JPH06246217A - Coating machine for magnetic coating - Google Patents

Abstract

PURPOSE:To make it possible to use a coated magnetic recording medium as a medium for high recording concn. by providing a magnetic field loading means in the neighborhood of a slit gap and applying an electric insulation treatment on at least a part of the connection of upper and lower member to decrease eddy electric current. CONSTITUTION:In a coating machine for a magnetic coating, upper and lower members 3 and 4 are formed of a one piece body of an electrically conductive material such as stainless steel and SUS440 and an insulating film 5 is provided on their edge contacting part to prevent a large eddy electric current circulating between the upper and lower members 3 and 4 from generating and a solenoid coil 12 which is a magnetic field loading means for applying a variable magnetic field to the magnetic coating in the neighborhood of a slit gap 2, is provided. As the result, as there exists substantially no generation of a large eddy electric current circulating in the upper and lower members 3 and 4 of the coating machine, there is no possibility of heating the coating machine and. required variable magnetic field can be given to the magnetic coating without loss of the magnetic strength generated by the coil 12 is the coating machine.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coating machine for uniformly coating a base film with a magnetic coating material used for manufacturing magnetic recording media such as floppy disks and magnetic tapes.

[0002]

2. Description of the Related Art In recent years, a large amount of magnetic recording media such as floppy disks and magnetic tapes 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 solvent.The defects on the surface of the magnetic layer are usually observed only when the dispersed state of the magnetic coating is insufficient. Most of them are due to agglomerates of magnetic powder in the magnetic paint. Usually, the dispersion step for obtaining a good dispersion state of the magnetic coating is carried out by using a mechanical means such as a ball mill to make the magnetic particles fine and a chemical means using a chemical dispersant. At the stage of the disperser, the magnetic paint is sufficiently evenly dispersed.

However, the transport process from the disperser to the coater,
The magnetic powder may re-aggregate inside the coater or the like, which often causes defects on the surface of the magnetic layer. For example, a die coater is used as a means for applying the magnetic paint to the base film. A die coater is a device that forms a manifold and a slit gap with an upper member and a lower member, distributes the magnetic paint supplied in the die with the manifold, extrudes it in a thin film form from the slit gap, and applies it to the running base film. Yes, and is usually made of conductive stainless steel. In this case, since the magnetic paint flows at a certain speed or more in the transport pipe to the die, shearing force acts to substantially prevent reaggregation of the magnetic powder in the magnetic paint, but In the large manifold portion, the magnetic powder is likely to re-aggregate due to the retention of the magnetic paint.

On the other hand, by applying a fluctuating magnetic field to the magnetic paint,
A method for dispersing these re-aggregated lumps is disclosed in Japanese Examined Patent Publication No. 3-503.
It is proposed in No. 31 and so on. For example, a magnetic layer having a good surface property is formed by applying a fluctuating magnetic field to the magnetic paint present in the manifold or slit gap inside the coater. However, on the other hand, since the applicator is usually made of a conductive material such as stainless steel, if a varying magnetic field is applied to the magnetic paint present in the manifold or slit gap, the varying magnetic field will cause a large eddy current in the coater. Occurs, and the applicator itself is heated and becomes dangerous, and the fluctuating magnetic field is shielded by the generation of the eddy current and cannot be sufficiently transmitted to the inside.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and is formed of a conductive material if a coating machine is subjected to a specific electrical insulation treatment. Even if the coater is placed in a fluctuating magnetic field, a large eddy current is not substantially generated, and therefore, the coater is not heated, and the fluctuating magnetic field is not shielded by the generation of the eddy current and is well dispersed. It is based on finding that the state can be realized.

That is, the gist of the present invention is to provide a magnetic paint coating machine in which an upper member and a lower member each made of a conductive material are provided, and a slit gap is formed by a combination of the upper member and the lower member. A magnetic field applying means for applying a magnetic field in the vicinity of the slit gap, and the upper member and the lower member so as to substantially reduce an eddy current circulating between the upper member and the lower member. A magnetic paint coating machine is characterized in that at least a part of the connection portion is electrically insulated.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of a specific embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view of an applicator for magnetic paint showing one embodiment of the present invention, and FIG. 2 is a view of I-of the applicator of FIG.
It is sectional drawing by the I line. The magnetic paint enters the applicator manifold 1 through the transport pipe 7 and the slit gap 2
Through the head 6 to be applied and applied on a base film (not shown). The manifold 1 and the slit gap 2 are formed by combining the upper member 3 and the lower member 4 of the coating machine. A ceramic material such as silicon carbide may be used for the head 6,
Since the positioning of the head with respect to the coating film is required with high accuracy, the upper member 3 and the lower member 4 are made of an integral material of a conductive material such as stainless steel or SUS440c.

In this embodiment, in order to prevent generation of a large eddy current circulating between the upper member 3 and the lower member 4,
An insulating film 5 is provided at those connecting portions. The insulating film 5 is made of, for example, a film of polyethylene terephthalate having a thickness of about 10 μm (in FIG. 2, the thickness of the insulating film 5 is shown enlarged). Also, 14
Is a side plate for holding the magnetic paint existing in the manifold 1, and at least one of the side plates is made of Teflon or the like in order to prevent generation of a large eddy current circulating between the upper member 3 and the lower member 4. Insulation is performed using a non-conductive material or a plate having a non-conductive material attached to a stainless steel surface and having an insulating property. Upper member 3 and lower member 4
If they are completely insulated, an induced voltage may be generated between the upper member 3 and the lower member 4 when they are placed in a magnetic field. It is desirable to have only one side. Further, the side portion 20 of the slit gap is covered with, for example, an insulating film in order to prevent side leakage of the magnetic paint in the slit gap, but the side portion 20 may be covered by extending the end portion of the side plate. Also in this case, it is preferable that the insulating treatment is performed on only one side.

Reference numeral 12 is a magnetic field applying means for applying a fluctuating magnetic field to the magnetic paint near the slit gap 2, and is constituted by a solenoid coil in this example. The coil 12 generates a fluctuating magnetic field by a fluctuating current i from a power source unit (not shown). The fluctuating magnetic field to be generated is not particularly limited, but examples thereof include a stationary alternating magnetic field and an alternating magnetic field whose strength is periodically attenuated to substantially zero. The direction of the fluctuating magnetic field is H in FIG. The direction of the magnetic field parallel to the flow of the magnetic paint in the slit gap 2 as shown by is preferable.

Next, an experimental example using the coating machine shown in FIG. 1 will be shown. The temperature of the manifold portion was measured when a fluctuating magnetic field having a frequency of 100 Hz and a maximum magnetic field strength of 1 kOe as shown in FIG. 3 was applied to the coating machine shown in FIG. As a result, the temperature of the manifold is 25 ° C even after 5 minutes of power application.
It was found that the temperature increased from 2 to 27 ° C. by about 2 ° C. and did not increase thereafter. The magnetic field strength inside the manifold was also measured, but no reduction was found within the measurement error with respect to the magnetic field strength in the air core coil state.

On the other hand, when a similar fluctuating magnetic field is applied to a conventional stainless steel coating machine in which the upper member and the lower member are not electrically insulated, the temperature of the manifold rises with time and about 5 From 25 ℃ to 84 ℃ in minutes,
It also rose by about 59 ° C. It is considered that this is because eddy currents circulating in the upper and lower components were generated. Further, the magnetic field strength in the manifold was reduced by about 6% with respect to the magnetic field strength in the air core coil state.

In the embodiment described above, an insulating film is sandwiched between the upper member and the lower member, and at least one of the side plates is also subjected to an insulating treatment. The configuration is not limited to this, and any configuration that substantially reduces the eddy current circulating between the upper member and the lower member can be preferably used.

[0013]

According to the coating machine of the present invention, as a result of electrically insulating a part of the connecting portion between the upper member and the lower member of the coating machine, a large eddy current circulating in the upper and lower portions of the coating machine is generated. Since there is substantially no generation, the coating machine is not heated. Further, the magnetic field strength generated in the coil is hardly reduced even in the coating machine, and the desired fluctuating magnetic field can be applied to the magnetic coating material in the coating machine. Therefore, the reaggregated mass of magnetic powder can be easily dispersed in the coating machine. be able to.
Therefore, the magnetic recording medium coated by using the coating machine capable of preventing the re-aggregation of the magnetic powder has reduced noise, can be used as a medium for high recording density, and has an extremely low error rate.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of a magnetic paint coating machine of the present invention.

FIG. 2 is a cross-sectional view taken along the line I-I of the coating machine of FIG.

FIG. 3 is a conceptual diagram of a fluctuating magnetic field applied to a coating machine in Examples.

[Explanation of symbols]

 1 Manifold 2 Slit Gap 3 Upper Member 4 Lower Member 5 Insulating Film 12 Coil 14 Side Plate

Claims (1)

[Claims] 1. A magnetic paint coating machine having an upper member and a lower member each made of a conductive material, wherein a slit gap is formed by a combination of the upper member and the lower member, in the vicinity of the slit gap. At least a part of the connecting portion between the upper member and the lower member so as to substantially reduce the eddy current circulating between the upper member and the lower member, having magnetic field applying means for applying a magnetic field. An applicator for magnetic paints, characterized in that it is electrically insulated.