Photographic processing solutions

A photographic aqueous processing solution containing at least one solid compound that has a maximum solubility therein corresponding to a desired operating level, which solution is kept in equilibrium with the solid form of the compound, thus maintaining its concentration at the desired level without the need for a replenishing system.

FIELD OF THE INVENTION 
This invention relates to photographic processing solutions and in 
particular, to the control of the concentration of components therein. 
BACKGROUND OF THE INVENTION 
In photographic processing solutions, the concentrations of the various 
components need to be kept close to certain aim levels. The normal way to 
maintain chemical levels is to replenish the components at the same rate 
as they are consumed. Consumption rates vary with exposure (and hence the 
amount of silver developed), and losses due to aerial oxidation, 
evaporation, etc., can vary widely for different processes and processing 
machines. Even with a particular machine and process, simply replenishing 
at a calculated rate can lead to undesirable variability. It is normal for 
processing chemicals to be as soluble as possible to facilitate solution 
preparation. 
The problem to be solved is how to maintain the desired concentration of a 
processing solution component in a simple but accurate way. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a photographic 
processing solution containing at least one compound that has a maximum 
solubility therein corresponding to a desired operating level, which 
solution is kept in equilibrium with the solid form of the compound thus 
maintaining its concentration at the desired operating level. 
This invention also provides a method for processing a photographic 
material by contacting it with the photographic processing solution 
described above. 
The concentration of the dissolved solid compound in the photographic 
processing solution is maintained at the desired level regardless of 
degree of consumption, evaporation, aerial oxidation or other 
deterioration. 
A desired level of, for example, an antioxidant can be maintained 
automatically without any need to take account of the consumption rate if 
the solubility is limited to, say, 0.06 molar or some other effective 
level. This means that the system can be used universally regardless of 
high or low utilization conditions. 
In addition, another benefit has been found in that lower dissolved levels 
of antioxidant than those in which a more soluble antioxidant would 
normally be useable are advantageous because the solid material is 
oxidized by the air at a lower rate than that in solution. 
The process does not require replenishment pumps nor any expertise to keep 
it within control limits. However, other processing solution compounds 
will, of course, still need replenishment. 
DETAILED DESCRIPTION OF THE INVENTION 
The principle of using a solid dissolvable compound that slowly dissolves 
in a solution for replenishment by virture of an approximately controlled 
dissolution rate is known. In this invention, the principle is specific 
limited solubility. In the former case, the dissolution rate is not 
related to the final solubility of the compound involved and so the level 
is not related to the level in solution at any one time. In this 
invention, the compound level in the solution determines how much more of 
the solid compound will dissolve up to the point of maximum solubility, 
which is set as the operating level or the highest operating level. 
The solid compound may be kept in a filter housing or in some similar 
containment device through which the solution circulates, or it may be 
located elsewhere, e.g., in the processing tank or a supply tank. 
In order to assist dissolution of the solid compound in the processing 
solution, a "solvent bridge" material may be employed. Hence, the 
processing solution may contain a solvent for the solid compound. The 
solvents may be water-miscible or non-water-miscible. Examples of such 
solvents include an organic alcohol, ketone or ester, and preferably 
isopropanol or cyclohexanone. 
It is envisaged that the solid compound could be color or black-and-white 
developing agents, auxiliary developing agents or electron transfer agents 
such as pyrazolidinones, or other components such as antioxidants, such as 
substituted hydroxylamines. In the field of color image formation by a 
redox amplification (RX) process, sparingly soluble sources of RX oxidants 
such as peroxy or other compounds (such as hydrogen peroxide) as well as 
antioxidants such as substituted hydroxylamines could be used as the solid 
component. 
Of the substituted hydroxylamines, the commonly used ones have a relatively 
high solubility. Diethyl hydroxylamine, for example, is essentially 
miscible in all proportions with water and is used from concentrated 
solutions of 85% or 97%. This material and all other photographic 
antioxidants used commercially are much too soluble to be used for the 
present invention. Less soluble derivatives of hydroxylamine that are 
commercially available such as mono-t-butyl-hydroxylamine are also too 
soluble. On the other hand, dibenzyl-hydroxylamine is commercially 
available but is almost entirely insoluble in water even with the 
assistance of surfactants. 
A preferred group of substituted hydroxylamines is the alkyl and cycloalkyl 
substituted hydroxylamines with straight or branched chain alkyl groups 
having from 5 to 8 carbon atoms to give a solubility of up to 0.06 molar 
for example: 
n-pentylhydroxylamine 
iso-pentylhydroxylamine 
N-ethyl-N-propylhydroxylamine 
hexylhydroxylamine 
cyclohexylhydroxylamine 
N,N-dipropylhydroxylamine 
heptylhydroxylamine 
octylhydroxylamine 
hydroxyoctylhydroxylamine 
hydroxynonylhydroxylamine 
hydroxydecylhydroxylamine 
carboxydecylhydroxylamine. 
The above hydroxylamine compounds may be further substituted with 
hydrophilic (e.g., carboxy or sulfo) and/or hydrophobic groups such that 
the desired solubility is obtained. 
Mono-N-cyclohexylhydroxylamine(MCH) has a solubility of about 3.9 to 4 g/l 
at developer pH (10.0) or about 0.026 molar and is at a level needed for 
effective use. Another compound that may be used is 
4,5-dihydroxylamino-2-propylamino-1,3,5-triazine (CSD). 
Diethylhydroxylamine and its sulfonated derivatives, such as 
disulfodiethylhydroxylamine, are used in current commercial formulations 
from close to zero up to some 0.06 molar. It is estimated that mono alkyl 
substituents comprising between 5 and 8 carbon atoms would cover the range 
from almost zero solubility up to 0.06 molar as the maximum solubility of 
the antioxidant. It is clear that a maximum solubility of about 0.06 molar 
could be achieved by a multitude of combinations of substituents 
comprising hydrophobic and hydrophilic groups. This is a highly desirable 
practical range. 
The cyclic derivative of hydroxylamine (3) referred to above as CSD with 
lower solubility (between 0.5 and 1 g/l or about 0.005 molar) than 
cyclohexyl-hydroxylamine was synthesized and its method of synthesis is 
described below. 
Preparation of 4,6-dichloro-2-propylamino-1,3,5-triazine (2) 
##STR1## 
Cyanuric chloride (1) (36.9 g, 0.2 mole) was dissolved in acetone (600 ml) 
and cooled in an ice/acetone bath. Potassium hydrogen carbonate (25.03 g, 
0.25 mole) was dissolved in water (150 ml) with propylamine (11.82 g, 0.2 
mole) and added dropwise to the solution of (1) while maintaining the 
temperature below 0.degree. C. The mixture was stirred for 1 hour at 
0.degree. C. and then stirred for 1 hour at room temperature. The acetone 
was evaporated off under reduced pressure and the residue (300 ml) was 
poured into water (11). The resulting white solid was filtered, washed 
with water and dried under vacuum. 
Yield=38.2 g (92%). 
The product had nmr, mass and ir spectra that were consistent with the 
proposed structure. 
Preparation of 4,5-dihydroxylamino-2-propylamino-1,3,5-triazine (3) 
##STR2## 
Hydroxylamine hydrochloride (120.0 g, 1.73 mole) was dissolved in water 
(250 ml). Sodium hydroxide (62.5 g, 1.563 mole) was dissolved in water 
(175 ml) and slowly added to the first solution while maintaining the 
temperature below 20.degree. C. by means of an ice/acetone bath. Compound 
(2) (38.1 g, 0.184 mole) was dissolved in 1,4-dioxane (250 ml) and the 
aqueous mixture was added dropwise to this while maintaining the 
temperature below 15.degree. C. On completion of the addition, a pale 
purple-colored, waxy precipitate was formed. The mixture was heated to 
60.degree. C. for 1 hour then to reflux for a further 3 hours. The mixture 
was cooled and poured into water (11) and left overnight. The mixture was 
extracted with diethyl ether (total of 31 that was discarded) and the 
aqueous layer left standing for 72 hours. The resulting precipitate was 
filtered, washed with water and dried under vacuum. 
Yield=12.1 g (33%). 
The product had nmr, mass and ir spectra that were consistent with the 
proposed structure. 
Examples of other types of the compounds having limited solubility are 
color and black-and-white developing agents. Specific examples are listed 
below: 
(a) Color developing agents 
These need to be in the solubility range of from 0 to about 0.015 molar or 
6.5 g/l of a commonly used color developing agent such as CD3 (methyl 
sulfonamidoethyl ethylamino toluidine sesquisulfate hydrate). This agent 
is however soluble to about 12 g/l or 0.028 molar, that is, about twice 
its normal upper operating limit, and so does not fall within the scope of 
the present invention. The following color developing agents have suitably 
lower solubilities: 
N,N-diethyl-p-phenylenediamine 
N,N-diethyl-3-methyl-p-phenylenediamine 
N,N-dipropyl-p-phenylenediamine 
N,N-dipropyl-3-methyl-p-phenylenediamine 
N,N-dihydroxypropyl-3-methyl-p-phenylenediamine 
(b) Black-and-White developing agents 
These are used usually within the range of from 0 to 0.01 molar or about 2 
g/l of a commonly used auxiliary developing agent such as 
4,4-dimethyl-1-phenyl-3-pyrazolidone that would come within the scope of 
the present invention but at the higher solubility limit. The following 
compounds have suitable lower solubilities: 
4-ethyl-1-phenyl-3-pyrazolidone 
4,4-dimethyl-1-phenyl-3-pyrazolidone 
4,4-diethyl-1-phenyl-3-pyrazolidone 
4-n-pentyl-1-phenyl-3-pyrazolidone 
4-hydroxypentyl-1-phenyl-3-pyrazolidone 
4,4-dimethyl-1-phenyl-4'-methyl-3-pyrazolidone 
4-n-pentyl-1-phenyl-4'-methoxy-3-pyrazolidone. 
The processing solutions and photographic material processed thereby may be 
any of those described in Research Disclosure, Item 36544, September 1994, 
Sections XVII to XX, published by Kenneth Mason Publications, Emsworth, 
Hants, United Kingdom.

The following Examples are included for a better understanding of the 
invention. 
EXAMPLE 1 
A circulation system of about 500 ml capacity was set up in which solid 
N-monocyclohexyl hydroxylamine (MCH) was retained behind a removable 
filter paper filter. The solution circulated was potassium carbonate at 
pH=10.5. The solution was left to circulate for 30 minutes and the amount 
of MCH in solution was determined by removing the paper filter that 
retained the MCH, drying and weighing it. This gave the amount of solid 
not in solution and hence, by difference from that on the filter 
initially, the amount in solution. An extra volume of potassium carbonate 
solution that did not contain MCH was added to the system and after 30 
minutes the amount of MCH in solution was determined. The volume was 
increased by increments of 10%. In a second part of the experiment most of 
the solution was removed from the system and evaporated to reduce its 
volume, again in increments of 10%. Solid MCH came out of solution and was 
collected on the filter and weighed as before. The amount of MCH in 
solution during this dilution or evaporation procedure is shown in Table 
1. 
TABLE 1 
______________________________________ 
Equilibrium Levels of N-cyclohexyl hydroxylamine 
Volume % 
Relative to initial 
MCH in Solution 
______________________________________ 
150 3.96 g/l 
140 4.05 g/1 
130 4.11 g/l 
120 3.87 g/l 
110 3.81 g/l 
100 3.80 g/l 
90 3.88 g/l 
80 3.92 g/l 
70 4.03 g/l 
______________________________________ 
This shows that regardless of any dilution that might occur by addition of 
a replenisher solution that did not contain MCH or loss of volume by 
evaporation, the level of MCH automatically adjusted itself to the initial 
level within 30 minutes. 
EXAMPLE 2 
The compounds CSD and MCH were compared with diethyl hydroxylamine at 
equimolar levels in a developer of the composition shown in Table 2. 
TABLE 2 
______________________________________ 
Developer Composition 
Component Concentration 
______________________________________ 
AC5 0.6 g/l 
K.sub.2 CO.sub.3 25 g/l 
KBr 28 mg/l 
KCl 6.0 g/l 
TEA (85%) 5.5 ml/l 
REU 1.0 g/l 
Antioxidant see below. 
CD3 4.35 g/l 
pH 10.05 
______________________________________ 
Where AC5 is a 60% W/W solution of 1-hydroxyethylidene-1,1-diphosphonic 
acid. TEA is an 85% solution of triethanolamine in water. REU is a 
commercially available optical brightener called PHORWITE.TM.REU. CD3 is 
N-2-(4-amino-N-ethyl-m-toluidino) ethyl!-methanesulfonamide sesquisulfate 
hydrate. 
The antioxidant level was equivalent to 3.0 ml/l diethyl 
hydroxylamine(85%); which is about 0.029 molar. The three developers were 
as follows; 
______________________________________ 
Developer Antioxidant Amount 
______________________________________ 
Dev 1 (Control) 
diethyl hydroxylamine (85%) 
3 ml/l 
Dev 2 (Inv.) CSD (Mwt 200.2) 5.73 g/l 
Dev 3 (Inv.) mono-N-cyclohexyl- 4.34 g/l 
hydroxylamine hydrochloride 
______________________________________ 
These developers were placed in 500 ml measuring cylinders and stirred 
continuously with magnetic stirrers to create a vortex depth of about 5 mm 
in each case in order to ensure continuous aeration. The diethyl 
hydroxylamine was completely in solution. CSD was about 10 to 15% in 
solution. The rest was a solid swirling in the solution. About 90% of the 
N-cyclohexyl hydroxylamine was in solution with the rest as a solid 
swirling in solution. Samples were taken each day and analyzed for CD3 
content. The results are shown in Table 3 below. 
TABLE 3 
______________________________________ 
Limited Solubility Antioxidants 
Age CD3 concentration (g/l) 
(weeks) Dev 1 Dev 2 Dev 3 
______________________________________ 
0 4.5 4.4 4.3 
1 3.4 4.3 3.9 
2 2.1 3.7 2.8 
3 0.8 3.2 2.0 
4 0 2.8 1.5 
5 0 2.3 1.2 
______________________________________ 
It can be seen that the control developer has lost all its CD3 in just over 
3 weeks whereas Dev 2 has lost only 30% and Dev 3 about 60%. It is 
interesting that the developer that had the least concentration of 
antioxidant at any one time, Dev 2, was the best preserved. This is an 
unexpected and additional benefit of the invention. It appears that while 
the antioxidant is in its solid form it is not itself oxidized by the air 
and so is able to maintain a reservoir of potentially active material. The 
control developer that contains the same molar amount of antioxidant will 
be prone to loss of antioxidant not only in preserving the color 
developing agent but also by direct aerial oxidation. Developer 3 shows 
behavior intermediate between the other two as reflects its intermediate 
solubility. Thus, it appears that limited solubility antioxidants are not 
only capable of maintaining a desired level automatically, independent of 
usage rate(since this level is equal to the maximum solubility), but also 
they can be used at lower dissolved levels because they are continuously 
replaced from the solid source and while in the solid phase are oxidized 
by the air at a lower rate. 
The invention has been described in detail with particular reference to 
preferred embodiments thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention.