Apparatus for liquid processing of photographic sheet material

The apparatus comprises a housing (10) defining a treatment vessel (12.sup.2) having entrance and exit openings (16, 20) defining a sheet material path (22) therethrough. The lower opening (20) is closed by a pair of path-defining rollers (28, 26) biased into contact with each other to form a nip (28) through which the sheet material path (22) extends. The housing (10) includes a collecting chamber (50) positioned to collect treatment liquid which in use falls from the treatment vessel (12.sup.2) through one or both of the openings. The collecting chamber (50) is a closed chamber (50) and means (52) are provided to return treatment liquid from the collecting chamber (50) to the treatment vessel (12.sup.2). The construction has the advantage that the wastage of treatment liquid is reduced without requiring the use of complicated and costly sealing devices.

FIELD OF THE INVENTION 
This invention relates to an apparatus and method for processing 
photographic sheet material, such as X-ray film, pre-sensitised plates, 
graphic art film and paper, and offset plates. More particularly the 
invention relates to improvements in apparatus in which photographic 
material is transported through one or more treatment units. 
BACKGROUND OF INVENTION 
As a rule, a processing apparatus for photographic sheet material comprises 
several vessels each of which contains a treatment liquid, such as a 
developer, a fixer and a rinse liquid. As used herein, the term sheet 
material includes not only photographic material in the form of cut 
sheets, but also in the form of a web unwound from a roll. The sheet 
material to be processed is transported through these vessels in turn, by 
transport means such as one or more pairs of drive rollers, and thereafter 
optionally to a drying unit. The time spent by the sheet material in each 
vessel is determined by the transport speed and the dimensions of the 
vessel in the sheet feed path direction. 
In a typical apparatus for liquid processing of photographic sheet 
material, a housing defines a treatment vessel having entrance and exit 
openings defining a sheet material path therethrough. The housing may 
include a collecting chamber positioned to collect treatment liquid which 
in use falls from the treatment vessel through the lower opening or 
through both of the openings, depending upon the orientation of the 
apparatus. 
Usually, the treatment liquid collected in the collecting chamber is 
discarded. This is because exposure of the collected liquid to the 
atmosphere causes oxidation and/or evaporation of the liquid, and renders 
it less suitable for further use. However, such a practice is wasteful. 
Where a vessel opening is closed by a pair of path-defining rollers biased 
into contact with each other to define a nip through which the sheet 
material path extends, it has been proposed to incorporate sealing devices 
between these path-defining rollers and the housing to reduce the quantity 
of liquid which falls through into the collecting chamber during use. The 
structure of such sealing devices can be complicated and costly, if the 
quantity of liquid falling into the collecting chamber is to be 
significantly reduced. United States patent U.S. Pat. No. 4,166,689 
(Schausberger et al. assigned to Agfa-Gevaert AG) describes such an 
apparatus in which liquid escapes form the lower opening and is 
intercepted by the tank of a sealing device with two squeegees located in 
the tank above a horizontal passage in line with the lower opening. One or 
more pairs of drive rollers in the vessel close the lower opening and also 
serve to transport the sheet material along a vertical path which extends 
between the openings of the vessel. 
OBJECTS OF INVENTION 
It is an object of the present invention to reduce the wastage of treatment 
liquid without requiring the use of complicated and costly sealing 
devices. 
SUMMARY OF THE INVENTION 
We have discovered that this and other useful objectives can be achieved by 
the use of a closed collecting chamber and by the return of the collected 
treatment liquid to the treatment vessel. 
Thus, according to a first aspect of the invention there is provided an 
apparatus for liquid processing of photographic sheet material, comprising 
a housing defining a treatment vessel having entrance and exit openings 
defining a sheet material path therethrough, the housing including a 
collecting chamber positioned to collect treatment liquid which in use 
falls from the treatment vessel through one or both of the openings, 
characterised in that the collecting chamber is a closed chamber and means 
are provided to return treatment liquid from the collecting chamber to the 
treatment vessel. 
According to a second aspect of the invention, there is provided a method 
for the liquid processing of photographic sheet material, comprising 
passing the sheet material along a sheet material path through a treatment 
vessel having entrance and exit openings defining the sheet material path, 
and collecting treatment liquid which falls from the treatment vessel 
through one or both of the openings in a collecting chamber, characterised 
in that the collecting chamber is a closed chamber and treatment liquid is 
returned from the collecting chamber to the treatment vessel. 
Although the volume of liquid falling into the collecting chamber may be 
much less than the volume of liquid in the vessel, so that its surface 
area is relatively high, the use of a closed collecting chamber means that 
oxidation and evaporation of this collected liquid is low. By the term 
"closed" in relation to the collecting chamber we mean that there is 
substantially no exchange between the collecting chamber and the 
atmosphere, as is the case with "open" chambers. The "air cushion" above 
the collected liquid in the collecting chamber will quickly come to 
equilibrium with the collected liquid following start-up of the apparatus, 
after which oxidation and evaporation will be reduced to a minimum. The 
quality of the collected liquid does not therefore differ significantly 
from the quality of the treatment liquid in the vessel. It is therefore 
possible to return this liquid to the vessel, without significantly 
disturbing the treatment process taking place therein. It is possible, 
though not essential, for the "air cushion" above the collected liquid to 
be filled with an inert gas, such as nitrogen or carbon dioxide, depending 
upon the nature of the treatment liquid. 
In a usual construction of the apparatus, the vessel opening is closed by a 
path-defining roller biased into contact with a reaction surface to form a 
nip through which the sheet material path extends. 
The reaction surface towards which the roller is biased to define the nip 
will usually be the surface of another roller, or for the reaction surface 
to be in the form of a belt or a fixed surface with a low friction 
coefficient. Where this general description refers to the use of two 
rollers, it is to be understood that the second roller may be replaced by 
any other reaction surface, such as those referred to above. 
The path-defining rollers may be driven rollers, thereby constituting 
transport means for driving the sheet material through the treatment 
vessel, or they may be freely rotating rollers in which event alternative 
transport means may be provided. In order to reduce the torque required to 
rotate the rollers, the ratio of the maximum roller diameter to the length 
of the nip is preferably greater than 0.012. 
Typical rollers have a core provided with a covering of elastomeric 
material, although it is possible for the roller to be elastomeric 
throughout its cross-section. As the sheet material leaves a given liquid 
treatment vessel it is necessary to remove any liquid carried on the sheet 
material as efficiently as possible, to prevent carryover of liquid into a 
next treatment vessel and to reduce edge effects which arise from 
non-homogeneous chemistry on the sheet material after squeegeeing. To do 
this job properly, the rollers must exert a sufficient and homogeneous 
pressure over the whole width of the sheet material. Also, to reduce edge 
effects, it is desirable that the opposite roller surfaces are in contact 
with each other beyond the edges of the sheet material. To put this 
problem in context, rollers used in conventional processing apparatus for 
example have a length of 400 mm or more and a diameter of from 24 to 30 
mm. The sheet material typically has a width of from a few millimetres up 
to 2 m and a thickness of 0.05 mm to 0.5 mm. In view of the nature of 
elastomeric material, it is in fact impossible to totally eliminate any 
gap between the roller surfaces at the edges of the sheet material as it 
passes through the nip. It is desirable that the roller surfaces be in 
contact with each other within as short a distance as possible from the 
edges of the sheet material i.e. that the size of the leak zone should be 
minimised. It is important however that the force between the rollers is 
sufficient to prevent leakage when no sheet material is passing through. 
However, the force must not be so high as to risk physical damage to the 
sheet material as it passes through the nip. 
The objective of a minimum leak zone referred to above can be achieved if 
the ratio of the diameter of the roller to its length is above a critical 
limit. 
To achieve this, at least one of the rollers, and preferably each roller, 
comprises a rigid core carrying a covering of elastomeric material, the 
ratio (.PHI./L) of the maximum diameter (.PHI.) of the elastomeric 
material covering to the length (L) thereof being at least 0.012, most 
preferably between 0.03 and 0.06. Where the reaction surface towards which 
the roller is biased to define the nip is the surface of another roller, 
it is preferred that the roller requirements referred to above apply to 
this, second, roller also. Indeed, it will be usual for the two rollers to 
be identical, although it is possible that the diameters (.PHI.), and 
therefore the ratios (.PHI./L), of the two rollers need not be identical. 
It is also possible that the reaction surface may be formed by the surface 
of a second roller which does not conform to the above requirements, such 
as for example, a roller having no elastomeric covering, or for the 
reaction surface to be in the form of a belt. 
The elastomeric material covering preferably has a thickness of between 1 
mm and 30 mm. The elastomeric material may be selected from 
ethylene/propylene/diene terpolymers (EPDM), silicone rubber, 
polyurethane, thermoplastic rubber such as Santoprene (Trade Mark for 
polypropylene/EPDM rubber), styrene-butyl rubber and nitrile-butyl rubber. 
The hardness of the elastomeric material may be between 15 Shore (A) and 
90 Shore (A), as measured on the roller surface. In one embodiment of the 
invention, the diameter (.PHI.) of the elastomeric material covering is 
constant along the length of the roller. Alternatively the roller may have 
a radial dimension profile which varies along the length thereof. In the 
latter case, the diameter (.PHI.) in the expression .PHI./L is the maximum 
diameter. In a preferred embodiment, such a roller comprises a 
non-deformable core, the thickness of the elastomeric material covering 
varying along the length thereof. Alternatively or additionally, the 
diameter of the core varies along the length thereof. 
Ideally, the radial dimension profile of such a roller is such in relation 
to the force applied by the roller to sheet material passing through the 
nip as to be substantially even over the width thereof. 
The radial dimension of the roller ideally decreases towards the ends 
thereof i.e. a convex profile, especially a parabolic profile. 
Preferably, the core has a flexural E-modulus of between 50 GPa and 300 
GPa. Suitable materials for the rigid core include metals, such as 
stainless steel, non-ferrous alloys, titanium, aluminium or a composite 
thereof. 
In one embodiment of the invention, the core is hollow. Alternatively the 
core may be solid. 
The rollers may be biased together by a variety of methods. The rollers may 
be biased together for example by making use of the intrinsic elasticity 
of the elastomeric material, by the use of fixed roller bearings. 
Alternatively, use may be made of resilient means such as springs which 
act on the ends of the roller shafts. The springs may be replaced by 
alternative equivalent compression means, such as e.g. a pneumatic or a 
hydraulic cylinder. 
In a convenient arrangement, the housing further includes a return liquid 
inlet opening into the vessel and the means to return treatment liquid 
from the collecting chamber to the vessel comprises a liquid return pipe 
extending from the collecting chamber to the return liquid inlet. The 
return liquid inlet may be positioned above the liquid level in the 
treatment vessel. Otherwise, it may be necessary to prevent liquid from 
the vessel passing along the pipe to the collecting chamber. Preferably a 
pump is positioned along the length of the liquid return pipe. 
In a preferred embodiment, the vessel is also closed. This ensures that 
substantially no evaporation and oxidation of the treatment liquid take 
place in the vessel. Means may be provided to connect the air cushion 
above treatment liquid in the collecting chamber with the air cushion 
above liquid in the vessel, such as a passage extending from the 
collecting chamber to the vessel. Thus as the collected liquid is returned 
to the vessel, air from the air cushion above the treatment liquid in the 
vessel replaces it. Thereby no external air is drawn into the apparatus 
and substantially no suction effect is produced in the collecting chamber 
which would cause further treatment liquid to fall through the or each 
opening of the vessel. 
In a preferred embodiment, sealing means are provided for sealing the 
path-defining rollers to the housing, the collecting chamber being 
positioned below the sealing means. These sealing means may be in the form 
of stationary sealing members, or rotatable sealing rollers, carried by 
the housing and positioned in contact with the path-defining rollers. 
In a conventional processing apparatus the sheet material is transported 
along a generally horizontal feed path, the sheet material passing from 
one vessel to another usually via a circuitous feed path passing under the 
surface of each treatment liquid and over dividing walls between the 
vessels. While the present invention is applicable to such an horizontally 
configured apparatus, it finds its greatest value in vertical processors, 
i.e. processing machines having a substantially vertical orientation in 
which a plurality of vessels are mounted one above the other in a stack, 
each vessel having an opening at the top acting as a sheet material inlet 
and an opening at the bottom acting as a sheet material outlet or vice 
versa. 
In the present context, the term "substantially vertical" is intended to 
mean that the sheet material moves along a path from the inlet to the 
outlet which is either exactly vertical, or which has a vertical component 
greater than any horizontal component. The use of a vertical orientation 
for the apparatus leads to a number of advantages. In particular the 
apparatus occupies only a fraction of the floor space which is occupied by 
a conventional horizontal arrangement. Furthermore, the sheet transport 
path in a vertically oriented apparatus may be substantially straight, in 
contrast to the circuitous feed path which is usual in a horizontally 
oriented apparatus. The straight path is independent of the stiffness of 
the sheet material and reduces the risk of scratching compared with a 
horizontally oriented apparatus. 
In preferred embodiments of the present invention, there are provided means 
for connecting each vessel to adjacent vessels in the stack in a closed 
manner. By the term "closed manner" in this specification is meant that 
each vessel is so connected to adjacent vessels that no vessel is open to 
the environment. By connecting vessels together in this manner, contrary 
to the apparatus described in U.S. Pat. No. 4,166,689, the evaporation, 
oxidation and carbonisation of treatment liquids can be significantly 
reduced. 
The housing wall of each vessel may comprise an upper housing wall part and 
a lower housing wall part, the upper housing wall part being so shaped in 
relation to the lower housing wall part of the next higher vessel as to 
provide a substantially closed connection between adjacent vessels. For 
example, the upper and lower housing wall parts may be provided with 
flanges, means being provided to secure the flange of the upper housing 
wall part with the flange of the lower housing wall part of the next 
higher vessel thereby to provide the substantially closed connection. 
The rollers and associated sealing means of the top-most vessel of the 
stack serve to provide a gas-tight cover for the apparatus. 
The top-most vessel will not normally be a liquid-containing vessel, 
serving simply as the gas-tight cover for the apparatus. 
A lower part of the housing wall of each vessel may be so shaped as to 
define the collection chamber. 
Each vessel may be of modular construction and provided with means to 
enable the vessel to be mounted directly above or below an identical or 
similar other vessel. Alternatively, the apparatus may take an integral or 
semi-integral form in which the means for connecting each vessel to 
adjacent vessels in the stack in a closed manner is constituted by a 
common housing wall of the apparatus. By the term "semi-integral form" we 
intend to include an apparatus which is divided by a substantially 
vertical plane passing through all the vessels in the apparatus, 
particularly the plane of the sheet material path, enabling the apparatus 
to be opened-up for servicing purposes, in particular to enable easy 
access to the rollers. 
The vessel may include guide plates positioned on either side of the sheet 
material path to divide the vessel into a plurality of regions, including 
a first region, through which the sheet material path extends, in 
communication with at least one second region remote from the sheet 
material path. The housing may include a fresh treatment liquid inlet 
opening into the vessel to supply fresh treatment liquid to the first 
region and a used treatment liquid outlet exiting from the vessel to 
remove used treatment liquid from the at least one second region. The 
fresh treatment liquid inlet and the used treatment liquid outlet can 
thereby be conveniently positioned on the same side of the apparatus. 
One or more of the vessels of the apparatus may include additional features 
if desired. Cleaning means may be provided for acting upon the rollers to 
remove debris therefrom, as described in European patent application EP 
93202862 (Agfa-Gevaert NV), filed Oct. 11, 1993. Additional rollers, such 
as a roller pair or staggered rollers may be provided for transporting the 
sheet material through the apparatus, and these rollers will normally be 
driven rollers. Additional roller pairs may be provided for breaking the 
laminar fluid at the surface of the sheet material as it passes through 
the apparatus, and these rollers may be driven rollers or freely rotating 
rollers. Even when additional roller pairs are present, the rollers to 
which the (.PHI./L) criterium applies and their associated sealing means 
will usually constitute the lower roller pair, serving to close the lower 
opening of the vessel. Spray means may be provided for applying treatment 
liquid to the sheet material. Guide means may be included for guiding the 
passage of the sheet material through the apparatus. Heating means may be 
provided in one or more vessels so that the vessel becomes a sheet 
material drying unit, rather than a wet treatment unit. While liquid 
pumping, heating, cooling and filtering facilities will normally be 
provided outside the vessels, it is possible for some elements of these 
features to be included in the vessels themselves. Any combination of 
these additional features is also possible.

Although only one specific embodiment of an apparatus according to the 
invention is shown in the Figures, the invention is not restricted 
thereto. The apparatus for the wet processing of photographic sheet 
material such as X-ray film. These vessels may be arranged to provide a 
sequence of steps in the processing of sheet photographic material, such 
as developing, fixing, rinsing and drying. The vessels may be of a modular 
structure as shown or may be part of an integral apparatus. 
An apparatus for liquid processing of photographic sheet materials is shown 
in the Figures. The apparatus comprises a housing 10 defining a plurality 
of the vessels 12.sup.1, 12.sup.2, 12.sup.3 are arranged one above another 
in a stack, one vessel 12.sup.2 being shown in full. 
The vessel 12.sup.2 which is of generally rectangular cross-section 
comprises a housing defined by a housing wall so shaped as to provide an 
upper part 14 having an upper opening 16 and a lower part 18 having a 
lower opening 20, the sheet material 30 moving in a downwards direction as 
indicated by the arrow A. The vessel 12.sup.2 is closed from the 
atmosphere. Upper entrance and lower exit openings 16, 20 define a sheet 
material path 22 through the vessel 12.sup.2. The lower exit opening 20 is 
closed by a pair of path-defining rollers 24, 26 biased into contact with 
each other to form a nip 28 through which the substantially vertical sheet 
material path 22 extends. The vessel 12.sup.2 contains treatment liquid 
32. The distance H between the surface 34 of the liquid 32 and the nip of 
the rollers of the next upper vessel 12.sup.1 is as low as possible. 
Each path-defining roller 24, 26 is of the squeegee type comprising a 
stainless steel hollow core 36 carrying an elastomeric covering 38. The 
core 36 is in cylindrical form having constant internal and external 
diameters along the length thereof. The path-defining rollers 24, 26 are 
biased towards each other with a force sufficient to effect a liquid tight 
seal but without causing damage to the photographic sheet material 30 as 
it passes there-between. The line of contact between the path-defining 
roller surfaces defines the nip 28. The sheet material preferably has a 
width which is at least 10 mm smaller than the length of the nip, so as to 
enable a spacing of at least 5 mm between the edges of the sheet and the 
adjacent limit of the nip 28, thereby to minimise leakage. The 
path-defining rollers 24, 26 are coupled to drive means (not shown) so as 
to constitute drive path-defining rollers for driving the sheet material 
30 along the sheet material path 22. 
Sealing means are provided for sealing the path-defining rollers 24, 26 to 
the housing 10. Each path-defining roller 24, 26 is in sealing contact 
along its length, with a respective rotatable sealing roller 40,42 carried 
on a sealing support 44, which in turn is secured to the wall of the 
vessel 12, the sealing rollers 40, 42 serving to provide a gas- and 
liquid-tight seal between the path-defining rollers 24, 26 on the one hand 
and the housing wall on the other. The treatment liquid 32 is therefore 
retained in the vessel 12 by the path-defining rollers 24, 26 and the 
sealing rollers 40, 42. The sealing rollers 40, 42 are formed of hardened 
or PTFE coated metal. 
The upper and lower housing wall parts 14, 18 are provided with flanges 46, 
48 respectively provided with bolts (not shown) to enable the vessel 
12.sup.2 to be mounted directly above or below an identical or similar 
other vessel 12.sup.1, 12.sup.3, as partly indicated FIG. 1. In the 
illustrated embodiment, the adjacent vessels 12.sup.1 and 12.sup.3 are 
non-liquid containing vessels. At least the adjacent vessel 12.sup.3 is 
preferably a closed cell. The upper housing wall part 14 is so shaped in 
relation to the lower housing wall part 18 as to provide a substantially 
closed connection between adjacent vessels. Thus, treatment liquid from 
vessel 12.sup.2 is prevented from falling into the lower vessel 12.sup.3 
by the path-defining rollers 24, 26 and sealing rollers 40, 42, while 
vapours from the lower vessel 12.sup.3 are prevented from entering the 
vessel 12.sup.2 or escaping into the environment. This construction has 
the advantage that the treatment liquid in the vessel 12.sup.2 is not 
contaminated by contents of the adjacent vessels and that by virtue of the 
treatment liquids being in a closed system evaporation, oxidation and 
carbonisation thereof is significantly reduced (and any other undesirable 
exchange between the treatment liquid and the environment). 
The lower part 18 of the housing wall 14 is so shaped as to define a 
collecting chamber 50. Any treatment liquid which may escape between the 
path-defining rollers 24, 26 and the associated sealing rollers 40, 42, or 
even through the nip 28, in particular as the sheet material 30 passes 
therethrough, drips from the path-defining rollers and falls into the 
collecting chamber 50. For this reason, the collecting chamber 50 is 
positioned below the sealing rollers 40, 42. The collecting chamber 50 is 
closed from the atmosphere. A liquid return pipe 52 extends from the 
collecting chamber 50 to a return liquid inlet 54 opening into the vessel 
12.sup.2 and serves to return treatment liquid from the collecting chamber 
50 to the vessel 12.sup.2. A pump 56 is positioned along the length of the 
liquid return pipe 52. 
A passage 58 extends from the collecting chamber 50 to the vessel 12.sup.2 
serves to connect the air cushion above treatment liquid in the collecting 
chamber 50 with the air cushion above liquid in the vessel 12.sup.2. 
The vessel 12.sup.2 includes guide plates 60 positioned on either side of 
the sheet material path 22 which divide the vessel 12.sup.2 into three 
regions 62.sup.1, 62.sup.2, 62.sup.3, including an inner region 62.sup.2 
through which the sheet material path 22 extends. The guide plates do not 
extend as far as the end walls of the housing, but are spaced therefrom 
outside the width of the sheet material, enabling the inner region 
62.sup.2 to be in communication with two outer regions 62.sup.1, 62.sup.3 
remote from the sheet material path 22. A fresh treatment liquid inlet 64 
opens through the far end wall of the housing, as viewed in the figures, 
into the vessel 12.sup.2 to supply fresh treatment liquid to the inner 
region. Re-circulating treatment liquid outlets 66 exit through the same 
far end wall of the housing from the vessel 12.sup.2 to remove used 
treatment liquid from the outer regions 62.sup.1, 62.sup.3. The fresh 
treatment liquid inlet 64 and the recirculating treatment liquid outlet 66 
are thereby conveniently positioned on the same side of the apparatus. It 
is possible to reverse the functions of the inlets and outlets, so that 
treatment liquid is supplied through inlets 66 and recirculating liquid is 
removed through outlet 64.