Coating processes – Falling curtain of coating material utilized
Reexamination Certificate
1997-12-26
2001-06-19
Lamb, Brenda A. (Department: 1734)
Coating processes
Falling curtain of coating material utilized
C118SDIG004
Reexamination Certificate
active
06248406
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a coating method generally called free-falling vertical curtain coating, and in particular, to curtain coating used in manufacture of photographic light-sensitive materials.
As a technology to form layers of various types by coating some emulsions on a support (paper, metal, synthetic resin or the like) conveyed continuously, there are given a slide bead coating method, a rod coating method, an extrusion coating method and a curtain coating method. In the method called the curtain coating method among the aforesaid methods, a coating solution flowing out of slits provided on the slide surface flows down uniformly along the slide surface, then, goes down in the state of a curtain formed between edge guides provided on both sides of the lower part on the slide surface to fall on the support so that a coating layer is formed. When comparing with a conventional slide hopper coating method, for example, this curtain coating method can coat thinner layers at higher coating speed, and it is superior to the slide bead coating method in terms of mass production and of energy conservation.
On the other hand, however, there is caused an edge unevenness tendency in the curtain coating method, because “a process to form a coating solution to be curtain-shaped” is newly added. This is a tendency wherein a thickness of an edge portion in the conveyance direction on a layer coated and formed is increased, resulting in uneven layer thickness of a total coating layer. With regard to this point, various studies which have been made up to now show that unevenness of the curtain thickness in the lateral direction is increased as the curtain flows down between edge guides.
In addition, a flow speed of the curtain (coating solution) is especially slow in the vicinity of an edge guide, which sometimes causes destruction of an edge portion on the curtain.
Namely, there is required, for the appropriate curtain coating, a technology to keep the layer thickness constant in the lateral direction while forming the curtain itself stably,
For these requirements, there have been suggested technologies disclosed in (1) TOKKAISHO 51-57734 and (2) TOKKAIHEI 4-354563, for example. However, the technology in (1) above has a problem that unevenness in the lateral direction increases, though the curtain itself therein is stabilized. This problem is remarkable especially when a coating solution having low surface tension is used. In the case of the technology in (2) above, an effect is insufficient totally, and in particular, when the flow rate of a coating solution is lowered, unstable and uneven portions on the curtain are increased.
Therefore, there have been suggested technologies relating to the so-called “side solution” wherein a solution which is different from the coating solution is caused to flow down along the edge guides to support a curtain, such as those disclosed in (3) TOKKAISHO 59-132966, (4) TOKKAIHEI 3-50085, (5) TOKKAIHEI 1-199668 and (6) TOKKAIHEI 5-293429.
Even in these technologies, however, a problem of “unevenness in the lateral direction” has not been solved sufficiently, though they are effective on the point of “forming the curtain stably”. When the flow rate of the side solution is great, in particular, mixture of the side solution and the coating solution is caused in the vicinity of the edge guide, resulting in an increase of “unevenness in the lateral direction”, which is a problem.
This unevenness of a layer thickness on the edge portion is one shown in
FIG. 6
, and proposed technologies for letting the side solution flow down as stated above, for absorbing the coating solution on the edge portion after coating, and for improving physical properties of the coating solution, have not yet solved the problem of unevenness of a layer thickness effectively, and these technologies can not cope with high speed coating presently.
SUMMARY OF THE INVENTION
An object of the invention is to form a curtain stably and to solve the problem of the layer thickness unevenness, and thereby to realize highly productive curtain coating which can easily be realized with an extremely simple structure, and can lower the manufacturing cost.
After various studies, the inventors of the invention obtained the following findings, taking into consideration that layer thickness of a coating layer itself is increased when the flow rate of a side solution (auxiliary solution) is increased, though the curtain is stabilized. Namely, the findings show that the minimum quantity of the side solution which is necessary to form a curtain stably exists, and even when the flow rate is increased from this minimum and necessary supply quantity, the state of unevenness on the edge portion remains unchanged if the increase of the flow rate is within a certain range, but when this range is exceeded, unevenness on the edge portion is increased.
Therefore, the inventors of the invention found, after intensive studies, that it is possible to reduce the unevenness on the edge portion by using a side solution and by thinking out, in particular, a flow rate, a position for the solution to start flowing down, and physical properties. In the case of the flow rate, in particular, they found the critical point where it is possible to make the mixture with a coating solution to be minimum and thereby to reduce the unevenness on the edge portion by determining the upper limit and the lower limit. They also found that the effect to overcome the unevenness on the edge portion is greater when the position to start supplying the side solution is on the upper stream side of the curtain, though a range of an amount of the side solution to be supplied is not affected by the position for supplying.
The present invention has been achieved based on the findings mentioned above, and it is structured by the following technical means.
(1) A coating apparatus for coating a conveyed support with a coating solution by letting the coating solution flow down between a pair of edge guides so as to form a curtain layer of the coating solution. The coating apparatus includes a slide surface, having thereon slits for supplying the coating solution and inclined for a prescribed angle to the horizontal axis, side plates, provided on both edges of the slide surface, a pair of edge guides, provided on the edges of the slide surface, and solution injecting means each of which is provided on respective one of the side plates and supplying auxiliary solution from solution injecting outlets being in contact with the slide surface, in which coating is conducted while the auxiliary solution is being flowed down along the edge guides at a flow rate between 0.3 cc/min. and 3.0 cc/min. from each of the solution injecting means on both sides.
Namely, the invention makes it possible to form a curtain stably by supplying an appropriate amount of side solution from a solution injecting outlet, and thereby to form a coating layer having less unevenness on the edge portion, which leads to cost reduction and an increase in yield. Further, reduction of thick layers on the edge portion also reduces a load on a process to dry after coating, which leads to advantages of low cost in the viewpoint of manufacturing facilities.
(2) A coating apparatus wherein the solution injecting outlet is in contact with the slide surface either at the height which is the same as that of the slit for supplying a coating solution, or at the height upper than that of the slit for supplying a coating solution.
Namely, the invention surely reduces unevenness on the edge portion caused by a side solution, because it is possible to increase the flow speed at an edge portion of a coating solution which flows down along the slide surface, by letting the side solution flow down from the solution injecting outlet either at the height which is the same as that of the slit for supplying a coating solution, or at the upstream side.
(3) A coating apparatus wherein a coating solution at a flow rate ranging from 0.5 cc/min. to 10.0 cc/min. is supplied from th
Fukazawa Koji
Kondo Yoshikazu
Nishiwaki Akira
Bierman Jordan B.
Bierman, Muserlian and Lucas
Konica Corporation
Lamb Brenda A.
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