JP3213972B2 - Coating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extrusion type coating apparatus called a die coater.

[0002]

2. Description of the Related Art Conventionally, as a method of applying a magnetic paint when manufacturing a coating type magnetic recording medium, a roll coating method using a roll, such as a gravure roll method or a reverse roll method, is mainly used. Has become. However, in these roll coating methods, the output quality fluctuates due to coating thickness unevenness due to poor transfer of the paint from the roll to the base film, the dropout due to paint scattering, and the paint quality due to the surplus paint being returned to the mixing process. There are problems such as deterioration, and these problems tend to become more remarkable as the coating speed becomes higher.

In recent years, attention has been paid to an extrusion (die) method as a new coating method capable of solving these problems, and a part thereof has already been put into practical use in a process of manufacturing a coating type magnetic recording medium. The extrusion method has a narrow slit with a predetermined width at the tip and uses a die formed by making the vicinity of the tip a doctor edge, and paints continuously extruded toward the surface of the moving support by the doctor. It is applied on a support with a uniform thickness by an edge, and has been used in the field of photographic film, photographic paper and the like.

[0004]

In the extrusion coating apparatus, the shape of the tip surface of the die and the interval between the slits that come into contact with the flexible support greatly affect the quality of the coating film. Therefore, usually, a pair of blades made of cemented carbide or the like are provided along the slit at the tip of the die, the gap position of the slit outlet (lip portion) is ensured by the relative positions of these blades, and the support member is used. The contact surface is processed into an appropriate shape to function as a front blade and a smoothing blade.

However, it has been found that when the above-described coating apparatus is used for manufacturing a coating-type magnetic recording medium, the magnetization at the lip becomes a serious problem. That is, since the cemented carbide constituting the blade is a magnetic material and has a high coercive force Hc to some extent, it is easily magnetized by a magnet chuck used to fix the blade during processing. Normally, the magnet chuck has N.
Since the S poles are alternately arranged, the lip is magnetized in a wave shape. At this time, if the magnet chuck is not used to fix the blade, it will not be magnetized,
Since high-precision machining is required for the blade, the use of a magnet chuck is indispensable.

On the other hand, the paint used in the manufacturing process of the magnetic recording medium is a magnetic paint containing a large amount of magnetic powder, and since this magnetic paint is a so-called magnetic fluid,
The magnetic force acts as a resistance to paint flow. Therefore, when a magnetic paint is applied using a die with a magnetized lip,
Vertical stripe-shaped coating unevenness occurs due to the aforementioned wavy magnetization pattern. Further, when the lip portion is magnetized, it attracts a magnetic foreign material floating in the air around the lip portion or a magnetic foreign material attached to the base film during traveling, and the like.
These foreign substances may adhere to the smoothing blade surface and cause streaks on the coating film surface.

Accordingly, the present invention has been proposed in view of such conventional circumstances, and can eliminate vertical stripe-shaped coating unevenness due to magnetization, and has a smooth coating surface with a uniform coating thickness and no streaks. It is an object of the present invention to provide a coating apparatus capable of forming a coating film having the following.

[0008]

In order to achieve the above-mentioned object, a coating apparatus according to the present invention applies a coating material to a continuously running flexible support while extruding the coating material through a slit provided at the tip of a die. In the extrusion type coating apparatus described above, at least the paint flow path surface of the die is formed of a cemented carbide, and the magnetic flux density is reduced to 1 gauss or less by demagnetization.

[0009]

When applying a magnetic paint which is a magnetic fluid, the magnetic force acts as a resistance to the paint flow. Therefore,
If the die (especially, the lip) is magnetized, coating unevenness occurs along the magnetized pattern. In the present invention, the magnetic flux density of the portion of the die that comes into contact with the magnetic paint is set to 1 Gauss or less due to demagnetization, the influence of the magnetic force generated from the die on the paint flow is eliminated, and coating unevenness and streaks are greatly reduced. Is suppressed.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below in detail with reference to the drawings. The coating apparatus of the present embodiment is used for applying a magnetic paint in a manufacturing process of a coating type magnetic recording medium, and as shown in FIG. 1, a pocket (paint pool) of a die (extruder) 1.
The magnetic paint 3 is supplied into the inside 2, supplied to the slit 4, extruded, and applied onto the base film 7 running through the guide rolls 5, 6 and the like.

As shown in FIG. 2, the die 1 is made of a metal block having a substantially rectangular parallelepiped shape having a predetermined width, and the tip is cut off obliquely to form a so-called wedge. As shown in FIG. 3, a front blade 8 and a smoothing blade 9 made of a cemented carbide or the like are integrally attached to the lip portion of the portion 1a. A slit 4 is formed in the die 1 according to the application width so as to face the tip end surface 1a of the die 1. The slit 4 serves as a gap through which the paint is extruded. It is a very narrow gap of about 01 to 2 mm. In the present embodiment, the gap at the exit (lip) of the slit 4 is accurately controlled by the front blade 8 and the smoothing blade 9.

On the back side of the slit 4, a pocket 2 communicating with the slit 4 is formed as a cylindrical space having a length substantially equal to the width of the slit 4. The paint supply ports 10 and 11 having an inner diameter smaller than the inner diameter of the pocket 2 are provided at both ends of the pocket 2.
The magnetic paint 3 is supplied to the inside of the pocket 2 from both sides 1b and 1c. Therefore, the pocket 2 serves as a space for receiving the paint pumped from the paint supply device and has a function of an accumulator.

In the coating device having such a configuration, the magnetic paint 3 supplied from the precision paint supply device to the pocket 2 of the die 1 has a uniform paint pressure due to the accumulator effect, and is uniformly pushed out to the slit 4. It is. The base film 7 includes a front blade 8 and a smoothing blade 9 provided at an exit end of the slit 4.
The magnetic paint 3 extruded from the slit 4 is continuously formed on the smoothing blade 9 into a coating film having a uniform coating thickness and a smooth surface.

At this time, the slit 4, which is a paint passage portion,
When the front blade 8 and the smoothing blade 9 are magnetized, a magnetic field H is generated as shown in FIG. 3, and the flow of the magnetic paint 3 is affected by resistance due to magnetism. For example, as shown in FIG. 4A, if the size and the direction (about ± several tens of gauss) of the magnetic φ periodically change in the width direction of the slit 4 due to the magnetization by the magnet chuck, FIG. As shown in (1), thickness unevenness occurs in the width direction of the base film 7.

Therefore, in this embodiment, the front blade 8 and the smoothing blade 9 and the slit surface 4a through which the paint passes are demagnetized so that there is no magnetism exceeding 1 gauss. The demagnetization may be performed by an ordinary method, and for example, a method such as AC erasing can be adopted. Further, the magnetic flux density of the front blade 8 and the smoothing blade 9 can be easily measured by a commercially available Gauss meter.

Next, the effect of the present invention was confirmed by actually applying a magnetic paint while changing the magnetic flux density of the die in various ways. The configuration of the die used in the experiment is as follows. <Die configuration> Die: Extrusion die with a total width of 340 mm and application width of 290 mm Pocket: A cylindrical hole with a diameter of 40 mm penetrated in the width direction of the die Slit: 0.2 mm gap Front blade: 5 mm thick carbide Alloy Smoothing blade: 5mm thick cemented carbide

The coating conditions are as follows. <Coating conditions> Base film: polyethylene terephthalate film having a width of 305 mm and a thickness of 15 μm Tension: 5 kg over the entire width of the base film Coating speed: 50 to 150 m / min Coating thickness: 3 to 6 μm after drying

Table 1 shows the measured magnetic flux densities and the state of the coating thickness unevenness at that time.

[0019]

[Table 1]

As is apparent from Table 1, the magnetism remaining on the die has a great effect on the coating state, and particularly when the magnetic flux density is 20 gauss or more, the coating thickness unevenness is remarkable, and the magnetic recording medium cannot be used. do not become. On the other hand, when the magnetic flux density was reduced to 1 gauss or less by demagnetization, there was almost no effect on the paint flow, and the coating thickness unevenness was completely eliminated.

The effects of the present invention have been confirmed as described above.
The present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, only the lip portion (front blade and smoothing blade) is formed of a hard metal, but the entire die is formed of a hard metal or the like. The present invention can also be applied to a coated coating device. Needless to say, dimensions, materials, shapes, and the like can be appropriately changed without departing from the spirit of the present invention.

[0022]

As is clear from the above description, in the present invention, the magnetic flux density of the die is reduced to 1 gauss or less by demagnetization. Generation can be eliminated, and a coating film having a uniform coating thickness and a smooth surface without any streaks can be formed.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a schematic configuration example of a coating apparatus to which the present invention is applied.

FIG. 2 is a schematic perspective view showing a die partially broken.

FIG. 3 is a schematic cross-sectional view of a main part, showing a die tip portion in an enlarged manner.

FIG. 4 is a schematic diagram showing a magnetized state at a tip end of a die and a state of uneven coating thickness due to the magnetized state.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Die 4 ... Slit 7 ... Base film (support) 8 ... Front blade 9 ... Smoothing blade

Claims (1)

(57) [Claims] 1. A die on a continuously running flexible support.
In an extrusion-type coating apparatus for applying a coating while extruding the coating through a slit provided at a tip , at least the coating flow path surface of the die is formed of a cemented carbide.
And the magnetic flux density is reduced to 1 gauss or less by demagnetization.
Coating and wherein the that.