GB2139525A - Processing photographic paper or film - Google Patents

Abstract

The processing of photographic paper on film is effected (Fig. 5) by running the paper or film 32 through processing fluid with emulsion faces 33 in counterflow and sufficiently close to impose shear on the processing fluid therebetween and provide mixing and agitation. In an alternative (Fig. 6), an inert partition 34, is provided between the emulsion faces 33, the spacing between each of the latter and the adjacent partition surface being selected to provide the aforesaid shear in the fluid therebetween. <IMAGE>

Description

SPECIFICATION Photographic Paper Processing This invention relates to a machine for, and a method of, processing photographic paper or film (hereinafter and in the claims for convenience simply called "paper") and it is an object of the present invention to provide a processing machine and method which, when compared with present processing machines and methods, has a substantially increased output for a given machine size while maintaining high print quality and at the same time reducing maintenance requirements and costs.

A number of chemical processes for the development of exposed photographic paper are in commercial use and while the following discussion of prior art is directed to the processing of photographic paper to produce colour prints it is to be clearly understood that the present invention is not so restricted and that the principle of this invention is applicable generally to the processing of photographic paper whatever chemical system is used.

Typically photographic paper (either in a single sheet or continuous roll form) is processed by immersing the exposed paper successively in developer and bleach-fix, followed by a washing and finally a drying stage. The physical conditions required in the wet stages of one widely used process are shown in the following Table: Solution Developer Bleach-fix Water Temperature 32.8+0.3 30-34 30-34 (CC) Time (Mins) 32 12 32 Solution Replenishment 0.323 0.323 6.5-10.8 Rate (l/m2) The continuous processing of photographic paper is currently carried out in three basic types of machine.

1) Belt driven (see Fig. 1 of the drawings) The photographic paper is attached by clips or other means to continuous belts 20 which carry the paper over rollers 21 in and out of the processing tanks. The paper path in such a machine (generally suitable only for roll paper) is shown in Fig. 1, which also shows a typical tank configuration for a machine rated at a paper output of 1.75 metres/minute. The tank configuration is a developing section 22, a bleach-fix section 23 and a water wash section 24. The liquid level in the tanks 22 to 24 is indicated by arrow A.

2) Roller driven (see Fig. 2 of the drawings) In this case the photographic paper 25 is transported through the machine by a system of coupled staggered rollers 26 as illustrated. The configuration of a single processing tank is shown in Fig. 2. This type of machine is self threading and will take roll paper or single sheets.

3) Blanket driven (not illustrated) A variation of the roller system incorporates fabric blankets which support the paper on part of its path through the machine.

In general terms both the belt and roller driven machines occupy the same order of space for a given output speed. The belt driven machine can be driven faster and much higher output speeds achieved but only by increasing the number of tanks or the linear size of the machine.

With given chemical and physical conditions, development time is fixed at, say,32 minutes immersion in the developer. The only way to increase output is to increase the rate of paper transport.

Development time can then only be held at 32 minutes by proportionately increasing the length of paper in the developer. In the aforesaid existing machines this results in more or larger tanks. The same rule applies to the bleach-fix (12 minutes immersion) and washing stages (3+ minutes immersion).

Photographic paper consists of a strong paper backing carrying the multilayer photographic emulsion which is physically fragile particularly if pulled past stationary particles of detritus.

Usually although not universally the paper is fed into the machine emulsion side down and hence emulsion side out as the paper goes through a single rack (see, for example Fig. 2).

These existing machines suffer from the following drawbacks.

a) Too slow in relation to their size.

b) Occupy too much space (faster machines occupy more space). (a and b are relative).

c) Contamination by oxidation of the developer due to air time in transfer from tank to tank.

d) Physical damage to emulsion by foreign bodies.

e) High maintenance level required to keep machine clean.

Quality control in such machines is maintained by processing control strips of paper pre-exposed by the manufacturer under controlled conditions and comparing the density of different colour spots on the control strip with the density of an identically exposed reference strip processed under controlled conditions by the manufacturer.

A study of the chemical and physical processes concerned in development of photographic images shows that diffusion in, out and through the emulsion layers is an important step in all stages of the process and that consequently good agitation is of crucial importance in providing fresh chemicals at the emulsion surface and to remove the waste products of reaction.

It is also a matter of practical experience that good agitation is vital in the first minute of development and that some of the best colour saturation results were achieved using early spinning drum processors. In these the emulsion side of the print is held against the smooth or only slightly embossed circumference of a rotating horizontal cylindrical drum which dips into the developer solution so that a thin film of fresh developer is swept continually past the emulsion surface.

According to the present invention there is provided a machine for processing photographic paper comprising a flow path through the machine along which photographic paper is constrained to move through a processing fluid with an emulsion face thereof sufficiently close to a surface to impose high shear on the fluid between the emulsion face and the surface so that excellent mixing and agitation of the fluid is achieved.

Preferably the flow path of the photographic paper through the machine is such that two emulsion faces of the photographic paper pass one another in counter-flow with only the processing fluid therebetween and sufficiently close to impose the aforesaid high shear on the fluid.

Preferably, the surface is provided by an inert partition.

A modification of the machine according to the invention in which the machine comprises, between the counter-flowing emulsion faces and within the processing fluid, an inert partition disposed sufficiently close to the emulsion faces to subject the processing fluid between each emulsion face and the adjacent surface of the inert partition to the aforesaid high shear.

A consequence of running the photographic paper with emulsion faces adjacent one another, with or without the intervention of the inert partition, through, for example, the developing and bleachfix sections of a machine is that the machine length for a given immersion length is greatly reduced and consequently faster and more compact machines can be built.

Alternatively, or additionally, to the inert partition rollers may be interposed between adjacent counter-flowing emulsion faces to maintain separation between the faces or the faces and the partition.

Injector means may be provided at predetermined locations in the machine to inject processing fluid into the machine so that it is entrained into the high shear areas adjacent the emulsion faces.

The counter flow path through the machine may be defined by rollers, belts or blankets.

Also according to the present invention there is provided a method of processing photographic paper, the method comprising the step of moving photographic paper through a processing fluid with an emulsion face sufficiently close to a surface to impose high shear on the fluid between the emulsion face and the surface so that excellent mixing and agitation of the fluid is achieved.

Preferably the surface is either another emulsion face of the photographic paper moving in counterflow, or the surface of an inert partition.

In the apparatus and method of the present invention the level of high shear may be such as to cause turbulent flow conditions to be approached or attained within the fluid.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 3 is a diagrammatic view of a photographic paper developing tank illustrating the principle of the present invention; Fig. 4 is similar view showing an alternative paper path configuration; and Figs. 5 and 6 are detail views applicable to both Figs. 3 and 4.

In Fig. 3, the developing tank is designated by the reference 30 and within the tank 30 is a layout or rollers 31 which permits photofiraphic paper 32 to be moved through the developing tank 30 with emulsion faces 33 adjacent and in counter-flow as can be seen by the arrows (see especially Fig. 5).

The processing fluid between the emulsion faces 33 is, as aforesaid, in high shear.

Inert metal or plastics partitions 34 can be inserted between emulsion faces 33 (see Fig. 6) to separate and prevent contact therebetween. If the separation between each emulsion face 33 and the partition 34 is half the separation between the two emulsion faces 33 with the partition 34 omitted then the same level of shear is maintained and consequently the same mixing and agitation efficiency.

Rollers 35 (also inert) may, instead of the partitions 34, or additional to the partitions 34 as shown in Fig. 6, be provided to separate the emulsion faces 33 or the latter and the partition 34.

Injector devices (not shown) may be provided, say, at locations 36 to add fresh developing fluid so that same is entrained by the moving photographic paper 32 into high shear regions.

An alternative roller configuration is illustrated in Fig. 4.

The development fluid sections illustrated in Figs. 3 and 4 corresponds to four racks in a conventional machine.

Typically the developer and bleach stages of a 1.75 metres/minute conventional machine may occupy a length of 95 cms. In comparison the face to face configurations might occupy lengths of the order of 37.5 cms for a 2.5 metres/minute machine or 75 cms for a 5 metres/minute machine.

Much of the mechanical damage to emulsion surfaces in conventional machines is caused by emulsion faces running past a static surface carrying extraneous particles. To remove these the machine has to be shut down. By running the machine with emulsion face to face any particulate matter will be carried out of the machine which in effect will be self cleaning.

The machine according to the invention substantially reduces the "air time" the time when the paper wet with developer is exposed to oxidation by air before being reimmersed. Typically in machines currently available the wet paper in air may be 12.5% or more of the total wet path whereas with the machine of this invention it may be less than 7%.

Reduced air time and the self cleaning effect will substantially reduce maintenance requirements and improve quality.

The machine of this invention is more conveniently suited to continuous rolls of paper using the belt drive system.

This machine can be made to be self threading in a blanket driven machine and is suitable for roll paper or single sheets.

The machine also incorporates conventional drive mechanisms to control accurately the paper speed and is light tight as required. All solution concentrations are maintained accurately by continuous or batch addition and metering related to paper throughput. Solutions are agitated, circulated and maintained accurately at the appropriate temperatures.

Process control can be maintained using established methods and control strips and established quality criteria.

Claims (14)

1. A machine for processing photographic paper comprising a flow path through the machine along which photographic paper is constrained to move through a processing fluid with an emulsion face thereof sufficiently close to a surface to impose high shear on the fluid between the emulsion face and the surface so that excellent mixing and agitation of the fluid is achieved.

2. A machine as claimed in claim 1 in which the emulsion face and adjacent surface are arranged sufficiently close to impose on the fluid a level of high shear to cause turbulent flow conditions to be approached or attained within the fluid.

3. A machine as claimed in claim 1 or 2, in which the flow path of the photographic paper through the machine is such that two emulsion faces of the photographic paper pass one another in counter-flow with only the processing fluid therebetween and sufficiently close to impose the aforesaid high shear on the fluid.

4. A machine as claimed in claim 1 or 2, in which the surface is provided by an inert partition.

5. A modification of the machine as claimed in claim 3, comprising, between the counter-flowing emulsion faces and within the processing fluid, an inert partition disposed sufficiently close to the emulsion faces to subject the processing fluid between each emulsion face and the adjacent surface of the inert partition to the aforesaid high shear.

6. A machine as claimed in claim 3 in which rollers are interposed between adjacent counterflowing emulsion faces to maintain separation between the emulsion faces.

7. A machine as claimed in claim 4 or 5, in which rollers are additional to the inert partition interposed between the emulsion faces and the adjacent face of the inert partition.

8. A machine as claimed in any one of claims 1 to 7 in which injector means are provided at predetermined locations in the machine to inject processing fluid into the machine so that it is entrained into the high shear areas adjacent the emulsion faces.

9. A machine as claimed in any one of claims 1 to 8 comprising a developer section, a bleach-fix section and a washing section with the aforesaid flow path extending through at least one of these sections.

10. A machine as claimed in any one of claims 1 to 9, in which the flow path through the machine is defined by rollers, belts and/or blankets.

11. A method of processing photographic paper, the method comprising the step of moving photographic paper through a processing fluid with an emulsion face sufficiently close to a surface to impose high shear on the fluid between the emulsion face and the surface so that excellent mixing and agitation of the fluid is achieved.

12. A method as claimed in claim 11 in which the level of high shear is such that turbulent flow conditions within the fluid are approached or attained.

13. A method as claimed in claim 11 or 12 in which the surface is constituted by another emulsion face of the photographic paper moving in counter-flow.

14. A method as claimed in claim 11 or 12 in which the surface is provided by an inert partition.

1 5. A machine for processing photographic paper substantially as hereinbefore described with reference to Figs. 3 to 6 of the accompanying drawings.

1 6. A method of processing photographic paper, substantially as hereinbefore described with reference to Figs. 3 to 6 of the accompanying drawings.