Liquid passage system for photographic coating devices

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.

FIELD OF THE INVENTION 
The present invention relates to a device for applying liquid photographic 
coatings to a paper or film support. 
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. Pat. 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. 
Pat. 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. Pat. 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. Pat. 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. Pat. 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 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 connected to 
the expansion section has a defined, preferably, constant width which is 
greater than the width 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.

DETAILED DESCRIPTION OF THE DRAWINGS 
FIG. 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 FIG. 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 may be of the type disclosed in U.S. patent 
application Ser. No. 07/766,945, now U.S. Pat. No. 5,234,500, entitled 
"Liquid Distribution System for Photographic Coating Devices" to Solomon 
T. Korokeyi. 
As is apparent from FIG. 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. 
FIG. 2 is a side cross-sectional view of the liquid passage system between 
plates 8 and 10 of the slide hopper of FIG. 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 .phi. at which wall section 56b is inclined from wall section 56a 
ranges from 5.degree. to 45.degree., preferably 25.degree.. 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. 
FIG. 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 FIG. 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 FIG. 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 .phi.' at which wall section 54b is inclined from wall section 
54a ranges from 5.degree. to 45.degree., preferably 25.degree.. 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 FIG. 2, wall sections 54a, 54b, and 54c are 
joined by rounded transition surfaces. 
FIG. 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 FIGS. 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 .phi. and .phi.' are 2.5.degree. to 22.5.degree., preferably 
12.5.degree.. 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 FIGS. 2 
and 3, rounded transitions connect wall sections 54c and 56a-c. 
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. Pat. 
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 spirit and scope of the invention which is 
defined by the following claims.