Process and apparatus for reducing turbulence during curtain-coating
First Claim
1. A process for curtain-coating a base with at least one layer of a coating solution, in a coating zone of which process a free-falling liquid curtain comprising one or more layers of coating solutions is formed, the liquid curtain has a length, the process comprising the steps of(a) wetting curtain holders with the liquid curtain at curtain edges(b) spreading and holding the liquid curtain between the curtain holders during free fall of the liquid curtain,(c) passing a web-shaped base continuously through the coating zone, and the curtain edges are separated from the liquid curtain and conducted away, characterized by the steps of(d) removing the curtain edges by a separating element that penetrates the plane of the liquid curtain in a penetration zone in the immediate vicinity of a base and next to the curtain holders, and wherein the separating element is a free jet of a separating liquid, the flow speed of the free jet is greater than the drop speed of the liquid curtain in the penetration zone and greater than the speed of the base and(e) splitting the liquid curtain with the separating element at the penetration zone into a free-falling curtain center and free-falling curtain edges and wherein only the curtain center coats the base;
- wherein the curtain holders extend to substantially the entire length of the liquid curtain.
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Accused Products
Abstract
Non-uniform liquid flows in the curtain limit the process speed and cause defects during coating. These liquid streams are equalized by auxiliary liquids in the curtain holder. If the curtain edge is separated by a free jet of a separating liquid, turbulence in the curtain edge is isolated from the curtain center. The maximum attainable speed is increased. Because the free jet also removes liquid from the curtain in the penetration area, a beaded edge is not generated on the base, and it is possible to coat uniformly thick to the outer edge of the base. The process is especially suitable for making photographic films.
29 Citations
17 Claims
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1. A process for curtain-coating a base with at least one layer of a coating solution, in a coating zone of which process a free-falling liquid curtain comprising one or more layers of coating solutions is formed, the liquid curtain has a length, the process comprising the steps of
(a) wetting curtain holders with the liquid curtain at curtain edges (b) spreading and holding the liquid curtain between the curtain holders during free fall of the liquid curtain, (c) passing a web-shaped base continuously through the coating zone, and the curtain edges are separated from the liquid curtain and conducted away, characterized by the steps of (d) removing the curtain edges by a separating element that penetrates the plane of the liquid curtain in a penetration zone in the immediate vicinity of a base and next to the curtain holders, and wherein the separating element is a free jet of a separating liquid, the flow speed of the free jet is greater than the drop speed of the liquid curtain in the penetration zone and greater than the speed of the base and (e) splitting the liquid curtain with the separating element at the penetration zone into a free-falling curtain center and free-falling curtain edges and wherein only the curtain center coats the base; wherein the curtain holders extend to substantially the entire length of the liquid curtain. - View Dependent Claims (2, 3, 4, 5, 7)
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6. A process for curtain-coating a base with at least one layer of a coating solution, in a coating zone of which process a free-falling liquid curtain comprising one or more layers of coating solutions is formed, the process comprising the steps of
(a) wetting curtain holders with the liquid curtain at curtain edges (b) spreading and holding the liquid curtain between the curtain holders during free fall of the liquid curtain, (c) passing a web-shaped base continuously through the coating zone, and the curtain edges are separated from the liquid curtain and conducted away, characterized by a flat free jet intercepting and conducting away the curtain edge and only the free-falling curtain center coating the base.
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8. A curtain-coater to coat a web-shaped base with at least one coating liquid, comprising
(a) a transport device to move and guide the base through a coating zone, (b) a coating head to make a liquid curtain that drops freely onto the coating side of the base wherein the base is wider than the liquid curtain, wherein the liquid curtain has a length, (c) two curtain holders that spread and hold the free-falling liquid curtain at the curtain edges, wherein the curtain holders extend to substantially the entire length of the liquid curtain, (d) free jet means for separating the liquid curtain into a free-falling curtain center and into free-falling curtain edges, said jet having a circular cross-section and (e) means for removing the curtain edges before contact with the base so that only the curtain center coats the base.
Specification