EP0856771A1

EP0856771A1 - Photographic image-forming process

Info

Publication number: EP0856771A1
Application number: EP97200273A
Authority: EP
Inventors: Gareth Bryn C/O Kodak Limited Evans; Peter Jeffery C/O Kodak Limited Twist
Original assignee: Kodak Ltd; Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1997-01-31
Filing date: 1997-01-31
Publication date: 1998-08-05

Abstract

A process for the development of an imagewise exposed photographic material having at least one silver halide layer which comprises forming an image therein in a solution which contains a developing agent, which solution is replenished wherein:

the process is carried out in an apparatus comprising at least one processing tank in which the ratio of the tank volume to maximum area of material which can be accommodated in the tank (i.e. maximum path length times width of material) is less than 25 dm³/m²,

substantially all the replenishers are added as solids direct to said developer solution together with additional water which may contain a minor amount of replenisher chemicals,

and wherein the average residence time of the processing solution in the developing tank defined by the formula: Average residence time = V x 100 x 3R x T x U x 60

where V is the volume of the processing tank (litres), R is the replenishment rate (litres/m²), T is the transport speed (m²/min) and U is the percent utilisation as the percentage of a working day (8 hours) that the processor is running,

is less than the useful lifetime of the solution, said useful lifetime being the time at 35°C for which the Dmax values for red, green and blue (or the silver image Dmax of a black-and-white material) remain at or above 80% of the value(s) produced by a freshly prepared solution.

Description

Field of the Invention

This invention relates to a photographic image-forming process.

Background of the Invention

It is desirable to reduce the volume of chemicals added to processing solutions so as to reduce overflow from processes and hence reduce waste and pollution. It is also desirable to add chemicals in concentrated form, even as solids, so that transport and packaging costs can be minimised. However, the minimum practical limits of replenishment volume are set, not by the upper limits of concentration of chemicals added, but by other considerations such as the maximum tolerable concentrations of materials produced or released during processing.

Low volume processing tanks have been described which operate at rapid tank turn-over rates. US specification 5 436 118 describes such tanks in combination with replenishment systems wherein chemicals are added in a concentrated liquid form.

Systems of largely solid chemical replenishment have been described for conventional colour development processes in conventional developing tanks in which tablets of chemical mixtures are added to the tanks directly. Water is then added to control the overflow and hence the removal of undesirable chemicals from the tank.

Problem to be solved by the Invention

The use of small volumes of replenisher results in variable sensitometric results. Particularly when processors are working at less than full throughput or intermittently.

The problem to be solved is to provide the advantages of adding components in as concentrated a form as possible without the processing solutions undergoing undesirable loss of activity.

Summary of the Invention

According to the present invention there is provided a process for the development of an imagewise exposed photographic material having at least one silver halide layer which comprises forming an image therein in a solution which contains a developing agent, which solution is replenished wherein:

the process is carried out in an apparatus comprising at least one processing tank in which the ratio of the tank volume to maximum area of material which can be accommodated in the tank is less than 25 dm³/m²,

By

tank volume' or processing solution volume' is meant the volume of the solution within the processing tank/channel together with that of the associated recirculation system, which includes, for example, pipework, valves, pumps, filter housings etc.

By maximum area of the material which can be accommodated in the tank', or immersed in the solution, is meant the product of the maximum width of the material processed and the path length taken by the material through the processing solution within the tank.

Advantageous Effect of the Invention

The use of the low volume tank and the specified low residence time provides environmentally desirable minimal replenishment without suffering loss of activity of the processing solution or its replenishers in both conventional colour development and redox amplification processes.

The faster tank turnover rate reduces the problem of biogrowth and chemical instability.

The lower tank volume results in lower wastage and solution volume needed to refill the tank, lower energy requirements to heat the solution and less sensitometric variability.

The use of solid replenishers without a low volume tank can lead to chemical instability, eg instability of phospate buffers.

Brief Description of the Drawings

In the accompanying drawings Fig 1 is a schematic diagram showing the method of adding solids to a processing solution.

Detailed Description of the Invention

The photographic material may be a black-and-white or colour material.

The developing solution may contain an antioxidant developing agent preservative. Preferably such antioxidants are solids. Examples of such solid antioxidants are an alkali metal sulphite, hydroxylamine may be in the form of a salt thereof such as hydroxylamine chloride, phosphate or, preferably, sulphate, or a substituted hydroxylamine. The substituted hydroxylamines may be alkyl or aryl substituted, such alkyl and aryl being possibly further substituted with hydroxy, carboxy or sulpho groups, for example:

Diethylhydroxylamine, hydroxyethyl-ethylhydroxylamine, or dipropylhydroxylamine preferably in the form of their hydrochloride or sulphate salt or disulphoethylhydroxylamine as the dialkali metal salt, eg the dipotassium salt.

The material being processed may be a film or paper material.

The material may comprise the emulsions, sensitisers, couplers, supports, layers, additives, etc. described in Research Disclosure, September 1994, Item 36544, published by Kenneth Mason Publications Ltd, Dudley Annex, 12a North Street, Emsworth, Hants P010 7DQ, U.K.

In one preferred embodiment the photographic material comprises a resin-coated paper support and the emulsion layers comprise more than 80%, preferably more than 90% silver chloride and are more preferably composed of substantially pure silver chloride.

In another preferred embodiment the material is a black-and-white material which may be a high contrast material for the graphic arts.

The pH of the developer may be in the range 9.5 to 12. Preferably the pH is in the range 10 to 12, particularly from 10 to 11.7. For some applications the preferred pH is from 11.0 to 11.7, preferably 11.0 to 11.4.

The developer solution may contain an alkali material that buffers it. Examples of such materials are alkali metal carbonates, silicates and phosphates, for example sodium or potassium carbonates or phosphates. Additional alkali may also be present, eg an alkali metal hydroxide. The carbonates may be present in the solution in amounts of 10 to 60 g/l, preferably 15 to 45 g/l and particularly 20 to 30 g/l as potassium carbonate while the phosphates may be present in the solution in amounts of 20 to 80 g/l, preferably 25 to 65 g/l and particularly 30 to 50 g/l as potassium phosphate.

A colour developer solution may contain from 1 to 12 g/l of developing agent, preferably from 3 to 8 g/l.

The colour developing agent may be a p-phenylenediamine, for example:

4-amino-3-methyl-N,N-diethylaniline hydrochloride,

4-amino-3-methyl-N-ethyl-N-β-(methanesulphonamido)- ethylaniline sulphate hydrate,

4-amino-3-methyl-N-ethyl-N-β-hydroxyethylaniline sulphate,

4-amino-3-β-(methanesulphonamido)ethyl-N,N-diethylaniline hydrochloride,

4-amino-N-ethyl-N-(2-methoxy-ethyl)-m-toluidine di-p-toluene sulphonate, or

4-N-ethyl-N-(β-methanesulphonamidoethyl)-o-toluidine sesquisulphate.

The concentration range of the antioxidant component in a colour developer is preferably from 0.5 to 10 and especially from 1 to 4 g/l (as hydroxylamine sulphate).

Examples of black-and-white developing agents that may be used include hydroquinones, p-aminophenols and pyrazolidinones of the formula:

wherein R¹ to R⁴ are alkyl or aryl groups which may be substituted with, for example, alkyl, halo, or hydroxy groups.

Examples of such black-and-white developing agents are hydroquinone, N-methyl-p-aminophenol, 1-phenyl-4-methyl-pyrazolidinone and 4-hydroxymethyl-4-methyl-1-phenylpyrazolidinone.

A black-and-white developer solution preferably contains from 0.2 to 12 g/l of black-and-white developing agent or a combination of such developing agents. Typically hydroquinone will be used in a superadditive combination with a p-aminophenol or pyrazolidinone developing agent.

Black-and-white developers also contain an antioxidant developing agent preservative. Typically this is an alkali metal sulphite in concentration levels of 1-100 g/l, preferably 10-50 g/l (as sodium sulphite).

The colour photographic materials can be single colour materials or multicolour materials. Multicolour materials contain dye image-forming units sensitive to each of the three primary regions of the spectrum. Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the materials, including the layers of the image-forming units, can be arranged in various orders as known in the art.

A typical multicolour photographic material comprises a support bearing a yellow dye image-forming unit comprised of at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, and magenta and cyan dye image-forming units comprising at least one green- or red-sensitive silver halide emulsion layer having associated therewith at least one magenta or cyan dye-forming coupler respectively. The material can contain additional layers, such as filter layers. As stated above, the process of the invention employs a tank of relatively small volume and in a preferred embodiment the ratio of the tank volume to maximum area of material which can be accommodated in the tank, that is that can be immersed in the solution, is less than 20 dm³/m², i.e. 20mm, more preferably less than 11 dm³/m² i.e. 11mm and particularly less than 3 dm³/m² i.e. 3mm.

The process may be carried out in what is known in the art as a minilab for example the tank volume may be below 5 litres and sometimes below 3.0 litres conveniently in the range 1.5 to 2.5 litres and may be about 1 litre. Solid replenishment is a convenient, accurate and consistent means of maintaining a developer and shows a particular advantage with low volume tanks and minimum replenishment rates. The replenishers contain components such as chelating agents and hydrogen peroxide which have traditionally been available as solutions. All these are available as solids, 1-hydroxyethylidene-1,1'-diphosphonic acid is available as the solid sodium salt (although it has to be converted to the potassium salt because the mixed calcium/sodium salt is prone to precipitate in developer solutions), diethyltriamine-pentaacetic acid is available as the solid free acid, "pentetic acid". Some subsituted hydroxylamine antioxidants are liquids, eg diethylhydroxylamine but others are solids and these should be used in preference.

The replenishment is preferably accomplished entirely by the addition of solid replenishers plus water.

The material to be processed is conveniently passed through the tank and preferably the developer solution is recirculated through the tank at a rate of 0.1 to 10 tank volumes per minute. The preferred recirculation rate is from 0.5 to 8 especially from 1 to 5 and particularly from 2 to 4 tank volumes per minute.

The recirculation with or without replenishment may be carried out continuously or intermittently. In one method of working both can be carried out continuously while processing is in progress but not at all or intermittently when the tank is idle.

Replenishment may be carried out by introducing the required amount of replenisher into the solution in the recirculation system, preferably just before it enters the processing tank.

The shape and dimensions of the processing tank are preferably such that it holds the minimum amount of processing solution while still obtaining the required results. The tank is preferably one with fixed sides, the material being advanced therethrough by drive rollers. Preferably the photographic material passes through a thickness' of solution of less then 20mm, preferably less than 11mm, more preferably less than 5mm and especially less than 3mm.

The shape of the tank is not critical but it may conveniently be in the shape of a shallow tray or, preferably U shaped.

It is preferred that the dimensions of the tank be chosen so that the width of the tank is the same as or only just wider than the width of the material being processed.

The total volume of the processing solution within the processing channel of a processing tank and its recirculation system is relatively smaller as compared with prior art processes. In particular the total amount of processing solution in the entire processing system for a particular module (that is, the processing channel and the recirculation system) is such that the total volume in the processing channel is at least 40% of the total volume of the processing solution in the entire system. Preferably the volume of the processing channel is at least about 50% of the total volume of the processing solution in the system.

In order to provide efficient flow of the processing solution through the opening or nozzles into the processing channel, it is desirable that the nozzles/opening that deliver the processing solution to the processing channel have a configuration in accordance with the following relationship: 0.6 ≤ F/A ≤ 23

where F is the flow rate of the solution through the nozzle in litres/minute and

A is the cross sectional area of the nozzle provided in square centimetres.

Providing a nozzle in accordance with the foregoing relationship assures appropriate discharge of the processing solution against the photosensitive material.

Such low volume thin tank systems are described in more detail in the following patent specifications: US 5,294,956; 5,179,404; 5,270,762; EP559,025; 559,026; 559,027; WO92/10790; WO92/17819; WO93/04404; WO92/17370; WO91/19226; WO91/12567; WO9207302; WO93/00612 and WO92/07301.

If the residence time of components of the developer solution is defined as the total time needed to reach one tank turnover (1TTO), then it is given by the following formula: 1TTO = V x 100R x T x U

where V is the volume of the processing tank (litre), R is the replenishment rate (litres/m²), T is the transport speed (m²/min) and U is the percent utilisation as the percentage of a working day (8 hours) that the processor is running paper.

The tank volume includes the volume of the associated recirculation system, as hereinbefore defined.

The processor is idle overnight for 16 hours and this time is part of the total standing time. In the case of conventional processing the chemical loss rates overnight will be lower than during a working day because the temperature is lower and the recirculation is switched off thus reducing aerial oxidation. However there will still be some extra losses overnight which must be taken into account. In the case of an RX developer/amplifier there will also be reduced loss overnight but since RX developer/amplifiers are generally less stable chemically than conventional developers overnight standing could cause greater sensitometric deterioration. In order to account properly for overnight losses the concept of the average time to reach one tank turnover is proposed. This is defined as 24 hours divided by the number of tank turnovers possible during a working day of eight hours for a particular utilisation, replenishment rate and tank volume. This works out simply to be 3 times the time to reach 1TTO during the working day. So equation (1) can be modified to account for this and to convert to hours instead of minutes to give equation (2) below. Average time to 1TTO = V x 100 x 3R x T x U x 60

Table 1 below was constructed to show the relative times for different utilisations and for normal (0.161 litres/m² ) and low (0.033 litres/m²) replenishment rates. This latter rate is about the minimum replenishment rate possible in order to maintain tank volume but to produce no overflow. If the volume of the developer tank is reduced to 1.80 litres instead of 22.414 litres, the residence times are correspondingly reduced for the period when the processor is working.

These volumes are those for a standard Kodak Model 52 paper processor (22.414 litres) and a modified Kodak Model 52 processor with a much smaller developer tank (1.80 litres). The word Kodak is a Registered Trade Mark.

The process will normally be carried out with recirculation.

Utilisation	Residence Time (hours)
	Large tank (22.4 l)	Small tank(1.8 l)
	low	normal	low	normal
100%	112.2	22.4	9	1.8
20%	561.0	112.2	45	9
2%	5610.0	1122.0	450	90

It can be seen from Table 1 that even at modest utilisation rates of 20% the low replenishment rate gives a time of about 3 weeks. The lowest utilisation rate of 2% although unusual in practice gives a time of about 30 weeks. Clearly, this illustrates the difficulty of maintaining a process in a conventional tank at the replenishment rates desired for improved environmental impact and economy. Even the most stable common process for colour materials would not be reliable. Some of the common processes, particularly those with inferior antioxidant protection or poor pH buffering would be impractical at even modest utilisation rates. However, with the low volume tank used in this illustration, even a processing solution whose useful life was as low as four days could be used even at the lowest utilisation shown while taking full advantage of the use of solid replenishment.

In the present specification a developer solution is considered to be acceptable if the D max values are at or above 80% of the values of a freshly prepared solution and the useful lifetime of a solution is the time taken at 35°C for the solution to deteriorate to less than 80% of the Dmax values of a fresh solution.

The Dmax values are measured by the well known sensitometric methods using a pre-exposed test strip.

In the following examples the addition of solid materials to the processing tank can conveniently be added to the solution in the form of individual or composite pellets in the filter housing just before it passess through the filter. This is shown in Figure 1 in which filter houseing (1) contains a filter member (2) through which processing solution passes before being pumped by pump (3) into the processing tank (4). The solids and water are added directly to the filter housing as shown by arrow (5).

The following Examples are included for a better understanding of the invention.

EXAMPLE 1

A colour paper developer was made to the formulation:

K₃AC5	0.8g/l
K₂CO₃	25g/l
DEH.HCl	6g/l
Phorwite™ REU	2.3g/l
Total KCl (2.7g/l comes from the DEH.HCl)	2.8g/l
KBr	0.02g/l
CD3	4.85g/l
Li₂SO₄	2.7g/l
pH	10.12

where DEH is diethylhydroxylamine hydrochloride. This material can be replaced with 15g/l of the di-potassium salt of di-sulphoethyl hydroxylamine if desired.

The solid addition rates and water to achieve an overall replenishment rate of 32ml/m² are as follows:

K₃AC₅	15.9mg/m²
K₂CO₃	0.8g/m²
DEH.HCl	0.7g/m²
Phorwhite REU	0.07g/m²
CD3	0.54g/m²
LiSO₄	0.086g/m²
KOH	0.25g/m²
water	32ml/m²

The volume taken-up by the solids is approximately equal to the water evaporation rate of the processor.

EXAMPLE 2

A black and white developer was made to the formulation:

Sodium sulphite	16g/l
N-methyl-p-aminophenol sulphate	1.45g/l
Hydroquinone	2.9g/l
KBr	0.93g/l
Quadraphos™	1.29g/l
Na₂CO₃	25g/l

where Quadraphos is tetrasodium pyrophosphate.

The solid addition rates for an overall replenishment rate of 320ml/m² and a silver bromide coating containing 1.08g/m² of silver at an average exposure of 25% of Dmax, are as follows:

Sodium sulphite	5.69g/m²
N-methyl-p-aminophenol sulphate	0.46g/m²
Hydroquinone	1.06g/m²
Quadraphos	0.41g/m²
Na₂CO₃	8.0g/m²
Water	320ml/m²

EXAMPLE 3

A black and white developer was made to the formulation:

Sodium sulphite	16g/l
N-methyl-p-aminophenol sulphate	1.45g/l
Hydroquinone	2.9g/l
KBr	3.72g/l
Quadraphos™	1.29g/l
Na₂CO₃	25g/l

The solid addition rates for an overall replenishment rate of 80ml/m² and a silver bromide coating containing 1.08g/m² of silver at an average exposure of 25% of Dmax, are as follows;

Sodium sulphite	1.95g/m²
N-methyl-p-aminophenol sulphate	0.14g/m²
Hydroquinone	0.39g/m²
Quadraphos	0.14g/m²
Na₂CO₃	2.5g/m²
Water	80ml/m²

Claims

A process for the development of an imagewise exposed photographic material having at least one silver halide layer which comprises forming an image therein in a solution which contains a developing agent, which solution is replenished wherein:

the process is carried out in an apparatus comprising at least one processing tank in which the ratio of the tank volume, as hereinbefore defined, to maximum area of material which can be accommodated in the tank is less than 25 dm³/m²,

substantially all the replenishers are added as solids direct to said developer solution together with additional water which may contain a minor amount of replenisher chemicals,

and wherein the average residence time of the processing solution in the developing tank defined by the formula: Average residence time = V x 100 x 3R x T x U x 60

where V is the volume of the processing tank (litres), as hereinbefore defined, R is the replenishment rate (litres/m²), T is the transport speed (m²/min) and U is the percent utilisation as the percentage of a working day (8 hours) that the processor is running,

is less than the useful lifetime of the solution, said useful lifetime being the time for which the Dmax values for red, green and blue (or the silver image Dmax of a black-and-white material) remain at or above 80% of the value(s) produced by a freshly prepared solution.
A process as claimed in claim 1 wherein the ratio of the tank volume to maximum area of material which can be accommodated in the tank is less than 20 dm³/m².
A process as claimed in claim 2 wherein the ratio of the tank volume to maximum area of material which can be accommodated in the tank is less than 11 dm³/m².
A process as described in claim 3 wherein the ratio of the tank volume to maximum area of material which can be accommodated in the tank is less than 3 dm³/m².
A process as claimed in any one of the preceding claims in which the developer solution contains an antioxidant developing agent preservative.
A process as claimed in any of one of the preceding claims which comprises forming a dye image in a colour developer solution.
A process as claimed in either of claims 5 and 6 in which the colour developer solution contains from 1 to 12 g/l of colour developing agent
A process as claimed in any one of claims 5-7 in which the antioxidant is hydroxylamine salt or a solid substituted hydroxylamine.
A process as claimed in any one of claims 1-5 which comprises forming a silver image in a black-and-white developer solution.
A process as claimed in claim 9 in which the antioxidant is an alkali metal sulphite.
A process as claimed in either of claims 9 and 10 in which the developer solution contains from 0.2 to 12 g/l of black-and-white developing agent or a combination of such developing agents.
A process as claimed in any one of the preceding claims wherein the replenishment rate is in the range from less than 215ml/m² down to the rate necessary to maintain tank volume but produce no overflow.