JPH01169730A - Production of magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a disk-shaped magnetic recording medium which is uniform in the degree of orientation in a circumferential direction while eliminating the influence of mechanical orientation by traveling a thin strip which is already coated with a magnetic coating compd. and is prior to solidification by drying between a pair of horseshoe-shaped magnets and subjecting the strip to pseudo circumferential orientation then further to magnetic orientation circumferentially. CONSTITUTION:A pair of the horseshoe type magnets 1, 2, the spacing (g) between the magnetic poles of which has the size smaller than the diameter of the disk-shaped magnetic recording medium are disposed to face each other. A raw sheet 3 which is coated with the magnetic coating compd. and is not yet subjected to solidification of said compd. by drying is inserted between a pair of such magnets 1 and 2 and is passed through the center of the spacing between an S pole and S pole (N pole and N pole), i.e., while the equal spacing from both the magnetic poles 1 is maintained, in the direction intersecting nearly orthogonally with the S-N pole direction. The sheet 3 subjected to the pseudo circumferential orientation in such a manner is circumferentially magnetically oriented around one point on the center line of the spacing (g) between the magnetic poles of the magnets 1, 2, by which the disk- shaped magnetic recording medium having the uniform degree of orientation in the circumferential direction with substantially non influence of the mechanical orientation is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a disk-shaped magnetic recording medium suitable for high-density recording.

[Prior Art] In recent years, flexible disk-shaped magnetic recording media have been widely used, such as flexible disks as large-capacity storage devices for computers and magnetic sheets for still video cameras.

However, when using this type of magnetic recording medium, the magnetic head slides along the circumference to read and write records, whereas normally manufactured magnetic recording media Because the magnetic powder that forms the layer is not oriented in a circumferential manner, the squareness ratio is poor and the residual magnetization is lower than that of a magnetic tape in which the magnetic powder is oriented. Therefore, in this disk-shaped magnetic recording medium, there is an effect of widening the track width in order to obtain sufficient output, which hinders high density.

In addition, when using needle-like magnetic powder with a large axial ratio, such as those normally used in tapes, it is possible to avoid using an orientation device during the coating and drying process in the coating direction of the non-magnetic support sheet (e.g. Even if a signal with a constant amplitude is recorded circumferentially on a disk-shaped punched disk, the residual magnetization is larger in the longitudinal direction.
There was also the problem that the envelope waveform was not constant and the output fluctuated periodically.

[Problem that the invention seeks to solve]

For this reason, in the currently dominant floppy disks and video floppies, attempts are made to weaken the mechanical orientation during the coating process, or use magnetic powder with a small axial ratio to make the envelope as flat as possible. However, such a method suppresses the original characteristics of the acicular magnetic powder. This point will be clarified by comparing it with metal tape.

The axial ratio of the metal magnetic powder of the metal tape can be selected from about 5 to 11, but usually about 7 to 9 is used. The squareness ratio of a tape using such long needle-shaped magnetic powder is about 0.55 in the case of no orientation, but becomes about 0.6 to 0.65 when mechanical orientation is added. Furthermore, as disclosed in Japanese Patent Publication No. 34-2536, magnetic field orientation is imparted using a device in which a sheet coated with magnetic paint before solidification is passed between two plate magnets with the same magnetic poles facing each other. For example, the squareness ratio increases to about 0.8 to 0.85. −
Magnetic line mechanical orientation with a numerically large shape anisotropy, that is, a large axial ratio, is easily applied, and a large squareness ratio can be obtained as a result of the orientation. On the other hand, a metal video floppy whose orientation is suppressed has a squareness ratio in the circumferential direction of about 0.6 to 0.65, which lowers the output by about 3 dB when compared with tape.

Remove mechanical orientation before application, such as circumferential (concentric circles)
Many methods have been proposed in the past for orientation. For example, Japanese Patent Publication No. 40-23626 discloses a method of circumferentially orienting by an externally applied magnetic field. In this method, in a state where the magnetic paint is not solidified, the rotating magnetic pole surfaces are kept stationary relative to the rotational axis of the original material, the magnetic pole surfaces are brought close together, the magnetic powder is oriented concentrically, and then separated. It is something. In the example of this method, a rotating magnetic field is applied from one side of the original material, but in the case of a tape, as shown in Japanese Patent Publication No. 34-2536, in the case of a disk, it is applied from the opposite side. It is better to install a rotary magnetic pole surface having the same magnetic pole on the opposite side of the web. A conceptual diagram of such a device is published in Japanese Unexamined Patent Application Publication No. 1986-
It is shown in the 62505 publication.

In the orientation caused by these rotating magnetic fields, the self-edge before the magnetic field is
Basically, it is the same at any position on the circumference. On the other hand, as mentioned earlier, the mechanical orientation force is strong in the direction of fabric running, so even after applying the magnetic field orientation, the orientation in the direction parallel to the running direction of the fabric is perpendicular to the running direction within the plane of the fabric. Differences in orientation in the direction remain. As a result, the squareness ratio at any position in the circumferential direction in a disk-shaped magnetic recording medium with conventional orientation is 0.75 to 0.8, and the squareness ratio in the longitudinal direction in the case of magnetic tape etc. is 0.75 to 0.8. squareness ratio (0
, 8 to 0.85) and are not sufficiently oriented. This is extremely difficult because in order to orient the ferromagnetic particles aligned in the longitudinal direction in the circumferential direction using mechanical orientation, the ferromagnetic particles must be rotated up to 90 degrees in the width direction of the ribbon. It's for a reason.

An object of the present invention is to provide a disk-shaped magnetic recording medium which has a constant degree of orientation in the circumferential direction without being affected by mechanical orientation, and has a degree of orientation as high as the longitudinal direction orientation in a magnetic tape.

[Means for solving the problem] The above purpose is to apply a magnetic paint containing magnetic powder onto a moving wide thin non-magnetic support, form a magnetic layer through drying treatment, and then In a method for manufacturing a magnetic recording medium punched into a disk shape, a pair of horseshoe-shaped magnets whose magnetic pole gap is smaller than the diameter of the disk-shaped magnetic recording medium to be manufactured are spaced so that the same poles face each other. The thin ribbon coated with the magnetic paint and before being dried and solidified is held between the magnets at approximately the same distance from both magnets, and is approximately perpendicular to the straight line connecting the S and N poles of the magnets. The thin strip with this orientation is magnetically oriented in a circumferential manner around a point on the center line of the magnetic pole gap of the horseshoe-shaped magnet on the thin strip. This can be achieved by a method for manufacturing a disk-shaped magnetic recording medium, which is characterized by including the steps of:

The present invention first performs pseudo-circumferential orientation using a horseshoe-shaped magnet while the magnetic paint is unsolidified, and then applies a circumferential orientation magnetic field to the magnetic coating at any position on the track that is not affected by mechanical orientation. This method produces a disk-shaped magnetic recording medium with an equal degree of orientation in the magnetic field, and thereby increases the degree of orientation to the same level as that of a magnetic tape oriented by a magnetic field in the longitudinal direction.

In the present invention, since a horseshoe type magnet is used especially for performing the uniform orientation, the structure of the apparatus is simple.

Hereinafter, typical embodiments of the method for manufacturing a magnetic recording medium according to the present invention will be explained in more detail with reference to the drawings.

The quasi-circumferential orientation is important to the invention and for this purpose a pair of horseshoe magnets 1.2 are arranged as shown in FIG. The spacing g between the magnetic poles of these orientation magnets is set to have a width smaller than the diameter 2r of the disk-shaped magnetic recording medium.

Preferably, if the diameter of the center track of the disc-shaped magnetic recording medium is 2r', then the relationship is set as follows: Σr'.

This is because it is desirable that the ratio of orientation in the length direction and the width direction be approximately the same.

Between such horseshoe-shaped magnets 1 and 2 for pseudo circumferential orientation,
A non-magnetic support sheet (original sheet) 3 coated with a magnetic paint made by dispersing ferromagnetic powder in a binder vehicle is inserted. Then, the distance between the S pole and the S pole (N pole and N pole) is adjusted between the original fabric sheet 3! In other words, while maintaining a substantially equal distance from both magnets 1.2, the magnet 1.2 is caused to pass in a direction substantially perpendicular to the S-N pole direction (in the direction of arrow 4 in the drawing),
A pseudo-circumferential orientation of magnetic powder in magnetic paint is performed.

At this time, the magnet spacing l is set so that a magnetic field approximately 1 to 5 times the coercive force of the magnetic powder used is applied to the original sheet, although it varies depending on the viscosity of the magnetic paint and the coating speed.

Note that a permanent magnet such as Sm-Co or an electromagnet can be used as the horseshoe magnet. It is also possible to arrange two or more pairs of horseshoe-shaped orientation magnets in the width direction of the original fabric to perform orientation of a plurality of magnets at the same time.

FIG. 2 is a side view showing an example of an apparatus used to implement the present invention. The transport rolls 9 and 10 can move the web 3 at a constant speed. Circumferentially oriented magnets 5a, 5b
, 5C, . . . rotates in the direction of arrow 8 at a constant circumferential speed synchronized with the web running speed.

Circumferentially oriented magnets 6a, 6b, 6 are placed symmetrically across the original fabric 1.
An orientation magnet holding device 12 for holding c... is installed,
This also rotates in the direction of arrow 7 at the same circumferential speed as the orientation magnet holding device 11. The circumferentially oriented magnet 5.6 is movable so as to maintain a stationary state relative to the original fabric.

In front of the orientation magnet holding device 11.12, the horseshoe magnet 1.2 shown in FIG. 1 is provided.

When this device is operated, the original fabric 3 is transferred to the conveying roller 9.10.
The magnet is sent between the horseshoe magnets 1.2 to be non-oriented. Subsequently, the original fabric 3 is transferred to a rotating orientation magnet holding device 11.
By means of a circumferential orientation device 5.6 held at 12,
It is oriented circumferentially around a point on the center line of the magnetic pole gap g of the horseshoe-shaped magnet.

It should be noted that either a permanent magnet or an electromagnet can be used as the circumferentially oriented magnet 5.6. Further, these circumferentially oriented magnets can be used either in a method using rotating magnetic poles or in a method using fixed magnetic poles. However, those that achieve the same purpose,
That is, it is not limited to these as long as it can form a circumferential magnetic field. In addition, in the example shown in Figure 2, a circumferential orienting magnetic field of the same magnetic pole was applied from both sides of the original fabric.
Even if it is applied only from one side, the orientation effect of the present invention can be obtained.

The strength of the magnetic field applied in the present invention varies depending on various factors, but is usually about 1 to 5 times the coercive force of the magnetic powder used for both pseudo-circumferential orientation and circumferential orientation.

〔Example〕

Example 1 Acicular magnetic metal powder (Fe-Ni alloy, major axis 0.25 parts 1 m, axial ratio 10.Hcl 4500e) 100
The parts by weight were divided into 25 parts of binder (6:4 mixture of vinyl chloride-vinyl acetate-vinyl alcohol copolymer and polyurethane elastomer), 1 part by weight of lecithin (dispersant), and α-alumina (abrasive, particle size 0). A magnetic paint prepared by dispersion-mixing with 10 parts by weight (1:1 mixture of methyl ethyl ketone and toluene) and 240 parts by weight of a solvent (1:1 mixture of methyl ethyl ketone and toluene) was applied onto a PET sheet to a dry thickness of 3 μm.

Next, using the apparatus shown in FIG. 2, the orientation treatment was performed as described above, and punching was performed to obtain a disk-shaped magnetic recording medium (diameter: 47 m).
m).

For orientation, the horseshoe-shaped oriented magnet and the circumferential oriented magnet, which are opposite to each other with the same polarity, are set so that a magnetic field of 3000 0 e is applied to both, and the magnetic pole gap g of the horseshoe-shaped oriented magnet is 25 mm.
! is 10 mm.

Comparative Example 1 A disc-shaped magnetic recording medium was produced in the same manner as in Example 1, except that no orientation by a magnetic field was performed.

Comparative Example 2 Same as Example 1 except that pseudo circumferential orientation was not performed.
A disc-shaped magnetic recording medium was fabricated.

Comparative Example 3 A disk-shaped magnetic recording medium was produced in the same manner as in Example 1, except that circumferential orientation was not performed.

Example 2 A magnetic recording medium was produced in the same manner as in Example 1, except that the horseshoe-shaped oriented magnets with the same polarity facing each other were replaced with 20000e magnets.

(Evaluation) Characteristics such as squareness ratio and residual magnetization of Examples, Comparative Examples, and Reference Examples were investigated. The results are shown in Table 1.

From this table, the effect of the present invention can be clearly confirmed.

[Effects of the Invention] As explained above, according to the manufacturing method of the present invention, the degree of orientation is constant in the circumferential direction with almost no influence of mechanical orientation, and the degree of orientation is as high as the longitudinal direction orientation in magnetic tape. A disk-shaped magnetic recording medium having a high squareness ratio and a high squareness ratio can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing the mutual arrangement of the original fabric sheet and the horseshoe-shaped magnet in the pseudo circumferential orientation process of the present invention;
The figure is a schematic side view showing one embodiment of the magnetic field orientation device used in the present invention. 1.2: Horseshoe-shaped magnet 3: Original fabric 4: Original fabric running direction 5a, 5b, 5c..., 6a, 6b, 6C...: Circumferentially oriented magnet 7.8: Rotation direction 9.10: Conveyance Roller 11.12/Orienting magnet holding device Patent applicant Canon Co., Ltd.

Claims (1)

[Claims] 1) Magnetic paint containing magnetic powder is coated on a running wide thin non-magnetic support, a magnetic layer is formed through drying treatment, and the magnetic layer is punched out into a disk shape. In a method for manufacturing a recording medium, a pair of horseshoe-shaped magnets whose magnetic pole gap is smaller than the diameter of a disc-shaped magnetic recording medium to be manufactured are arranged at a distance so that the same poles face each other, and Then, while holding the thin strip coated with the above-mentioned magnetic paint and before drying and solidifying it at approximately the same distance from both magnets, the ribbon was run in a direction approximately perpendicular to the straight line connecting the S and N poles of the magnets. and magnetically orienting the oriented ribbon in a circumferential manner around a point on the center line of the magnetic pole gap of the horseshoe-shaped magnet on the ribbon. A method for manufacturing a magnetic recording medium. 2) The method for manufacturing a magnetic recording medium according to claim 1, wherein a plurality of the horseshoe-shaped magnets are arranged in a direction perpendicular to the running direction of the thin ribbon coated with magnetic paint and before being dried and solidified. 3) The method for manufacturing a magnetic recording medium according to claim 1, wherein the horseshoe-shaped magnet is a permanent magnet. 4) Claim 1, wherein the horseshoe-shaped magnet is an electromagnet.
A method for manufacturing a magnetic recording medium as described in .