JPH0135409B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for magnetic field orientation of a magnetic recording medium. Generally, a magnetic recording medium is one in which a support such as a polyester base is coated with a magnetic paint, which is a mixture of magnetic particles and a binder. In this coating step, it is necessary to align the axis of easy magnetization of the magnetic particles with the direction of the recording track, that is, to align them with a magnetic field. It is well known that this is a necessary means for improving the sensitivity, output, S/N, and other characteristics of magnetic recording media. As a magnetic field orientation method, a method in which DC electromagnets or permanent magnets are arranged so as to generate a magnetic field in the direction of the recording track of a magnetic recording medium is currently commonly used. However, as there has recently been a demand for high-performance magnetic recording media that use magnetic particles with higher density relative to the binder in magnetic paints and magnetic particles with high residual magnetic flux density, the viscosity of magnetic paints has increased. However, a drawback has emerged in that the magnetic particles in the magnetic paint become difficult to move in the direction of the external magnetic field. For this reason, if the external magnetic field is forcibly strengthened, the magnetic particles will agglomerate, causing the surface of the coating to become rough and resulting in a reduction in high-frequency sensitivity. The latter drawback is particularly likely to occur in magnetic particles with a large residual magnetic flux density. One attempt to solve this problem is to place auxiliary electromagnets or permanent magnets close to the magnetic recording medium being manufactured, in addition to the main DC magnetic field generated by the above-mentioned DC electromagnets or permanent magnets. A method has been proposed in which the degree of orientation is improved by applying a magnetic field to magnetic particles in a magnetic paint (Japanese Patent Publication No. 13043/1982). However, this method has problems such as the need to use a strong electromagnet or permanent magnet to generate the auxiliary magnetic field and the need to strictly control the magnetic field distribution, which inevitably increases costs. Furthermore, this method has the disadvantage that the surface becomes rough and the sensitivity in the high frequency range decreases. The inventors of the present invention have conducted intensive research to improve these drawbacks, and have discovered that an excellent effect can be produced by orienting the magnetic paint in the following manner immediately after applying the magnetic paint to the support. . In other words, a thin rod made of a soft magnetic material is placed in or near the gap of a device conventionally used to create an orienting magnetic field, which is made by placing two permanent magnets with the same polarity facing each other in the width direction of the support. installed parallel to
The support is made to lightly touch the top of the support. In other words, by using a simple soft magnetic bar instead of the auxiliary magnet that has been proposed in the past, the same orientation effect can be obtained while preventing surface roughening.
That is, in the present invention, a soft magnetic bar is placed near the center of the gap between the same-polar facing permanent magnets, close to the magnetic recording medium that has just been coated with magnetic paint, and thereby the magnetic field of the main orientation magnetic field is intensively enhanced. Act on magnetic particles in magnetic paint. As described above, according to the present invention, there is no need for a complicated and expensive auxiliary magnetic field generating device, and the cost of the device can be significantly reduced.Moreover, the alignment effect is comparable to that of conventional methods, and the number of times the magnetic particles are reversed can be reduced. By limiting the amount, roughening of the surface of the magnetic layer can be suppressed and deterioration of characteristics in the high frequency region can be prevented. It has been found that by simply doing this, the degree of orientation of the recording medium obtained can be improved by 20 to 30%, and, taking the electromagnetic conversion characteristics of an audio cassette tape as an example, the sensitivity can be improved by more than 1 dB. This will be explained in detail in Examples below. Although FIGS. 1 to 7 show various aspects of the magnetic field orientation method of the present invention, the principle of the present invention will first be explained with reference to FIGS. 1 to 2. In these figures, 1 and 2 are permanent magnets or DC electromagnets with the same poles facing each other, which are conventionally used for magnetic field alignment, and a support 3 such as a plastic film and an undried magnetic coating film just applied to its surface. A magnetic recording medium consisting of 4 is passed between these two magnets 1 and 2. The magnets 1 and 2 extend in the width direction of the support 3 and are arranged so that a similar orienting magnetic field is applied to any part of the magnetic coating 4. According to the invention,
Between these two magnets, a rod-shaped body 5 made of a soft magnetic material (generally a soft magnetic material) is arranged in the width direction of the support 3 and parallel to and close to the support 3 . Preferably, this rod-shaped body is arranged on the support surface side.
When the support 3 carrying the undried magnetic coating film 4 moves in the direction of the arrow, the magnetic coating film 4 receives an orienting magnetic field from the magnets facing the same polarity. The rod-shaped body is magnetized in the same direction by the magnetic field of the orienting magnetic field by the opposing magnets and generates its own magnetic field, thereby enhancing the magnetic field of the orienting magnetic field by the opposing magnets in substantially the same direction. Therefore, when the magnetic coating film 4 passes close to the rod-shaped body 5, the magnetic particles dispersed in the magnetic coating material are subjected to the action of an enhanced magnetic field. It is thought that this allows even magnetic particles dispersed in a binder with a fairly high viscosity to overcome the viscosity of the binder and become oriented in the direction of movement of the support. In this way, according to the present invention, great alignment effects not possible with conventional magnetic field alignment devices can be achieved. Embodiment As shown in FIGS. 1 and 2, a cylindrical rod of soft magnetic material is placed in the gap of permanent magnets 1 and 2 of the same pole facing type, which have been conventionally used to orient magnetic particles. 5 (material: S45C, diameter 8 mm, length 200 mm) with the longitudinal direction of the rod 5 parallel to the magnetic pole surface of the permanent magnet facing the same polarity, from the bottom of the base 3 coated with the magnetic film 4, parallel to the base surface. Fix it so that it touches. A base 3 in an undried state coated with a magnetic film 4 is inserted between the permanent magnets 1 and 2 of the same polarity facing type fixed in this state.
was passed in contact with a circular rod 5 made of a soft magnetic material. The magnetic tape manufactured in this way is different from the magnetic tape manufactured by passing the base 3 coated with the magnetic film 4 through a magnetic field composed of only the permanent magnets 1 and 2 of the same polarity facing type (conventional method). The degree of orientation and electromagnetic characteristics of audio cassette tapes were compared.
As shown in Table 1, the results showed that placing the cylindrical rod 5 made of soft magnetic material was superior to simply aligning with permanent magnets of the same polarity facing type. Note that FIGS. 3 to 7 are diagrams when the position where the soft magnetic rod 5 is placed is changed. In this case, although the degree of orientation and electric characteristics changed little by little, results were at least better than when only permanent magnets were used with the same poles facing each other. The following can be seen from the first result. First, when there is a soft magnetic bar in the position shown in Figures 3 and 4, the magnetic particles in the magnetic paint are gradually magnetized by the action of the orienting magnetic field from the upstream side (right side in the figure) of the magnet facing the same polarity, and are magnetized in that direction. Orient. Next, the magnetized magnetic particles pass through the center of the magnets with the same polarity and enter the reversed orientation magnetic field, and the magnetized magnetic particles reverse in the direction of the magnetic field. At this time, when passing near the soft magnetic bar 5, the magnetic field of the orientation magnetic field by the main magnet is enhanced by the soft magnetic bar 5, so the magnetic particles are strongly attracted by the enhanced magnetic field and their orientation improves. Next, when there is a soft magnetic bar in the position shown in Figures 6 and 7, the magnetic particles in the magnetic paint are gradually magnetized by the action of the orienting magnetic field from the upstream side (right side in the figure) of the magnet facing the same polarity, and move in that direction. Begins to orient. At this time, when passing near the soft magnetic bar 5, the magnetic field of the orientation magnetic field by the main magnet is enhanced by the soft magnetic bar 5, so the magnetic particles are strongly attracted by the enhanced magnetic field and are strongly magnetized. Next, the magnetized magnetic particles pass through the center of the magnets with the same polarity and enter the reversed orientation magnetic field, and the magnetized magnetic particles reverse in the direction of the magnetic field. Since magnetic particles are strongly magnetized, they are strongly influenced by an orienting magnetic field and their orientation improves. At the position shown in FIG. 5 (the figure is drawn at the center of the opposing magnets, but actually closer to the downstream side), it is thought that the same effect as in FIGS. 3 and 4 is working. In addition, even if the position is closer to the upstream side,
It is thought that the same effect as shown in Figure 7 is occurring. In the conventional AC auxiliary magnet (Japanese Patent Publication No. 48-13043) cited earlier, the magnetic particles reverse many times even while the magnetic recording medium passes through the alignment magnetic field.
Also, in the case of a DC auxiliary magnet, the reversal occurs three times, which increases the surface roughness of the magnetic recording medium and reduces the recording and reproducing sensitivity in a high frequency range, but in the present invention, the reversal is only one time. , deterioration of surface smoothness can be prevented.

[Table] *The conventional method uses only permanent magnets with the same poles facing each other.The manufacturing conditions other than the magnetic field orientation process for the experimental tape are as follows. That is, after applying the magnetic paint to the base, it was dried by passing through a conventional hot air drying zone, and then surface-treated and cut into cassette width pieces. The coating speed was 60 m/min. The thickness of the base was 12μ, and the coating thickness of the magnetic paint was approximately 6μ after drying. In addition, the experiments were conducted with the magnetic fields of the same-polarity opposing magnets all set at approximately 1800 Gauss. The magnetic paint used in this experiment was prepared by kneading and dispersing the raw materials shown in Table 2 in a ball mill.

【table】

[Table] Note that although a soft iron round bar was used as the rod-shaped body 5 in the above embodiment, a magnetic material having any other arbitrary cross-sectional shape may be used. For example, similar results have been confirmed using a triangular flat plate shape or a square rod.According to the present invention, it is possible to improve the degree of orientation by 20 to 30% and the sensitivity by dB or more, and is particularly effective for highly viscous paints.

[Brief explanation of drawings]

FIG. 1 is a plan view of a magnetic field orientation apparatus for carrying out the method of the present invention, FIG. 2 is a front view of the same, and FIGS. FIG. 7 is a front view showing a modified embodiment.

Claims (1)

[Claims] 1. A magnetic paint in which magnetic particles are dispersed is applied to the surface of a sheet-like non-magnetic support, and while the magnetic paint still retains fluidity, the non-magnetic support coated with the magnetic paint is coated with a pair of identical supports. In a method for manufacturing a magnetic recording medium, the magnetic particles are fed in a main alignment magnetic field formed by pole-opposed magnets to align the magnetic particles in the direction of the alignment magnetic field, wherein the main magnetic particles are fed along one surface of the support. The method is characterized in that an elongated plate-like or rod-like object made of a soft magnetic material is arranged in a direction substantially perpendicular to the direction of the magnetic field of the orienting magnetic field, and an auxiliary magnetic field that enhances the magnetic field of the main orienting magnetic field is applied to the magnetic paint. A method for manufacturing a magnetic recording medium.