JPH0341894B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a magnetic recording material, and in particular,
The present invention relates to a method for manufacturing a magnetic recording material with excellent orientation of magnetic materials.

Magnetic recording materials include barium ferrite, barium in barium ferrite, iron partially replaced with Ca, Sr, Pb, Co, Ni, and other metals, MnBi, and Mn and Bi replaced with Se and other metals on a non-magnetic support. The particles are coated with a ferromagnetic material and a binder, such as those in which the particles are flat in shape and the axis of easy magnetization is perpendicular to the plane.

In this manufacturing method, the magnetic particles are oriented in the recording direction in a magnetic field before the coating film dries after the magnetic paint is applied, and the electromagnetic conversion characteristics in that direction are improved. acicular r-Fe ₂ O ₃ is already known and has been put into practical use.
−23626, Special Publication No. 1977-2065, Special Publication No. 1977-21251
(as shown in patent publications such as No.

The present invention improves the method described in Japanese Patent Publication No. 56-856 and uses a plate-shaped magnetic material having magnetic anisotropy in a direction perpendicular to the plate surface. The aim is to create a magnetic recording medium in which the easy axis of magnetization of the particles is oriented and is suitable for magnetic recording using a perpendicular magnetization component.

Regarding the superiority of perpendicular magnetization recording in terms of high recording density magnetic recording, see ``Nikkei Electronics (1978.8.7.) pp. 100-111'' and ``IEEE
TRANSACTIONS ON MAGNETICS” VOL.
MAG-15, No. 6, pp. 1561-1563 (November 1979)
is explained in.

The first object of the present invention is to provide a method for producing a magnetic recording material having a high degree of orientation in the perpendicular direction, and the second object is to provide a novel method for applying a magnetic paint. As a method of vertically aligning the magnetic field,
Proposals include a method that increases the strength of the magnetic field perpendicular to the web surface (Japanese Patent Laid-Open No. 57-58246), and a method that substantially ends the drying of the coating film in a strong magnetic field (Japanese Patent Laid-Open No. 57-58241). has been done.

To create a vertically oriented magnetic recording medium using a ferromagnetic material that has a flat plate shape and an axis of easy magnetization perpendicular to the flat surface, it is necessary to disperse it in a magnetic binder. A coating liquid is applied onto the web, and a magnetic field is applied perpendicularly to the web to perform a magnetic field orientation treatment to align the axes of easy magnetization of the flat magnetic particles perpendicular to the web surface. It is desirable to apply a strong magnetic field perpendicular to the web surface and dry in that strong magnetic field, as shown in the method.

However, if this process is carried out industrially while the web is running continuously, it will be difficult to substantially prevent drying in the magnetic field unless the part that supports the strong magnetic field is made very long.

The present inventors have developed two magnetic field regions: a first magnetic field region that forms a strong magnetic field that performs magnetic field orientation, and a second magnetic field region that creates a smaller magnetic field than the former in order to maintain the effect of the oriented magnetic field orientation. By dividing the web into two parts, the magnetic field orientation effect can be sustained over a long area with less energy, and by drying the web during this time, the drying can be completed while the web's magnetic field orientation is maintained. They discovered that it is possible to do this, and completed the present invention.

That is, in the present invention, ferromagnetic particles having a flat plate shape and whose direction of easy magnetization is perpendicular to the flat plate surface are dispersed in a binder, and a web in which the ferromagnetic particles are coated on a non-magnetic support is applied to the support surface. A method for manufacturing a magnetic recording medium oriented in a direction perpendicular to a support surface, which comprises drying while being oriented in a perpendicular magnetic field, a first magnetic field region for orienting flat ferromagnetic particles in a perpendicular direction; A magnetic recording medium having a magnetic field smaller than the magnetic field of the magnetic field region and drying the medium by continuously passing through a second magnetic field region for maintaining the orientation state of the flat ferromagnetic particles. This is the manufacturing method.

The present invention will be explained in detail below.

The first magnetic field region needs to be a strong magnetic field, as will be described later, and requires efforts such as using an electromagnet or narrowing the distance between the magnetic poles of a strong permanent magnet. Although such a strong magnetic field is required to orient the magnetic particles, a lower magnetic field is generally required to maintain the orientation of the magnetic particles in the second magnetic field region until drying. . Therefore, even when the distance between adjacent magnetic poles or opposing magnetic poles is increased, or when permanent magnets are used, there is an advantage that the magnetic force is small and therefore inexpensive magnets can be used. Coating liquid 1 with the formulation shown in Example 1
The sample was coated on a polyester base to a dry thickness of 4 μm and dried in an electromagnet. This drying took about 10 seconds, and the strength of the magnetic field and the degree of orientation SQ⊥ in the vertical direction are shown in Figure 1 of the attached drawings. As is clear from the figure, the degree of orientation rises suddenly up to 3000 Gauss and is almost saturated at a magnetic field of 5000 Gauss. Furthermore, in the same manner, the drying was completed by placing it in a magnetic field of 5000 Gauss for the first 2 seconds, and then immediately lowering the magnetic field to a predetermined value. Orientation degree SQ⊥ at that time
FIG. 2 shows the relationship between the strength of the orientation maintaining magnetic field and the strength of the orientation maintaining magnetic field.
In this example, it is effective at about 500 gauss or higher and from 1500 to
It is almost saturated at about 2000 Gauss. Applying this discovery, as shown in Fig. 3, the magnetic poles with opposite polarities are divided into a plurality of parts. The gaps between these divided magnetic poles C ₁ , C ₂ ...
At the lower part b ₁ , b ₂ … point, a ₁ , a ₂ … directly below the magnetic pole, etc.
Although the magnetic field is weaker than that of a point, it still has a large magnetic field.
In general, the magnitude of the magnetic field between magnetic poles a ₁ , a ₂ . . . _{a o can} be increased as the distance between magnetic poles z ₁ , z ₂ . Considering the magnetic field near the magnetic poles 1, 1'; 2, 2', when the distance z ₁ becomes larger than the point where it is equal to the length x ₁ of the magnetic poles, the magnetic field in the a ₁ portion decreases rapidly. Conversely, the magnetic field at b ₁ between the magnetic pole pair begins to decrease suddenly when Y ₁ exceeds the point where it is equal to Z ₁ . Therefore, an arrangement in which X ₁ , Z ₁ , and Y ₁ are approximately equal is efficient. (However, it goes without saying that if the magnetic force of the magnetic poles is sufficiently large compared to the magnetic field required for orientation, it is possible to deviate from the relationship in which X ₁ , Z ₁ , and Y ₁ are approximately equal.) An example of measuring the strength of the magnetic field at the height of the center of the magnetic pole and the position where the web passes is shown.

As the length of the magnetic poles X, the distance Y between adjacent magnetic poles, and the distance Z between opposing magnetic poles, X=Y=Z, and
An example of measuring the strength of the magnetic field when =ZY=1/2X is shown in the upper part of FIGS. 4 and 5.

Therefore, by applying this, the magnetic poles were arranged as shown in Figure 3. In this case, it was arranged so that X=Y=Z. Drying can also be made more efficient by using this gap C to send drying air from here. A ₁ , b ₁ between the magnetic poles 1, 1'; 2, 2'; n, n';
...A web 11 coated with a magnetic liquid and in an undried state is introduced from the left end of the figure into a strong magnetic field formed at the a _o and b _o sections. A drying air 21 is sent to this web from between the magnetic poles 1 and 2.

Drying air can be similarly sent through each gap between the successive magnetic poles 2, 3, . . . n. In addition, if the running path of the web in the magnetic field is long, an appropriate web support roll may be provided to keep the web running path constant, and drying air or wind may be applied to the bottom surface of the web from between the lower magnetic poles. You can send it.

With this configuration, a first magnetic field region that generates a strong magnetic field is created, and a second magnetic field region that is weaker than the first magnetic field region is created, thereby doubling the effective range of magnetic field orientation in this example. This effect can be further promoted by making the drying process easier and by blowing drying air from the area between the magnetic poles.

The magnetic poles 1, 1', 2, 2'...n, n' may be formed by electromagnets, air-core solenoids, or permanent magnets such as ALNICO, cobalt rare earth magnets.

Referring to FIGS. 1 and 2, the strength of the magnetic field is greater than twice the coercive force of the magnetic material used, preferably three times or more. Due to the large demagnetizing field generated within the magnetic coating, a larger orienting field is required compared to the case of normal longitudinal magnetization. When using magnetic powder with a coercive force of 800 to 1000 Oe, it is preferably 1000 Oe or more, preferably 3000 Oe.
A magnetic field of ~5000 Oe or more is used.

The length X of the magnetic poles is the same size for the upper and lower pair,
Based on material and shape. However, the neighboring Xi,
The size of Xi ₊₁ may be changed as necessary.

When the magnetic poles are made of permanent magnet plates, they may be laminated as appropriate to change the Xi. When the magnetic poles are made of electromagnets, electromagnets with different Xi may be lined up, or the magnetic poles of the electromagnets may have a width equal to or greater than the web width. A hole with a width Yi in the direction may be provided.

Hereinafter, the effects of the present invention will be explained with reference to Examples.

Example Ba ferrite substituted with Co [tabular grains with an average grain size of 0.1 μm and an average thickness of 0.03 μm, coercive force
1320 Oersted] 300 parts graphite powder (average particle size, approximately 5 microns)
15 parts vinyl chloride-vinylidene chloride copolymer (copolymerization ratio
80:20, molecular weight 45000) 45 parts amyl stearate 10 parts silicone oil 4 parts lecithin 3 parts dimethyl ethyl ketone 300 parts toluene 300 parts The components of the above composition were placed in a ball mill and mixed and dispersed. Next, 50 parts of polyester polyol was added and mixed uniformly, and then 30 parts of polyisocyanate was added and mixed and dispersed again to obtain a curable magnetic paint.

Incidentally, a portion of this coating liquid was taken and used in the experiment described above.

On the other hand, the above paint was applied to a polyethylene terephthalate film of 25 microns which had been subjected to a corona discharge treatment using a gravure roll to a dry thickness of 4 microns.

The magnetic field orientation was performed in the arrangement shown in FIG.

In this example, X=Y=Z.

Next, for comparison, an arrangement in which Y=O and X=Z, that is, the magnetic poles were integrated, was created, and magnetic field orientation and drying were performed in this arrangement. In the case of the comparative example, the length covered by the magnetic field is approximately half that of the example.

The table shows the results of examining the degree of vertical orientation of the coating film obtained by changing the web speed in this manner.

table Web Speed SQ⊥ Example Comparative example 20m/min 0.51 0.46 25 〃 0.51 0.42 30 〃 0.50 0.39 35 〃 0.46 0.39

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between the magnetic field strength and the degree of vertical orientation (SQ⊥) when drying takes about 10 seconds. A graph showing the relationship between the orientation maintaining magnetic field and SQ⊥ when the magnetic field is then lowered to finish drying.
FIG. 3 is a schematic diagram showing the arrangement of magnetic poles in the present invention,
4 and 5 are diagrams showing changes in the strength of the magnetic field in the gap with respect to changes in the gap between the pair of magnetic poles.

Claims (1)

[Scope of Claims] 1. Ferromagnetic fine particles having a flat plate shape and whose easy magnetization direction is perpendicular to the flat plate surface are dispersed in a binder, and a web in which the ferromagnetic particles are coated on a non-magnetic support is placed on the support surface. In a method for manufacturing a magnetic recording medium oriented in a direction perpendicular to a support surface, which comprises drying while being oriented in a magnetic field perpendicular to Continuously passing through a first magnetic field region for vertically aligning the particles and a second magnetic field region having a smaller magnetic field than the first magnetic field region and for maintaining the oriented state of the flat ferromagnetic particles. A method for manufacturing a magnetic recording medium, characterized by drying the medium while drying the medium. 2. The method of manufacturing a magnetic recording medium according to claim 1, wherein each of the first magnetic field region and the second magnetic field region is constituted by a plurality of pairs of opposite magnetic poles arranged in series. 3. The method of manufacturing a magnetic recording medium according to claim 2, wherein a plurality of pairs of opposite magnetic poles are arranged with appropriate gaps, and drying air is sent from the gaps to the running web. 4. The method for manufacturing a magnetic recording medium according to any one of claims 1 to 3, wherein the magnetic field strength in the first magnetic field region is at least twice the coercive force of the ferromagnetic fine particles. 5 Claims 1 to 4, wherein the strength of the magnetic field in the second magnetic field region is greater than the coercive force of the ferromagnetic fine particles.
A method for manufacturing a magnetic recording medium according to any one of Items 1 and 2.