This invention relates to photographic silver halide processing solutions and particularly to colour developing solutions.

It is well understood that the parameters of colour development, such as time, temperature, component content, pH, etc have to be carefully controlled in order to obtain consistent sensitometric results. This usually means that there has to be close control over, for example, the temperature and replenishment of colour developing agent. The cost of such control is clearly significant in a commercial operation.

US Patent 4 465 762 discloses silver halide colour materials containing a pyrazolidinone of formula (I). The present pyrazolidinones can only be derived by selecting substituents from two separate lists. No specific such compounds are described.

US Patent 4 266 002 describes the use of pyrazolidinones as an electron transfer agent in a dye diffusion transfer element. No chromogenic dye development is described.

US Patent 4 483 919 describes a photographic colour material containing a compound that releases a pyrazolidinone upon development. The release is therefore imagewise.

US Patent 4 155 763 describes colour developing solutions comprising an aromatic amine colour developing agent and a 1-aryl-pyrazolidone having two substituents at the 4-position of the pyrazolidone. The advantages are said to include faster image dye formation and a more stable colour developing solution. The English language abstract of Japanese application 62/178251 describes a colour developing solution comprising a para-phenylenediamine colour developing agent and an auxiliary developing agent including, inter alia, 1-phenyl-pyrazolidone. Image formation is described as "highly sensitive" and forming "excellent gradation". It is also said to be "free from the influence of agitation.

The above two references indicate that the use of a second developing agent in colour developing solutions provides higher developing activity as it would in black and white developer solutions wherein, for example, the activity of a hydroquinone developing agent is very much increased by the addition of Metol or 1-phenyl-pyrazolidone.

The present invention provides a method of developing an imagewise exposed silver halide colour material to provide sensitometric results of reduced variability which comprises
   carrying out colour development in an aqueous colour developing solution containing a colour developing agent in the presence of one or a combination of the pyrazolidinone silver halide developing agents of the general formula:
wherein
   R¹ and R² are each hydrogen or an alkoxy group having 1-4 carbon atoms, and
   R³ and R⁴ are each hydrogen or an alkyl group having 1-10 carbon atoms,
with the proviso that either one of R¹ or R² is an alkoxy group or either one of R³ or R⁴ is an alkyl group of 3-7 carbon atoms,
   incorporated in said silver halide colour material in an inactive form from which the active form is released in the alkaline developer solution, characterised in that the nature of the pyrazolidinone silver halide developing agent(s) is such that in low activity conditions development is accelerated while in high activity conditions development is decelerated thus reducing the variability in the density versus LogE curve (the characteristic curve) caused by changes in development time.

The pyrazolidinone developing agent may also be present in the colour developer solution.

In the present invention (unlike the prior art) not only are the low activity conditions accelerated by the presently used ETA's but also high activity conditions are decelerated thus leading to less variation in sensitometric results under both high and low activity conditions. This is seen graphically as a compression of the spread of the characterisitic curves as shown in, say, Figs 2 and 3 compared to Fig 1.

When it is incorporated in the photographic material it is in a form which is inactive until processing takes place. For example it could be inactivated by a blocking group which is hydrolysed off when the material is immersed in the developing solution (which is usually alkaline).

A number of ETA's have been examined for their effectiveness in lowering sensitometric sensitivity to process variables. The reduction of sensitivity to development time is used as an example. Three broad types of behaviour for different ETA's can be observed and these are as follows:

• (1) A reduction of sensitometric spread with control of Dmin increase caused by time and maintenance of aim contrast. See Fig 10 of the accompanying drawings in which the solid lines represent the control and the broken lines the effect of the added ETA. This convention is also used in Figs 11 and 12.
• (2) A reduction of sensitometric spread with control of Dmin increase caused by time and an increase of contrast. See Fig 11 of the accompanying drawings.
• (3) A modest reduction in sensitometric spread but with little Dmin control, a reduction in contrast and still a considerable variability. See Fig 12 of the accompanying drawings. These results are clearly not acceptable particularly with respect to the increase in Dmin. The use of Type (3) ETA's alone is therefore not part of the present invention.
  Type (1) is the preferred behaviour exhibited by the preferred compounds. Type (2) is another useful and beneficial behaviour and could, in certain cases, be preferred over Type (1) if an increase in contrast or corresponding trade-off was desired. The present invention also includes the use of combinations of ETA's. Combinations of Type (2) and (3), for example, can give an overall behaviour similar to Type (1). Combinations of Type (1) and (3) also give good results in that the spread of the sensitometric curves is particularly well controlled.

A useful group of Type (1) ETA's of formula (I) are those in which at least one of R¹ and/or R² is an alkoxy group of 1-4 carbon atoms, eg -OCH₃, R³ is hydrogen or an alkyl group of 1-4 carbon atoms, eg - CH₃ and R⁴ is hydrogen or a hydroxyalkyl group of 1-4 carbon atoms, eg -CH₂OH.

A useful group of Type (2) ETA's of formula (I) are those in which R¹, R² and R³ are hydrogen and R⁴ is an alkyl group of 3-7 atoms, eg -C₅H₁₁

The preferred black-and-white developers are: 1-(4-methoxyphenyl)-3-pyrazolidone, 1-(3,4-dimethoxyphenyl)-3-pyrazolidone, and 1-phenyl-4-n-pentylpyrazolidone.

The black-and-white developing agent may be present in the developer solution at a concentration up to 5 g/l preferably in the range 0.05 to 0.5 g/l. When incorporated in the photographic material it may be present in one or more layers thereof. Instead of incorporating them per se in the photographic material they are, as indicated above, in the form of a compound that releases them as a function of the pH of the processing solution.

It has been found, in particular, that the presence of the black-and-white developing agent improves variability caused by variations in time and temperature of development, pH, bromide ion concentration and colour developing agent (eg CD4) concentration in the colour developer solution. The reduced risk of sensitometric variations further means that replenishment rates can be reduced thus resulting in less overflow and effluent. The sometimes needed bromide ion removal from the developer solution may also be avoidable.

The present invention is particularly applicable to the processing of colour negative film but is also applicable to other processes, eg colour paper. The material to be processed comprises a support bearing at least one silver halide emulsion layer having a colour coupler associated therewith. The term "associated therewith" here takes its normal meaning in art. The coupler may be incorporated in the emulsion layer or in a layer adjacent thereto. The preferred colour materials comprise three dye image forming units each containing one or more emulsion layers having couplers associated therewith and each sensitised to a different region of the spectrum. A typical colour material would contain such units sensitised to blue, green and red light and capable of forming yellow, magenta and cyan image dyes respectively.

Examples of colour photographic materials and methods of processing them are described in Research Disclosure Item 308119, December 1989 published by Kenneth Mason Publications, Emsworth, Hants, United Kingdom.

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

A single layer coating of a silver bromoiodide emulsion comprising tabular grains having a mean grain area of 1.05 mµ² containing a colour coupler (A) of the formula:
dissolved in di-tert-butylphthalate (coupler to solvent ratio of 1:0.5) was coated at 1.0 g/m² (as silver) and 0.6 g/m² of coupler.

The following basic colour developing solution was used:

Table 1 below gives process details of concentration of 1-(4-methoxyphenyl)-3-pyrazolidone and development time at 37.8°C.

The sensitometric results for these twelve processes are shown as sets of three time series in Figures 1, 2 and 3 each for a different level of ETA. In Figure 1 (control), without any ETA, the effect of time is considerable giving increases in Dmin, speed, Dmax and contrast. In Figure 2 with 0.1 g/l of ETA the sensitometric spread caused by time is very much reduced. In Figure 3 with 0.3 g/l ETA the curves are even closer together. The optimum level of ETA is probably between 0.1 and 0.3 g/l. The essential difference between this result and that expected is that not only do short process times show acceleration (as might be expected) but the long process times show a reduction (which is not expected).

This unexpected compression of sensitometric spread from both high and low activity conditions is also shown with other process variables as is shown below in Examples 2 and 3.

Similar results were found with the couplers (B) and (C) having the formulae:
coated with the same emulsion and processed in the same solution.

A set of experiments with sodium bromide levels from 0.45 to 2.15 g/l and ETA levels of 0, 0.1 and 0.3 g/l was carried out on the same coatings as mentioned above. The results are shown in Figures 4, 5 and 6. Again with zero level of ETA there is a considerable sensitometric spread caused by changing bromide ion level and as the ETA level is increased this is reduced as shown in Figures 5 and 6. The optimum level of ETA is probably between 0.1 and 0.3 g/l.

A single layer coating of a silver bromoiodide emulsion as described in Example 1 was tested by the procedure of Example 1 was followed except that the time of development was kept constant at 2.5 minutes while varying the CD4 and ETA concentrations as set out in Table 2 below.

The sensitometric results for these fifteen processes are shown as sets of three CD4 level series in Figures 7,8 and 9. In Figure 7 (control) without any ETA the effect of CD4 level is considerable giving increases in Dmin, speed, Dmax and contrast. In Figure 8 with 0.1 g/l of ETA the sensitometric spread is caused by CD4 is very much reduced. In Figure 9 with 0.3 g/l ETA the curves have separated again but are still better than the control especially in similarity of contrast.

Similar results were found with other couplers (B) and (C) coated with the same emulsion and processed in the same solution.