JPH0690793B2 - Method of manufacturing magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a magnetic recording medium of magnetic powder having excellent dispersibility, and more specifically, it relates to a method for solidifying a magnetic coating material by volatilizing a solvent. The present invention relates to improvement of a method for treating a magnetic paint or a magnetic recording medium in a state.

[Prior Art and its Problems] Generally, magnetic recording media such as magnetic tapes and flexible magnetic disks are prepared by magnetic powder, binder and other necessary additives in a volatile solvent on a non-magnetic support such as polyester film. It is manufactured by coating and drying a magnetic paint that is mixed and dispersed. However, if there is a foreign substance such as a dispersion of magnetic powder or reaggregate in the magnetic paint, a noise pulse after DC erase Since it causes a noise represented by an extra pulse error, a foreign substance in the magnetic coating material is removed by using a filter in the liquid feeding system of the magnetic coating fluid immediately before coating.

However, the method using the filter has the following problems.

The smaller the pore size of the filter immediately before coating is, the more effective it is in removing foreign matter in the magnetic paint, but if the pore size is too small, additives such as magnetic powder itself or additives for the purpose of reinforcing the durability of the magnetic layer, etc. In some cases, the magnetic recording medium is removed and the performance as a magnetic recording medium cannot be maintained.

In addition, magnetic powder etc. is likely to be clogged in the filter, and the filter must be replaced frequently, and the applicator must be stopped each time, and if the filter pore size is too small, the operating rate will decrease and the workability will also deteriorate at the same time. .

However, in order to prevent the increase of noise such as extra pulse error, in reality, it is unavoidable to frequently replace the filter even if productivity and workability are ignored. Therefore, there is an urgent need to develop a technique that can reduce the frequency of filter replacement in the coating process without impairing the performance.

[Object of the Invention] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetic recording medium which is coated with a magnetic coating material in a stable dispersed state and has few extra pulse errors.

Another object of the present invention is to extend the service life of the filter of the coating liquid feeding system and improve the operating rate and workability such as the frequency of filter replacement.

[Structure and Action of the Invention] In order to achieve the above-mentioned object, the present invention is a method for producing a magnetic recording medium in which a magnetic coating material is applied onto a non-magnetic support, and is applied before the solvent volatilizes and the magnetic coating material solidifies. An alternating magnetic field is applied to the liquid to apply it, completely dry it, and calendering it if necessary.

That is, the present invention is to apply a magnetic paint dispersed in a volatile solvent together with a magnetic powder, a binder and other necessary additives to a non-magnetic material while sending it through a filter, and volatilize the solvent to form a magnetic paint. A method for producing a magnetic recording medium, characterized in that, when the magnetic recording medium is produced by solidification, an AC magnetic field is applied to the magnetic paint in a transport pipe upstream from the filter to disperse the magnetic powder.

Hereinafter, the present invention will be described with reference to the drawings.

FIG. 1 shows an example of an embodiment of the present invention.

The magnetic coating material 1 sent from the previous step and uniformly dispersed in the volatile solvent together with the magnetic powder, the binder and other necessary additives is introduced into the storage tank 2 and stored therein. During storage, stir with a stirrer to prevent precipitation and aggregation.

The magnetic coating material 1 is applied by a liquid feed pump 3 to a non-magnetic support after passing through an AC solenoid 4 to which AC is supplied by an AC power supply 5 and a filter 6. When the viscosity of the magnetic paint when an alternating magnetic field is applied is adjusted to about 5 to 100 poise, the magnetic powder is well dispersed by the magnetic field.

By the way, the magnetic field strength of the alternating magnetic field used in the present invention is
Viscosity of magnetic paint, flow rate, size / shape / coercive force of magnetic particles, AC power supply frequency, AC magnetic field passage length, magnetic field application time, etc. should be determined by field tests. Gauss to 700 gauss, particularly 70 gauss to 350 gauss are preferably used.

AC power supply frequency is related to the above factors in the same way, but above 20Hz
The range below 50 KHz is preferably selected.

As the AC magnetic field generator, other known means than the AC solenoid described above is used.

The magnetic powder used in the present invention is, for example, γ-
Fe ₂ O ₃ powder, Fe ₃ O ₄ powder, Co-containing γ-Fe ₂ O ₃ powder, Co-containing Fe ₃
In addition to O ₄ powder, various conventionally known magnetic powders such as Fe powder, Co powder, and metal powder such as Fe—Ni powder are widely included.

Further, as the binder, a vinyl chloride-vinyl acetate copolymer, a fibrin resin, a butyral resin, a polyurethane resin, a polyester resin, an epoxy resin, a polyether resin, an isocyanate compound and the like have been conventionally used widely. Any binder resin that is present is used.

Examples of the volatile solvent include ketone solvents such as cyclohexanone, methyl ethyl ketone, and methyl isobutyl ketone,
Aromatic hydrocarbon solvents such as benzene, toluene, xylene, sulfoxide solvents such as dimethyl sulfoxide, ether solvents such as tetrahydrofuran, dioxane, etc. Solvents suitable for dissolving the binder resin to be used are particularly limited. They are used alone or as a mixture of two or more.

In addition, various additives that are normally used, such as a lubricant, an abrasive, an antistatic agent, and a rust preventive, may be appropriately added to the magnetic paint.

[Example 1] A magnetic paint having the following composition was prepared by a conventional method.

CO deposition γ-Fe ₂ O ₃ (Coercive force 600 Oe, particle size 0.4 μm, needle ratio 7 /
1) 100 parts by weight Alumina 4 parts by weight Carbon black 10 parts by weight Dispersant 5 parts by weight Urethane resin 32 parts by weight Coronate L (Nippon Polyurethane Industry Product) 10 parts by weight Stearate ester 5 parts by weight Cyclohexanone, methyl ethyl ketone, toluene mixed solvent 350 parts by weight Part The magnetic coating liquid thus obtained is stored in the storage tank 2 as shown in Fig. 1 and the internal dimensions provided in the transportation pipe of the liquid feeding line are 250 mm in width, 40 mm in height, 60 mm in depth and 100 windings. After applying the AC solenoid 4 at a frequency of 60 Hz and a magnetic field strength of 205 gauss, the magnetic paint was continuously fed from the liquid feed pump,
It is guided through a filter 6 to a coating machine and dried on a polyethylene terephthalate film having a thickness of 75 μm to have a thickness of 1.5 μm.
It was applied so as to be m. After the magnetic particles in the magnetic layer coated on the base film were randomized in the orientation within the coating surface, they were introduced into a drying chamber, dried, and calendered. A disk having a diameter of 130 mm was punched out and subjected to a polishing treatment, and then a sample was put in a jacket for a floppy disk.

[Example 2] In the same magnetic coating liquid as in Example 1, an AC solenoid was installed in the transportation pipe of the circulation line as shown in Fig. 2 to perform the same magnetic coating liquid circulation process as in Example 1. An AC magnetic field was applied, a part of the magnetic coating liquid in the circulation system was extracted, and similar coating was performed in a continuous state, to prepare a sample.

Comparative Example 1 As shown in FIG. 3, an AC solenoid was placed in the same magnetic coating liquid as in Example 1 at a position where the volatile organic solvent had not volatilized and the magnetic coating did not solidify before entering the drying chamber. After applying the same alternating magnetic field as in Example 1 and applying the same coating, a sample was prepared.

[Comparative Example 2] A magnetic coating solution similar to that of Example 1 was applied in the same manner without applying an alternating magnetic field, and then a sample was prepared.

For the magnetic recording media of Examples 1 and 2 and Comparative Examples 1 and 2 obtained as described below, the measurement result of the extra pulse error and the progress until the discharge pressure of the filter in the above operation reaches 5 kg / cm ^2. The times are shown in Table 1.

Note that the extra pulse records a flux reversal frequency of 250,000 flux reversals / second, then performs DC erasing, and the peak value of the reproduced signal becomes a signal that exceeds 20% of half the average signal width. As the extra pulse error, the extra pulse of all tracks was measured, and it was defined as the ratio of the samples in which one or more extra pulses were generated.

In addition, the reason why we evaluated the elapsed time for the discharge pressure of the filter to reach 5 kg / cm ² is that the clogging of the filter during the filtration process in this experiment gradually increased, and the discharge pressure was 5 kg / cm ^2.
Since there is a concern that the piping will rupture more than cm ² and foreign matter larger than the pore size of the filter will be forced through, the filter must be replaced when the discharge pressure approaches 5 kg / cm ² This is because it serves as a guide.

As is clear from Table 1, the methods of Examples 1 and 2 are
Compared to the comparative example 2 of the conventional example which does not use an AC magnetic field, the extra pulse error is smaller, and the filter 5 kg / cm ² arrival time is longer than those of the comparative examples 1 and 2, so that the frequency of filter replacement is reduced and the workability is large. Improved width. This indicates that this example is superior to the comparative example.

[Brief description of drawings]

1 and 2 are schematic process diagrams showing an embodiment of the present invention and FIG. 3 is a comparative example 1. In the drawing, 1 is a magnetic paint, 2 is a storage tank, 3 is a liquid feed pump, 4 is an AC magnetic field, 5 is a magnetic field generating power supply (AC), and 6 is a filter.

Claims (5)

[Claims] 1. A magnetic paint obtained by dispersing and dissolving magnetic powder, a binder and an additive in a volatile solvent and applying the magnetic paint onto a non-magnetic material while sending it through a filter and volatilizing the solvent. A method for producing a magnetic recording medium, characterized in that, when the magnetic powder is solidified to produce a magnetic recording medium, an AC magnetic field is applied to the magnetic paint in the transport pipe upstream of the filter to disperse the magnetic powder. 2. The method for producing a magnetic recording medium according to claim 1, wherein the alternating magnetic field applied to the magnetic paint is in the range of 35 to 700 gauss. 3. The alternating magnetic field applied to the magnetic paint is 20 Hz to 50 KH.
The method for producing a magnetic recording medium according to claim 1 or 2, wherein z is z. 4. A method of manufacturing a magnetic recording medium according to claim 1, wherein an alternating current magnetic field generator is an alternating current magnetic field generator. 5. The viscosity of the magnetic paint when an alternating magnetic field is applied
The method for producing a magnetic recording medium according to any one of claims 1 to 4, which is in a range of 5 to 100 poises at a temperature of 25 ° C.