Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
2002-09-25
2004-12-21
Bareford, Katherine (Department: 1762)
Coating processes
Magnetic base or coating
Magnetic coating
C427S128000, C427S345000, C427S356000, C427S358000, C427S359000, C427S361000, C118S062000, C118S602000, C118S118000, C118S123000, C118S126000, C118S410000, C118S413000, C118S414000
Reexamination Certificate
active
06833157
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coating method and apparatus, in particular to coating method and apparatus for use in manufacturing photosensitive materials and magnetic recording media.
2. Description of the Related Art
Photosensitive materials and magnetic recording media are manufactured through a coating step of forming a coating film by applying a prescribed coating liquid, such as magnetic liquid, to a continuously running sheet substrate strip (hereinafter referred to as “web”). In recent years, magnetic recording media such as magnetic recording tape particularly for broadcasting or computer use have been rapidly improved in capacity and recording density, and there has been needed a coating technology capable of providing a magnetic layer which is extremely thin and of which surface is smooth.
Coating apparatus for applying a coating liquid to the surface of a web include, for example, apparatus of types such as roll coater, gravure coating, roll coating plus doctor roll, extrusion coating, and slide coating; in recent years, apparatus of extrusion type have been commonly used.
One method which employs an extrusion type of apparatus and in which the tip of a coating head is pushed against a web, as described in Japanese Patent Application Publication No. 58-109162, has been commonly used in the field of manufacturing magnetic recording media, since a thin and uniform coating layer can be obtained just by increasing the fluid pressure at the tip of the coating head utilizing the web tension, thereby eliminating the air accompanying the web. However, even in the method of applying a single coat of coating liquid using this type of coating head, the reduction in coating thickness is limited.
As a further method for forming a much thinner coating layer, there is a method in which a very thin coating layer can be formed by applying a coating liquid to a web to excess using a web-pushing type of extrusion coater and then scraping-off the excess coating liquid with a blade disposed on the downstream side of the extrusion coater, as described in Japanese Patent Application Publication No. 7-287843. In this case, the device which applies a coating liquid to a web to excess is not necessarily limited to the web-pushing type of extrusion coater, but coaters such as roller coater type coater, gravure coater and extrusion coater equipped with a back-up roll can be used.
In the method using the conventional scraping-off type of extrusion coater shown in
FIG. 8
, however, since the coating liquid recovered by scraping-off, with a blade
6
, the excess amount of coating liquid having been applied to a web
5
at a coating head
3
has been once exposed to the atmosphere, the solvent contained in the coating liquid has been volatilized, thereby changes are caused in the fluid physical properties such as viscosity and solid content concentration. Thus, the method has a disadvantage in that, since the use of the coating liquid, as it is, of which viscosity has been changed adversely affects the amount of the coating liquid to be scraped-off or the final thickness of the coating film after being scraped-off with the blade
6
, the recovered coating liquid must undergo treatment for adjusting its physical properties such as viscosity and solid content concentration in a coating liquid adjusting tank
8
before reused. In addition, since the recovering line for recovering the coating liquid is opened to the atmosphere, dust from the outside of the recovering line is likely to be included in the recovered coating liquid. Thus, the method also has a disadvantage in that dust cannot be fully removed even if the recovered coating liquid is filtered through a filter
9
when pumping the recovered coating liquid from a supply tank
1
to the coating head
3
with a pump
2
.
SUMMARY OF THE INVENTION
The present invention has been made in the light of such circumstances, and an object of the present invention is to provide coating method and apparatus which enable the reuse of the coating liquid having been scraped-off from a web without doing any one of the coating liquid adjusting treatment and the filtering treatment, while maintaining the features of the scraping-off type of extrusion coater, which is suitable for obtaining a uniform and extremely thin coating film layer.
Another object of the invention is to provide a coating apparatus which enables the obtaining of a uniform and extremely thin coating film layer equal to or superior to that provided by the scraping-off type extrusion coater equipped with a doctor blade and enables the reuse of the coating liquid having been recovered from a web without doing any one of the coating liquid adjusting treatment and the filtering treatment.
In order to accomplish the above-described object, the present invention is directed to a coating method, comprising the steps of: pre-coating one side of a continuously running sheet substrate strip with a coating liquid, using a pre-coating device, in an amount in excess of that capable of obtaining an intended final coating thickness; and then scraping-off an excess amount of coating liquid with a scraping-off device provided on a downstream side along a running direction of the substrate relative to the pre-coating device, wherein the coating liquid having been applied to the substrate is not opened to the atmosphere during a time from the pre-coating until the scraping-off.
According to the present invention, the coating liquid having been scraped-off from the continuously running substrate strip can be reused without doing any one of the coating liquid adjusting treatment and the filtering treatment, while maintaining the features of the scraping-off type of extrusion coater, which is suitable for obtaining a uniform and extremely thin coating film layer, since the coating liquid having been applied to the substrate is not opened to the atmosphere during the time from the pre-coating of the substrate with the coating liquid until the scraping-off of the express amount of the coating liquid.
The term “the coating liquid having been applied to the substrate is not opened to the atmosphere” herein used means the state in which at least the surface of the substrate to which the coating liquid has been applied is not opened to the atmosphere, and it does not matter whether the lateral edge portions of the substrate are opened to the atmosphere or not. And this is the same in the following.
In an aspect of the present invention, the coating liquid having been scraped-off is recovered through a recovering line as a closed system and the recovered coating liquid is reused. Allowing the recovering line to be a closed system enables the fluid physical properties, such as viscosity and solid content concentration, of the coating liquid to be reused to be much less changed and dust and the like to be not included in the coating liquid.
In an aspect of the present invention, a desired coating thickness is obtained by adjusting a fluid resistance of the recovering line. Changing the fluid resistance of the recovering line enables the coating thickness to be varied. This case also embraces one form of the method in which the adjustment of the fluid resistance of the recovering line is combined with at least any one of the adjustment of the coating speed, the adjustment of the coating liquid viscosity and the adjustment of the solid content concentration.
In an aspect of the present invention, a desired coating thickness is obtained by adjusting at least one of the amount of the coating liquid to be used for the pre-coating and an amount of coating liquid to be scraped-off. This method enables a desired coating thickness to be obtained in a simple and easy manner.
In an aspect of the present invention, the amount of the coating liquid used for the pre-coating and the amount of the coating liquid scraped-off are measured with flowmeters, respectively, and at least one of the amounts is adjusted to allow a difference between the two measured amounts to provide the
Mandai Toshihiro
Shibata Norio
Tomaru Mikio
Bareford Katherine
Fuji Photo Film Co. , Ltd.
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