB. Except for the above-mentioned problems, examples of circumferentially oriented magnetic recording media include hard disks obtained by spin coating. However, in the case of spin coating, since the support is formed into a disk shape and each recording medium is coated one by one, there are problems in that mass production is poor and the cost is high. A method of circumferentially oriented by an externally applied magnetic field is disclosed in Japanese Patent Publication No. 40-23626. In this method, the rotating magnetic pole surfaces are brought close to each other before the magnetic paint applied to the base film solidifies, and the magnetic powder is orientated concentrically while keeping the axis of rotation relatively stationary, and then separated. . In the example of this method, a rotating magnetic field is applied from one side of the original fabric, but in the case of tape, as shown in the earlier Japanese Patent Publication No. 34-2536, the same magnetic poles are applied oppositely to each other. It is better to also install the rotating magnetic pole surface having the same structure on the opposite side of the original fabric. A conceptual diagram of such a device is shown in Japanese Patent Laid-Open No. 53-62505. In addition, several other related technologies that are basically similar to the above-mentioned technologies have been known. (Problem B to be solved by the invention) However, in the above conventional example, the influence of mechanical orientation cannot be sufficiently removed, and the phenomenon of reorientation also occurs, so the squareness ratio in the circumferential direction is not improved much. In some cases, the amount of change in the envelope output is 10% or more, and in some cases, the squareness ratio in the circumferential direction is low, resulting in insufficient output.The present invention solves the process of applying a magnetic field that has the above-mentioned problems. An object of the present invention is to provide an improved method for manufacturing a magnetic recording medium in which the squareness ratio in the circumferential direction at any part of a circumferential track is equal and high. According to the method for manufacturing a disc-shaped magnetic recording medium, after about 1 coating treatment of a non-magnetic support, the coated film surface is dried and solidified. By applying a rotating magnetic field using a rotating magnet that is stationary relative to the support, it is possible to make the squareness ratio of the resulting magnetic recording medium equal and high in the circumferential direction. The circumferentially rotating magnetic field is generated by rotating magnets placed above and below the surface of the magnetically coated support, and the magnets move at the same speed as the transport speed of the support. Therefore, it is always stationary relative to the support, and a circumferentially rotating magnetic field can be directly applied to the support.Even if the moving speed of the magnet is faster than that of the support, At the latest, the above effect cannot be obtained.The rotation speed of the magnet to effectively apply a magnetic field to the support is 50
rpm or more, and at rotation speeds below this, the magnetic powder coated on the support cannot be oriented in the circumferential direction. Both permanent magnets and electromagnets can be used as the magnet, and the strength of the magnetic field, the gap between the upper and lower magnets, the time for applying the magnetic field, etc. are determined by the type of magnetic powder used, the thickness of the non-magnetic support, etc. It may be set as appropriate depending on the width, conveyance speed, etc. Furthermore, since the magnet moves together with the support, it is also possible to combine a plurality of magnets and move them continuously. The shape of the magnet is preferably such that the leakage magnetic field of the magnet coincides with the circumferential direction of the disk-shaped magnetic recording medium, and specifically, it is preferable to combine at least one pair of upper and lower fan-shaped magnets. Further, the S rod and NVj of the upper and lower magnets must face the support surface, and the upper and lower magnets must have the same polarity and face each other. Further, as a means to make the magnetic field in the inner peripheral part stronger than the magnetic field in the outer peripheral part, this can be easily achieved by designing the shapes of the magnets so that the distance between the upper and lower magnets in the inner peripheral part is closer than that in the outer peripheral part. The balance between the strength of the magnetic fields at the inner circumferential portion and the outer circumferential portion may be appropriately set depending on the type of magnetic particles, the diameter of the track used in the disc-shaped magnetic recording medium, and the like. It is difficult to further adjust the orientation of ferromagnetic particles with a large axial ratio, such as those used for high-density recording, but by applying a magnetic field as described above, even ferromagnetic particles can be In particular, Hc
This is effective when magnetic particles of 1400 Oe or more are used. Incidentally, after the magnetic particles are oriented in the circumferential direction, the steps other than punching out can be performed in the same manner as in a normal manufacturing method. As for the punching method, when the material is oriented circumferentially, it is marked with an inkjet, laser, stylus, etc., and then punched out.
It is also possible to detect the mark and punch out, or to install a recording head and a reproducing head in the part of the support before punching where the oriented part passes through, and to detect the oriented part and punch out by outputting a reproduction signal. . Specific examples will be described below. [Example] Example 1 Acicular metal magnetic powder (Fe-Ni alloy, major diameter 0.25μ
m, axial ratio 8, Hc 1450 Oe) 100 parts by weight, 25 parts by weight of binder (6:4 mixture of vinyl chloride-vinyl acetate-vinyl alcohol copolymer and polyurethane nylon tor), lecithin (dispersant J) 1ffl
First, α-alumina (abrasive material, particle size 0.4μ5) was dispersed and mixed with parts by weight of In and 240 parts by weight of a solvent (a 1=1 mixture of methyl ethyl ketone and toluene), and then 10 parts by weight of trifunctional polyester. Irisyanate crosslinking agent was added to obtain a magnetic paint. This was applied to a polyester film (thickness: 32 μm, width: 150 seconds) to a dry thickness of 3 μm, and the film was transported at a speed of 13 cm/cm using the apparatus shown in Figures 1 and 2. Second, magnetic field of inner circumference of rotation 3200Oe
, magnetic field at the outer periphery 2800Oe (average applied magnetic field 3KOe
) and the rotational speed of the magnet are set as shown in Table 1, and the orientation treatment is carried out by the method (e) above, followed by calender treatment and thermosetting treatment. A recording medium (diameter 47 mm) was obtained. As shown in Table 1, those processed at a rotational speed of 50 rpm or more had excellent magnetic properties. Table 1 Example 2 A disk-shaped magnetic recording medium was obtained in the same manner as in Example 1, except that granular metal magnetic powder (1300 Oe) was used as the magnetic particles and the rotation speed of the magnet was 2000 rpm. The resulting modulation and squareness ratios are 0 and 0.7, respectively.
It was 6. Actual H6 Example 3 Instead of the magnet used in Example 1, set the magnet so that the magnetic field is 3600 Oe on the inner circumference near the rotating shaft, 2800 Oe on the outer circumference (average applied magnetic field 32000 c), and the rotation speed is 2000 rpm. A disk-shaped magnetic recording medium was obtained in the same manner as in the example. Further, as a comparative example, a recording medium was obtained in the same manner by fixing the magnet instead of moving it. The magnetic properties of each are shown in Table 2, and even if a fixed magnet that does not move is used [Effects of the Invention] As shown below, by using a magnet that moves as the support is conveyed, 1 ferromagnetic Since the grains can be oriented in a circumferential manner, it becomes possible to manufacture a disk-shaped magnetic recording medium with good recording and reproducing characteristics.

[Brief explanation of the drawing]

Figure 1 is a schematic side view showing the circumferential orientation device used in Examples 1 and 2.3, and Figure 2 is a schematic perspective view showing the circumferential orientation magnet used in Example 1.2.3. be. 1: Raw fabric, 2.3 = Conveyance roller, 4: YX counter-travel direction, 7.8: Orienting magnet holding traveling device rotation direction, 9.10: Orienting magnet holding traveling device, 11, 12: Orienting magnet, 13: Orienting magnet fixing jig (non-magnetic), 14: Orienting magnet rotation direction, 15: Orienting magnet rotation axis, 16: Orienting magnet magnetization direction.

Claims (1)

[Scope of Claims] 1) A magnetic coating is applied on a wide thin strip-shaped non-magnetic support that runs in one direction to form a magnetic layer, and after going through processes such as drying and surface shaping, it is punched out into a disk shape. In a method for producing a magnetic recording medium, after the coating step and before the coating surface dries and solidifies, a magnetic field rotating in the circumferential direction at 50 rpm or more is applied to the coating surface while keeping it stationary relative to the support. 1. A method for manufacturing a magnetic recording medium, characterized in that the magnetic recording medium is applied by a rotating magnet in a state of . 2) The method for manufacturing a magnetic recording medium according to claim 1, wherein the magnetic field rotating in the circumferential direction is stronger at the inner circumference than at the outer circumference. 3) Hc of the magnetic particles used in the magnetic paint is 1400O
2. The method for manufacturing a magnetic recording medium according to claim 1, wherein the magnetic recording medium is greater than or equal to e.