JPS61175929A - Manufacture of magnetic recording medium - Google Patents

Abstract

PURPOSE:To smooth the surface of a magnetic recording medium, and to improve the degree of orientation by forming a magnetic coated film by applying a magnetic paint to the surface of a nonmagnetic base material, bringing said film to a vertical magnetic field orientation in a vertically oriented magnetic field, irradiating an electron beam after its orientation, and hardening the coated film. CONSTITUTION:When a magnetic coated film which is applied to the surface of a base material is brought to a vertical magnetic field orientation, if the orientation processing time in its magnetic field exceeds 5sec, as its time elapses, the surface becomes rough. Accordingly, it is necessary that this orientation processing is ended within 5sec. Also, in the coated film which is not dried yet, when an orientation magnetic field becomes zero, its magnetic particle starts a rotation before the first 1sec elapses, and its degree of orientation drops. Accordingly, in order to avoid a drop of the degree of orientation caused by its rotation, it is executed by hardening the coated film by an electron beam and restricting a rotation of the magnetic particle before 1sec elapses after the vertical magnetic field orientation processing is ended, desirably, before 0.5sec elapses.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a magnetic recording medium such as a magnetic tape, a magnetic disk, or a magnetic sheet, and particularly to a method of manufacturing a magnetic recording medium in which magnetic particles are perpendicularly magnetized.

(Prior Art) As is well known, this type of magnetic recording medium, such as a magnetic tape, is produced by coating a plastic film with a magnetic coating in which magnetic particles are dispersed in a solution together with appropriate additives to form a magnetic coating. The coating film was manufactured by performing a magnetic field orientation treatment while it was still wet, followed by heat drying, followed by calendering and cutting.

Regarding the magnetic field orientation treatment in the above manufacturing process.

Generally, magnetic particles are needle-shaped γ-Fe20. For those having shape anisotropy, the axis of easy magnetization is oriented along the horizontal direction (longitudinal direction) of the magnetic tape. Therefore, information is magnetically recorded and reproduced in the horizontal direction.

However, in recent years, instead of the above-mentioned horizontal recording and reproducing method, there has been a desire to develop magnetic recording media in which the magnetic field is oriented in the vertical direction (thickness direction), which enables high-density recording.

To manufacture such magnetic recording media, a magnetic paint with magnetic particles dispersed therein is applied to a tape or the like, and when the resulting magnetic coating film is still wet, it is passed through a perpendicular magnetic field to make it magnetic. The axes of easy magnetization of the particles are oriented in the vertical direction, and then the coating film is cured by methods such as heat drying or electron beam irradiation. It is sufficient to form a perpendicularly magnetized film in this way).

However, according to such an orientation method, (1) an action that lowers and stabilizes the magnetic potential energy of undried magnetic particles in a vertically oriented magnetic field acts, and the magnetic particles aggregate due to the electromagnetic force, causing unevenness on the surface. arise.

(2) In the wet coating film, the magnetic particles are 1 after magnetic field orientation treatment.
Since they can rotate within seconds, when the orientation magnetic field becomes zero, the magnetic particles rotate and the degree of orientation decreases.

(3) When an undried coating film oriented in the vertical direction by a magnetic field is removed from the magnetic field, the orientation is reduced by the demagnetizing field of the orienting magnetic field, and the magnetic properties tend to deteriorate.

Due to these problems, it has been extremely difficult to achieve complete alignment in the vertical direction.

In order to solve these problems, countermeasures have been considered, such as continuing magnetic field orientation during heat drying or hardening the magnetic coating film by electron beam irradiation immediately after magnetic field orientation, but the former method In the latter case, the electron beam from the electron beam irradiation device must be sufficiently separated from the orientation magnetic field in order to avoid the influence of the orientation magnetic field, which is difficult to achieve and it is difficult to achieve a sufficiently high orientation. could not be achieved.

(Problems to be Solved by the Invention) The present invention aims to smooth the surface and improve the degree of orientation when producing a magnetic recording medium that is vertically oriented in a magnetic field.

(Means for Solving the Problems) This invention applies a magnetic paint in which magnetic particles are dispersed together with additives to the surface of a non-magnetic base material to form a magnetic coating film.
The coating film is characterized in that it is oriented in a vertically oriented magnetic field within 5 seconds, and then electron beam irradiation is performed within 1 second after the orientation to cure the coating film.

(Function) When a magnetic coating film applied to the surface of a base material is oriented in a vertical magnetic field, if the orientation treatment time in the magnetic field is set to 5 seconds or less, there will be almost no change in the surface roughness. But 5
As time passes, the surface becomes rougher. This is thought to be due to the magnetizing force generated by the magnetization of the magnetic particles in the coating film, which causes the magnetic particles to repel and absorb each other and aggregate. Therefore, it is necessary that this orientation treatment be completed within 5 seconds.

Furthermore, in an undried coating film, when the orientation magnetic field becomes zero, the magnetic particles start rotating within the first 1 second, and the degree of orientation decreases. Therefore, in order to avoid a decrease in the degree of orientation due to the rotation, the coating film is cured with an electron beam within 1 second, preferably within 0.5 seconds, after the vertical magnetic field orientation process is completed. The rotation of the magnetic particles may be restrained by

(Example) The magnetic paint used in this invention has magnetic powder, a binder, and a coating solvent as main components, and in addition, dispersants, lubricants, abrasives, antistatic agents, rust preventives, etc. It is composed of additives.

The magnetic powder includes y-Fe, O,, Fe, O,,
7-Fe2O, and Fe, iron oxide in an oxidation state intermediate between 04, '1-Fe2O, containing Co, y-Fe containing Co
20. and Fe, iron oxide in the oxidation state intermediate between 04 and CO
Deposited iron oxide, CrO2, etc. are used.

As the binder, an electron beam curable resin, a known thermoplastic resin, a thermosetting resin, or a mixture of a reactive resin and an electron beam curable resin are used.

As the solvent, a low boiling point solvent such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, cyclohexanone, toluene, xylene, and a monomer having an electron beam functional group can be used.

Base materials include polyesters such as polyethylene terephthalate and polyethylene naphthalate, polyolefins such as polypropylene, secondary plastics such as cellulose triacetate, polyvinyl chloride, polycarbonate, and acrylic resin, non-magnetic metals such as Cu, Al, and Zn, and glass. , ceramics such as china can be used.

The base material may be in any form such as a film, tape, sheet, disk, card, or drum. Note that this base material may be back coated, for example, on the back surface for purposes such as antistatic and transfer prevention.

The strength of the orientation magnetic field is approximately 1000 to 10000
Use something on the order of Gauss. As the electron beam accelerator, scanning method, area beam method, curtain beam method, or broad beam method can be adopted, and the accelerating voltage is 100 to 100 OKV and the dose is 0.1 to 20.
This is Mrad.

FIG. 1 shows a typical manufacturing apparatus for this type of recording medium. 1 is a vertical magnetic field orientation device, which includes, for example, a pair of magnets IA,
It is constructed by arranging IBs with their different magnetic poles facing each other. Reference numeral 2 denotes a base material, such as a tape, on the surface of which the above-described magnetic coating is applied, and is configured to be run, for example, in the direction of the arrow between the two magnets.

As the tape 2 runs between the two magnets, the magnetic flux from the magnet passes through the tape 2, so that the magnetic particles in the coating film are oriented in the vertical magnetic field. Reference numeral 3 denotes an electron beam irradiation device, which irradiates the tape with an electron beam emitted from its irradiation window 3A, thereby curing the coating film.

Although manufacturing is possible with the configuration shown in FIG. 1, in order to shorten the time from the end of the magnetic field orientation process to the start of the electron beam irradiation process, the magnet and the electron beam irradiation device 3 may be placed close together. Suppose you set it up.

A part of the magnetic flux emitted from the magnet becomes leakage magnetic flux and may intersect with the electron beam of the electron beam irradiation device 3. Therefore, the electron beam may be deflected and scattered by electromagnetic force, causing it to spread out.

In order to prevent this, a magnetic shield 4 is installed between each magnet and the electron beam irradiation device 3, as shown in FIG. By doing this, the magnetic flux from the magnet, especially the return magnetic flux, will pass through the magnetic shield 4, and it can be avoided that it intersects with the electron beam. Therefore, there is no problem even if the magnet and the electron beam irradiation device are installed sufficiently close to each other, so it is extremely difficult to set the time from the end of the magnetic field orientation process to the start of the electron beam irradiation process to within 1 second. It becomes easier. Note that a magnetic shield 5 may be installed outside the magnet.

The configuration shown in FIG. 3 may be adopted instead of the configuration shown in FIG. 2. In this case, a magnetic field device 6 having the same configuration as the vertical magnetic field orientation device 1 is also installed behind the electron beam irradiation device 3. The magnetic field device 6 is constructed by arranging a pair of magnets 6A and 6B with their different magnetic poles facing each other. Each magnet is arranged on the same surface of the tape 2 so that magnetic poles of the same polarity face each other.

According to such a configuration, since the magnetic flux of the magnets IA and IB and the magnetic flux of the magnets 6A and 6B repel each other, the magnet IA and the magnetic flux of the magnets 6A and 6B repel each other.
Intersection of the magnetic fluxes from A and IB with the electron beam is avoided. Therefore, the electron beam is not affected by magnetic flux.

This also allows the vertical magnetic field orientation device 1 and the electron beam irradiation device 3 to
and can be installed sufficiently close to each other. Note that a magnetic shield 7 may be installed outside each magnet as shown in the figure.

Next, an experimental example conducted by the present inventor will be explained.

The following compositions 1 to 1 are used as magnetic paints that can be cured by electron beams.
3 was prepared, placed in a ball mill, kneaded for 48 hours, filtered through a filter with an average pore size of 1μ, and prepared 1.
It was coated onto a tape made of a 7μ polyethylene terephthalate film using a doctor blade to a film thickness of 5μ and held in a +5000 Gauss magnetic field for 5 seconds, during which it was vertically aligned. Then, within 0.5 seconds thereafter, irradiation with an electron beam of 5 Mrad was started at an accelerating voltage of 200 Kv. The tape running speed was 150 m/min, and the experiment was conducted using the apparatus shown in FIG.

Composition 1 y-Fe20. 1
00 carbon black 4 alumina powder 2 lecithin 2 stearic acid 1 n-butyl stearate 1 nitrocellulose
10 urethane acrylate
6 trimethylolpropane triacrylate 4 methyl ethyl ketone
125 toluene
125 silicone oil 2
Composition 2 Co-y-Fe20.
100 carbon black 4
Alumina powder 2 Lecithin 2 Stearic acid 1 Stearic acid n-
Butyl 1 Nitrocellulose
10 urethane acrylate
6N-vinylpyrrolidone
4 methyl ethyl ketone
125 toluene
125 silicone oil
2 Composition 3 Hexagonal Ba ferrite 100 Alumina powder 2 Lecithin 2 Stearic acid 1 N-Butyl stearate 1 Urethane acrylate
2ON-vinylpyrrolidone
5-trimethylolpropane triacrylate 5-methyl ethyl ketone
125 toluene 1
25 Silicone Oil 2 All numbers in the table above indicate parts by weight.

The following table shows the characteristics of the obtained magnetic tape.

For comparison, the orientation magnetic field holding time is 1 for composition 1.
Comparative Example 1 is shown for 0 seconds, and Comparative Example 2 is shown for irradiation with the electron beam 2 seconds after passing through the magnetic field.

Uniformity/force 10s Mold composition 1
0.01 360 0.47 Comparative example 1
0.05 360 0.23 Comparative example 2
0.01 360 0.27 Composition 2
0.01 1360 0.43 Composition 3 0.006 700 0.5
6 As can be seen from the above table, compositions 1 to 3 are all superior to Comparative Example 1.2 in terms of roughness, coercive force, and squareness ratio.

Next, FIG. 4 shows the results of measuring the average surface roughness with respect to the holding time in the orientation magnetic field for composition 3. According to this, the roughness of one surface hardly changes if the holding time in the magnetic field is less than 5 seconds, but after this time, it rapidly becomes rougher, and after 10 seconds, it becomes approximately 0.
05μ, and after 30 seconds, it becomes about 0.21μ. From this result, if the holding time in the magnetic field is within 5 seconds,
It can be seen that the surface does not become too rough and the original smoothness remains maintained.

(Effects of the Invention) It is possible to produce magnetic recording media with excellent surface properties and high orientation.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an example of an apparatus used in carrying out the present invention, Figs. 2 and 3 are front sectional views showing another apparatus, and Fig. 4 shows surface roughness versus retention time in a magnetic field. FIG. 1... Vertical magnetic field alignment device, 2... Tape (base material),
3...Electron beam irradiation device

Claims (1)

[Claims] A magnetic paint containing dispersed magnetic particles is applied to a base material to form a magnetic coating film, which is oriented in a vertically oriented magnetic field within 5 seconds, and then exposed to an electron beam within 1 second. A method for manufacturing a magnetic recording medium, comprising curing the coating film by starting irradiation.