Coater for low flowrate coating

Abstract: It is well-known to use large baths for applying developer solution to a photographic material. However, excess amounts of the developer solution are required to produce the desired results. Described herein is a coater arrangement in which developer solution can be coated on to a photographic material at a rate which does not exceed the maximum swell rate of the material. This allows developer solution to be applied to the photographic material without leaving behind liquid effluent. The coater features a delivery channel (32) leading from a manifold chamber (30) to a slit orifice(34), the channel (32) being improved in that it contains a plurality of spaced-apart wall portions (38) connecting the opposed flow surfaces (35, 36) of the delivery channel (32) which extend in a direction towards the slit orifice (34). A further structure is provided inside the orifice (34) for coalescing the individual streams fed by these wall portions (38) into a continuous strip of liquid to be dispensed by the slit orifice (34).

Description: This invention is directed to a coater for applying liquid uniformly and intermittently, at a slow rate which, in the case of photographic products being coated, does not exceed the swell rate of the products. A key concern of the '90's is how to preserve the environment. Preservation efforts include the elimination or detoxification of effluents, including waste water from photographic processors. Conventionally, large baths are used by such processors, which contain chemicals of various toxic types to develop photographic images. Such excess aqueous solutions have only two options for disposal - either they have to be constantly reused (to avoid disposal entirely), or they have to be disposed of in a way which is not harmful to the environment. The former solution has the disadvantages of requiring constant adjustments to the chemical concentrations to deal with depletion of desired chemicals and the possible build-up of, or contamination from, undesired chemicals. For example, the use of baths of excess developer solution means that if subsequent stations are used for a treatment of continuous streams of photographic product, each at a different concentration, there is a risk of cross-contamination as the product moves from one station to another. The alternative of dumping a contaminated bath in favor of a fresh batch has the disadvantages of requiring removal of the noxious chemicals, if possible, prior to dumping, or contamination of the environment, if not possible. Such disadvantages could be obviated entirely if excess developer solutions could be avoided. Although such an approach suggests as a solution, using only the amount of developer solution needed to swell and develop a given print, and no more, it has not been possible to apply such an amount of effluent-free developer to photographic material using conventional coaters. As used herein, "effluent-free" means free of liquid effluent, since the swelling of the gelatin has to be reduced by removing the water in a heater as vapor. However, such a gaseous effluent is less harmful than liquid effluents. Conventional coaters typically apply a continuous stream which exceeds in volume and rate that which the underlying support can absorb, so that there are fewer demands on the coater. However, if the liquid to be coated is delivered only at the volume and at a rate which can be absorbed for development purposes, the coater has to be able to stop and start intermittently, and at the same time produce a liquid wavefront which is controlled and of uniform width, depth, and length. The document Research Disclosure vol. 230, June 1983, Havant GB, pages 212-214, by Bubb et al. "Devices for Coating Sheets with Fluid" discloses several coaters which are aimed at this purpose. However, a fully satisfactory coating operation has not been possible using coaters of the prior art. Furthermore, to be commercially viable, the coater must be able to be mass produced, preferably of injection molded plastic, and require minimum operator attention to function properly. This means that the effectiveness of the coater must not depend on machining tolerances which are unrealized by traditional techniques for fabricating injection molded parts (tolerances of less than 127µm (0.005")). Finally, it has been suggested in the past that a liquid effluent-free process of development is possible if one sprays developer onto the photographic product. Such a process is described in Canadian Patent 663,837. The problem with spraying is that a fine mist, high pressure spray produces a saturating mist of caustic pH which is itself intolerable. A low pressure, coarse mist spray avoids this problem, but fails to produce a coating which is sufficiently uniform. Hence, prior to this invention it has been problem to provide effluent-free development of a photographic product using only the volume and rate of liquid which can be absorbed by that product during development, for example, from 5.0 to 100ml/m 2 over 30s, since no coater was available which had this capability. (As noted above, "effluent-free" as used in this application refers to freedom from significant liquid effluent, that is free from amounts of liquid effluent which have to be disposed of in ways that risk contamination of the environment. Any coater which inadvertently leaves a few drops of developer behind is not considered to produce "significant" liquid effluent.) In accordance with one aspect of the present invention, there is provided a coater for the delivery of a processing liquid in a uniform layer on to a surface of a photographic product, the coater comprising:- a body having an internal manifold chamber of a width generally equal to the width of said photographic product, conduit means for introducing the liquid at a point within the chamber, a slit orifice shaped to deliver a uniform layer of liquid, and a delivery channel having a length extending from the manifold chamber to the orifice, characterized in that the delivery channel comprises spaced-apart opposed surfaces connected together for the majority of the delivery channel length at spaced intervals by a plurality of wall portions extending between the surfaces in a direction toward the orifice to confine liquid flow into spaced-apart individual streams of flow between the wall portions, and coalescing means inside the orifice and downstream from the wall portions for coalescing the individual streams together into a substantially continuous strip of liquid while still inside the orifice. Accordingly, it is an advantageous feature of the invention that a developing process is provided using a coater which produces no significant liquid effluent which has to be re-used or disposed of. It is a related advantageous feature of the invention that the coater provided for this purpose is readily manufacturable on a repeated basis. Another advantageous feature of the invention is that baths of developer solutions need not be monitored and/or modified after use since the amount of solution used has only a single use, once dispensed. Another related advantageous feature of the invention is the prevention of cross-contamination of various developer solutions, since they remain either in closed containers (the coater) or are quickly absorbed into their assigned photographic product. For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which:- Figure 1 is a transverse sectional view of a coater of the prior art; Figure 2 is a sectioned view taken generally along the line II-II of Figure 1 of the prior art; Figure 3 is a perspective view of a coating operation of a comparative example, of the prior art; Figure 4 is a schematic view of both a sectional coater and the resultant print produced therefrom, as a comparative example; Figure 5 is a schematic view illustrating the contact angle measurements made as described hereinafter; Figure 6 is a sectioned view similar to that shown in Figure 2, but illustrating one embodiment of a coater constructed in accordance with the present invention; Figure 7 is a sectioned view taken generally along the line VII-VII of Figure 6; Figure 8 is an enlarged, fragmentary sectioned view similar to, but of the portion of, Figure 6 which is marked as "VIII", showing the coater with liquid in the quiescent mode; Figure 9 is a sectioned view similar to that shown in Figure 4, illustrating yet another comparative example; Figure 10 is a fragmentary sectioned view similar to that shown in Figure 7, but of a second embodiment of the present invention; Figure 11 is a fragmentary sectioned view similar to that shown in Figure 8, but of a third embodiment of the present invention; Figure 12 is a sectioned view similar to that shown in Figure 7, but illustrating another alternate embodiment of the present invention; Figure 13 is a schematic view similar to that shown in Figure 4, but of a coater and the resulting print of the present invention; and Figure 14 is a print produced by the present invention. The invention is hereinafter described in connection with the preferred embodiments, in which the coater is described for development of preferred photographic paper using certain preferred, developer solutions. In addition, the coater can be used to apply any kind of liquid to any kind of surface whether or not the surface is absorptive or part of a photographic product. As used herein, "developer liquid" means any solution effective to develop a latent photographic image in the surface on to which the solution is applied. Most preferably, the developer solution is free of known surfactants. Instead, surfactants, if needed at all, are preferably found in the surface being coated. Regarding the photographic product which is the surface to which the developer solution is applied, that product, as noted, needs to be absorptive at the rate the developer solution is applied. This usually requires a layer of gelatin, or its equivalent, which will absorb the liquid and swell during development. Most preferably, to preclude the wavefront of liquid from breaking into discontinuous puddles on contact with the product due to high surface tension, the product also, in addition to being absorptive, is sufficiently wettable to uniformly attract the wavefront, thus preventing wavefront break-up. (Such break-up is illustrated in Figure 3, a comparative example. The illustrated break-up of wavefront W produces fingers which run together, as shown by arrows 10, 12, to create entrapped air pockets which are insufficiently treated. Instead, what is desired is a uniformly continuous wavefront W', shown in phantom, out of the orifice of coater 20. Otherwise, characteristically the product develops in streaks, as shown in Figure 4, also a comparative example.) A convenient and preferred measure of this wettability is the contact angle the developer solution makes with the photographic product. It has been determined that, in order to maintain the proper wavefront (W' as shown in Figure 3), the contact angle should be less than 45° when measured by standard goniometer techniques 400s after applying liquid. Figure 5 is an illustration of the contact angle in question. A wide variety of photographic products provides such contact angles. For example, those that bear on their surface an unhardened layer of gelatin, such as conventional X-ray film or paper commonly have a contact angle of 28° (for example, for "Min-R"™ X-ray paper available from Eastman Kodak Company) and hence are useful. Referring now to Figures 1 and 2 which illustrates a coater of the prior art, the coater of the present invention has in common certain features with the prior art. Both of them comprise a body 22 into which is fed the solution to be coated, via a supply line 23, as shown in Figure 1, from a closed storage vessel (not shown). To introduce the liquid into the coater at a point, the supply line exits at an aperture 24, as shown in Figure 2. This aperture in turn feeds directly to an internal manifold chamber 30 having a width generally equal to the width of the desired wavefront. Beyond the manifold chamber and fluidly fed therefrom is a delivery channel 32 which leads from a junction surface 33 with chamber 30, to a slit orifice 34 on an exterior edge of the coater, which deposits the liquid wavefront on to the support or photographic product. As is more clearly shown in Figure 1, channel 32 is much narrower in height h than the manifold for the entire width of the channel, with height h being generally on the order of 0.05mm ± 1%, thus producing a very high pressure drop across the channel 32. This pressure drop is needed to spread the point source of the liquid throughout chamber 30 before it exits through channel 32. There are several problems with such a coater. One is that such a narrow channel tends to produce local discontinuities, as shown in Figure 3, at the wavefront. This is particularly true when applying developer solutions to photographic products at a rate (0.02 - 0.05ml/m 2 /s) which is no more than the product can absorb. Such a coating rate is much slower than the rate the conventional coater uses. These slower rates induce the wavefront to break up more than occurs at the faster, conventional rates. The reasons include local variations in at least the absorptivity of the support at the wavefront, and in the wettability of the support. Also higher coating rates ensure that a substantial excess of liquid is delivered to the surface to accommodate any variability in absorptivity. It is the elimination of such excesses that is the motivation behind the current invention. Still further, the high precision for height h precludes making the coater out of inexpensive materials. In accordance with the present invention, and as a solution to the abovementioned problems, it has been found that the same coater 120, shown in Figures 6 and 7, is drastically improved by constructing channel 32 so that the spaced-apart, opposing surfaces 35 and 36 (Figure 7) defining the major flow contact within channel 32, are connected together for the majority of the channel length, at spaced intervals, by wall portions 38. By "majority", it is meant that at least 50% of the length of channel 32, as shown for example in Figure 7 from its inception at edge 33 to the orifice 34, is occupied by the wall portions 38. Wall portions 38 preferably extend substantially completely across the space between surfaces 35 and 36, and can be spaced along the width w, as shown in Figure 6, at regular or irregular intervals, provided there are enough of them. Substantially complete extension between surfaces 35 and 36 is preferred, as otherwise the wall portions 38 tend not to be effective to break up the flow into individual streams. Preferably they extend in a direction from chamber 30 to orifice 34, and most preferably in a direction which is perpendicular to the edge of coater 120 defining orifice 34. The function of wall portions 38 is to divide up the liquid flow into discrete, individual streams 40, as is more clearly shown in Figure 8. Most preferably such streams, and therefore the wall portions 38, are generally parallel. The reason for the success of the discrete streams is not completely understood. However, the following is one possible explanation: Without the break-up of the liquid into individual streams by the wall portions, the advancing meniscus is free to advance unevenly towards the orifice, so that upon exiting, a non-linear, uneven wavefront is deposited. However, the wall portions in contrast break up the liquid into the individual streams which do not form a continuous wavefront again until immediately at the orifice. The length of the coalescing means that provides this reformation is discussed below. Regarding the number of occurrences of wall portions 38, along the width w, it will be apparent that, as the number decreases, one eventually reaches a condition little different from that shown in Figure 4 where there are none. The minimum number needed varies, depending on the nature of the liquid being coated. However, for a developer solution used with photographic products, preferably that number is such that the spacing s (Figure 8) between most of them is less than 5mm. The reason is illustrated in Figure 9 which shows a comparative example where wall portions 38 were about 5.0mm apart, at regular intervals, and the developed print was considered to be just barely unacceptable due to the variations in the density produced. Thus, preferred examples of a useful spacing include, for example, one in which the walls are between 0.4 and 0.8mm apart, across the width w, as shown in Figure 6. (In all the examples showing a developed print, that is, in Figures 4, 9 and 13, the concentration of developer was watered down by about 50%, to more clearly denote flow irregularities.) It will be readily appreciated that walls 38 can be too close together, at which point they form pores which are so small compared to the impermeable wall space that the performance is unacceptable. For developer solutions, spacing less than 0.1mm is considered too close together to be particularly useful for a uniform spacing. If the spacing is irregular, a few can be this close if most are spaced at 0.4 to 0.5mm. To allow for maximum air displacement when liquid first enters chamber 30, it is preferred that connecting walls 38 not extend back through delivery channel 32 to the junction surface 33, as shown in Figure 7. Instead, walls 38 start at a position 60 away from surface 33, towards slit orifice 34. The spacing distance 1 between position 60 and junction surface 33 can be from 0.1mm to 1.0mm, with a spacing of 0.3mm preferred. Such spacing provides an open, continuous flow chamber, in contrast to the case if walls 38 were to lengthwise extend all the way from junction surface 33. To create the coalescing pocket 50, shown in Figures 7 and 8, for coalescing the individual streams 40 into a substantially continuous strip or bead of liquid just inside orifice 34, when the liquid is ejected, wall portions 38 do not extend all the way to orifice 34. Instead, they stop short at edges 52. When liquid is no longer to be coated, the previously-coated liquid breaks off at edges 52, leaving, as shown in Figure 8, individual menisci M of the individual streams 40. Such behavior is important, because without coalescing pocket 50, the coater while quiescent will produce a meniscus which traverses the entire width of channel 32. When that happens, air intrusion occurs due to the large surface area exposed, and the long meniscus starts to fall out in puddles, leaving unacceptable quantities of liquid at the work station, possibly on the next product to be exposed. This in turn produces uneven amounts, and possibly excessive amounts, of developer on the next product. In addition, the air which has intruded into the hopper forms pockets which obstruct liquid flow during the next coating cycle, producing grossly non-uniform fluid delivery which cannot be compensated for, by the coalescing means at the orifice. Preferably, to further induce the menisci M to stop at edge 52, pocket 50 is constructed so that spaced-apart surfaces 35 and 36, Figures 7 and 10, are stepped abruptly farther apart in pocket 50 than they are in channel 32. This creates at least one edge surface 54 in surface 35 or 36 as shown in Figure 10, to induce menisci M (Figure 8) to stop at edge surface 52. Most preferably, as shown in Figure 7, there are two such edge surfaces 52. For example, whereas spacing h, as shown in Figure 10, can be about 0.4mm, the spacing h' of surfaces 35 and 36 at pocket 50 is 0.5mm. The length of pocket 50, measured in the direction extending from edge 54 to orifice 34, is preferably no greater than 2.5mm, so as to avoid the problem noted above of a non-uniformly located meniscus which is created by the prior art orifice which lacks the wall portions completely. The substantially continuous strip of liquid which must be produced by the coalescing means, refers to a strip which is sufficiently continuous as to not produce noticeable streaking upon development. Alternatively, the connecting wall portions can lengthwise extend all the way to the slit orifice and still create a coalescing pocket, if those wall portions are feathered in width at the slit orifice, as shown in Figure 11. Parts similar to those previously described bear the same reference numeral to which the distinguishing suffix "A" is appended. Thus, coater 120A features the same manifold chamber 30A, delivery channel 32A and slit orifice 34A as before, with connecting wall portions 38A connecting the opposed flow surfaces (of which only surface 36A is shown). As before, wall portions 38A commence at position 60A spaced away from junction surface 33A. However, unlike the previous embodiments, wall portions 38A do extend to slit orifice 34A, but only in a form having a tapered transverse thickness t which decreases to an infinitesimally small edge 62 at the orifice. This is sufficient to minimize liquid flow vortices which would occur without the taper, thus producing a coalesced flow that exits orifice 34A. Stated in other words, the tapered edges 62 are so thin that the liquid "sees" the orifice as a continuous slit. The distance D of the taper can be varied considerably. A useful example is 1.0mm (at least two times the spacing between wall portion 38A). As an optional additional feature, as shown in Figure 12, means can be added to increase viscous resistance to flow of liquid from the slit orifice on to a surface, thereby further damping out vortices which may remain due to the presence of connecting wall portions at or adjacent to the slit orifice. Parts similar to those previously described bear the same reference numeral, to which the distinguishing suffix "B" is appended. Thus, coater 120B comprises chamber 30B, delivery channel 32B, slit orifice 34B, and wall portions 38B connecting opposed flow surfaces 35B and 36B. Wall portions 38B stop short of orifice 34B, as in the embodiment shown in Figure 7. However, the walls 70 and 72 defining slit orifice 34B are of substantially different thickness d 1 and d 2 (Figure 12). In particular, d 2 is made substantially larger than in other embodiments, to substantially increase the viscous resistance to flow between the face 73 and the receiving surface. There are two primary considerations in the choice of d 2 :- (1) The resistance should be great enough to ensure that the liquid spans the entire space between face 73 and the receiving surface, at the prescribed fluid delivery rate and surface speed, and (2) The distance d 2 should be large enough to viscously damp out eddies formed upstream at surface 70 and in channel 34B. That is, d 2 is substantially greater in value than the gap g. Most preferably, d 2 should be at least 5 times the spacing between surface 73 and the receiving surface to be effective. For example, d 2 ≥ 0.9mm for a flow gap g of 0.18mm. On the other hand, the thickness d 1 of wall 70 is not critical, but should be minimized to facilitate the formation of a continuous film of liquid on this upstream edge that bridges the distance between face 73 and the receiving surface. Most preferably, d 1 should be of the same order as the gap width g, for example, ≈ 0.2 mm. Coater 120 can be manufactured from a variety of materials, but preferably from plastics resistant to the liquid being coated. For developer liquids, useful materials comprise polystyrene or polytetrafluoro-ethylene such as "Teflon"™. Because these latter are non-wetting, a positive pressure should be applied at the inlet orifice until the hopper is completely filled, to minimize the possibility of air entrapment. The coater of the present invention has been effective in repeatedly and intermittently applying a thin, low volume, uniform coating of developer liquid onto photographic products (for example, via line 23 in Figure 7). The application rate has been no greater than that needed to swell the developable layers being coated, for example, at a rate of between 1 and 20µl/cm of width/s. The result is a substantially liquid effluent-free developing process. Figure 13 illustrates the greater uniformity of flow and coating provided, using coater of Figure 6. This is in marked contrast to the results of Figure 4, a comparative example. (As in the case of Figure 4, the developer concentration has been drastically reduced, by 50%, to allow flow discrepancies to be distinguishable.) The spacing apart of wall portions 38 in the transversed direction in this coater was approximately 0.4mm. An actual color print developed using a coater of this invention is shown in Figure 14. The embodiment was that as shown in Figure 13, wherein the transverse spacing A between wall portions 38 (Figure 8) was 0.4mm. The developer process used was Eastman Kodak Company's conventional CD3 and carbonate formulation applied to the paper separately: 34µl/sec of potassium carbonate (112g/l) in water from a 100mm (4") hopper to paper moving at 25mm/s (1in/s), that is, at an application rate of about 1.25ml/ft 2 (swell = 2.5ml/ft 2 ). After allowing the activator to soak in for 20s, the above application was repeated using Kodak developer, CD3 (37.5g/l) in water. Development was complete in 50s at 21°C, and there was no effluent. The processed coating was put through a conventional bleach-fix treatment, washed and dried. The maximum density readings for this print were:- cyan = 1.32 magenta = 1.35 and yellow = 0.93. The print is offered in color as the best evidence to substantiate the assertions herein that excellent uniformity in developer coatings are produced by this invention, while still producing substantially no liquid effluent. The lack of streaking is very apparent from this photographic print.

Claims: A coater (120; 120A; 120B) for the delivery of a processing liquid in a uniform layer on to a surface of a photographic product, the coater comprising:- a body having an internal manifold chamber (30; 30A; 30B) of a width generally equal to the width of said photographic product, conduit means (23) for introducing the liquid at a point within the chamber (30; 30A; 30B), a slit orifice (34; 34A; 34B) shaped to deliver a uniform layer of liquid, and a delivery channel (32; 32A; 32B) having a length extending from the manifold chamber (30; 30A; 30B) to the orifice (34; 34A; 34B), characterized in that the delivery channel (32; 32A; 32B) comprises spaced-apart opposed surfaces (35, 36; 35A, 36A; 35B, 36B) connected together for the majority of the delivery channel length at spaced intervals by a plurality of wall portions (38; 38A; 38B) extending between the surfaces (35, 36; 35A, 36A; 35B, 36B) in a direction toward the orifice (34; 34A; 34B) to confine liquid flow into spaced-apart individual streams (40) of flow between the wall portions (38; 38A; 38B), and coalescing means (50) inside the orifice (34; 34A; 34B) and downstream from the wall portions (38; 38A; 38B) for coalescing the individual streams (40) together into a substantially continuous strip of liquid while still inside the orifice (34; 34A; 34B). A coater according to claim 1, wherein the coalescing means (50) are defined by the termination of the connecting wall portions (38; 38A; 38B) just inside the orifice (34; 34A; 34B) to define a pocket (50) within the orifice (34; 34A; 34B) and extending generally perpendicular to the direction of liquid flow out of the orifice (34; 34A; 34B) which is free of the wall portions (38; 38A; 38B) so as to provide the coalescing of the parallel streams (40). A coater according to claim 2, wherein the spaced-apart surfaces (35, 36; 35A, 36A; 35B, 36B) are spaced abruptly further apart at the orifice (34; 34A; 34B) than at a location just inside the orifice (34; 34A; 34B) to provide at least one edge surface (52, 54) for pinning a meniscus (M) within the orifice (34; 34A; 34B) when flow has temporarily been terminated. A coater according to any one of claims 1 to 3, wherein the wall portions (38A) extend substantially completely across the gap between the surfaces (35A, 36A) and to the orifice (34A) with a thickness which tapers sufficiently as the orifice (34A) is reached as to aid coalescence of the separate streams (40) at the orifice (34A). A coater according to any one of claims 1 to 4, wherein the wall portions (38; 38A; 38B) confining the liquid into the parallel streams (40) are spaced away from and do not extend to the junction (33; 33A) of the delivery channel (32; 32A; 32B) and the manifold chamber (30; 30A; 30B) so that a continuous flow chamber is provided at the junction (33; 33A) sufficient to allow maximum air displacement when liquid enters the manifold chamber (30; 30A; 30B) from the conduit means (23). A coater according to any one of claims 1 to 5, wherein the wall portions (38; 38A; 38B) extending between the surfaces (35, 36; 35A, 36A; 35B, 36B) have a transverse thickness which decreases as the wall portions (38; 38A; 38B) approach the orifice (34; 34A; 34B) so as to minimize liquid flow vortices which can be created by the wall portions (38; 38A; 38B). A coater according to any one of the preceding claims, further including at the orifice (34B), resistance means for increasing viscous resistance to flow of liquid outside of the orifice (34B) and on to the surface being coated. A coater according to claim 7, wherein the resistance means comprise an edge of the coater at the orifice (34B) which is substantially greater in thickness in the direction of flow of liquid from the orifice (34B) on to the surface than the spacing of the coater orifice (34B) from the surface being coated. A coater according to any one of claims 1 to 7, further including means for providing a developer solution to the conduit means (23) whereby the coater (120; 120A; 120B) is used to develop photographic film.

Inventors: COLUMBUS RICHARD LEWIS, PALMER HARVEY JOHN, COLUMBUS, RICHARD LEWIS, PALMER, HARVEY JOHN, COLUMBUS, RICHARD LEWIS, C/O EASTMAN KODAK CO., PALMER, HARVEY JOHN, C/O EASTMAN KODAK CO.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1992
Main classification: G03D5
IPC codes: G03D5