JPH06234942A - Method for filtering magnetic coating material - Google Patents

Abstract

PURPOSE:To prevent clogging of a filter with a magnetic coating material without detriment to the particle-catching capability of the filter by applying a fluctuating magnetic field to the material near the filter to destroy agglomerates in the material. CONSTITUTION:A magnetic coating material 15 dispersed with a dispersing machine is fed through a fluid delivery pipe 16 to a filter 12. The material is filtered there while simultaneously being dispersed by applying a fluctuating magnetic field to the filter 12 by passing a fluctuating electric current from a power source 13 through a coil section 11 wound around the filter 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for filtering a magnetic paint used for producing magnetic recording media such as floppy disks and magnetic tapes.

[0002]

2. Description of the Related Art In recent years, a large amount of floppy disks, magnetic tapes and the like have been used for recording information in computers and word processors. As the density of these information recording media has increased, defects on the surface of the magnetic layer have become a serious problem. The magnetic layer is formed by coating the base film with a magnetic coating that has been previously dispersed, and then removing the organic solvent.However, defects on the surface of the magnetic layer are observed when the dispersed state of the magnetic coating is insufficient. Most of them are caused by agglomerates of magnetic powder of magnetic paint.

Generally, a good dispersion state of a magnetic coating material is achieved mainly by a kneading step and a dispersing step, either alone or in combination. The kneading step is mainly provided before the dispersing step or in the middle of the dispersing step. In the kneading step, an apparatus having a strong kneading force, for example, an open kneader, a pressure kneader, a continuous kneader or the like is used. The dispersing step is ideally provided to disperse the magnetic powder into individual particles in the magnetic coating material by mechanically applying a high shearing force or the like. In this process, for example, two rolls, three rolls, ball mill, sand grinder,
A mechanical means using a high speed mixer, a high speed impact mill, a homogenizer, an ultrasonic disperser, etc., and a chemical means using various dispersants are used.

However, even with the magnetic paint well dispersed in this way, it is usual that fine agglomerates are observed in the paint, and filtration is often performed during the preparation of the solution. Even after the dispersion process, the magnetic powder will re-aggregate during transportation from the disperser to the coating process, during retention in the stock container before the pump, or during transport from the stock container to the coater. A filter is usually installed between the two.

[0005]

In these filtration steps, undispersed lumps, large aggregates, etc. are captured by this filter, and at the same time, gel substances such as re-aggregated lumps are also captured by the filtration conditions. It However,
When operated under such conditions, the filter becomes clogged with time, and the pressure loss gradually increases.
Therefore, in order to protect the filter from use below the pressure resistance limit value and to prevent the flow velocity from becoming unstable, it is often necessary to replace each filter even during coating.

[0006]

Means for Solving the Problems As a result of studies to solve the above problems, the present inventors have found that a magnetic paint near a filter existing between the dispersion process of the magnetic paint and the coating portion of the base film is present. When a fluctuating magnetic field is applied to the
The pressure loss in the filter is reduced and the life of the filter is extended, the viscosity of the magnetic paint is reduced and the amount of liquid fed under a constant pressure can be increased compared to when a variable magnetic field is not applied. It was found that a uniform magnetic layer having an excellent surface property can be formed by applying the coating method to reach the present invention.

That is, the gist of the present invention resides in a method for filtering magnetic paint with a filter, which is characterized in that a varying magnetic field is applied to the magnetic paint near the filter. Hereinafter, the present invention will be described in detail. The magnetic coating material used for coating in the present invention contains magnetic powder, a binder resin, an organic solvent, and may further contain an abrasive, a dispersant, a lubricant, a conductivity-imparting agent and the like. The components constituting these magnetic paints are not particularly limited as long as they are used in the production of ordinary magnetic recording media.

The variable magnetic field applied in the present invention is
It means a magnetic field whose direction and / or strength changes with time, and examples thereof include a stationary alternating magnetic field and an alternating magnetic field whose strength periodically decays to substantially zero. For example, in the case of needle-shaped magnetic powder that is preferably used in the present invention,
It is considered that the fluctuating magnetic field momentarily aligns the magnetization directions of the individual magnetic powders to a constant direction, and then the magnetic powders are dispersed to achieve the dispersion of the gel-like reaggregated lumps. The conditions such as the frequency and strength of these fluctuating magnetic fields are appropriately selected and optimized depending on the properties of the magnetic paint and the shape of the magnetic powder, but generally the maximum magnetic field strength is the average of the magnetic powder in the magnetic paint. A guideline is about 1 to 3 times the coercive force, and there is a tendency that finer magnetic powders require higher frequencies.

An example of how to apply the fluctuating magnetic field is to install a coil outside the filter and to apply a fluctuating current from the power supply to the coil. FIG. 1 is a schematic diagram showing an example of a liquid supply pipe and a filter for carrying out the method of the present invention. The magnetic coating material 15 is dispersed by a disperser, and then enters the filter 12 through a liquid delivery pipe 16. Normally, magnetic powder reaggregates in this liquid feeding step and in a portion where the liquid velocity is still slow immediately after passing through the filter, but a coil portion 11 including a copper coil is provided for the filter, and an external power supply 13 is provided. By passing a fluctuating current through the conductor to the coil, the magnetic paint in the filter is subjected to a fluctuating magnetic field to be in a good dispersion state and is sent to the coating machine. At this time,
A coolant 14 such as water is flown through the coil portion 11 to prevent heating of the coil.

In the present invention, the coil may be wound only on the filter portion as shown in FIG. 1, but the coil may be wound only on the pipe portion before the filter to give a varying magnetic field, or a combination thereof may be used. Good. Also in this case, dispersibility
Filterability is improved. Also, if a coil is wound around the pipe between the filter and the coating machine and a fluctuating magnetic field is applied,
It is possible to maintain a good dispersion state just before the coating machine. Furthermore, if a fluctuating magnetic field is applied to the magnetic coating material inside the coater, a magnetic layer having a more excellent surface property can be obtained.

[0011]

EXAMPLES The embodiments of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded. Examples 1 and 2 Magnetic paints were prepared according to the compositions shown below.

[0012]

[Table 1] Co-γ-Fe ₂ O ₃ (Hc = 700 Oe, SSA = 20 m ² / g) 100 parts by weight Polyurethane (manufactured by Nippon Polyurethane Company; N2304, MDI-based polyester polyurethane) 18 parts by weight Vinyl chloride / vinyl acetate / Vinyl alcohol copolymer (manufactured by Union Carbide Co., USA; VAGH) 18 parts by weight α-alumina (particle size; 0.5 μm) 3 parts by weight Carbon black (Mitsubishi Kasei; # 3250B) 8 parts by weight Lecithin 5 parts by weight butyl Stearate 5 parts by weight Methyl ethyl ketone 170 parts by weight Cyclohexanone 170 parts by weight

After passing through the dispersing step, the above-mentioned magnetic paint was put into a stock container, and passed through the liquid feed pipe through the filter portion shown in FIG. 1 by the pressure difference (filtration pressure) before and after the filter portion shown in Table-1, The flow rate was measured. The filtered magnetic paint was applied onto a polyethylene terephthalate base film. The filter used had an absolute accuracy of 1 μm. A constant alternating current of 50 Hz was applied to the coil portion of FIG. 1 while flowing cooling water inside, and a fluctuating magnetic field having the maximum magnetic field strength shown in Table 1 was applied to the magnetic paint in the liquid transfer pipe and in the filter portion. . After applying and drying the magnetic paint, the magnetic layer formed on the base film is gloss meter (Suga Test Instruments Co., Ltd.) without calendering.
Was used to measure the surface gloss (incident angle 60 °).
The results are shown in Table-1. Comparative Example 1 The flow velocity and gloss were measured in the same manner as in Example 2 except that the changing magnetic field was not applied. The results are shown in Table-1.

[0014]

[Table 2]

According to Table 1, when the fluctuating magnetic field is applied (Examples 1 and 2), the gloss (%) on the surface of the magnetic layer is superior to that when the fluctuating magnetic field is not applied (Comparative Example 1). Therefore, it can be seen that a uniform magnetic layer is formed. Further, it is apparent that the flow velocity for a constant pressure is increased by adding the fluctuating magnetic field.

[0016]

According to the present invention, a magnetic coating material can be formed by applying a fluctuating magnetic field to the magnetic coating material in the vicinity of the filter provided during the transfer of the dispersed magnetic coating material from the kneading / dispersion step to the coating section. Even if re-aggregation occurs, the agglomerates are destroyed without impairing the particle capturing ability of the filter itself,
A good dispersion state can be realized. As a result, the clogging of the filter due to the agglomerates is significantly reduced and the pressure loss can be suppressed as much as possible, so that the filter will last longer and the replacement of the filter during application can be reduced. In addition, since the viscosity of the magnetic paint is reduced by applying the fluctuating magnetic field, it is possible to increase the liquid sending amount under a constant pressure as compared with the case where the fluctuating magnetic field is not applied. Thereby, for example, in the case of coating with an extrusion type die head, a method of circulating the magnetic paint in the liquid reservoir inside the die through an external flow path is generally used, but the circulation speed is kept while keeping the pressure loss of the filter portion low. It is possible to raise. Furthermore, according to the present invention, since it is possible to filter with a filter having finer meshes than the conventional one,
As a result smaller undispersed masses and impurities can be removed. Therefore, the magnetic layer formed by coating and then drying becomes more uniform, and the surface property becomes extremely good. By adopting such a filtering method, variations in quality as a magnetic recording medium are reduced, noise is reduced, and an error rate is also extremely reduced, so that it is suitable as a medium for high density recording.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a liquid supply pipe and a filter for carrying out the method of the present invention.

[Explanation of symbols]

 11 coil part 12 filter 15 magnetic paint 16 liquid transfer pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masahiro Yamamoto Inventor Masahiro Yamashita Kasei Co., Ltd.

Claims (1)

[Claims] 1. A method for filtering a magnetic coating material by filtering a magnetic coating material with a filter, wherein a varying magnetic field is applied to the magnetic coating material near the filter.