EP0425562A1

EP0425562A1 - Curtain coating method and apparatus.

Info

Publication number: EP0425562A1
Application number: EP89908604A
Authority: EP
Inventors: Thomas C Reiter; Richard Allan Gilkey; Kenneth J Ruschak
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1988-07-20
Filing date: 1989-07-18
Publication date: 1991-05-08
Anticipated expiration: 2009-07-18
Also published as: BR8907561A; EP0425562B1; DE68919699T2; WO1990000939A1; WO1990001179A1; KR900702413A; KR920004629B1; DE68919699D1; AU4032489A; ATE114514T1; AU626316B2

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

CURTAIN COATING METHOD AND APPARATUS Field of the Invention

The present invention relates to curtain coating of continuously moving supports. More particularly, but not exclusively, it relates to an improved curtain coating method and apparatus for the manufacture of photographic materials such as photographic film and paper. Background of the Invention In coating apparatus of the curtain coating type, a moving support is coated by causing a free-falling curtain of coating liquid to impinge onto the moving support to form a layer on said support. An apparatus is described in Hughes US Patent 3,508,947 wherein a multilayer composite, including a plurality of distinct layers, is formed on a slide hopper and caused to impinge onto a moving support to form a layer thereon. US Patent 3,508,947 particularly describes the manufacture of multilayer photographic materials such as photographic film and paper.

In the curtain coating process, particularly as used to manufacture multilayer photographic materials, the quality of coating is largely determined by the properties of the liquid curtain. It is important to ensure that a laminar flow of liquid is formed by the slide hopper and that a laminar-flow liquid curtain is formed from that liquid. To prevent lateral contraction of the falling curtain under the effect of surface tension, it is known that the curtain must be guided at its edges by curtain edge guides.

In general, edge guides are stationary, solid members which are attached to the slide hopper used to supply coating liquid to the curtain and extend downwardly from where the liquid enters a free fall condition. Wetting contact of the edges of the falling curtain with the edge guides should be maintained throughout the entire length of the edge guide to avoid a break in the curtain. The wetting contact of the edges of the curtain with the edge guides causes nonuniformities in the coating in the margins of the coating on the support because of viscous drag between the falling curtain liquid and the edge guides. By making the curtain wider than the support, a substantially uniform coating can be formed on the support. However, when the curtain extends over the edges of the support, there is a serious risk of the coating liquid wetting the edges of the support and also running onto the backside of the support before the coating has gelled. Liquids which coat the backside of the support will transfer to the rollers transporting the support and will gel in the dryer, requiring premature termination of the coating pr-ocess in order to clean the downstrear. rollers.

The curtain edge guides can be arranged in such a way that the moving support is coated (a) up to the edge, (b) leaving an uncoated margin on the support edges, or (c) in such a way that the curtain extends beyond one or both of the support edges. The use of edge band liquids can be advantageous when it is desirable to have the curtain wider than the support to be coated. Liquids used in the edge bands may be different to the liquid to be coated on the support and need not include all of the expensive ingredients used for photographic materials. Furthermore, the edge band liquid may be collected and recirculated to the edge band—liquid supply, for reuse. Customarily, the edge bands can be up to 10 centimeters in width. It is also advantageous to supply such a quantity of edge band liquid that the thickness of each edge—band region of the curtain is somewhat greater than the thickness of the rest of the curtain, thereby increasing the stability of the curtain against curtain breaks originating at the edge guides. A curtain coating process using such edge band-liquid technique is disclosed in US Patent 4,019,906 issued April 26, 1977, and in Research Disclosure, 17553, dated November, 1978, in which the edge band liquid is introduced onto the lateral margins of the slide—hopper surface adjacent the coating liquids flowing down the slide surface so as to feed the curtain with edge bands of liquid of any desired width and thickness. When a curtain wider than the support impinges on the support, the support is coated edge-to—edge. The curtain naturally separates at the edge of the support, and the portions of the curtain outboard of the edges of the support , which may contain exclusively edge band liquid, will neck in toward the edge guides and fall into a catch basin. The coating roller must be narrower than the support so that the margins of the roller do not become contaminated by the curtain liquids. Consequently, when the width of the support to be coated is substantially changed, as is often the case, the coating roller must also be changed, which is a time—consuming and disadvantageous procedure.

It is customary to have the margins of the film support embossed by a knurling wheel to increase the effective maximum thickness of the support. The increased thickness of the margins protects the sensitive photographic materials from higher localized winding pressure which would otherwise occur as a result of minute variations in support thickness. It is desirable to avoid applying any coating compositions to the knurled areas because inherent tackiness of photographic coatings at high humidity makes it difficult to unwind the support during finishing operations. One way of achieving this is to give the curtain a width less than the width of the support. Thus, techniques for providing coating— ree margins would be highly useful in connection with edge—knurling of the support. One prior—art attempt to maintain the knurled edge portions coating—free, has been to locate the edge guides in—board of the edges of the support. However, it has been found that this causes beads along the edges of the coating adjacent both edges of the support. The support margins, including the beads, must be cut off to provide a completely uniformly coated support. Prior to a costly and wasteful trimming operation, however, such excessively thick beads of coating liquid can adversely affect the coating along the edges by a defect which results from the entrainment of air bubbles between the coating and the support. Also there is the contamination of downstream transport rollers.

It would be desirable to sever the falling curtain before it impinges on the moving support and divert the severed margins of the curtain away from the coated area, thereby reducing the width of the curtain which impinges on the support so that it is less than the width of the support. A known technique for achieving this object uses curtain interceptors, disposed between the coating hopper and the web, for intercepting marginal zones of the curtain, which would otherwise fall on the support margins which are to be left uncoated. One method and apparatus for accomplishing this is disclosed in US Patent 4,559,896 issued March 3, 1987. Previous to this disclosure, attempts to use curtain severing devices and devices for diverting fluids in the margins of the curtain, failed because the curtain edge—guiding means used in such devices created heavy edge bands of fluid which were deposited as corresponding thickened edges in the resulting coating. As disclosed in US Patent 4,559,896, a second, lower curtain edge—severing device is used to remove the heavy curtain edge bead produced by the first upper curtain-severing device. Summary of the Invention

It is an object of the present invention to provide a curtain coating process and apparatus by which uniform coatings can be formed on a moving support while leaving marginal portions of the support uncoated.

The object is achieved in accordance with the present invention by including in a method of curtain coating a support with a liquid, which includes moving a support along a path, forming a free-falling curtain having a width greater than the width of the coating to be formed on the support, providing a severing device having a blade for severing and laterally displacing a margin of the curtain, and disposing the blade in a plane approximately parallel to the plane of the support where the composition impinges on it. The blade is disposed over the support upstream of the curtain, extends through the curtain, and is disposed outboard of the support downstream of the curtain. Also according to the invention, purging liquid is passed over the upwardly facing surface of the blade to carry outboard of the support the material in the curtain incident on the blade. With such a method, the width of the coating applied to the support may be accurately controlled and there is no bead created at the edge of the coating on the support. Liquid in the curtain outboard of the desired edge of the coating on the web is carried laterally outboard of the support by the purging liquid flowing over the blade and may be drained away from that outboard location.

Beneficially, the speed of the purging liquid is of the same order as the speed of the support along its path. Advantageously the purging liquid has 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 approximately 500 cms per second. B Advantageously the free— alling curtain is guided at its edges with edge guides and flushing liquid is flowed down the edge guides, the curtain being in contact with the flushing liquid.

In some embodiments the margins of the '-- curtain are formed from a liquid other than the coating liquid. Such embodiments have the advantage that coating liquid, which may include expensive materials, is not wasted.

The edge guides may be hollow tubes and 5 terminate above the plane of the severing device. Liquid may be flowed down through such hollow edge guides to form, in effect, extensions of the tubes, whereby material severed from the curtain necks into the extensions. Such shorter edge guide has 0 advantages in relation to operation of the coating apparatus.

The present invention also resides in apparatus for curtain coating a support with at least one layer of coating liquid. The apparatus includes 5 conveying means, including a coating roller, for moving a support along a path. Hopper means are provided for forming at least one layer of coating liquid into a free-falling curtain which intercepts, and extends transversely of, the path of the support.. The curtain is wider than the desired width of the coating to be formed on the support. The apparatus further includes curtain-severing means for intercepting and diverting the margins of the curtain. In accordance with the invention, such curtain-severing means includes a blade disposed in a plane approximately parallel to the plane of the support where the composition impinges on it. The blade is disposed over the path upstream of the plane of the curtain, extends through the plane of the curtain and is disposed outboard of the path of the support downstream of the plane of the curtain.

Means are provided for passing purging liquid over the upper face of the blade for carrying intercepted material in the curtain outboard of the path of the support. The present invention also provides apparatus for performing other method steps in the various embodiments of the invention.

Some of the advantages of a method and apparatus of curtain coating in accordance with the present invention are summarized as follows:

Curtain liquid, excess to that wanted in the coating on the support, can be removed from the margins of the falling curtain to provide a uniform coating thickness of the layers of photographic compositions across the entire width of the coating, including the edges of the coating, thereby improving drier efficiency and reducing product waste.

The width of the coating can be optimized according to the desired product requirement. An uncoated margin can be produced with an e fectiveness which results in significantly reducing the waste resulting from unusable support material. Coating a width less than the width of the support allows knurled margins to be free from coating material. The ability to coat a width less than the width of the support also eliminates coating liquid getting on the underside of the support, which occurs with a curtain coating technique wherein the falling curtain impinging on the support is wider than the support to be coated. Undried coating liquid on the underside of the support would adversely affect downstream conveying equipment which transports the coated support through the drier.

In the prior art, with a curtain wider than the support, a coating roll of a width less than that of the support is desirable to avoid coating onto the coating roller surface. Thus, frequent changes of coating rollers having different widths has been required to accommodate particular widths of the support. The method and apparatus of the present invention allows for use of a universal width support roller because all coating may be accomplished within the support edges. Brief Description of the Drawings

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a simplified perspective view of a curtain coating apparatus of the slide—hopper type in accordance with a preferred embodiment of the invention; Fig. 2 is a scrap view, partially in section, of a marginal potion of a marginally knurled support, on a coating roll, with the curtain falling onto the support and extending laterally beyond the support into contact with a solid edge guide, in accordance with the prior art; Fig. 3 is a simplified perspective view of a curtain—severing device according to the present invention;

Fig. 4 is a sectional view taken on the line 4-4 in Fig. 3;

Fig. 5 is a plan sectional* view, taken on the line 5-5 in Fig. 1;

Fig. 6 is a view similar to that of Fig. 2, but including a curtain—severing device in accordance with an embodiment of the invention; and

Fig. 7 is a view similar to that of Fig. 6, but of another embodiment of the invention. Detailed Description of the Invention

The invention will now be described embodied in the known curtain coater, of a slide-hopper type, shown in Fig. 1. The coating liquids are delivered laterally to a slide hopper 10, ascend to exit slots 12 and each is deposited in the form of a layer on a respective inclined surface 14. Under the effect of gravity, the individual layers flow down the surfaces 14, flow over one another, and flow to the coating edge 16 where free-falling composite curtain 18 is formed. The slide hopper can be any desired width, such as from several inches to several feet. The free-falling composite curtain 18, which extends transversely of the path of a moving support 20, drops over a height which, under typical conditions, will be in the range from about 5 to about 40 centimeters and impinges onto the continuously advancing support 20 to form a composite of layers. Preferably, the curtain 18 impinges on the support 20 where the latter is trained about a coating roller 22. The coating roller 22 forms part of conveying means for moving the support along a path. When the support is to be coated completely, that is full width, the width of the coating roller can be chosen to be somewhat smaller than the width of the support guided around it. The coating roller 22 is mounted on, and preferably driven by, a motor, which is not shown. The layers of photographic coating liquids can be coated on a variety of supports. Typically, photographic supports include polymeric film, webs of wood fiber, e.g., paper, metallic sheet and foil, and glass and ceramic supporting elements, provided with one or more subbing layers to enhance the adhesive, antistatic, dimensional, abrasive, hardness, functional, antihalation and/or other properties of the support. The supports may be coated in the form of discrete sheets or, as is more usually the case, in continuous form.

The free— alling liquid curtain 18 is guided by two edge guides 24 and 24' which are vertical and act to hold and stabilize the free-falling curtain before it impinges on the support 20. Fig. 1 illustrates one type of curtain guiding system, wherein the edge guides 24 and 24' are arranged outside the edges of the moving support 20 to be coated, so that the curtain 18 is wider than the support 20 to be coated. In this case, the support is completely coated over its entire width. In such a case, any marginal irregularities in the curtain are situated adjacent the edge guides and are outside the useful width of the support 20. The coating liquids which drop past the edges of the support are collected in catch basins 28,28' for reuse, if practical.

Reference is now made to Fig. 2. One of the known ways to maintain stability of the free—falling curtain 18 in the region of the edge guides 24,24' is to deliver a low—viscosity liquid to the outer surface of the solid edge guide 24. Fig. 2 is a view, partially in section, of a marginal portion of a typical free-falling curtain 18, showing a solid edge guide 24 flushed with a flushing liquid 30 and an edging band liquid 32 contiguous with the flushing liquid 30 which are shown being dispensed into the catch basin 28, leading to a drain (not shown). It can be seen that liquid from the curtain wets the backside of the support 20 at the edges of the support at 34 and also coats the knurled area 26. The liquids which coat the backside of the support 20 will transfer to subsequent conveyance rollers and eventually require termination of the coating process in order to clean downstream conveyance rollers. The coating applied on the knurled area 26 results in problems in the finishing operation due to the tacky nature of the gelatin and the high winding pressures associated with knurls.

To avoid the drawbacks of the known ^•apparatus, there is provided, in accordance with the invention, at each margin of the falling curtain 18, a curtain-severing device 40,40' , respectively. Each device 40,40* includes a blade 42. Viewed in plan, each blade 42 makes an acute angle with the edge of the moving support in the sense that it is disposed over the support upstream of the curtain, extends through the plane of the curtain, and is disposed outboard of the support downstream of the curtain. The arrow 41 in Fig. 1 indicates the direction of movement of the support 20. Each blade 42 has an upper surface disposed in a plane approximately parallel to the plane of the support 20, where the curtain 18 impinges on it and, in the present example, wherein the support is trained about coating roller 22, that plane of the support is tangential to the coating roller. In the present embodiment the blade is formed of sheet material, in fact, stainless steel or titanium. Liquid forming the curtain 18 starts its free fall by falling off the coating edge 16 of the slide hopper 10 and is severed, at each margin, just above where it would impinge on the support 20. The curtain is parted by the blades 42,42' so that the center portion of the severed curtain impinges on the support, leaving margin 48 uncoated. The laterally outer portions of the severed curtain 18 are drawn toward the contiguous edge guides 24,24* so that all of the edging band liquid 32 flows into the catch basins 28,28^*.

Figs. 3 and 4 illustrate the curtain—severing device 40'. The curtain—severing device 40' comprises the protruding blade 42', a housing 44 and purging liquid—supply connections 46. Either liquid—supply connection 46 can be used depending upon how the curtain—severing device is mounted. The curtain—severing device 40 is structurally the sarr.e as the curtain severing device 40' but is a mirror image of it so that it can have the desired relationship to the edge of the support, that is, forming an acute angle, being over the support upstream of the curtain and outboard of the support downstream of the curtain. B At least the top surface, and preferably both surfaces, of each blade 42,42' are purged with a liquid, preferably water, through slots 50 located contiguous with the blade and preferably extending the entire width of the blade where it leaves the 0 housing 44. The curtain liquids which impinge on the blades 42 and 42', will be diverted to catch basin 28 or 28', respectively, by the force of purging liquid supplied to the top of the blade. Preferably, the bottom surfaces of the blades 42 and 42' are also 5 purged with a liquid in order to minimize any tendency for solids from the curtain liquids drying on the edges of the blade. The tendency of the bottom purge is to surround the edges of the blade. To meet the requirements for the necessary volume and velocity of the purging liquid, the height of each slot 50 is preferably in the range of 0.006 to 0.025 centimeter.

Fig. 5 is a plan view of the preferred curtain—severing device showing in greater detail the location and disposition of the blades 42 and 42' for severing the falling curtain. The width of each blade 42 and 42' where it leaves the slots 50 is preferably slightly greater than that of the outboard portion of the blade. Preferably the width gradually narrows from the slots to the location of impingement of the curtain with the blade. Outboard at the impingement location on the blade, the width of the blade is essentially uniform. This slight narrowing of each blade helps to ensure that the purging liquid envelops the edges of the blade. Each blade 42,42' is disposed at an acute angle φ with respect to the direction of travel of the support and its plane is parallel to the plane tangential to the coating roller 22 at the line of impingement of the curtain on the support, so as to divert the marginal portion of the falling curtain which impinges on the blade. Purging liquid is projected along the surfaces of each blade 42 and 42' in a direction inclined at the same angle φ with respect to the direction of travel of the support, to flush the margin of the curtain away from the edge of the support into the catch basin 28 or 28', respectively. It can be appreciated that the length and width of each blade and its angle with respect to the direction of support travel are interrelated variables and the selection of them depends also on the velocity and volume of purging liquid supplied to the blade surface. The blade 42 or 42' should be as wide as needed to provide the desired width of the uncoated margin 48 on the support and to allow for lateral displacement of the support. Lateral displacement of the moving support is very difficult to eliminate even with the most sophisticated support—guiding devices. The width of the blade preferably is in a range of 0.3 to 3.0 centimeters and the angle φ of the axis of the blade with respect to the direction of the moving support can be in the range of 5° to 60°, and preferably 20° to 40°. The length "L" (see Fig. 4) of the blade should be sufficient to permit collection of the curtain liquid and purging liquid, and has been found to be satisfactory when in the range of 2 to 5 centimeters, and preferably should be 4 centimeters. The speed of the purging liquid across the blade surface is preferably of the same order as the speed of the support along its path and may be half to one and a half times the speed of the support. Advantageously the purging liquid flow is laminar. Thus, for example, if the support speed is 200 to 650 cms per second, then the speed of the purging liquid along the blade is preferably about 500 cms per second. For a purging liquid speed in the range of 200 to 800 centimeters per second, the volume of purging liquid may be about 2 to 10 cubic centimeters per second per centimeter of slot 50 width, and preferably j> to 7 cubic centimeters per second per centimeter of slot 50 width.

Fig. 6 shows low—viscosity flushing liquid 30 having been delivered to the top of the solid edge guide 24 and flowing down the entire height of the edge guide to where the edge guide terminates below the level of the blade 42. An edging band liquid 32 is supplied in the margins of the curtain to increase the stability of the curtain and reduce waste. When using an edging band liquid, it may be advantageous to supply a sufficient quantity of edging band liquid to the end portions of the slide hopper so that the thickness of the curtain in its margins, and thus the flow rate of edging band liquid, are somewhat greater than the thickness of and flow rate in the middle portion of the curtain, thereby greatly increasing the stability of the curtain at and adjacent the edge guides and thus avoiding curtain breaks. It can be appreciated that the width and thickness of the curtain edging band liquid are such that a relatively large quantity of edging band liquid may be required, typically one liter per minute, or more. The process provides good results when the viscosity of the edging band liquid approximates the viscosity of the liquids in the middle portion of the curtain. Gelatin solutions of appropriate concentration and with added wetting agents, are suitable. To achieve a well-defined and distinct layered edge region of the composition coating 54 inboard of the edges of the support 20, it is important that the height of the severing blades 42 and 42' above the support at the impingement location be as small as is practical from an operating point of view. It is found that this height should be less than about 0.4 centimeter and preferably about 0.15 centimeter. Because the blades of the curtain—severing device 40,40' are closely spaced to the support, it will, of necessity, be parallel to the moving support 20 on the coating roller 22 at the impingement location of the curtain.

The margins of the falling curtain 54 having been severed by the blades 42,42' and located adjacent the edge guide 24,24', will naturally tend to neck in toward the edge guides and facilitate flow of flushing liquid 30 and edging band liquid 32 to the catch basin 28. With the assistance of the flow of purging liquid over the surface of the blade 42 projected from slots 50, an uncoated margin over the knurled area 26 is assured.

Fig. 7 illustrates another embodiment of the invention, in which each edge guide 56 is fabricated from a hollow tube. Flushing liquid is supplied through the hollow tube from a source, not shown. Each edge guide 56 terminates a short distance above its associated severing blade 42. Liquid flowing out of the edge guide creates a liquid extension which combines with flushing liquid 30 to extend and stabilize the edge region of the falling curtain. The use of a shorter edge guide 56 allows for the slide hopper to be moved into a coating position and avoid mechanical interference with a fixed severing device 40. It was found that liquid flowing from the end of the edge guide acts as an effective extension of the edge guide when the hollow tubes had inside diameters of about 0.035 to 0.240 centimeter, and an outside diameter of about 0.075 to 0.300 centimeter and the fluid flow rate is from 10 to 200 cubic centimeter per minute. If these conditions are not met, then the jet, projected from the edge guide, may tend to break up before the severed margin of the liquid has completed its necking in toward the axis of the edge guide, resulting in an uneven and pulsating breakup of the severed margin of the curtain and the possibility of contaminating with curtain liquids the apparatus in its immediate vicinity including the coating roller and also the edge of the support.

It has been found that, when the curtain—severing blade is used to part the curtain, according to the preferred embodiment described above, then all of the curtain liquids impinging on the blade are directed by the purging liquid to the catch basin. The width of that part of the severed curtain deposited on the support can be reduced by changing the width of the blade and the position of the blade with respect to the edge of the support. To allow for lateral displacement of the moving support (sometimes called "weaving") at the impingement location, the preferred position of the blade is with the point of intersection of its axis and the line of impingement of the curtain on its surface, located just above the edge of the support on the coating roller. In this position, the width of the uncoated margin of the support will be equal to half the dimension of the blade along the curtain impingement line, with variation from this width, more or less, depending on the amount the support weaves as it travels around the coating roller. It has been found that, if the blade is approximately parallel to a tangent to the coating roller at the impingement location and spaced above the coating roller by no more than .15 centimeter, then any edge bead of coating which may form on the support will not exceed 20 percent of the thickness of the remaining coating and is easily dried before the film is wound at the end of the coating machine.

Furthermore, flushing liquid 30, edge band liquid 32, fluid edge guide extension 57 and the purging liquid emitted from slot 50 of the curtain—severing device are all preferably a low-viscosity liquid having a viscosity of 0.5 to 10 centipoise.

Claims

WHAT IS CLAIMED IS:

1. A method of curtain coating a support with liquid, comprising the steps of: a) moving the support along a path; b) forming a free—falling curtain of said coating composition in which form the composition impinges on said moving support, the curtain having a width greater than the desired width of the coating to be formed on the support; c) providing a severing device having a blade for severing and laterally displacing a margin of the curtain, and disposing the blade in a plane 5 approximately parallel to the plane of the support where the composition impinges on it, the blade being disposed over the support upstream of the curtain, extending through the curtain, o and being disposed outboard of the support downstream of the curtain; and d) passing purging liquid over the upwardly facing surface of the blade to carry outboard of the support the material in 5 the curtain incident on the blade.

2. A method as claimed in claim 1, wherein the speed of the purging liquid over the blade is in the range of one half to one and a half times the speed of the support along its path. 0

3. A method as claimed in claim 2, wherein the speed of the purging liquid over the blade approximates the speed of the support along its path.

4. A method as claimed in claim 2, wherein the flow of purging liquid is laminar. 5

5. A method as claimed in claim 2, wherein the support has a speed in the range of 150 cms per second to 1000 cms per second and the purging liquid has a speed of about 500 cms per second.

6. A method as claimed in any one of the preceeding claims, including guiding the curtain at its edges with edge guides and flowing flushing liquid down the edge guides, the curtain being in contact with the flushing liquid.

7. A method as claimed in any one of the preceeding claims, including forming the margins of the curtain from a liquid other than the coating liquid.

8. A method as claimed in claim 6 or claim 7 when appendant to claim 6, wherein said edge guides are hollow tubes terminating above the plane of the blade of the severing device, and including the step of- flowing liquid down the hollow tubes to form, in effect, extensions of the tubes, whereby severed from the curtain necks into the extensions.

9. A method as claimed in any one of the preceding claims, including passing purging liquid across also the downwardly facing surface of the blade.

10. Apparatus for curtain coating a support with at least one layer of coating liquid, comprising: a) conveying means, including a coating roller, for moving a support along a path; b) hopper means for forming at least one layer of coating liquid into a free-falling curtain which intercepts, and extends transversely of, said path, the curtain being wider than the desired width of the coating to be formed on the support; c) curtain—severing means for intercepting and diverting the margins of the curtain, including a blade disposed in a plane approximately parallel to the plane of the support where the composition impinges on it, the blade being disposed over the path upstream of the plane of the curtain, extending through the plane of the curtain and being disposed outboard of the path of the support downstream of the plane of the curtain; and d) means for passing purging liquid over the upper face of the blade for carrying intercepted material in the curtain outboard of the path of the support.

11. Apparatus as claimed in claim 10, wherein said means for passing purging liquid over the upper face of the blade is adapted to give the purging liquid on the blade a speed in the range of one half to one and a half times the speed of the support along its path.

12. Apparatus as claimed in claim 11, wherein said means for passing purging liquid over the upper face of the blade is adapted to create laminar flow of the purging liquid on the blade.

13 Apparatus as claimed in claim 10, 11 or 12, further including guide means for guiding the edges of the curtain. 14. Apparatus as claimed in claim 13, wherein said guide means at each edge of the curtain is hollow and. terminates above the plane of the path of said support, and said apparatus further includes means for passing liquid downwardly through said hollow guide means whereby liquid leaving each hollow guide means forms, in effect, an extension of the guide means whereby severed coating liquid necks into the liquid from the hollow guide means. 15. Apparatus as claimed in any one of claims 10 to 14, further including means for passing purging liquid across the lower face of the blade.