Coating apparatus – Control means responsive to a randomly occurring sensed...
Reexamination Certificate
2000-11-09
2003-02-25
Bareford, Katherine A. (Department: 1762)
Coating apparatus
Control means responsive to a randomly occurring sensed...
C118S712000, C118S713000, C118S050000, C118S067000, C118S324000, C118S325000, C118S326000, C118S410000, C118SDIG004
Reexamination Certificate
active
06524388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coating apparatus and a coating method, applicable to paper coaters of paper manufacturing machines or to a coating process in steel plate manufacturing machines, for coating various coating materials (hereinafter called “web ”) such as paper web and sheet, steel, and plastic film by applying a coating colors.
2. Background Art
The three following types of conventional coating apparatuses are known for improving the coating performance: (A) a coating apparatus provided with an air nozzle, (B) a coating apparatus provided with a gas chamber, and (C) a coating apparatus provided with an air nozzle and a gas chamber.
(A) A Coating Apparatus Provided With an Air Nozzle
FIG. 3
shows a structure of a coating apparatus provided with an air nozzle, disclosed in Japanese Utility Model Registration No. 2532902 by the same inventors as the present application.
FIG. 3A
is a side view, and
FIG. 3B
is a cross-sectional view showing the detail of the coating nozzle shown in FIG.
3
A.
This conventional apparatus comprises a rotatable backing roll
1
for supporting and carrying the web, a slit-type nozzle
5
for applying aa coating color film
3
, disposed above the web
1
in an non-contact state, and an air nozzle
40
disposed upstream adjacent to the slit nozzle
5
.
This apparatus is constituted such that an air layer accompanied by the running web
1
can be removed by injecting air from the nozzle
40
, and the injection amount and the injection speed of the air can be controlled by measuring the film thickness meter
45
and by an order form of the control unit
46
based on the measured results. Here, the numeral
4
denotes a coating color delivery slit nozzle, numeral
5
denotes a coating color nozzle body,
40
denotes an air injection nozzle, and
41
denotes an air chamber.
(B) A Coating Apparatus Provided With a Gas Chamber
FIG. 4
shows a structure of a coating apparatus provided with an air chamber, which is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 6-218313 by the same inventors as the present application. This apparatus also comprises the rotatable backing roll for supporting and carrying the web, a slit nozzle disposed in the non-contact state above the web
1
for applying coating color.
In this conventional apparatus, a gas chamber
52
is provided at an upstream position adjacent to the slit nozzle
5
, and, prior to application of the coating color onto with the web surface, an air layer accompanied by the web
1
is replaced by a cohesive vapor layer which is soluble in the coating color and which coheres on the web surface.
The replacement of air accompanied by the web with the vapor layer allows not only the reduction of the contact pressure between the web surface and the coating color but also changes the contact angle of the coating color to the web surface into a bigger obtuse angle, which prevents involvement of air under the coating color film. Here, a jet nozzle
50
for the soluble liquid vapor
51
is provided in the gas chamber
52
. The numeral
53
denotes a recovery pipe for recovering excessive vapor.
(C) An Apparatus Provided With Both of the Air Nozzle and the Gas Chamber
FIG. 5
shows a structure of a conventional coating apparatus, provided with both of the air nozzle and the gas chamber, which is disclosed in Japanese Patent (Granted) Publication No. 2917116.
As shown in
FIG. 5
, this conventional apparatus is provided with a gas chamber
32
and an air nozzle
30
at an upstream position adjacent to the coating color delivery nozzle
5
. Carbon dioxide gas or a solvent gas is injected through a gas nozzle
31
into the gas chamber
32
. High pressure air is injected through the air nozzle
30
. In addition, a recovery box
33
is provided for recovering excessive high pressure air. Excessive air inside of the recovery box
35
is removed by a blower
27
.
The above constitution allows removal of the air layer on the web
1
accompanied by the transfer of the web
1
by injecting high pressure air, and the gas is injected into the gas chamber
32
to change the inside of the gas chamber
32
into a negative pressure by the coanda effect due to the air ejection of air nozzle, and the air inside the gas chamber is replaced with the gas before coating the web surface for the purpose of improving the quality of the coated layer on the web.
The structure of the coating apparatus shown in
FIG. 5
makes it possible to remove the surface air layer accompanied by the transfer of the web and covering the surface of the web with the gas layer inside of the gas chamber, so that it is unlikely that air is involved between the web surface and the coating color.
However, removal of the air involvement can be kept in good conditions provided that the web transfer speed and the coating speeds are maintained constant. That is, the removal of the air involvement is attained only when coating conditions, such as the web transfer speed, the pressure condition of the gas chamber, and the coating speed of the coating color, are suitably adjusted.
For example, when the coating is done under the higher air amount from the air nozzle suitable for the transfer speed, the negative pressure in the gas chamber increases, so that the web
1
is likely to rise from the backing roll, so that the dragging force between the web and the backing roll becomes insufficient. In addition, since the gas injected from the gas chamber does not reach to the web surface or since the retention time of the gas layer on the web surface is not sufficient because of the low negative pressure of the gas chamber, the replacement of the air layer with the gas layer becomes insufficient.
In contrast, when the coating is done under the lower air volume suitable for the transfer speed, the involvement of the air may occur or the excessive air in the color layer may remain by the insufficient replacement of the air layer with the gas layer.
When such a discrepancy from the optimum conditions occurs, air enters between the coating color film and the web surface, and the thus entrained air remains as tiny bubbles, which cause the degradation of the coat layer.
The above described Japanese Patent (Granted) Publication No. 2917116 also discloses a structure, as shown in
FIG. 6
, which provides a suction tube having an opening close to the web surface. This structure, however, is liable to generate a local area, in which the pressure is a higher negative pressure, so that the web
1
is liable to rise away from the backing roll. That is, this structure has a problem that such a local area at a higher negative pressure may be caused.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide an coating apparatus capable of maintaining coated products with a constant good coating quality even when the process conditions vary by automatically maintaining the negative pressure in the gas chamber within a predetermined range. That is, the present coating apparatus and the coating method are obtained by recognizing the fact that a control of the negative pressure in the gas chamber within a predetermined range is an important factor for coated products with a good coating quality.
Accordingly, it is an object of the present invention to provide a coating apparatus and a coating method capable of stable formation of the coating film under the optimum conditions even when the process condition such that the base material transfer speed or the process conditions fluctuate.
The first aspect of the present invention provides a coating apparatus comprising: a rotatable backing roll, the outer periphery of which forms the base material carrying path; a die for delivering in the form of a coating color curtain onto the base material; a gas chamber disposed above the base material upstream to said coating color delivery die and comprises therein a gas injection mechanism and a pressure detecting sensor; and an air injection device disposed upstream to said gas chamber;
Miura Hiroshi
Sugihara Masahiro
Yamada Kenji
Armstrong Westerman & Hattori, LLP
Bareford Katherine A.
Mitsubishi Heavy Industries Ltd.
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