JPH0371428A - Device for orienting magnetic recording medium and method for orienting treatment - Google Patents

Abstract

PURPOSE:To orient magnetic particles by inversion of magnetization by making the intensity of magnetic field higher than the coercive force of the magnetic particles and using specified magnets to produce the magnetic field. CONSTITUTION:The intensity of magnetic field of counter magnets is made higher than the coercive force of the magnetic particles of the magnetic record ing medium. Magnets M1, M2 which produce the magnetic field have the ratio l/w, wherein l is the effective length and (w) is the effective width, larger than 4/3. By disposing the magnets M1, M2 with facing N-N or S-S poles, the produced counter magnetic field easily orients the magnetic particles in the magnetic recording medium. By this method, method of applying magnetic field such as AC magnetic field or pulse magnetic field which cost a lot are not required. Thereby, orientation treatment of magnetic particles using inver sion of magnetization can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an alignment processing apparatus and an alignment processing method for a magnetic recording medium.

[Background of the invention]

Magnetic recording media used in various devices such as audio or video tape recorders are made by coating magnetic paint on a non-magnetic support such as polyester film.
In order to improve the magnetic properties, orientation treatment is performed to orient the magnetic particles in the magnetic coating in a specific direction. That is, for example, when a magnetic paint in which acicular magnetic particles are dispersed together with a binder is applied to a predetermined thickness on a non-magnetic support, the applied paint has not yet dried and solidified, and the acicular magnetic particles in the coating film are Once the particles are able to move, the support coated with magnetic coating is run through a magnetic field to orient the acicular magnetic particles in the magnetic coating in the direction of the magnetic field. By doing so, the squareness ratio in the alignment direction is increased, and the sensitivity of the magnetic recording medium is improved.

Conventionally, this orientation process has been carried out by applying a DC magnetic field using a permanent magnet or a DC electromagnet.

By the way, in this method, even if the applied magnetic field is strengthened in order to increase the degree of orientation, the degree of orientation cannot be increased that much.In fact, if the magnetic field is increased beyond a certain level, the surface smoothness of the magnetic coating will deteriorate. It is said that there is a drawback.

Therefore, various methods for improving such alignment processing have been proposed.

For example, Japanese Patent Publication No. 41-30722 discloses a device in which an auxiliary magnetic field device is arranged near a main orientation device using permanent magnets or DC electromagnets to superimpose an AC auxiliary magnetic field on the upper orientation magnetic field.

Also, as shown in Japanese Patent Application Laid-Open No. 54-98205, the direction of orientation perpendicular to the main orientation direction caused by the DC magnetic field? A method has been shown in which an R magnetic field or mechanical vibration is superimposed to facilitate the alignment of particles.

Further, Japanese Patent Application Laid-open No. 54-88101 discloses the effect of applying an alternating current magnetic field in addition to a direct current magnetic field in the magnetic disk orientation process to add vibration to the particles to facilitate orientation.

However, all conventional magnetic field orientation methods, including all of these methods, are directed using a direct current magnetic field, and the alternating current magnetic field is given as an auxiliary weak magnetic field, and merely provides vibrations that make particles easier to move during orientation. do not have.

Even if an alternating current magnetic field is applied as an auxiliary like this, basically the orientation is performed directly by the magnetic field.
Even if the strength of this orientation magnetic field is in a small range below the coercive force Hc of the magnetic particles, a certain degree of orientation effect will occur. Even if the magnetic field is increased to, for example, more than the coercive force Hc of the magnetic particles, a sufficiently high squareness ratio cannot be obtained, and rather the surface properties of the coating film deteriorate as described above.

In particular, when magnetic particles with poor dispersibility or magnetic particles with high cohesion are used as a magnetic paint, or when the content ratio of magnetic particles to binder in the magnetic paint becomes large, it is difficult to achieve good orientation. It is not possible to increase the squareness ratio.

Regardless of whether or not an alternating current magnetic field is applied auxiliary, if the orientation is actually performed by a direct current magnetic field, a sufficiently high squareness ratio cannot be obtained because of the orientation in the direct current magnetic field. Opinions have begun to emerge that this is due to the fact that particle magnetization reversal is hardly involved in the mechanism.

In other words, conventionally, magnetic recording media coated with magnetic paint are processed by moving the magnetic particles through a magnetic field generating means that mainly applies a DC magnetic field while the coating film is not yet dry and the magnetic particles can move. In this case, the DC magnetic field applied to the magnetic particles of the magnetic recording medium has a steep rise from the time it enters the magnetic field generating means, and is immediately set by the vL magnetic field generating means. the magnetic field, i.e. the required strength for orientation l4
It does not rise in a straight line, but rather shows a rise with a certain degree of slope, in which the closer it gets to the magnetic field generating means, the more it is influenced by the magnetic field from the magnetic field generating means. Therefore, in this case, even if the orientation magnetic field Hor is selected to be larger than the coercive force Hc of the magnetic particles, the magnetic particles will always undergo a state where they are subjected to a magnetic field that is less than the coercive force Hc of the magnetic particles, even if it is only for a short time. That's it. In this state, reversal of magnetization does not occur, but the particles themselves begin to rotate. in this case,
Regarding magnetic particles whose direction of spontaneous magnetization is tilted in the direction of the orienting magnetic field I, they can be oriented in the direction of the orienting magnetic field H with a relatively small rotation angle φ of 90°.
If the direction of spontaneous magnetization is so to speak in the opposite direction to the direction of the alignment magnetic field H, it will be rotated by a large angle φ of up to 180° to align it in the direction of the alignment magnetic field H. Therefore, in this case, since a large movement is required to complete the orientation, not only does it take a long time to complete the orientation, but even if the orientation processing time, that is, the application of a magnetic field is continued for a long time, the particles will not be able to interact with each other. Their large rotations tend to cause them to become caught in each other, causing them to stop midway through their orientation. This phenomenon is
This is particularly noticeable when using magnetic particles with poor dispersibility or magnetic particles with high cohesion as described above, or when the content ratio of magnetic particles to binder in the magnetic paint becomes large.

In this way, when considering direct current magnetic field orientation, the movement of individual particles during the orientation process is often unreasonable, and this sometimes causes entanglement between particles, which has the opposite effect on orientation, and the orientation magnetic field is used as a strong magnetic field. Some people have argued that not only is it not very promising to improve the orientation, but it also leads to deterioration of surface smoothness.
No. 336 discloses a magnetic recording medium characterized in that orientation treatment is performed by applying an alternating magnetic field parallel to the orientation direction and having a magnitude greater than the coercive force of the magnetic particles! ! In addition, in JP-A-56-119938, a first step of applying a pulsed magnetic field that is greater than the coercive force of the magnetic particles in parallel to the orientation direction, and a second step of applying a DC magnetic field. A method of manufacturing a magnetic recording medium has been proposed, which is characterized by performing an orientation treatment by steps.

However, the use of means for applying an alternating magnetic field or a pulsed magnetic field increases costs accordingly.

[Disclosure of the invention]

The first object of the present invention is to
An object of the present invention is to provide a technology that can perform particle orientation processing.

A second object of the present invention is to provide a technique that allows orientation processing of magnetic particles using magnetization reversal without using, for example, means for applying an alternating magnetic field or a pulsed magnetic field.

An object of the present invention is to provide an apparatus for orienting magnetic particles of a magnetic recording medium using an N-N opposing magnetic field or an SS opposing magnetic field, wherein the magnetic field strength of the magnetic field is greater than the coercive force of the magnetic particles of the magnetic recording medium. and the magnet that forms the magnetic field has a ratio of an effective length l in a direction perpendicular to the magnetic recording medium running direction to an effective width W in the magnetic recording medium running direction l/
This is achieved by a magnetic recording medium alignment processing apparatus characterized in that w is larger than 4/3.

In addition, the magnetic field strength is greater than the coercive force of the magnetic particles of the magnetic recording medium, and the ratio of the effective length l to the effective width W is 1.
Orientation of a magnetic recording medium characterized by running a magnetic recording medium provided with a magnetic layer on a non-magnetic support between N-N opposing magnets or S-3 opposing magnets with /w greater than 4/3. This is achieved through a processing method.

In addition, the maximum magnetic field strength B of the N-N opposing magnetic field or the S-3 opposing magnetic field may ≥ coercive force Hc of the magnetic particles of the magnetic recording medium,
It is sufficient if the ratio C/W of the effective length l to the effective width W of the magnet is 4/3, but it is more desirable that Bmax≧2Hc and 1/w≧2.

That is, the magnetic field formed by the N-N opposing magnets or the S-3 opposing magnets, as shown in FIG.
It is maximum near both ends of , and gradually weakens as it moves away from magnet MM2.

Now, suppose that the magnets M, , M are rectangular parallelepipeds (length l, width W
), the leakage magnetic field (the range is indicated by A) a formed outside the width W of the magnets M+ and Mz is a>w compared to the width W of the magnet, and the magnetic particle It is thought that the magnetic field has a greater influence on the orientation than the magnetic field within the magnet width W.

Therefore, it is considered that increasing the leakage magnetic field a leads to an improvement in the degree of orientation. The leakage magnetic field a can be increased by increasing the length l of the magnet.

In Fig. 1, if the maximum strength Bmax of the opposing magnetic field is less than the coercive force Hc of the magnetic particles of the magnetic recording medium, the magnetic particles oriented in the region of
It makes a large rotation of 80 degrees and reorients itself in the direction of the magnetic field. In this case, the orientation in the magnetic field (2) is completely useless.

However, if Baa is ≧Hc, then the magnetic field is at B - Hc (indicated by Hc in Figure 1).
The direction of magnetization of the magnetic particles is reversed, and the subsequent magnetic field (2) acts in a direction that further enhances the orientation state of the magnetic particles oriented by the magnetic field (2).

Therefore, it is considered that the shorter the section (the shaded area in FIG. 1) in which the orientation state in the magnetic field (2) is disturbed, the better the degree of orientation will be. That is, magnetic field strength BmaX≧coercive force HC,
Moreover, it is considered that the narrower the width W of the magnet, the higher the degree of orientation.

Based on the above idea, a magnetic recording medium is run at a running speed V between a pair of magnets M and M2 with a magnetic field strength Bmax, a length l, and a width W, and the orientation of the magnetic particles is examined. As a result, the optimal If-N for orientation in the in-plane longitudinal direction
Alternatively, for the S-5 facing magnet, Bll1ax≧Hc, more preferably Bmax≧2Hc, and the ratio of the length l to the width W of the magnet is l/w≧4.
/3, and more preferably l/w≧2.

Note that if the magnets M, Mz are rectangular parallelepipeds, there is no problem since the length l and width W of the magnets are the same as their geometric dimensions, but if the magnets MI, Mz are not rectangular parallelepipeds, then It is sufficient to consider a rectangular parallelepiped-shaped magnet corresponding to the magnetic field of this non-rectangular parallelepiped-shaped magnet, and calculate using the length l and width W of the geometric dimensions of this magnet.

Moreover, the number of N-N opposing magnets (or S-8 opposing magnets) is not limited to one, but two or more may be combined. In such a case, for example, N-N opposing magnets, N-N opposing magnets, or S-5
It is preferable that NN opposing magnets and S-3 opposing magnets are arranged alternately, rather than arranging homogeneous opposing magnets such as opposing magnets and S-3 opposing magnets.

[Example] Rectangular parallelepiped magnet (width W-'3 cm, @field strength Bmax=
A magnetic tape is run between a pair of N-N opposing magnets using a coercive force Hc (twice the coercive force Hc (680 oersted) of magnetic particles of a magnetic recording medium) at running speeds of 50 m/l 1 inch and 200 m/min, The magnetic recording medium was subjected to orientation treatment in the in-plane longitudinal direction.

And when the length of the magnet is changed, l/
When we investigated the relationship between the value of w and the OR ratio (the ratio of the squareness ratio in the longitudinal direction to the squareness ratio in the orthogonal direction) of the obtained magnetic tape, we found that it was as shown in the graph of Figure 2. , the ratio of magnet length i to width W is 7! If /w≧4/3, more preferably 1/w≧2, the OR ratio will be large, indicating that the degree of orientation in the in-plane longitudinal direction of the magnetic recording medium is good.

Also, a rectangular parallelepiped magnet (width w m 3 Ca1, length e = 6
A magnetic tape was run between a pair of N-N opposing magnets using a magnetic recording medium at a running speed of 50 m/sin and 200+w/a+in to perform orientation treatment in the in-plane longitudinal direction of the magnetic recording medium.

Then, the OR of the value of BIIax/Hc and the obtained magnetic tape when the magnetic field strength Bmax of the magnet is changed.
When we investigated the relationship between the
If max≧2Hc, the OR ratio is large and it can be seen that the degree of orientation in the in-plane longitudinal direction of the magnetic recording medium is good.

That is, the magnetic field strength of the opposing magnetic field is larger than the coercive force of the magnetic particles of the magnetic recording medium, and the magnet forming the magnetic field has a ratio of effective length l to effective width W of 1/w.
is larger than 4/3, then such a magnet is
-N facing or S-3 facing allows the magnetic particles of the magnetic recording medium to be highly oriented by the opposing magnetic fields formed thereby, and it is not necessary to use expensive alternating magnetic field or pulsed magnetic field application means. It is possible to perform orientation processing of magnetic particles using magnetization reversal at low cost.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing that the apparatus of the present invention can perform orientation processing of magnetic particles using magnetization reversal, and FIGS. 2 and 3 show orientation processing of magnetic tape using the orientation processing apparatus shown in FIG. 1. It is a graph which shows the ratio of the squareness ratio about the longitudinal direction and the squareness ratio about the orthogonal direction in case. M,,M...Magnet, l...Length, W...Width.

Claims (2)

[Claims] (1) An apparatus for orienting magnetic particles of a magnetic recording medium using an N-N opposing magnetic field or an S-S opposing magnetic field, wherein the field strength of the magnetic field is greater than the coercive force of the magnetic particles of the magnetic recording medium. , and the magnet that forms the magnetic field has a ratio l/w of an effective length l in a direction perpendicular to the running direction of the magnetic recording medium to an effective width w in the running direction of the magnetic recording medium, which is larger than 4/3. An apparatus for aligning a magnetic recording medium, characterized in that: (2) It has a magnetic field strength greater than the coercive force of the magnetic particles of the magnetic recording medium, and the ratio l of its effective length l to effective width w
Orientation of a magnetic recording medium characterized by running a magnetic recording medium provided with a magnetic layer on a non-magnetic support between N-N opposing magnets or S-S opposing magnets with /w greater than 4/3. Processing method.