CA2073765A1

CA2073765A1 - Photographic bleaching solution and use thereof in photographic color processing

Info

Publication number: CA2073765A1
Application number: CA002073765A
Authority: CA
Inventors: David G. Foster; Keith H. Stephen
Original assignee: Individual
Current assignee: Eastman Kodak Co
Priority date: 1990-01-24
Filing date: 1991-01-18
Publication date: 1991-07-25
Also published as: JPH0693108B2; JPH05503791A; EP0514457A1; WO1991011753A1; EP0514457B1; DE69100446T2; DE69100446D1

Abstract

An environmentally advantageous photographic bleaching solution for use in the color processing of photographic elements comprises (1) as a bleaching agent, a potassium salt of a ferric complex of an aminopolycarboxylic acid, (2) as an agent which functions to convert silver to silver halide, a potassium halide, and (3) as an agent which functions to inhibit bleach induced dye formation, a water-soluble aliphatic carboxylic acid. The bleaching solution is especially useful in the processing of photographic elements containing a low pKa, high-activity, yellow-dye-forming coupler in that it serves to effectively avoid the undesirable increase in blue Dmin that can occur in such elements as a result of bleach induced dye formation.

Description

WOs1/117~3 PCT/US91/00377 7~7~
- PHOT~RAPHIC BLEAC~ING SOLUTION AND USE
THEREOF IN PHOTOGRAPHIC ~OLOR PRoc~ssING
FIELD OF THE INV~NTION
. This invention relates in general to photography and in particular to a novel bleaching .; solution for the bleaching of photographic elements.
More specifically, this invention relate~ to an environmentally advantageous photographic bleaching solution which is useful in the coior processing of lO photographic elements. . :
BACKGROUND OF THE INVENTION -~
In the production of color photographic images, it is necessary to remove the silver image . :~:
which is formed coincident with the dye image. This . 15 can be done by oxidizing the silver by means of a suitable oxidiæing agent, commonly referred to as a bleaching agent, in the presence of halide ion, followed b~ dissolving the silver halide so formed in a silver halide solvent, commonly referred to as a ZO fixing agent. Alternatively, the bleaching agent and ~ .
fixing agent can be combined in a bleach-fixing solution and the silver removed in one step by use of such solution.
' A wide variety of bleaching agents are known for use in photographic processing, for example, ferricyanide bleaching agents, persulfate bleaching ~.
agents, dichromate bleaching agents, permanganate bleaching agents, ferric chloride, and water-soluble :-quinones. : : -i It is particularly well known to ulse a ferric~
complex of an aminopolycarboxylic. acid as a bleaching . agent in photographic color proCeiYSing. Such : . .
~ compIexes are used in.both bleaching compo~itions and ~.
.. . bleach-fixing compositions. A very~~làrge number.of~
different compounds of the aminopolycarboxylic;acid: `
. class are disclosed;in the prior-art as:being useful :

: -photographic bleaching agents. However, th~ usual commercial practice is to use an ammonium or alkali metal salt of a ferric complex of ethylenediarnine-.. 5 tetraacetic acid (EDTA) or of a ferric complex of propylenediaminetetraacetic acid (PDTA). ~ ~
Among the numerous patents describing the use : ::
of ferric complexes of aminopolycarboxylic acids in bleaching and~or bleach-fixing baths are United States.
patents 3,241,966, 3,615,508 and 3,767,401 and British patents 1,365,453, 1,392,163 and 1,39g,357. -~
Other patents of interest are U.S. patent 4,242,442 which describes a photographic bleaching bath containing a ferric ion complex, a bromate and a water- u ~
15 soluble chloride and optionally containing an aliphatic ~ ::
carboxylic acid, an aliphatic phosphonic acid or an aliphatic phosphonocarboxylic acid; U.S. patent 4,268,618 which describes a photographic bleaching bath containing an organic acid iron (III) complex salt, an 20 alkali metal or ammonium salt of bromic acid, a water- `:.
.~ - soluble halogenide, a compound of the formula :
X- ~R')~n COOM or the formula O . :
. 25 //
R2 - C ~ ., i ~NH ,, ,~", R3 - C=O
.~-.
and a compound of the formula .
R4 - NH ~ :
~ 35 \ . :~
.. `~ ,,. / ;
,, -2a-and British patent 1,319,721 which describes a photographic bleaching bath which contains a complex ferric salt and an aliphatic dicarboxylic acid.
The prior art indicates that ferric complexes of an aminopolycarboxylic acid can be employed in photographic bleaching solutions in the form of ammonium or alkali metal salts such as sodium or potassium salts. However, the use of ammonium salts is undesirable from an environmental standpoint and the use of sodium salts provides an undesirably sluggish ! bleaching action. Thus, it is especially advantageous to utilize photographic bleaching solutions which -compri e a potassium salt of a ferric complex of an aminopolycarboxylic acid as the bleaching agent, since these solutions are both fast-acting and environmentally acceptable.
A serious problem is encountered, however, in ~`
- utilizing a photographic bleaching solution containing a potassium salt of a ferric complex of an aminopolycarboxylic acid. In particular, when such a bleaching solution is used to bleach a photographic ;
element containing a low pKa, high-activity, yellow-dye-forming coupler, a significant and highly undesirable increase in blue Dmin results from bleach induced dye formation. The term ~bleach induced dye fo~mation~ refers to reaction between the coupler and oxidi~ed developing agent that takes place in the bleaching solution and leads to the generation of image dye and thus to stain formation. Formation o~ yellow image dye in this manner and resulting increase in blue Dmin is particuIarly acute with the low pKa, high-activity, yellow-dye-forming couplers that are used in many photographic films. The problem also occurs with the other image layers, but to a much lesser extent.
It is toward the objective of providing an improved photographic bleaching solution that is fast-acting, and environmentally acceptable -- and sufficiently resistant to the phenomenon of bleach ;~
10 induced dye formation that it is highly useful with~ ~ -photographic elements containing a low pKa, high activity, yellow-dye-forming coupler -- that the present invention is directed.

In accordance with this in~ention, an environmentally advantageous photographic bleaching solution for use in the color processing of photographic elements is an aqueous acidic solution which is substantially free of fixing agents, bromates and ammonium salts and comprises (1) as a bleaching agent, a potassium salt of a ferric complex of an aminpolycarboxylic acid, (2) a3 an agent which functions to convert silver to silver halide, a potassium halide, and (3) a sufficient amount of a water-soluble aliphatic carboxylic acid to inhibit bleach induced dye formation. ;
The pxesent invention is based, in major part, ,on the unexpected discovery that water-soluble aliphatic carboxylic acids, when used in sufficient concentration, will effectively eliminate the problem of bleach induced dye formation and thus avoid unwanted staining that occurs in photographic processing. While water-soluble aliphatic carboyxlic acids have been commonly used in photographic bleach solutions heretofore, they have usually been used to adjust ~ ' ~

WO 91/11753 PCl/IJS91/00377 .. . , .--`.
- 20 ~3 765`'i 4_ `
p~ and use for this purpose does not require the high concentration of acid that ls optimally used to effectively ellminate the problem of bleach induced dye formation.
DESCRIPTION OF THE PR~F~RR~D EMBODIMENT~
--. As indicated above, the essential components of the novel bleaching solution of this invention are ~ a potassium ~alt of a ferric complex of an aminopolycarboxylic acid, a potassium halide, and a 10 water-soluble aliphatic carboxylic acid.
The potassium salt of the ferric complex of :
an aminopolycarboxyl`~c acid can be employed in any effective amount~,' with useful amounts ~ypically being at least 0.1 moles per liter of bleaching solution, .
; 15 and preferably at least 0.5 moles per liter. Examples ~ of the many useful ~erric complexes include complexes .~.
of~
nitrilotriacetic acid, . : .
ethylenediamine tetraacetic acid~
propylenediamine tetraacetic acid, , diethylenetriamine pentaacetic acid, :, ortho-diamine cyclohexane tetraacetic acid, . ethylene glycol bis(aminoethyl ether) ~ `:
! tetraacetic acid, ` :
diaminopropanol tetraacetic acid, ; .
N-(2-hydroxyethyl)ethylenediamine triacetic :
acid, ethyliminodipropionic acid, iminodiacetic acid, methyliminodiacetic acid, ethyliminodiacetic.acid, and the.like. . . . :...... . :
. In some instances the use of a.mixture-of .
' 1 bleaching agents is preferred over the.use of ;., 35 indiYidual bleaching agents,.:since.a mixture can .;.
`. provide a desired level of bleaching power .~

.
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intermediate that of the individual bleaching agents of which it is composed. Examples of particularly useful mixtures include a mixture of the ferric complex of ethylenediaminetetraacetic acid and the ferric complex ; of propylenediaminetetraacetic acid, a mixture of the ferric complex of ethylenediaminetetraacetic acid and the ferric complex of methyliminodiacetic acid, and a mixture of the ferric complex of iminodiacetic acid and the ferric complex of methyliminodiacetic acid.
Potassium halides useful in the bleaching solutions of this invention include potassium chloride and potassium bromide. The potassium halide can be employed in any effective amount, with useful amounts typically being at least 0.1 moles per liter, and preferably at least 0.25 moles per liter. -Water-soluble aliphatic carboxylic acid~
useful in the bleaching solutions of this invention include all of the many members of this well-known class of acids, such as, for example~
acetic acid citric acid propionic acid hydroxyacetic acid butyric acid malonic acid succinic acid, and the like.
The water-soluble aliphatic carboxylic acid can be employed in any effective amount, with useful amounts preferably being at least 0.7 moles per liter of bleaching solution, and most preferably at least 0.9 moles per liter. ',, !, ii5 The bleaching solutions of this invention are aqueous acidic solutions preferably having a pH in the range of from about 4 to about 6.8 and most preferably in the range-of from 4.5 to 5.5. ,~

24. 02 92 ~ 3STlTU~ T

The bleaching solutions of this invention can contain other addenda known in the art to be useful in bleaching compositions, such as sequestering agents, sulf ite9, and non-chelated salts of aminopolycarboxylic acids.
The compositions of this invention are bleachin~ solutions and not bleach-fixing solutions, and thus they are substantially free of fixing agents.
The term ~bleaching solution~ as used herein is intended to exclude bleach-fixing solutions. The bleaching solutions of this invention are also substantially free of bromates such as are employed in U.S. patents 4,242,442 and 4,268,618.
A particularly useful sequestering agent which can be included in the bleaching solution of this invention to avoid the unwanted precipitation of salts is 1,3-diamino-2-propanol tetraacetic acid. ~ -The bleaching solutions of this invention are especially useful in the color processing of ~- photographic elements, including photographic films utilized in negative-positive processes or in color reversal processes. Useful processes include a three-step process -- comprising the steps of color developing, bleaching and fixing -- and a six step process -- in which the film is processed in a fixst developer, a reversal bath, a color developer, a conditioning bath, a bleach bath and a fixing bath.
The processing i9 typically carried out using a color 30 developing solution which contains a primary aromatic ;~ -amino color developing agent. These color developing agents are well known and widely used in a variety of color photographic processes. They include aminophenols and p-phenylenediamines.

' " ' , Examples o~ aminophenol developing agents include o-aminophenol, p-aminophenol, 5-amino-2- `
hydroxytoluene, 2-amino-3-hydroxytoluene, 2-hydroxy-3-S amino-1,4-dimethylbenzene, and the like.

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Wo~1/11753 PCT/~S91/00377 207:376~
Particularly useful primary aromatic amino color developing agentg are the p-phenylenediamines and especially the N-N-dialkyl-p-phenylenediamines ~n which the alkyl groups or the aromatic nucleus can be substituted or unsubstituted. Examples of useful p-phenylenediamine color developing agents include:
N-N-diethyl-p-phenylenediaminemonohydro-chloride, 4-N,N-diethyl-2-methylphenylenediamine monohydrochloride, 4-(N-ethyl-N-2-methanesulfonylaminoethyl)-2-methylphenylenediamine sesquisulfate ' monohydrate, 4-(N-ethyl-N-2-hydroxyethyl)-2-methyl-phenylenediamine sulfate, -4-N,N-diethyl-2,2'-methanesulfonylamino-ethylphenylenediamine hydrochloride, and the like.
In addition to the primary aromatic amino color developing agent, color developing solutions typically contain a variety of other agents such as alkalies to control p~, bromides, iodides, benzyl alcohol, anti-oxidants, anti-foggants, solubilizing agents, brightening agents, and so forth.
2S Photographic color developing compositions are employed in the form of aquèous alkaline working solutions having a p~ of above 7 and most typicaIly in the range of from about 9 to about 13. To provide the necessary pH, they'contain one or more of the well 30 known and widely used p~ buffering agents, such as the ' ;
alkali metal carbonates or phosphates. Potassium carbonatè is especially useful as a pH buffering`agent.
: ' ~'-''In both the negative-positive process and the color~reversa~'process, the fixing bath converts alL
silver halide into soluble silver complexes which~
diffuse out of the emulsion layers. Fixing bath `` ! :

W~91/11753 . PCTIUS91/00377 ~ .
...... ...
207-3`765- -8-retained within the layers of the photographic element is removed in a subsequent water washing step.
Thiosulfates, including ammonium thiosulfate and alkali metal thiosulfates such as sodium thiosulfate and potassium thiosulfate, are particularly useful as fixing agents. Other components of the fixing bath include preservatives and sequestering agents.
A commercially important process.intended for use with color negative photographic elements which contain the couplerq in the silver halide emulsion layers,.~or ïn layers contiguous thereto, utilizes, in order, ~he following proces~ing baths: color developer, wash (optional), bleach, fix, wash and : -stabilizer. In accordance with this invention,.such a :
process is carried out using the novel bleaching solution described hereinabove.
A commercially important process intended for use with color reversal photographic elements which contain the couplers in the silver halide emulsion :.
20 layers, or in layers contiguouq thereto, utilizes, in .~ ~
order, the following processing baths: first : :
developer, wash, reversal bath, color developer, ~.. .
bleach, fix, wash and stabilizer. In this process, the first developer reduces the exposed silver halide to metallic 9ilver; the reversal bath nucleatei the silver halide that remains after first development, the color developer converts the nucleated silver halide to metallic silver and forms the dye images, the bleach converts all metallic silver to silver 30 halide, the fix converts the silver halide into .
soluble silver complexes.that are washed from the element, and the stabilizing bath improve~ image dye . :
stability. In accordance with this invention, such a :~
process is carried out.:.using the-novel bleaching .~. , .
solution described hereinabove. ~
- ; ' ;':':' . ~ ,, .

!; ~ . . ~, " ' , . , ' wo91/t17~3 PCT/US9l/00377 :2073~65 The novel bleaching solutions o~ the present invention can be utilized with any of a wide variety of photographic elements. For a detailed description of useful photographic elements and methods for their manufacture, reference can be made to Research Disclosure, Item 17643, Vol. 176, December, 1978, published by Industrial Opportunities Ltd., Homewell, Havant Xa~pshire, P09 lEF, United Kingdom.
The photosensitive layers present in the photographic elements processed with the novel bleaching solutions of this invention can contain any of the conventional silver halides as the photo-sensitive material, for example, silver chloride, silver bromide, silver bromoiodide, silver chlorobromide, silver chloroiodide, silver chloro-bromoiodide, and mixtures thereof. These layers can contain conventional addenda and be coated on any of the photographic supports, such as, for example, cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polycarbonate film, polystyrene film, polyethylene terephthalate film, polymer-coated paper, and the like.
It i9 generally convenient for the ferric complèx of the aminopolycarboxylic acid to be formed in sitù in the bleaching solution by reaction of a ferric salt, such as ferric sulfate or ferric nitrate, with an aminopolycarboxylic acid or mixture of aminopolycarboxylic acids.
In the present invention, potassium hydroxide is advantageously incorporated in the bleaching so~ution for the purpose of providing the desired potassium ions and maintaining the p~ within the desired range. - .
~ ~ The bleaching solution of this invention is free, F at least~substantlally free..of.ammonium salts,;

~ .
. . .. , .. . . , . . ... .... , . , .. ~

Wo91/11753 PCT/US91/00377 ` 20a3~ O-as the presence of ammonium ions in a photographic bleaching solution is environmentally disadvantageous.
It is especially desiràble that the bleaching solution of this invention have a total iron content of less than lO grams per liter. For environmental reasons, it is preferred to keep the total iron content of photographic bleaching solutions as low as possible.
The problem of bleach induced dye formation is more severe with a bleaching solution containing potassium salts than with an otherwise comparable bleachi~g solution containing ammonium salts.
Applicants are uncertain of the theoretical explanation for this, but it is believed that ammonium ions may act -~
as an acid in the bleaching solution while potassiu.m ~ -ions do not. The acidity imparted by the ammonium ions is believed to reduce the tendency for bleach induced dye formation to occur. ;~ :
As indicated hereinabove, a very serious problem exists in processing photographic films that contain low pKa, high-activity, yellow-dye-forming couplers since such films tend to undergo a highly undesirable increase in blue Dmin resulting from bleach induced dye formation. Acid strengths in water solutions are defined in terms of the equilibrium constant, Ka, for the reaction:
.. ~ .
~A + ~2 ~ ~30t + A ~
.
pKa is defined by the equation:
pKa - - LOG Ka where ~ ;
CH30~]~A-]
Ka = .
The greater the value of Ka, and sma11er the value of pKa, the stronger-:the-acid. Couplers having 35 .a low-pKa tend-to be completely~:ionized in^water.-~The activity of a coupler refers to its ability to form : ~
: .

wo~ 7s3 Pcr/us9l/oo377 2073i6~
dye by reaction with oxidized developing agent. ~igh activity couplers tend to produce very high ~max values and are especially beneficial for this reason.
Low pKa, high-activity, yellow-dye-forming coupler~ are well known in the prior art and are described, for example, n U.S. patents 4,352,873, 4,476,219 and 4,522,916.
The invention is further illustrated by the following examples of its practice.
An aqueous acidic photographic bleaching solution was prepared in accordance with the following formulation:
1,3-propylenediaminetetra-acetic acid - 37.4 grams (0.122 moles) 15 Potassium hydroxide ~45% solution~ - 70 milliliters Acetic acid* - 50 milliliters 1,3-diamino-2-propanol `
tetraacetic acid - 0.8 grams 20 Potassium bromide - 30 grams (0.25 moles) Fe(N03)3-9~20 44.85 grams in 100 milliliters of water Water to one liter. pH = 4.75 ~5 * l mole of acetic acid corresponds to 60 grams or 57 milliliters The above-described bleaching solution was employed in the processing of a photographic negative-positive color film utilizing a conventional process comprising the steps of color developing, bleaching, fixing, washing and stabilizing. The film contained a low pKa, high-activity yellow-dye-forming coupler of the formula:

. .:

wosl/117s3 PCT/US91tO0377 20~3~

Cl CH30~ -COfHCONH-~
O~N~O C2C12~25 7 t Contact with the bleaching solution was carried out at 33C for 3 minutes. ~ ~ -The content of acetic acid in the bleaching solution was varied as indicated below, while all ~:
other factors were held constant, and for each 15 sample of bleaching solution tested the blue Dmin -~ ~
was measured. Adju~tment of pH of the bleach ~ ~.
solution, necessitated by change in the acetic acid : :
content, was accomplished by addition of sulfuric ~
acid or potassium carbonate to give in each case a ;:: :
P~ f 4'75' : :
Results obtained were as follows~
. .
Concentration of Acetic Acid . ;
Blue Dmin ~ -25 ~iLlill~ Moles 0.175 1.15 0.350 0.86 . .. ~;
0.700 0.80 ;
0.875 0.80 . .~.
1.05 0 ?9 `
1.40 0.79 As indicated by the above data, the blue :~
Dmin declines sharply as the acetic acid concentration is increased to a level of about 0.7 .' ' ~ ~ ~ ` ' ' '` ' wo91/11753 PCT/US91/0~377 20737~
-13- ;
moles per liter of bleaching solution and then levels off. This results from the fact that, over the effective range, increasing the acetic acid level causes a corresponding decrease in bleach induced dye formation. Thus, amounts o acetic acid ; of at least 0.7 moles per liter are preferred and, to provide added assurance of maintaining optimum conditions,.amounts of at least 0.9 moles per liter are particularly preferred. The ability of water-soluble aliphatic.carboxylic acids, such as acetic acid, to provide this improved result is clearly unexpected on the basis of what was known heretofore in the prior art.
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Claims

WE CLAIM:

1. An aqueous acidic photographic bleaching solution which comprises a potassium salt of a ferric complex of an aminopolycarboxylic acid, a potassium halide and a water-soluble aliphatic carboxylic acid and is substantially free of fixing agents, bromates and ammonium salts; characterized in that said water-soluble aliphatic carboxylic acid is present in said bleaching solution in an amount of at least 0.7 moles per liter.

2. A bleaching solution as claimed in claim 1 wherein the pH is in the range of from about 4 to about 6.8, said potassium salt of a ferric complex of an aminopolycarboxylic acid is present in an amount of at least 0.1 moles per liter of bleaching solution, and said potassium halide is present in an amount of at least 0.25 moles per liter of bleaching solution.

3. A bleaching solution as claimed in claims 1 or 2 wherein said ferric complex is a ferric complex of ethylenediaminetetraacetic acid.

4. A bleaching solution as claimed in claims 1 or 2 wherein said ferric complex is a ferric complex of propylenediaminetetraacetic acid.

5. A bleaching solution as claimed in claims 1 or 2 wherein said solution comprises ferric complexes of both ethylenediaminetetraacetic acid and propylenediaminetetraacetic acid.

6. A bleaching solution as claimed in any of claims 1 to 5 wherein said potassium halide is potassium bromide.

7. A bleaching solution as claimed in any of claims 1 to 6 wherein said water-soluble aliphatic carboxylic acid is acetic acid.