Abstract:
A low volume processing apparatus having a narrow processing channel has the processing solution entering via passages located towards the inlet and outlet of the channel. The solution leaves the channel via a passage located in the middle thereof, the flow of solution pulling the film into a fixed position within the channel. The reversal of flow minimizes the amount of air entrained with the returning flow.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method and apparatus for processing photographic material. In particular, the invention relates to improving the flow of solution through the processor. 
     BACKGROUND OF THE INVENTION 
     The processing of photosensitive material such as photographic film involves a series of steps such as developing, bleaching, fixing, washing and drying. In this process, a continuous web of film or cut sheet of film is sequentially conveyed through a series of stations or tanks, with each one containing a different processing solution appropriate to the process step at that station. 
     A large photofinishing apparatus utilizes rack and tank configurations. Such an apparatus is disclosed in, for example, U.S. Pat. No. 5,980,130. This document discloses a rack for use in a low volume thin tank of a photographic processing apparatus. The rack is placed in a processing tank, defining a relatively narrow processing channel between the walls of the tank and the rack. U.S. Pat. No. 5,420,658 discloses a further low volume photographic material processing apparatus which utilizes a narrow substantially horizontal processing channel. The channel has an upturned entrance and exit to contain the processing solution within the channel. 
     In some conventional small low volume processors the processing solution is returned to the suction input of the circulation pump by allowing it to flow over a barrier at the ends of the processing track. This can lead to air entrainment which can oxidize the chemicals in the solution. Also the solution and aerated solution is returned to the processing chamber to process the film through jets. The position of the jets in relation to the film is not constant. This can give rise to process density variations. 
     The present invention aims to overcome the problems mentioned above. 
     SUMMARY OF THE INVENTION 
     According to the present invention there is provide a method of processing photographic material comprising the steps of; feeding the photographic material into a processing channel having an inlet and an outlet; circulating processing solution through the channel such that the solution enters the channel at solution inlets located towards the inlet and the outlet of the channel and exits at a solution outlet located between the inlet and the outlet of the channel, the flow of solution pulling the material down to a fixed position against the surface wall of the channel, and withdrawing the material from the channel once processing is complete. 
     The invention further provides an apparatus for processing photographic material, the apparatus comprising a module having an upper section and a lower section together defining a processing channel having an inlet and an outlet, a plurality of passages defined in the lower section, the processing channel being in fluid communication with a reservoir of processing solution via the passages, and pumping means for pumping the processing solution through the passages and the channel, wherein the pumping means is configured such that the processing solution enters the channel via the passages nearest to the inlet and outlet of the channel and exits the channel via the other passage, thereby pulling the material down to a fixed position against the surface wall of the channel and ensuring that substantially no air enters the passage through which the solution exits the channel. 
     Preferably the surface of the wall of the channel is textured. This achieves good agitation of the flow. 
     The apparatus and method of the invention prevents the drawing of air into the processing system and thus prevents the oxidation of the solution. By reversing the flow of solution overflow of the system is eliminated should the pump inlet be blocked. 
     By having the suction return from the lowest part of the processing channel the film is pulled downwards and becomes fixed with respect to the flow of solution. Uniform sensitometry is thus achieved. 
     The suction of the pump holds the film against the outlet to the pump at a constant predetermined distance. This raises the agitation of the solution by making use of the channeling properties of the surface pattern. 
     Good agitation of the solution over the film surface is achieved by wiping action over the textured surface of the processing module and the high velocity of the solution through the surface pattern. The textured surface allows free flow of solution over the sensitized surface of the material. 
     The invention can accommodate any process for color film, color paper, reversal film, reversal paper, black and white film or paper. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
     FIG. 1 shows a cross section of a low volume processing apparatus according to the invention; 
     FIG. 2 illustrates the flow of solution in the apparatus shown in FIG. 1; and 
     FIG. 3 is an enlarged view of part of the channel in the processing apparatus according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail, FIG. 1 shows a cross section of a process tank module. 
     The process tank module has an upper section  2  and a lower section  3 . A narrow curved processing chamber or channel  12  is defined between the upper and lower sections. The module has an inlet  14  for the material to be processed  1  to enter the processing channel and an exit  16  for the material to exit the channel. The inlet  14  and outlet  16  define the highest points of the curve of the channel. A pair of rollers  5  and  6  are provided at the inlet  14 . A further pair of rollers  7  and  8  are provided at the outlet  16 . These rollers,  5 ,  6 ,  7  and  8 , drive the material to be processed  1  through the processing channel, to exit in the direction of arrow  4 . 
     The lower section of the module  3  is provided with three passages  9 ,  10  and  11 . These passages run substantially vertically through the lower section  3  and connect the processing channel  12  to a supply of processing solution, not shown. Passages  9  and  10  are located towards the inlet  14  and outlet  16  respectively of the tank module. These passages are inlet passages for the flow of processing solution. Passage  11  is the outlet passage for the flow of processing solution and is located at the lowermost point of the lower section  3 . Thus the entrance points of passages  9  and  10  to the processing chamber are higher than the entrance to passage  16 . 
     A pump, not shown, is provided to pump processing solution up through passages  9  and  10 . 
     The process tank module may stand alone or be easily combined with other modules to form a continuous low volume unit for processing photographic materials. Any desired number may be provided. 
     In operation the processing solution enters the processing channel  12  via passages  9  and  10 . The solution exits the channel via the passage  11 . The solution is circulated through these passages by means of a pump, not shown. 
     As can be seen in FIG. 2 the level of solution pumped in via passages  9  and  10  is well above the level of the entrance to the passage  11 . By providing the outlet for the solution at the lowermost point of the lower section  3  the problem of air becoming entrained in the solution sucked back by the pump is considerably reduced. Thus the chemicals within the solution will not be subject to oxidation. 
     The material to be processed, for example film, is fed into the processing channel  12  by rollers  5  and  6 . The film may be in cut sheet or roll format. The material may contain an emulsion on either or both of its surfaces. FIG. 3 illustrates how the return flow of the solution through passage  11  draws the film  1  down to register against the bottom of the processing channel. This action fixes the film position with respect to the flow of processing solution. The action of continually applying processing solution through passages  9  and  10  and withdrawing the solution through passage  11  helps to improve agitation of the chemicals in contact with the material being processed. Once the film is processed the rollers  7  and  8  withdraw the film from the processing channel. 
     The surface of the channels is preferably textured. The textured surface prevents the photosensitive material from sticking to the surfaces of the channel due to surface tension. The textured surface also aids in uniform distribution of processing solution across the photosensitive material enhancing process uniformity and solution agitation. It encourages disturbance in the flow which leads to improved solution agitation and more uniform processing. Furthermore, a textured surface helps to prevent contaminants and debris from scratching, abrading or pressure sensitizing the photosensitive material. 
     The textured surface may be textured by any known process, e.g. knurling, molded, EDM electro-discharges machine or applied. 
     In the embodiment shown in FIG. 3 the surface is textured with a diamond relief pattern. However, any suitable profile may be utilized. The surface may be pyramidal, have a random surface or any other flow disturbing surface. The textured surface increases the agitation of the processing solution since the actual flow velocity is raised as the solution rushes along the open channels in the diamond relief pattern. The actual flow in the embodiment illustrated can be controlled by the dimensions of the grooves in the diamond pattern. The grooves can be modified to give the required flow. By changing the groove dimensions in each processing module the flow can be different in each module. As stated above, the film is fixed with respect to the flow of solution while it is being processed. 
     The invention has been described in detail with reference to a preferred embodiment thereof. It will be understood by those skilled in the art that variations and modifications can be effected within the scope of the invention. 
     PARTS LIST 
       1  material 
       2  upper section of module 
       3  lower section of module 
       5  roller 
       6  roller 
       7  roller 
       8  roller 
       9  passage 
       10  passage 
       11  passage 
       12  channel 
       14  inlet 
       16  outlet