KR920004629B1 - Curtain coating method and apparatus - Google Patents

Abstract

Method and apparatus for curtain coating one or a plurality of superposed layers of photographic liquids onto a moving support (20) with the width of the curtain being greater than the width of the coating to be applied to the support (20). A margin of the free-falling curtain (18) is intercepted and diverted just above where the curtain impinges on the support (20), by a curtain-severing device (40). The curtain-severing device has a blade disposed in a plane parallel to a plane tangential to the coating roller (22) at said impingement location so as to provide an uncoated margin (48) on the support (20). The blade (42) of curtain-severing device (40) interrupts the edge portion of the falling curtain (18). Purging liquid is projected onto blade (42). The blade diverges laterally from the support in the direction of travel of the support (20) to divert the purging liquid and the curtain fluids away from the support (20) into a catch basin (28).

Description

[Name of invention]

Curtain cloth method and apparatus

[Brief Description of Drawings]

Embodiments of the present invention will be described by way of example with reference to the accompanying drawings.

1 is a simplified perspective view of a curtain coating apparatus in the form of a slide-hopper according to a preferred embodiment of the present invention.

2 shows an edge portion of a support on which a curtain has been squashed, on a coating roll, with the curtain dropping on the support and extending beyond the support on the side and contacting the rigid edge guide according to the prior art. Partial section.

3 is a simplified perspective view of the curtain detachment apparatus according to the present invention.

4 is a sectional view taken along line 4-4 of FIG.

5 is a plan sectional view taken along line 5-5 of FIG.

6 is a cross-sectional view similar to that of FIG. 2, but including a curtain separator according to an embodiment of the invention.

7 is a cross-sectional view similar to FIG. 6 but showing another embodiment of the present invention.

Detailed description of the invention

[Field of Invention]

The present invention relates to a curtain coating of a continuously moving support. In particular, but not exclusively, the present invention relates to improved curtain coating methods and apparatus for the production of photographic materials such as photographic films and photo papers.

[Background of invention]

In the coating apparatus of a curtain coating form, a movable support body is coat | covered by making the free fall curtain of coating liquid collide on a moving support body, and forming a single layer on this support body. Such a device is described in Hughes, US Pat. No. 3,508,947, where a multi-layered composite comprising a plurality of individual monolayers is formed on a slide hopper and impinges on a moving support to form a monolayer thereon. U.S. Patent No. 3,508,947 describes the production of multilayer photographic materials such as photographic films and photo papers in particular.

In particular, the quality of the coating in the curtain coating process used to produce the multilayer photo material is largely dependent on the properties of the liquid curtain. It is important to ensure that the laminar flow of liquid is formed by a slide hopper and that a liquid curtain of laminar flow is formed from this liquid. It is known that the curtain must be guided by the curtain edge guides at its corners to prevent shrinkage on the sides of the drop curtain under the effect of surface tension.

In general, the edge guide is a stationary rigid member, which is attached to a slide hopper used to supply the coating liquid to the curtain and extends downward from the point where the liquid enters the free fall state. Wet contact of the edge of the drop curtain with the edge guide must be maintained over the entire length of the edge guide to avoid breakage in the curtain. Wet contact of the curtain edges and edge guides results in nonuniformities in the coating at the edge of the coating over the support due to the viscous drag between the drop curtain liquid and the edge guide. By making the curtain wider than the support, a sufficiently uniform coating can be formed on the support. However, if the curtain extends over the edge of the support, there is a serious risk that the coating liquid will wet the edge of the support and also transition to the back side of the support before the coating is gelled.

The liquid that coats the backing of the support is transferred to the roller that moves the support and gels in the dryer, thereby necessitating stopping the coating process to clean the downstream roller.

Conton edge guides may be arranged in the following manner. That is, the moving support is (a) covered to the edge, (b) leaving an uncovered edge on the support edge, or (c) the curtain extends past one or both sides of the support edge.

The use of edge band liquids may be useful when it is necessary to make the curtain wider than the coated support. The liquid used in the corner bands may be different from the liquid to be coated on the support and need not include all the expensive components for the photographic material. Furthermore, the corner band liquid can be integrated for reuse and recycled to the corner band liquid supply. Typically the edge band may be up to 10 centimeters wide. It is also beneficial to supply an amount of corner band liquid that allows the thickness of each corner-band area of the curtain to be somewhat thicker than the thickness of the rest of the curtain, thus reducing the curtain's stability against breakage of the curtain occurring at the corner guides. Increase. Curtain coating methods using the above edge band liquid technology are described in US Pat. No. 4,019,906 issued April 26, 1977 and in Research Disclosure of November 1978, where the desired width and thickness edges To provide a curtain with band liquid, edge band liquid is introduced at the lateral edge of the slide hopper in proximity to the coating liquid flowing down the slide surface.

When a curtain wider than the support impinges on the support, the support is covered from edge to edge. The curtain is naturally separated from the edge of the support, and the curtain portion outside the support edge, which may contain almost all edge band liquids, is narrowed toward the edge guide and lowered into the container. The coating roller must be narrower than the support so that the edge of the roller must not be contaminated by curtain liquid. As a result, the coating rollers must also change if the width of the support to be coated varies considerably as in the usual case, which wastes time and results in an inefficient process.

The edge of the film support is typically embossed by a knurling wheel to increase the effective maximum thickness of the support. The increased thickness of the edges protects the sensitive photographic material from locally high winding pressures, which would otherwise result in fine variations in the support thickness. Since the tenacity of the original photographic coating at high humidity makes it difficult for the support to be released during the finishing operation, it is necessary to avoid adding the coating composition to the curled areas. One way to accomplish this is to provide the curtain with a width less than the width of the support. Thus, the technique of providing an uncoated edge is very useful in connection with squaring the corner portions of the support.

One prior art attempt to keep the curled edge portions uncovered has been to place the edge guides inside the support edges. However, it has been found that this results in beads along the edge of the sheath close to both sides of the support edge. The edge portion of the support, including the beads, must be cut to provide a completely uniformly coated support. However, prior to costly and consumable trimming operations, the beads of such excessively thick coating liquid may be applied to the coating along the edges by defects resulting from trapping of air bubbles between the coating and the support. It can have a negative effect. In addition, contamination occurs on the downstream side of the transfer roller.

It is desirable to separate the drop curtain before the drop curtain impinges on the moving support, to move the edge of the separated curtain off the coated area, thereby reducing the width of the curtain impinging on the support and thus this support. It becomes smaller than the width.

Existing techniques for this purpose use a curtain interceptor disposed between the coating hopper and the web to intercept the edge area of the curtain, otherwise the curtain at the edge of the support should not be covered. This descents. One method and apparatus for doing this are described in US Pat. No. 4,559,896, issued March 3, 1987. Prior to the above specification, attempts have been made to use curtain separators and devices to move fluid at the curtain edges, which has resulted in the curtain edge guiding means used in the device generating very thick corner band fluids that result in This is because they are loaded as edges of corresponding thickness in the coating. As introduced in US Pat. No. 4,559,896, a second lower curtain edge separator is used to remove the thick curtain edge beads produced by the first upper curtain separator.

Overview of the Invention

It is an object of the present invention to provide a curtain coating method and apparatus in which a uniform coating can be formed on a moving support while the edge portion of the support is not covered.

The object of the present invention is achieved according to the method of the present invention for curtain coating a support with a liquid, comprising the following steps. That is to provide a separation device having a blade to move the support along the path, to form a free-fall curtain having a width larger than the width of the coating to be formed on the support, and to displace the edge portion of the curtain by lateral displacement, Where the composition impinges on the support, placing the blade in a plane approximately parallel to the support plane, and the like. The blade is disposed upstream of the support of the curtain and extends through the curtain and is disposed outward of the support downstream of the curtain. Also in accordance with the present invention, the purifying liquid is passed over the upwardly facing surface of the blades, leaving the composition out of the support in the projection of the curtain on the blade. In this way the width of the coating applied to the support can be precisely controlled and no beads are generated at the edges of the coating on the support. The liquid in the curtain outside the edge on which the sheath is desired on the web is moved outward on the side of the support by the purifying liquid flowing over the blade and drained away from the outer position.

The speed of the purifying liquid is advantageously at the same level as the speed of the support along the path. The purifying liquid is advantageously a laminar flow. In one embodiment, the support has a speed in the range of 150 cms per second to 1000 cms per second and the flushing liquid has a speed of approximately 500 cms per second.

The free fall curtain is guided at the edge of the curtain as an edge guide in contact with the flush liquid and the flush liquid flows downward to the edge guide.

In some embodiments, the edge of the curtain is formed from a liquid other than the coating liquid. Such an embodiment has the advantage that the coating liquid, which may comprise expensive materials, is not wasted.

The edge guide is a hollow tube and can terminate in the planar upper part of the separation device. The liquid flows downward through the corner guide, which is said cavity, to effectively form an extension of the tube, so that material separated from the curtain can narrow the neck to the extension. Such short edge guides have the advantages associated with the operation of the coating device.

The invention also relates to an apparatus for curtain coating a support with at least one monolayer of coating liquid. The apparatus includes a conveying means comprising a coating roller to move the support along the path. A hopper means is provided to form at least one monolayer of the coating liquid into the free fall curtain, which extends transverse to and intercepts the support path. The curtain is wider than the desired width of the coating to be formed on the support. The apparatus also includes curtain separating means for intercepting and moving the edges of the curtain. According to the invention, said curtain separating means comprises a blade which is arranged in a plane approximately parallel to the plane of the support on which the composition impinges. The blade is disposed upstream of the path of the curtain plane and extends through the curtain plane and out of the path downstream of the support downstream of the curtain plane. Means are provided for passing the liquid over the top side of the blade to move the intercepted composition in the curtain out of the path of the support.

The present invention provides an apparatus for performing other method steps in various embodiments of the invention.

The advantages of the curtain coating method and apparatus according to the invention are summarized as follows.

Curtain liquids in excess of the amount required for coating on the support may be removed from the edge of the drop curtain to provide a uniform coating thickness of the photo composition monolayer over the entire width of the coating including the edges of the coating, thus increasing drying efficiency. Improve and reduce waste in production.

The width of the coating can be optimized according to the needs of the desired product. Uncoated edges can be produced effectively, significantly reducing waste resulting from unusable support materials.

Covering a width smaller than the width of the support may prevent the curled edges from contacting the coating material. Covering a width smaller than the width of the support may prevent the curled edges from contacting the coating material. The ability to coat a width less than the width of the support prevents the coating liquid from sticking to the back side of the support. Such back contact of the same coating liquid occurs when using a curtain coating technique where the drop curtain impinging on the support is wider than the support to be coated. Undried coating liquid on the back side of the support will have a negative effect on the downstream side of the transfer equipment which moves the coated support through the dryer.

In the prior art, a coating roller of a width smaller than the width of the support, together with a curtain wider than the support, is required to avoid coating on the surface of the coating roller. Thus, a small replacement of coating rollers with different widths was necessary to accommodate the support of a particular width. The method and apparatus of the present invention allow the use of universal width support rollers since all coatings can be made within the support edges.

Detailed description of the invention

The invention will be described as implemented in the form of a slide hopper in a conventional curtain coater, as shown in FIG. The coating liquid moves laterally to the slide hopper 10 and descends into the outlet slot 12, each of which is loaded in the form of a monolayer on an individual inclined surface 14. Under the influence of gravity, individual monolayers flow below the surface 14 and flow to each other, forming a covering edge 16 that forms a composite curtain 18 that falls free. The slider hopper may be any width from several inches to several feet as needed. The free-falling composite curtain 18 extending laterally in the path of the moving support 20 falls over a length in the range of about 5 to 40 centimeters under normal conditions, and impinges upon the continuously advancing support 20 Form a monolayer. The curtain 18 is preferably impinged on the support 20 advanced by the coating roller 22. The coating roller 22 forms a part of the conveying means which allows a support body to move along a path | route. In order for the support to be completely covered over the entire width, the width of the coating roller should be somewhat smaller than the width of the support guided around the roller. It is preferable that the coating roller 22 is mounted and driven by the motor which is not shown in figure.

Monolayers of the photographic coating liquid may be coated on various supports. Typically the photographic support comprises a polymer film, a web of wood fibers such as paper, a thin sheet of metal and foil and a glass and ceramic support element, provided with one or more monolayers underneath the coating liquid. Thereby improving the adhesion properties, antistatic properties, dimension properties, polishing properties, hardness, functional properties, anti-halation properties and / or other properties of the support. The support may be coated in the form of individual thin plates or, more generally, in continuous form.

The free fall liquid curtain 18 is guided by two edge guides 24, 24 ′, which are vertical, which hold and stabilize the free fall curtain before the free fall curtain impinges on the support 20. It works. 1 shows one form of the curtain guide system, wherein the edge guides 24, 24 ′ are disposed outside the edges of the moving support 20 to be covered so that the curtain 18 is wider than the support 20 to be covered. You lose. In this case, the support is completely covered over the entire width. In this case the irregular part of the curtain edge is located close to the edge guide, which is the outer part of the width of the available support 20. The coating liquid descending past the edge of the support is integrated in the containers 28, 28 'when reuse is practical.

Referring to FIG. 2, the existing method of keeping the free fall curtain 18 stable within the range of the edge guides 24 and 24 'results in the application of low viscosity liquid to the outer surface of the rigid edge guide 24. To move on. FIG. 2 shows a partial cross-section of the edge of a typical free fall curtain 18, with a rigid edge guide 24 having a flush liquid 30 and an edge adjacent to the flush liquid 30. Band liquid 32 flows, and the two liquids are discharged into vessel 28 (not shown) to reach the drain. The liquid from the curtain wets the backing of the backing 20 at the edge of the backing at the sign 34 and also covers the chipped area 26. The liquid covering the back side of the support 20 is then transferred to the transfer roller, and eventually there is a need to stop the coating process to clean the downstream transfer roller. The coating added on the crushed portion 26 causes problems in the finishing operation, which is a problem of the sticky nature of the gelatin and the high wind pressure associated with the crushed portion.

In order to avoid the drawbacks of the existing device, according to the invention, curtain separators 40, 40 'are provided at the edges of each of the drop curtains 18. Each device 40, 40 ′ includes a blade 42. In plan view, each blade is positioned at an upstream side of the support of the curtain and is acute with the edge of the moving support in that it extends through the plane of the curtain and outwardly at the downstream side of the support of the curtain. Arrow 41 in FIG. 1 indicates the moving direction of the support 20. Each blade 42 has a top surface disposed in a plane substantially parallel to the plane of the support 20, in this example the curtain impinges on the top surface and the support is moved around the coating roller 22, The plane of the support is tangential to the coating roller. In the present embodiment the blade is formed of sheet material and is in fact stainless steel or titanium.

The liquid forming the curtain 18 begins free fall by falling off the covered edge 16 of the slide hopper 10 and descending, and at each support edge just above where the curtain impinges on the support 20. Are separated. The curtains are separated by blades 42 and 42 'such that the center portion of the separated curtains impinges on the support while leaving the edges 48 uncovered. Lateral outer portions of the separated curtain 18 are attracted toward adjacent edge guides 24 and 24 'such that band liquids at all corners flow into the containers 28 and 28'.

3 and 4 show curtain-separator 40 '. The curtain-separator 40 'includes a protruding blade 42', a housing 44 and a purifying liquid-supply connection 46. Each liquid-supply connection 46 may be used depending on how the curtain-separating device is mounted. The curtain separator 40 is structurally identical except that it is a mirror image, such as a mirror image, with the curtain separator 40 ', so it may have the necessary relationship with respect to the edge of the support. . Ie at an acute angle, arranged upstream of the support of the curtain and extending to the outer plate downstream of the support of the curtain.

At least the upper surface, preferably both surfaces, of each blade 42, 42 ′ are purged with liquid through the slot 50, and the liquid is preferably water, and the slot 50 is adjacent to the blade. It is desirable to extend over the full width of the blade where the blade leaves the housing. The curtain liquid impinging on the blades 42 and 42 'is moved to the respective containers 28 or 28' by the force of the purifying liquid supplied to the top of the blade. The bottom surface of the blades 42, 42 'is also preferably purged with liquid to minimize the tendency of solidification of the curtain liquid to dry at the edges of the blade. Bottom purging tends to surround the edges of the blade. Preferably, the height of each slot 50 is in the range of 0.006 to 0.025 centimeters to meet the required volume and velocity of the clarification liquid.

5 is a plan view of a preferred curtain-separating device, showing in more detail the location and loading of the blades 42, 42 'separating the drop curtain. The width of each blade 42, 42 ′ where the blade leaves the slot 50 is preferably slightly larger than the width of the blade outer portion. This width is preferably narrowed gradually from the slot to the position where it hits the curtain blades. The blade width outward from the impact location on the blade is essentially uniform. Slightly narrowing each blade as above ensures that the purge liquid surrounds the edge of the blade.

Each blade 42, 42 ′ is loaded at an acute angle ψ with respect to the direction of movement of the support so that the edge portion of the drop curtain impinging on the blade is moved, and the plane of the blade is covered with a coating roller ( Parallel to the plane tangential to 22). The purifying liquid has its respective blades 42 and 42 in a direction inclined at the same angle ψ relative to the direction of movement of the support such that the edge of the curtain is separated from the edge of the support and flows down into the container 28 or 28 ', respectively. Eject along the surface. It can be seen that each blade width and length and the angle to the direction of support movement are correlated to the parameters, and their choice also depends on the velocity and volume of the purge liquid supplied to the blade surface. The blade 42 or 42 'must be as wide as necessary to provide the required width of the uncovered edge 48 on the support and to allow lateral displacement of the support. Lateral displacement of the moving support is very difficult to remove even with the most precise support-guide device. The width of the blade is preferably in the range of 0.3 to 3.0 centimeters, and the angle ψ of the blade axis relative to the direction of the moving support may be in the range of 5 ° to 60 ° and preferably in the range of 20 ° to 40 °. It is known that the blade length " L " (of FIG. 4) should be sufficient to allow the integration of the curtain liquid and the purifying liquid, and is satisfactory when it is 2 to 5 centimeters. This is preferably 4 centimeters. The rate of purge liquid across the blade surface is preferably about the same as the speed of the support along the path, and may be half to one half the speed of the support. Purification liquid flow is advantageous for laminar flow.

Thus, for example, if the support speed is between 200 and 650 cms per second, the rate of purge liquid on the blade is preferably about 500 cms per second. For a purge liquid velocity in the range of 200 to 800 centimeters per second, the volume of purge liquid may be about 2 to 10 cubic centimeters per second per centimeter of the width of the slot 50, and 5 to 7 cubic second per centimeter of the slot 50 width. Preferably it is centimeters.

6 shows a low viscosity flush liquid 30, which is moved to the top of the rigid corner guides 24 so that the edge guides extend the entire height of the edge guides below the height of the blades 42. Flow down. The edge band liquid 32 is fed into the edge of the curtain to increase the stability of the curtain, thereby reducing waste.

When using edge band liquids, by supplying a sufficient amount of edge band liquid to the ends of the slide hopper, the curtain thickness of the edges, and thus the flow rate of the edge band liquid, is somewhat larger than the thickness and flow rate in the middle part of the curtain, and thus the edge It greatly increases the stability of the curtain in the guide and in proximity thereof and thus prevents the curtain from breaking. The thickness and width of the curtain edge bands may require a relatively large amount of edge band liquid, which is usually one liter or more per minute. The process gives good results when the viscosity of the edge band liquid is close to the viscosity of the liquid in the middle part of the curtain. Appropriate concentrations of gelatin solution with added wetting agent are suitable.

In order to form a corner region of the well-formed and clearly monolayered composition sheath 54 inside the edge of the support 20, the height of the separation blades 42, 42 ′ above the support at the impact location must be substantially small from the operator's point of view. It is important. It has been found that this height should be less than about 0.4 centimeters and preferably less than about 0.15 centimeters. Since the blades of the curtain separators 40, 40 ′ are closely spaced with respect to the support, this is inevitably parallel to the moving support 20 on the covering roller 22 at the impingement position of the curtain.

The edges of the drop curtain 54, separated by the blades 42, 42 ′ and located close to the edge guides 24, 24 ′, naturally narrowed towards the edge guides, flushing the liquid to the vessel 28. 30 and the edge band liquid 32 facilitate the flow. With the aid of clarification liquid flow over the surface of the blade 42 protruding from the slot 50, an uncoated edge portion is ensured over the crushed portion 26.

7 shows another embodiment of the present invention, wherein each corner guide is made of a cavity tube. Although not shown, flush liquid is supplied from a liquid source through a tube of a cavity. Each corner guide 56 terminates a short distance from the top of the separation blade 42 associated therewith. The liquid flowing out of the edge guide forms an extension of the liquid, which, in combination with the flush liquid, extends and stabilizes the corner area of the drop button. The use of the short edge guides 56 allows the slide hopper to move to the sheathed position to avoid mechanical interference with the fixed separation device 40. The liquid flowing from the end of the corner guide is an effective extension of the corner guide when the pupil tube has an inner diameter of about 0.035 to 0.240 centimeters and an outer diameter of about 0.075 to 0.300 centimeters and the fluid flow rate is 10 to 200 cubic centimeters per minute. It has been found to act as. If this condition is not achieved, the jet from the edge guide tends to break before the separated edge of the liquid narrows the neck towards the edge guide axis, resulting in a detachment of the curtain. There is a possibility that the edges are unevenly intermittently broken and contaminate the device with curtain liquid in the vicinity of the device, which also includes the edges of the skin roller and the support.

If a curtain separating blade is used to separate the curtain according to the preferred embodiment described above, all curtain liquids impinging on the blade are oriented by the purifying liquid into the container. The width of the portion loaded on the support of the separated curtain can be reduced by changing the position of the blade and the width of the blade with respect to the support edge. In order for the lateral displacement of the moving support (commonly referred to as "weaving") to be possible in the collision position, it is desirable that the blade position be at the intersection of the blade axis and the impact line on the curtain surface located just above the edge of the support on the clad roller. . In this position, the width of the uncoated edge of the support is equal to half the blade dimension along the curtain impingement line, which varies somewhat in width depending on the size of the support weaving as the support moves around the coating roller. If the blades are approximately parallel to the tangent to the cladding roller at the impact location and are spaced 0.15 centimeters or less above the cladding roller, any edge beads of the cladding that can form on the support are 20 percent of the residual cladding thickness. It does not exceed and the film is easily dried before it is wound on the end of the coating apparatus.

In addition, the purge liquid, the edge guide extension fluid 57, the edge band liquid 32 and the flush liquid 30 coming out of the slot 50 of the curtain separation device all have a viscosity of 0.5 to 10 centiposes. It is preferred to be a low viscosity liquid.

Claims (14)

In curtain coating a support with liquid, a) moving the support along a path, b) forming a free fall curtain of the coating composition, c) separating the edges of the curtain and laterally spaced apart. Providing a separation device having blades for forming the blades, the method comprising: placing the blades on a plane approximately parallel to the support plane on which the composition impinges; and d) moving material in the curtain falling on the blades out of the support. Passing a purging liquid onto the upward facing surface of the blade, the composition impinging on the moving support in the form of a free-fall curtain and the curtain being formed on the support. With a width wider than the required width of the sheath, the blade is placed upstream of the support of the curtain and extends through the curtain to extend the support of the curtain. Curtain coating method is disposed outwardly from the downstream side sieve. The method of claim 1, wherein the velocity of the purge liquid on the blades is in the range of 1/2 to 1.5 times the support velocity along the path. The method of claim 2, wherein the velocity of the purge liquid on the blade is close to the velocity of the support along the path. The method of claim 2, wherein the flow of purge liquid is laminar flow. The method of claim 2 wherein the support has a speed in the range of 150 cms per second to 100 cms per second and the purifying liquid has a speed of about 500 cms per second. 2. The method of claim 1, comprising guiding the curtain at its corners with an edge guide and flowing the flush liquid down to the edge guide, wherein the curtain is in contact with the flush liquid. 2. The method of claim 1 comprising forming the edge of the curtain with a liquid other than a coating liquid. 8. The method of claim 6 or 7, wherein the edge guides are hollow tubes terminating above the blade plane of the separator, and the liquid flows downward into the pupil tubes to effectively extend the tube and thus the curtain. A portion separated from the narrowing of the neck into the extension. 2. The method of claim 1 comprising passing the purge liquid over the face that faces downward of the blade. A curtain coating of a support with at least one coating liquid layer, comprising: a) conveying means comprising a coating roller for moving the support along a path, b) transversely extending through the path and intercepting the curtain Hopper means for forming at least one monolayer of the into a free-fall curtain; c) curtain separating means for intercepting and moving the edge of the curtain, including blades; and d) moving the intercepted material from the curtain outside the support path. Means for passing a purge liquid over the top surface of the blade to move the substrate, the curtain being wider than the desired width of the coating to be formed on the support, wherein the blade is approximately relative to the plane of the support against which the composition impinges On the parallel plane, it is placed upstream of the path of the curtain plane and extends through the curtain plane to support the curtain plane. A device disposed outside the retardation downstream path. The apparatus of claim 10 wherein said means for passing the purifying liquid to the upper surface of the blade is adapted to impart a rate to the purifying liquid on the blade in the range of 1/2 to 1.5 times the support velocity along the support path. 12. The apparatus of claim 11 wherein said means for passing purifying liquid over the top surface of the blade is adapted to generate a laminar flow of purifying liquid on the blade. 13. Device according to claim 10, 11 or 12, comprising guide means for guiding the edges of the curtain. 14. The apparatus of claim 13, wherein the guide means at each corner of the curtain are hollow and terminate at an upper portion of the support plane, the apparatus comprising means for passing liquid downward through the guide means of the pupil, respectively. The liquid leaving the pupil guide means of the apparatus effectively forms an extension of the guide means, such that the separated coating liquid narrows the neck into the liquid from the pupil guide means.