A liquid passage system for photographic coating devices

Abstract: The present invention relates to a coating hopper for applying one or more layers of photographic liquid onto a web of paper or film support. The device incorporates a liquid passage system with a metering slot of defined width which leads to an expansion section having an increasing width as liquid moves away from the metering slot. The expansion section is connected to a discharge slot having a defined width greater than that of the metering slot which delivers photographic liquid to a location on the coating device where a layer of that liquid is formed.

Description: BACKGROUND OF THE INVENTION In producing photographic film or paper, it is necessary to coat the film or paper support with discrete layers of photographic coatings. Some of these layers contain a radiation sensitive material like silver halides, diazonium salts, and light sensitive dyes as well as other photographic additives including matting agents, developing agents, mordants, etc. Other layers may contain materials which are not radiation sensitive like subbing layers, pelloid protective layers, filter layers, antihalation layers, and interlayers. Additionally, hydrophilic colloids, polysaccharides, surfactants, and synthetic polymers may also be incorporated in photographic coating liquids. The number of separate and discrete layers of photographic coatings applied to photographic paper or film support depends on the product's design. Typically, the number of layers varies between 1 to 15, more usually 3 to 13. A slide hopper is a known apparatus which will coat one or more liquids onto a solid support. The conventional multi-slide hopper performs its coating operation by metering a first coating liquid from a supply through a narrow slot which distributes the liquid uniformly across the top of a downwardly inclined slide surface. This layer of liquid moves down the slide surface by gravity to supply a steady, uniform, smooth coating layer to a coating bead across which it is applied to a moving web being coated. A second coating liquid is supplied to and distributed by, a second slot which directs a uniform layer of that liquid onto the top of a second slide surface. The second coating liquid first flows down its own slide surface and then onto the top of the layer of liquid issuing from the first slot without interlayer mixing. The layers of the first and the second liquids then together flow down to a coating bead where they are applied to the web. Additional liquids may be coated simultaneously by equipping the hopper with the appropriate number of slots and slide surfaces. Instead of applying photographic coatings from a multi-slide hopper to a web by use of a coating bead, multi-layer photographic coatings can be applied by passing the web beneath a liquid curtain formed by discharging the coating liquid from a terminal lip portion of the multi-slide hopper. Both the bead coating and curtain coating techniques are well known, as disclosed e.g. , in U.S. Patent No. 4,287,240 to O'Connor. In older photographic coating hopper arrangements, photographic liquids were pumped from a narrow feed conduit into a distribution channel where the liquid was spread transversely across the hopper. From the distribution channel, the photographic liquid was passed through a metering slot of constant width and discharged onto a slide surface. U.S. patent No. 2,761,417 to Russell et al. depicts such a system. It has been found that such conventional hoppers often tend to produce a defect in the final coating product which appears as a long line or lines running parallel to the direction of coating. These defects are not always visible in the product as coated and very often they become visible only after the product is dried and/or processed (if the coating web is a photographic product) and then is visually checked. One cause of such streaks is local deficiencies in the layer of coating liquid issuing from any slot which is thinner than the adjacent layer of coating liquid. The total thickness of the layers is constant throughout the coatings. Streaks may also result from the entrapment of particles and bubbles in areas of the coating system having low wall shear stress or regions of recirculation (i.e., vortices). In U.S. patent No. 3,005,440 to Padday, the line problem was attacked by terminating the metering slot at a discharge slot which abruptly widens at a right angle to the metering slot. This sharp right-angle corner produces the maximum amount of turbulence in the stream and heals lines formed by upstream blockages in the metering slot. With this configuration, any flow obstructing particles will be present only in the metering slot having a narrow width to maintain backpressure on the upstream distribution channel. The length of the wider discharge slot is sufficient to heal any turbulence created by blockages in the metering slot. Studies, however, indicate that streak-creating vortices can occur in the discharge slot at slot Reynolds Numbers of 5 or above. Another approach to elimination of lines, as discussed in U.S. patent No. 3,474,758, is to direct the exit end of the discharge slot at an angle to the slide surface on which liquid from the slot exits. Somewhat similar to this concept is the device disclosed in U.S. patent No. 4,041,897 to Ade where each emulsion is applied to a slide on the device through a slot having a vertically-extending upstream wall and an inclined downstream wall such that the slot widens as it approaches the slide. Such techniques, however, are susceptible to the adherence of streak-forming particles to the incline. Streaking is thus a significant problem in processes of coating a pack of photographic emulsion layers onto a support. There continues to be a need for an economical and effective procedure for correcting this problem. SUMMARY OF THE INVENTION The present invention relates to a coating device which can be used to apply one or more layers of photographic liquids onto a web of paper or film support. The device as claimed in claim 1 includes a liquid passage system which contains a metering slot having a defined, preferably, narrow width to maintain an upstream back pressure. Downstream of the metering slot is an expansion section which has a smoothly increasing width as liquid moves away from the metering slot. This width expansion can have a configuration which is linear or non-linear (e.g., exponential). A discharge slot provided with parallel walls and connected to the expansion section has a defined, constant width which is greater than the widths of the metering slot. The discharge slot delivers photographic liquid to a location in the coating device where a layer of that liquid is formed. The liquid passage system of the present invention is particularly useful in conjunction with a slide hopper. Such devices have a liquid-applying plate and a plurality of spaced, serially-arranged, layering plates defining a planar incline which directs layers formed on the incline to a coating application area. The liquid passage system of the present invention, which can be located between each of the layering plates and between the liquid-applying plate and its adjacent layering plate, supplies liquid-forming layers to the incline. Such hoppers can be used to apply photographic coatings to a support by either curtain coating or bead coating. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a side cross-sectional view of a curtain coating slide hopper in accordance with the present invention. Figure 2 is a side cross-sectional view of a liquid passage system of the slide hopper of Figure 1. Figure 3 is a side cross-sectional view of a second embodiment of a liquid passage system in accordance with the present invention. Figure 4 is a side cross-sectional view of a third embodiment of a liquid passage system in accordance with the present invention. DETAILED DESCRIPTION OF THE DRAWINGS Figure 1 is a side cross-sectional view of a photographic liquid coating slide hopper 2 in accordance with the present invention. Slide hopper 2 includes layering plates 4, 6, and 8 and curtain-forming plate 10. Layering plates 6 and 8 and curtain-forming plate 10 have upper planar surfaces 42, 44, and 46, respectively, which together form a wide incline at an angle of from 5 to 20 degrees, preferably 15 degrees, from horizontal. Protruding from the end of curtain-forming plate 10 which is distal from the layering plates is vertical lip 50. The spaces between layering plates 4, 6, and 8 and between layering plate 8 and curtain-forming plate 10 form passages for supplying photographic liquids to the incline formed by upper planar surfaces 42, 44, and 46. For top liquid T, this passage, which extends transversely to slide hopper 2 ( i.e. into and out of Figure 1), is defined by the space between layering plates 4 and 6 and includes primary distribution channel 24, metering slot 12, expansion section 30, and discharge slot 36, all of which extend transversely of hopper 2. Liquid T is fed to primary distribution channel 24 by feed conduit 18 which has a central or side location relative to the transverse extent of channel 24 across the width of hopper 2. As to middle liquid M, the space between layering plates 6 and 8, defined by primary distribution channel 26, metering slot 14, expansion section 32, and discharge slot 38, all of which extend transversely across hopper 2, constitutes the passage. Liquid M is supplied to primary distribution channel 26 by feed conduit 20 which is located centrally or at the end of the transverse extent of channel 26. Bottom liquid B's passage is between layering plate 8 and curtain-forming plate 10 and includes distribution channel 28, metering slot 16, expansion section 34, and discharge slot 40, all extending transversely of hopper 2. Feed conduit 22 supplies liquid B to primary distribution channel 28 and has a central or side location with respect to the transverse extent of channel 28 across the width of hopper 2. For liquids T, M, and B, the distribution channels reduce the resistance to transverse flow of liquid across hopper 2, while a high resistance to longitudinal flow is maintained by metering slots. As a result, liquid layers flowing onto the incline defined by planar surfaces 42, 44, and 46 are spread to a suitable width and have a high level of uniformity due to the substantial reduction in pressure variation achieved by the distribution channels. Instead of providing each photographic liquid passage with a single distribution channel, it is particularly desirable to utilize a pair of serially-arranged distribution channels (not shown) in each passage in accordance with pending U.S. patent Application Serial No. 07/766,945, entitled "Liquid Distribution System for Photographic Coating Devices" to Solomon T. Korokeyi, corresponding to EP-A- 0 534 869, published 31.3.93. As is apparent from Figure 1, top liquid T is discharged from discharge slot 36 onto planar surface 42. In turn, middle liquid M is deposited on and in contact with planar surface 44 beneath top liquid T. Likewise, bottom liquid B is deposited on and in contact with planar surface 46 of curtain-forming plate 10 beneath middle liquid M and top liquid T. Once applied to the incline defined by the upper planar surfaces of layering plates 4, 6, and 8 and curtain-forming plate 10, liquids B, M, and T maintain their identity as separate and discrete layers. The separate and discrete layers of liquids B, M, and T flow down planar surface 46, around transition section 48 and fall from lip 50 as a curtain C of liquid coating onto web W as layer L. Web W is transported into contact with curtain C by drive roller 52. Figure 2 is a side cross-sectional view of the liquid passage system between plates 8 and 10 of the slide hopper of Figure 1. As depicted, metering slot 16 is defined by upstream wall 54 and wall section 56a which are in parallel planes. Connected to metering slot 16 is expansion section 34 which is also defined by upstream wall 54 as well as wall section 56b. Discharge slot 40, which receives liquid from expansion section 34, is defined by wall section 56c and upstream wall 54 which are in parallel planes. Liquid emerging from discharge slot 40 onto upper planar surface 46 of curtain-forming plate 10 forms a layer of bottom liquid B. The liquid passage systems which form the layer of top liquid T and the layer of middle liquid M are similarly configured. The angle  at which wall section 56b is inclined from wall section 56a ranges from 5 to 45°, preferably 25°. The perpendicular distance between upstream wall 54 and wall section 56a is 0.1 to 0.6 mm, preferably 0.25 mm, and is substantially constant. The perpendicular distance between upstream wall 54 and wall section 56c is also substantially constant and ranges from 0.5 to 1.5 mm, preferably 0.9 mm. The length of wall section 56c between where it contacts wall section 56b and upper planar surface 46 ranges from 1.5 to 4.5 mm, preferably 2.7 mm. To avoid low wall shear stress and regions of flow recirculation, the location where wall section 56a meets wall section 56b and where wall section 56b meets wall section 56c are not defined by sharp edges but, rather, by rounded transition surfaces. Figure 3 is a side cross-sectional view of a second embodiment of a liquid passage system in accordance with the present invention. This configuration is essentially the same as that depicted in Figure 2 except that the passage expands in the upstream direction. As depicted, metering slot 16 is defined by downstream wall 56 and wall section 54a. Expansion section 34 is connected to metering slot 16 and is defined by downstream wall 56 and wall section 54b. From expansion section 34, liquid enters discharge slot 40 which is defined by wall section 54c and downstream wall 56. As in Figure 2, liquid emerging from discharge slot 40 flows onto planar surface 46 of curtain-forming plate 10 as a layer of bottom liquid B. The angle ' at which wall section 54b is inclined from wall section 54a ranges from 5 to 45°, preferably 25°. The perpendicular distance between downstream wall 56 and wall section 54a is 0.1 to 0.6 mm, preferably 0.25 mm, and is substantially constant. The perpendicular distance between downstream wall 56 and wall section 54c is also substantially constant and ranges from 0.5 to 1.5 mm, preferably 0.9 mm. The length of wall section 54c between where it contacts wall section 54b and upper planar surface 44 ranges from 1.5 to 4.5 mm, preferably 2.7 mm. Like the embodiment of Figure 2, wall sections 54a, 54b, and 54c are joined by rounded transition surfaces. Figure 4 is a side cross-sectional view of a third embodiment of a liquid passage system in accordance with the present invention. This arrangement, in essence, combines the features of Figures 2 and 3. Metering slot 16 is defined by wall sections 54c and 56c, expansion section 32 is formed by wall sections 54b and 56b, while discharge slot 40 is defined by wall sections 54a and 56a. The angles  and ' are 2.5 to 22.5°, preferably 12.5°. The perpendicular distance between wall sections 54a and 56a is 0.1 to 0.6 mm, preferably 0.25 mm, and is substantially constant. The perpendicular distance between wall sections 54c and 56c is 0.5 to 1.5 mm, preferably 0.9 mm, and is substantially constant. The length of wall section 56c between where it contacts wall section 56b and planar surface 46 and of wall section 54c between where it contacts wall section 54b are both 1.5 to 4.5 mm, preferably 2.7 mm. As in the embodiments of Figures 2 and 3, rounded transitions connect wall sections 54a-c and 56a-c, respectively. Metering slots 12, 14, and 16 must be configured to hold an upstream backpressure so that liquid will spread transversely through distribution channels 24, 26, and 28, respectively, and nonuniformities can be removed. The discharge slot is of sufficient length and width to prevent vortex formation on the slide surfaces and intermixing of coating layers above the discharge slot. The liquid passage system of the present invention has numerous advantages over prior art arrangements. It is able to handle liquid flowing at Reynolds Numbers of up to 50 without substantial vortex formation in the liquid passage system or on the downstream planar incline. This system is also able to operate without substantial interlayer mixing at similar Reynolds Numbers. The present invention also utilizes an economical and simplified structural arrangement. Moreover this arrangement can easily be retrofitted to existing coating hoppers like those disclosed by U.S. Patent No. 3,005,440 to Padday. Although the invention has been described in detail for the purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention which is defined by the following claims.

Claims: A coating device adapted to apply one or more layers of photographic liquid on a web of paper or film support and including: at least a substantially planar surface provided with at least a transverse elongated discharge opening of a first defined width through which the photographic liquid could be extruded so that a continuous layer of said liquid could be flowed over said planar surface from said discharge opening; a metering slot having a second defined width smaller than said first width and positioned to receive photographic liquid from a source thereof; and a section connecting said metering slot to said discharge opening; characterized in that: said section connecting said metering slot to said discharge opening includes a first part or expansion section having a width which progressively smoothly increases in size from the size of the metering slot to the size of the discharge opening and a second part or discharge slot having parallel walls defining a width equal to the width of said discharge opening and a length of a predetermined size. A device according to claim 1, wherein said first part widens linearly from said first width to said second width. A device according to claim 2, wherein said first part widens at an angle of 5° to 45° from said metering slot. A device according to any of claims 1 to 3, wherein said metering slot and said second part have substantially constant widths. A device according to claim 1, wherein the liquid passage system is located within said coating device. A device according to claim 5, wherein said coating device is a slide hopper comprising: a liquid-applying plate having an elongate planar upper surface which is inclined from horizontal and leads to an application area from which coatings can be applied to the web, and a plurality of layering plates spaced and serially arranged with respect to each other and each having a planar upper surface inclined from horizontal with one of said layering plates being adjacent said liquid-applying plate, wherein said liquid-applying plate and said plurality of layering plates are oriented to define with their upper surfaces a substantially planar incline leading to the application area, wherein said liquid passage system is located between each of said plurality of layering plates and between said liquid-applying plate and its adjacent layering plate and extends to the planar incline from a substantially opposite surface of said liquid-applying plate and said plurality of layering plates, whereby a photographic liquid passes sequentially through said metering slot, said first part, said second part, and said discharge opening on to the inclined planar surface of the adjacent layering plate or liquid-applying plate to form a layer of that photographic liquid, such that a plurality of layers of photographic liquids builds up on the planar incline, beneath any layers formed by layering plates farther from the application area, to form a pack of discrete superimposed liquid layers which advances down the planar incline to the application area from which the pack can be applied to the web. A device according to claim 6, wherein the slide hopper is configured so that a pack of photographic liquid layers is applied from the liquid-applying plate on to the web as a curtain with the application area being a lip portion from which the curtain falls. A device according to claim 6 or 7, wherein said first part expands in a direction toward said liquid-applying plate. A device according to claim 6 or 7, wherein said first part expands in a direction away from said liquid-applying plate. A device according to claim 6 or 7, wherein said first part expands in directions both toward and away from said liquid-applying plate. A device according to claim 6, wherein the incline is at an angle of 5° to 20° from horizontal. A device according to anyone of claims 1 to 11, wherein the width of the metering slot is in the range of 0.lmm to 0.6mm A device according to anyone of claims 1 to 12, wherein the width of the discharge opening is in the range of 0.5mm to 1.5mm A device according to anyone of claims 1 to 13, wherein the length of the second part is in the range of 1.5mm to 4.5mm.

Inventors: KOROKEYI SOLOMON T, KOROKEYI, SOLOMON T., Korokeyi, Solomon T., c/o Eastman Kodak Company
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1993
Main classification: G03C1
IPC codes: B05C9, B05C5, G03C1