Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
1998-04-09
2001-11-06
Bareford, Katherine A. (Department: 1762)
Coating processes
Magnetic base or coating
Magnetic coating
C427S131000, C427S358000, C118S410000
Reexamination Certificate
active
06312758
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a coating device and a coating method using an extrusion die, and particularly to a coating device and a coating method which are effective for high-speed coating with an organic solvent.
2. Description of the Related Art
Curtain coating has been known as a method of coating a polyethylene terephthalate film or a paper support with a non-magnetic paint, a solvent or water in a non-contact manner.
This coating method is adapted for causing a coating solution extruded from a die to drop by its tare weight so as to form and apply a coating film onto a support. Therefore, the flowing speed of the coating solution is low, and as high-speed coating is to be carried out, the coating solution is broken by an air film accompanying the support which travels at a high speed, or the air enters a contact surface between the support and the coating solution, thus generating uneven coating and deterioration in coating quality. With respect to a magnetic tape in particular, since a polyethylene terephthalate or polyethylene naphthalate film having a mirror surface is used, the air film is likely to be generated and therefore high-speed coating is technically difficult.
The curtain coating method does not enable high-speed coating for the following reasons. That is, since the flowing speed of the coating solution is limited to a low speed by the gravity due to drop by its tare weight, the rigidity of the coating solution film is low. Also, the coating solution film cannot endure the wind pressure of the air film accompanying the flexible support traveling in the traverse direction of the coating film, or the air enters between the coating solution film and the support.
According to the known information, patented inventions are reported such that a preventive measure against the air film is taken by providing a reduced-pressure chamber at the entrance of a coating portion or such that a preparatory chamber is filled with a gas which is likely to be absorbed in the coating solution. However, no significant increase in speed can be expected and devices therefor are complicated and more difficult to operate.
SUMMARY OF THE INVENTION
In view of the foregoing status of the art, it is an object of the present invention to provide excellent coating device and method which realize high-speed coating by improving the rigidity of the coating solution film and increasing the pressure of the coating solution film to the support so as not to be inferior to the wind pressure of the air film.
As a result of intensive studies to achieve the above-described object, the present inventors have found that the rigidity of a coating solution film of a solvent may be improved to deal with an air film by increasing the kinetic energy of the solvent.
A coating device according to the present invention has been completed on the basis of such finding. In a coating device for extruding and applying an organic solvent onto a continuously traveling support from a slit of an extrusion die prior to preparation of a magnetic tape by coating the support with a paint, the slit spacing is not greater than 50 &mgr;m and the gap between the support and the extrusion die is 0.5 to 2 mm. The extrusion speed of the organic solvent from the slit is not lower than 2.5 m/sec.
In the coating device according to the present invention, the extrusion angle of the organic solvent is not smaller than 0° and smaller than 90° upward from the horizontal line.
Also, in a coating method according to the present invention for extruding and applying an organic solvent onto a continuously traveling support from a slit of an extrusion die prior to preparation of a magnetic tape by coating the support with a paint, the slit spacing is not greater than 50 &mgr;m and the gap between the support and the extrusion die is 0.5 to 2 mm. The extrusion speed of the organic solvent from the slit is not lower than 2.5 m/sec.
In the coating method according to the present invention, the extrusion angle of the organic solvent is not smaller than 0° and smaller than 90° upward from the horizontal line.
That is, in the coating device and the coating method according to the present invention, the organic solvent is extruded from the slit of the extrusion die at a high speed, thereby forming a uniform film over a coating width only by the kinetic energy of the extruded solvent so as to enable realization of high coating film rigidity and coating solution pressure. Thus, high-speed coating onto the continuously traveling support may be carried out in a non-contact manner.
REFERENCES:
patent: 4424762 (1984-01-01), Tanaka et al.
patent: 4681062 (1987-07-01), Shibata et al.
patent: 4968528 (1990-11-01), Tanaka et al.
patent: 5105760 (1992-04-01), Takahashi et al.
patent: 5318804 (1994-06-01), Yoshida
patent: 5569494 (1996-10-01), Suzuki et al.
patent: 5704978 (1998-01-01), Maniwa
patent: 2 734 500 (1996-11-01), None
Webster's II New Riverside University Dictionary, The Riverside Publishing Company, p. 390, 1984.
Maniwa Osamu
Sato Shogo
Bareford Katherine A.
Bell Boyd & Lloyd LLC
Sony Corporation
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