Photographic developer-amplifier composition

FIELD OF THE INVENTION
This invention relates to photographic developer-amplifier compositions for use in redox amplification processes.
BACKGROUND OF THE INVENTION
Redox (RX) amplification processes have been described, for example in British Specification Nos. 1,268,126; 1,399,481; 1,403,418 and 1,560,572. In such processes, color materials are developed to produce a silver image (which may contain only small amounts of silver) and then treated with a redox amplifying solution (or a combined developer-amplifier) to form a dye image.
The developer-amplifier solution contains a color developing agent and a redox oxidizing agent that will oxidize the color developing agent in the presence of the silver image that acts as a catalyst.
Oxidized color developer reacts with a color coupler to form the image dye. The amount of dye formed depends on the time of treatment or the availability of color coupler and is less dependent on the amount of silver in the image as is the case in conventional color development processes.
Examples of suitable oxidizing agents include peroxy compounds including hydrogen peroxide and compounds that provide hydrogen peroxide, e.g., addition compounds of hydrogen peroxide; cobalt (III) complexes including cobalt hexammine complexes; and periodates. Mixtures of such compounds can also be used.
Because a developer-amplifier solution contains both a reducing agent (developing agent) and an oxidant, they can react together spontaneously thus leading to very poor solution stability. This leads to a failure to provide the desired dye density on processing. It is this phenomenon in particular that has inhibited commercial use of the RX process.
U.S. Pat. No. 4,330,616 discloses that the use of water-soluble metal salts (including zinc and magnesium), together with a diphosphonic acid, will inhibit the loss of hydroxylamine in a color developing solution. There is no mention of developer-amplifier solutions additionally containing a redox oxidant. Example 6 below shows that this combination does not satisfactorily stabilize a developer-amplifier solution.
Although a number of solutions to the problem of stability have been proposed, there is a constant need to improve the stability of developer-amplifier compositions.
SUMMARY OF THE INVENTION
According to the present invention there is provided a redox developer-amplifier composition comprising a color developing agent, a redox oxidizing agent, and a stabilizing amount of Zn.sup.++ or Mg.sup.++ ions.
This invention also provides a method of processing color photographic silver halide materials by treating the materials with the composition described above.
It has been found that the inclusion of Zn.sup.++ or Mg.sup.++ ions in RX developer-amplifier solutions reduces the instability of the solution and thus the density loss in the processed photographic material that occurs upon aging of the solution, for example, when the processing machine in which it is contained is standing idle.
DETAILED DESCRIPTION OF THE INVENTION
The redox amplification oxidant (or oxidizing agent) may be a persulfate, periodate, Cobalt(III) compound or, preferably, a peroxide. Examples of suitable peroxide oxidizing agents are peroxy compounds including hydrogen peroxide and compounds that provide hydrogen peroxide, e.g., addition compounds of hydrogen peroxide.
Other components that may be included in a developer-amplifier solution include a base, e.g., potassium or sodium hydroxide; a pH buffer such as a carbonate, borate, silicate or phosphate; antioxidants such as hydroxylamine sulfate, diethylhydroxylamine; metal-chelating compounds such as 1-hydroxyethylidene-1,1'-diphosphonic acid, catechol disulfonate and diethyltriaminepentaacetic acid.
The present processing solutions 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.
As indicated above, the developer-amplifier solution may also contain hydroxylamine as an additional preservative. The purpose for this is to protect the color developing agent against aerial oxidation. It is preferably used as a salt thereof such as hydroxylamine chloride, phosphate or, preferably, sulfate. The amount used is from 0.05 to 10 g/l, preferably from 0.1 to 5.0 g/l and, especially, from 0.4 to 2.0 g/l �as hydroxylamine sulfate (HAS)!.
The pH is preferably buffered, e.g., by a phosphate such as potassium hydrogen phosphate (K.sub.2 HPO.sub.4) or by another phosphate, or carbonate, silicate or mixture thereof. The pH may be in the range from 10.5 to 12, preferably in the range from 11 to 11.7 and especially from 11 to 11.4.
The zinc ions may be provided by a zinc compound. Examples of zinc compounds that may be used are: zinc sulfate, zinc chloride, zinc hydroxide, zinc nitrate, and zinc acetate. The magnesium ions may be provided by an analogous set of compounds.
Such compounds often have limited water solubility at higher pH values. Hence, it is preferred to solubilize the Zn.sup.++ or Mg.sup.++ ions by means of a chelating agent, for example, a polycarboxylic chelating agent (such as polyaminocarboxylic acid). An example of a suitable chelating agent is diethylenetriaminepentaacetic acid (DTPA).
DTPA is often used in developer-amplifier compositions to stabilize the hydroxylamine compound and the hydrogen peroxide against decomposition catalyzed by metal ions such as iron, copper and manganese. Hence, if it is used to chelate the zinc ions, the amount used should be in addition to that necessary to stabilize the hydroxylamine.
The preferred concentration range of the zinc ions (as zinc sulfate heptahydrate) is from 0.1 to 20 g/l, preferably from 0.5 to 10 g/l and especially from 1 to 5 g/l. Amounts of chelating agent needed to solubilize the zinc ions will be the molar equivalent amounts. Amounts of DTPA, for example, will be from 0.14 to 27.4 g/l, preferably from 0.7 to 14 g/l and especially from 1.4 to 6.8 g/l.
The concentration range of the hydrogen peroxide is preferably from 0.1 to 20 ml/l and especially from 0.5 to 2 (as 30% w/w solution).
The composition is preferably free of any compound that forms a dye on reaction with oxidized color developing agent.
The redox amplification solution preferably contains, dissolved in the solution, a compound having a hydrophobic hydrocarbon group and a group that adsorbs to silver or stainless steel solubilized, if necessary, with a non-ionic water-soluble surfactant. Examples of such compounds are alkyl amines, alkylaryl amines, secondary and tertiary alkyl amines, alkyl quaternary salts, alkyl heterocyclic quaternary salts, alkyl amino carboxylic acids, alkyl amino sulfonic acids, alkyl diamines, branched alkyl diamines, alkyl thiols, alkyl thiocarboxylic acids, and alkyl thiosulfonic acids. An especially preferred compound is dodecylamine.
A particular application of this invention is in the processing of silver chloride color paper, for example paper comprising at least 85 mole percent silver chloride, especially such paper having total silver levels from 5 to 700 mg/m.sup.2, and for image amplification applications, levels from 10 to 120 mg/m.sup.2 and particularly from 15 to 60 mg/m.sup.2.
Such color materials can be single color elements or multicolor elements. Multicolor elements 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 element, including the layers of the image-forming units, can be arranged in various orders as known in the art. In an alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer.
A typical multicolor photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler. The element can contain additional layers, such as filter layers, interlayers, overcoat layers, subbing layers, and the like.
While the present solutions may be used in conventional large scale or minilab processing environments, the present processing solutions are preferably used in a method of processing carried out by passing the material to be processed through a tank containing the processing solution which is recirculated through the tank at a rate of from 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, is carried out continuously or intermittently. In one method of working both could be carried out continuously while processing was in progress but not at all or intermittently when the machine was idle. Replenishment may be carried out by introducing the required amount of replenisher into the recirculation stream either inside or outside the processing tank.
It is advantageous to use a tank of relatively small volume. Hence, in a preferred embodiment of the present invention, the ratio of tank volume to maximum area of material that can be accommodated in the tank is less than 25 dm.sup.3 /m.sup.2, and preferably less than 11 dm.sup.3 /m.sup.2, more preferably, less than 5 dm.sup.3 /m.sup.2, and most preferably less than 3 dm.sup.3 /m.sup.2.
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.
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 less than 11 mm, preferably less than 5 mm and especially about 3 mm. The shape of the tank is not critical but it could 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 or only just wider than the width of the material to be processed.
The total volume of the processing solution within the processing channel and recirculation system is relatively smaller as compared to prior art processors. In particular, the total volume of processing solution in the entire processing system for a particular module is such that the total volume in the processing channel is at least 40 percent of the total volume of processing solution in the system. Preferably, the volume of the processing channel is at least about 50 percent 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.ltoreq.F/A.ltoreq.23
wherein:
F is the flow rate of the solution through the nozzle in liters/minute; and
A is the cross-sectional area of the nozzle provided in square centimeters.
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:
U.S. Pat. No. 5,294,956, EP-A-559,027, U.S. Pat. No. 5,179,404, EP-A-559,025, U.S. Pat. No. 5,270,762, EP-A-559,026, WO 92/10790, WO 92/17819, WO 93/04404, WO 92/17370, WO 91/19226, WO 91/12567, WO 92/07302, WO 93/00612, WO 92/07301, WO 92/09932 and U.S. Pat. No. 5,436,118.
The following Examples are included for a better understanding of the invention.

EXAMPLE 1
Some developer solutions were prepared to compare the effects with and without Zn.sup.2+ ion. Zn.sup.2+ is not soluble in phosphate solution at pH 11.4 and so an additional complexing agent was added to maintain it in solution. Diethylenetriaminepentaacetic acid (DTPA) is used to protect against Mn.sup.2+ catalyzed decomposition of the RX developer and DTPA is a good sequestrant for Zn.sup.2+. In view of this, it was used equimolar with the Zn.sup.2+ ion since it forms a 1:1 complex. There was an excess of DTPA equal to the original level used to protect against Mn.sup.2+ ion. The total Zn.sup.2+ level was equimolar with HAS level. It is thought that hydroxylamine will form a mixed complex such as Zn/DTPA/HAS in equilibrium with hydroxylamine sulfate in solution. The developers are shown in Table 1.
TABLE 1______________________________________Developer-amplifier Composition CompositionComponent Dev 1 Dev 2 Dev 3______________________________________AC5 0.6 g/l -- -->DTPA 0.81 g/l -- -->K.sub.2 HPO.sub.4.3H.sub.2 O 40 g/l -- -->KBr 1 mg/l -- -->KCl 0.5 g/l -- -->CDS 0.3 g/l -- -->HAS 1.0 g/l -- -->KOH(50%) 10 ml/l -- -->CD3 4.5 g/l -- -->TWEEN 80 0.8 g/l -- -->Dodecylamine 0.1 g/l -- -->H.sub.2 O.sub.2 (30%) 2.0 ml/l -- -->pH 11.4 -- -->ZnSO.sub.4.7H.sub.2 O 0 3.45 g/l 0DTPA 0 4.72 g/l 4.72 g/l______________________________________
AC5 is a 60% solution of 1-hydroxyethylidene-1,1-diphosphonic acid, DTPA is a 41% solution of the penta sodium salt of diethylenetriaminepentaacetic acid, CDS is catechol disulfonate, TWEEN 80 is a Trade Mark of Atlas Chemical Industries Inc. and is a non ionic surfactant. The Zn and DTPA were equimolar at 1.2.times.10.sup.-2 m so that all the excess DTPA is used to complex the Zn. These developers were monitored over a period of days with sensitometric strips with photographic silver halide color paper having a total silver coating weight of 62 mg/m.sup.2. The complete process cycle was as follows:
Dev/amp 45 seconds
Fix 45 seconds
Wash 2 minutes
Dry air
The Fixer was:
Glacial acetic acid 20 ml/l
NaOH solid 2 g/l
Sodium sulfite 50 g/l
Sodium thiosulfate 20 g/l
pH 6.0
The results of these standing tests in terms of neutral Dmax are shown in Table 2 below.
TABLE 2______________________________________Standing Tests (Dmax .times. 100)Age Dev 1 Dev2 Dev 3(hrs) R G B R G B R G B______________________________________0 225 237 226 241 230 218 207 213 21824 225 247 220 223 226 215 101 115 11048 242 242 222 221 221 208 75 74 76120 243 240 202 247 229 203 63 64 72162 264 232 204 255 232 205209 93 97 105 176 165 167282 63 66 75 62 64 75______________________________________
It can be seen that Dev 2 maintains Dmax better than Dev 1; for example, the loss in density up to 209 hours is 132(R), 140(G) and 121(B) without Zn and 65(R), 65(G) and 51(B) with Zn. Dev 3 that contains the extra DTPA but no Zn, is now considerably less stable than either Dev 1 or Dev 2. Thus, it is clear that Zn not only prevents the extra DTPA from causing decomposition but the combination is more stable than the control (Dev 1).
EXAMPLE 2
A procedure similar to that in Example 1 was repeated using a different source of DTPA. In this case, it was a 40% solution of the penta sodium salt at 5.83 ml/l. In addition, the ZnSO.sub.4 /DTPA-Na.sub.5 was at 6.times.10.sup.-3 molar, which is equivalent to 1.72 g/l ZnSO.sub.4. Excess DTPA-Na.sub.5 at 2.0 ml/l equivalent to 0.81 g/l DTPA was used to maintain protection against Mn.sup.2+. The results are shown in Table 3, where Dev 5 contains the added Zn/DTPA-Na.sub.5 and Dev 4 is the same as Developer 1 but with the 40% solution as the DTPA source.
TABLE 3______________________________________Standing Tests (Dmax .times. 100)Age Dev 4 Dev 5(hrs) R G B R G B______________________________________0 267 255 244 265 260 24418 256 254 237 252 256 22647 248 244 222 268 249 22595 251 243 217 243 248 205163 260 244 205 255 231 198189 249 220 199 264 233 198213 171 159 165 214 202 187231 112 109 116 147 146 147______________________________________
Here the density changes over 231 hours are Dev 4, R 155, G 146 and B 128; Dev 5, R 108, G 114 and B 97 which again shows that Zn/DTPA reduces density loss. In this case the effect is smaller than in Example 1 probably because of the lower Zn level.
EXAMPLE 3
A procedure similar to that in Example 2 was performed using the same source of DTPA. The ZnSO.sub.4 /DTPA-Na.sub.5 was at 6.times.10.sup.-3 molar, and an additional excess of DTPA-Na.sub.5 equivalent to 0.81 g/l DTPA was used as in Example 2. Dev 6 is without the ZnSO.sub.4 /DTPA-Na.sub.5, Dev 7 is with ZnSO.sub.4 /DTPA-Na.sub.5, and Dev 8 is identical to 7 with an increased HAS level (+40%). All solutions were prepared with the same peroxide level used in the Dev solutions of Example 2. The temperature of the solutions was maintained at 37.degree. C.
Here the initial rate of dye formation in a single red-sensitized layer was used as a measure of the developer activity, rather than sensitometry. Initial rates are more sensitive to activity change than sensitometric measures. The results are shown in Table 4.
TABLE 4______________________________________Standing Tests (s.sup.-1)Age Dev 6 Dev 7 Dev 8(hrs) R R R______________________________________1 0.076 0.072 0.05817 0.072 0.072 0.05324 0.088 0.080 0.05341 0.072 0.064 0.06447 0.088 0.080 0.06465 0.088 0.064 0.05872 0.064 0.064 0.06489 0.019 0.041 0.04896 0.015 0.017 0.039______________________________________
The losses in activity after 89 hours are Dev 6 0.057 s.sup.-1, Dev 7 0.031 s.sup.-1, and Dev 8 0.010 s.sup.-1. Dev 6 collapses completely beyond 90 hours, while the solutions containing ZnSO.sub.4 /DTPA-Na.sub.5 show much smaller changes in activity and longer overall lifetimes. The lower initial activity exhibited by Dev 8 is caused by the increased amount of HAS.
EXAMPLE 4
TABLE 5______________________________________Developer-amplifier Composition CompositionComponent Dev 9 Dev 10 Dev 11______________________________________AC5 0.6 g/l -- -->DTPA 0.81 g/l -- -->K.sub.2 HPO.sub.4.3H.sub.2 O 40 g/l -- -->KBr 1 mg/l -- -->KCl 0.5 g/l -- -->CDS 0.3 g/l -- -->HAS 1.5 g/l 1.5 g/l 1.5 g/lKOH(50%) 10 ml/l -- -->CD3 4.5 g/l -- -->TWEEN 80 0.8 g/l -- -->Dodecylamine 0.1 g/l -- -->H.sub.2 O.sub.2 (30%) 2.0 ml/l 3.0 ml/l 3.0 ml/lpH 11.4 -- -->ZnSO.sub.4.7H.sub.2 O 3.45 g/l 3.45 g/l 0DTPA 4.72 g/l 4.72 g/l 0______________________________________
These developer-amplifiers were made up with increased HAS and, apart from this change, Dev 9 is the same as Dev 2 in Table 1. The other two developers had increased peroxide level to compensate for the loss of initial activity caused by increased HAS. Dev 10 is with Zn/DTPA and Dev 11 is without Zn/DTPA. The standing tests were carried out as in the first example. The results are shown in Table 6.
TABLE 6______________________________________Standing Tests (Dmax .times. 100)Age Dev 9 Dev 10 Dev 11(hrs) R G B R G B R G B______________________________________0 153 180 165 267 261 245 253 258 24224 147 163 157 248 239 221 260 251 23048 144 170 155 231 245 208 250 245 220120 167 175 166 240 235 178 276 249 194168 192 191 176 265 233 180 273 241 178192 206 208 177 263 237 186 243 209 172216 205 190 174 202 173 160 128 126 127280 66 69 76 60 64 73 60 62 73______________________________________
The low starting densities of Dev 9 are compensated for by the increased peroxide in Dev 10 and the overall lifetime is about the same for these two developers. The overall lifetime with increased HAS (1.5 g/l compared with 1.0 g/l) is greater; compare Dev 11 with Dev 1, but the improvement with Zn is still maintained; compare Dev 10 (with Zn) to Dev 11 (without Zn). Here the density loss up to 216 hours is Dev 11, R 125, G 132 and B 115; and Dev 10, R 65, G 88 and B 85. The density loss in the red is halved in the presence of Zn.
EXAMPLE 5
It is the purpose of this example to show that the presence of a diphosphonic acid is not necessary for the present invention.
In U.S. Pat. No. 4,330,616, Kurematsu et al show a developer with a diphosphonic acid and metal ions, such as zinc and magnesium, that does not have precipitates and also has improved stability of hydroxylamine and color developing agent. In our previous examples a diphosphonic acid is present at 0.6 g/l of a 60% aqueous solution of 1-hydroxyethylidene-1,1-diphosphonic acid. This is a level used in current commercial non-RX developers. It is present as an anti-calcium agent and is also useful to prevent the catalytic properties of heavy metal ions such as iron ions in decomposing developer solutions. It is present for the same reasons in our RX developer-amplifier formulation. Some developer compositions are shown below which do not contain a diphosphonic acid but still show the improved stability in the presence of zinc ions.
TABLE 7______________________________________Developer Composition CompositionComponent Dev 12 Dev 13 Dev 14______________________________________DTPA 0.81 g/l -- -->K.sub.2 HPO.sub.4.3H.sub.2 O 40 g/l -- -->KBr 1 mg/l -- -->KCl 0.5 g/l -- -->CDS 0.3 g/l -- -->HAS 1.0 g/l -- -->KOH(50%) 10 ml/l -- -->CD3 4.5 g/l -- -->TWEEN 80 0.8 g/l -- -->Dodecylamine 0.1 g/l -- -->H.sub.2 O.sub.2 (30%) 2.0 ml/l -- -->pH 11.4 -- -->ZnSO.sub.4.7H.sub.2 O 3.45 g/l 0 0MgSO.sub.4 7H.sub.2 O 0 2.96 g/l 0DTPA 4.72 g/l 4.72 g/l 4.72 g/lTime 45 seconds -- -->Temperature 35.degree. C. -- -->______________________________________
These developers were kept over a period of time as in previous examples and monitored by means of control strips at intervals. The Dmax values as a function of developer age are shown in Table 8 below.
TABLE 8______________________________________The effect of zinc and magnesium in the absence of diphosphonic acidStanding Tests (Dmax .times. 100)Age Dev 12 Dev 13 Dev 14(hrs) R G B R G B R G B______________________________________0 252 230 228 272 245 235 263 254 23421 241 220 215 219 216 208 86 85 8347 229 216 212 178 179 176 64 65 6772 242 221 215 165 153 165 61 62 6796 239 225 212 168 147 155 60 61 67168 265 233 213 134 122 136 63 63 70192 243 218 198 124 110 131 60 62 67208 154 138 156 108 104 122 61 63 67232 84 81 94 81 80 99 68 68 78______________________________________
It can be seen from these data that zinc and magnesium ions improve the stability of the RX developer even though a diphosphonic acid is absent. Developers 12 and 13 are more stable than developer 14 that is the same but does not contain added zinc or magnesium ions.
EXAMPLE 6
The effect of magnesium ions with a diphosphonic acid
This example shows that the improvement in stability for a conventional developer shown by Kurematsu et al in the presence of a diphosphonic acid and metal ions, such as magnesium, does not occur with RX developers of the current formula.
TABLE 9______________________________________Developer Composition CompositionComponent Dev 15 Dev 16 Dev 17______________________________________AC5 0.6 g/l 5.1 g/l 5.1 g/lDTPA 0.81 g/l -- -->K.sub.2 HPO.sub.4.3H.sub.2 O 40 g/l -- -->KBr 1.5 mg/l -- -->KCl 0.45 g/l -- -->CDS 0.3 g/l -- -->HAS 1.2 g/l -- -->KOH(50%) 10 ml/l -- -->CD3 5.5 g/l -- -->TWEEN 80 0.3 g/l -- -->Dodecylamine 0.1 g/l -- -->H2O2(30%) 2.5 ml/l -- -->pH 11.5 -- -->MgSO.sub.4 7H.sub.2 O 0 0 3.59 g/lTime 45 seconds______________________________________
The results for standing tests on these developers are shown in table 10 below.
TABLE 10______________________________________The effect of magnesium and diphosphonic acidStanding Tests (Dmax .times. 100)Age Dev 15 Dev 16 Dev 17(hrs) R G B R G B R G B______________________________________0 286 258 259 280 263 257 290 263 26022 274 253 243 289 267 251 281 264 25346 265 252 243 277 271 260 285 253 250112 276 251 239 287 253 239 283 261 245160 244 216 214 270 243 228 206 189 199184 133 126 142 195 175 185 91 91 105______________________________________
Developer 15 is with our standard level of the diphosphonic acid and Developer 16 has the increased level used by Kurematsu et al but without any added magnesium ions whereas Developer 17 has the increased level of the diphosphonic acid with equimolar magnesium ions. It can be seen that although increased diphosphonic acid improves developer lifetime; magnesium ions lower developer lifetime.
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.

Number	Name	Date	Kind
4330616	Kurematsu et al.	May 1982
4880725	Hirai et al.	Nov 1989

Number	Date	Country
0 600 564 A	Jun 1994	EPX
49020537B	Feb 1974	JPX

Photographic developer-amplifier composition

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