US3676136A

US3676136A - Photographic stabilizer compositions

Info

Publication number: US3676136A
Application number: US48547A
Authority: US
Inventors: Rowland G Mowrey
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1970-06-22
Filing date: 1970-06-22
Publication date: 1972-07-11
Anticipated expiration: 1989-07-11
Also published as: FR2099781A5; GB1350296A; CA955788A

Abstract

AQUEOUS STABILIZER COMPOSITION COMPRISING (1) A WATER-SOLUBLE ADDITION COMPLEX OF AN ALKALI METAL BISULFITE AND AN ALDEHYDE THAT PREFERABLY CONTAINS FROM ONE TO SIX CARBON ATOMS AND FROM ONE TO THREE CARBONYL GROUPS WITH AT LEAST ONE OF THE CARBONYL GROUPS BEING PART OF AN ALDEHYDE GROUP IN THE CONCENTRATION RANGE OF FROM ABOUT 0.5 G./L. TO ABOUT 100 G./L. AND EITHER, (2) A SUFFICIENT AMOUNT OF AN ALKALI METAL HYDROXIDE OR AN ACID TO ADJUST THE PH OF THE COMPRISING IN THE RANGE OF FROM 3 TO 7, OR (3) A BUFFER COMPRISING (A) AN ACID, SUCH AS, SULFURIC, NITRIC, PHOSPHORIC, BORIC, HYDROCHLORIC ACIDS AND ORGANIC CARBOXYLIC ACIDS IN THE CONCENTRATION RANGE OF FROM ABOUT 0.5 G./L TO ABOUT 25 G./L AND (B) A SUFFICIENT AMOUNT OF AN ALKALI METAL HYDROXIDE TO BUFFER THE COMPOSITION AT A PH IN THE RANGE OF FROM 3 TO 7, ARE ADVANTAGEOUSLY USED AS A FINAL RINSE IN COLOR PHOTOGRAPHIC PROCESS TO STABILIZE THE DYE IMAGES EITHER IN THE PRESENCE OR ABSENCE OR RESIDUAL COLOR-FORMING COUPLER AGAINST THE STAINING AND/OR FADING EFFECTS OF EXPOSURE TO HIGH TEMPERATURES, HIGH HUMIDITY AND PROLONGE EXPOSURE TO LIGHT.

Description

United States Patent 3,676,136 PHGTOGRAPHIC STABILIZER COMPOSITIONS Rowland G. Mowrey, Rochester, N.Y., assignor to Eastman Kodak Company, Rochester, N.Y. No Drawing. Filed June 22, 1970, Ser. No. 48,547 Int. Cl. G03c 7/00 US. (Ii. 96-56 21 Claims AESTRACT OF THE DISCLOSURE Aqueous stabilizer compositions comprising 1) a Water-soluble addition complex of an alkali metal bisulfite and an aldehyde that preferably contains from one to six carbon atoms and from one to three carbonyl groups with at least one of the carbonyl groups being part of an aldehyde group in the concentration range of from about 0.5 g./l. to about 100 g./l. and either, (2) a sufficient amount of an alkali metal hydroxide or an acid to adjust the pH of the composition in the range of from 3 to 7, or (3) a buffer comprising (a) an acid, such as, sulfuric, nitric, phosphoric, boric, hydrochloric acids and organic carboxylic acids in the concentration range of from about 0.5 g./l. to about 2'5 g./l. and (b) a sufiicient amount of an alkali metal hydroxide to buffer the composition at a pH in the range of from 3 to 7, are advantageously used as a final rinse in color photographic processes to stabilize the dye images either in the presence or absence of residual color-forming coupler against the staining and/or fading effects of exposure to high temperatures, high humidity and prolonged exposure to light.

This invention is related to color photography, color photographic processing, photographic processing compositions and more particularly to photographic stabilization compositions and to the stabilization of color photographic images.

Multicolor, multilayer photographic elements are well known in the art of color photography. Usually, these photographic elements have three different selectively sensitized silver halide emulsion layers coated on one side of a single support. One emulsion layer is blue-sensitive, another green-sensitive and another red-sensitive. Although these layers can be arranged on a support in any order, they are most commonly arranged with the support coated in succession with the red-sensitized layer, the green-sensitized layer and the blue-sensitive layer (advantageously with a bleachable blue light-absorbing filter layer between the blue-sensitive layer and the greensen'sitized layer) or with the opposite arrangement and no filter layer. Colored photographic images are formed from latent images in the silver halide emulsion layers during color development by the coupling of oxidized aromatic primary amine color developing agent with couplers present either in the color developer solution or incorporated in the appropriate light-sensitive layers. Photographic elements containing incorporated couplers usually have a nondiifusible phenolic or naphthalic coupler that forms a nondilfusible cyan dye in the red-sensitized emulsion layer, a nondiifusible S-pyrazolone or 2-(a-cyanoacetyl)coumarone coupler that forms a nondiifusible magenta dye in the green-sensitized emulsion layer and a non-diffusible open-chain ketomethylene coupler that forms a nondiifusible yellow dye in the bluesensitive emulsion layer.

It is well known that the couplers and dyes used in color photographic systems are subject to degradation by heat, humidity and actinic radiation. Residual incorporated couplers in processed photographic elements generice ally turn yellow with such treatment, while dyes generally fade or change hue and fade. In medium-to-low density regions of color photographs, where excess coupler is present with the dye (in incorporated coupler systems), it is known that coupler and dye can react slowly with one another and thus degrade a color image.

It is known to use formaldehyde in the final rinse bath of a color process in order to react with the active methylene groups on residual color-forming couplers and thus prevent them from reacting with the image dyes.

US. Pat. 2,647,057 described the use in a color process of a final rinse containing an alkali, such as, borax, and sodium formaldehyde bisulfite to reduce fading and staining caused by exposure of the finished color photograph to high humidities and high temperatures. The pHs of the rinse solutions in this reference are 8.8 or higher.

Stabilizing baths are desired that not only reduce fading and staining from exposure to high humidities and high temperatures, but also reduce the dye image fading and hue shift produced by prolonged exposure to light. Stabilizing baths are also desired that will give this additional protection with shorter treatment times than is required by the prior art. Stabilizer baths are desired whose efiee tiveness does not change with concentration changes within the operating limits.

It is, therefore, an object of my invention to provide a novel stabilizer composition which is valuable as a final treatment bath in a color process to reduce dye image fading and hue shift caused in the finished color photograph by prolonged exposure to light, as well as to reduce the dye image fading and stains produced in the finished color photograph by exposure to high humidities and high temperatures.

It is a further object of my invention to provide a novel stabilizer composition which not only stabilizes the finished color photograph against the deleterious effects produced by exposure to light, high humidities and high temperatures, but gives this more comprehensive protection than is provided by the prior art, with a substantially shorter treatment time than the prior art requires.

It is a further object of my invention to provide a novel stabilizer composition which not only gives the broader protection than the prior art and in a shorter time than the prior art, but also provides a stabilizer Whose stabilizing effects do not vary with variations in stabilizer bath concentration within the operating limits.

It is still a further object of my invention to provide a novel stabilizer composition that is odorless and virtually non-toxic.

It is another object of my invention to provide a novel class of stabilizer which does not degrade the physical qualities of a finished color photograph.

It is another object of my invention to provide a novel process for stabilizing a finished color photograph against the deleterious effects of prolonged exposure to light, humidities and high temperatures.

Still other objects will become apparent from a consideration of the following specification and claims.

These and still other objects are accomplished according to my invention by providing and using my substantially odorless compositions for use in stabilizing a processed color photographic element, said composition com prising:

(1) At least one water-soluble addition complex of an alkali metal bisulfite and an aldehyde is advantageously used in aqueous solution having a pH in the range of from 3 to 7 and containing a total concentration of addition complex in the range of from about 0.5 g./l. to about g./l. with a particularly useful range being from about 1 g./l. to about 50 g./l.

A more preferred composition comprises:

(1) as defined above, and

(2) a suflicient amount of at least one of an alkali metal hydroxide and an acid to adjust the pH of the solution in the range of from 3 to 7.

An even more preferred composition comprises:

(1) as defined above,

(2) an acid in the concentration range of from about 0.5

g./l. to about 25 g./l., and

(3) a sufiicient amount of an alkali metal hydroxide (e.g., NaOH, KOH, LiOH, etc.) to buifer the solution at a pH in the range of from 3 to 7.

According to my invention, a dye image either in the presence or absence of excess reactants used to form the dye (i.e., color-forming coupler, etc.) is stabilized by contacting the dye image with my aqueous stabilizer solution having a pH in the range of from 3 to 7 and containing an addition complex of an alkali metal bisulfite and an aldehyde, and then drying the treated dye image in the presence of the stabilizer solution. My stabilizing process is advantageously used to stabilize the dye image, usually an indoaniline dye or an azomethine dye, regardless of the method used to form the dye image and regardless of the binder or carrier in which the dye image is formed.

The addition complexes of alkali metal bisulfite and aldehyde are advantageously made from any of the alkali metal bisulfites (e.g., sodium, potassium, lithium, etc.) and aldehydes that preferably contain from one to six carbon atoms and from one to three carbonyl groups with at least one of the carbonyl groups being part of an aldehyde group. Aldehydes used to advantage are included in those having the formulas:

Ito-H and (II) o o origami-1r wherein R is a member, such as, hydrogen, a lower alkyl group having from 1 to carbon atoms, e.g., lower alkyl (e.g., methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, n-am'yl, isoamyl, isopropyl, n-butyl, iso-butyl, tbutyl, n-amyl, isoamyl, t-amyl, etc.), hydroxy lower alkyl (e.g., hydroxyethyl, hydroxybutyl, hydroxyamyl, etc.), halogenated lower alkyl (e.g., chloroethyl, chlorobutyl, bromoethyl, fluoroethyl, etc.), lower alkoxy lower alkyl (e.g., methoxyethyl, ethoxyethyl, ethoxymethyl, etc.), lower alkyl carbonyl lower alkyl (e.g., acetonyl, methylcarbonylethyl, etc.), carboxy lower alkyl (e.g., carboxyethyl, carboxypropyl, carboxybutyl, etc.) and the furyl group, etc., and n represents an integer of from 1 to 5.

Acids used advantageously in my compositions include inorganic acids (such as, sulfuric acid, nitric acid, boric acid, hydrochloric acid, etc.) and organic carboxylic acid including those having the formula:

(III) R COOH wherein R represents a member such as hydrogen, a lower alkyl group having from 1 to 10 carbon atoms (e.g., methyl, ethyl, propyl, amyl, cyclohexyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, methoxyethyl, aminoethyl, N-methylaminoethyl, Z-methoxycarbonylethyl, 2-ethoxycarbonylethyl, sulfoethyl, sulfopropyl, sulfobutyl, carbamylethyl, carbamylpropyl, u-amino carbamylethyl, ahydroxybenzyl, benzyl, phenethyl, a-aminophenethyl, uamino-4-hydroxyphenethyl, etc.), a carbonyl group [e.g., an alkoxycarbonyl group (e.g., methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, etc.), an alkyl carbonyl group (e.g., methylcarbonyl, ethyl carbonyl, etc.)], a phenyl group (e.g., phenyl, ethylphenyl, tolyl, chlorophenyl, sulfophenyl, 4-hydroxyphen'yl, etc.), etc.; an organic carboxylic acid having the formula:

(IV) HOOCLCOOH wherein L represents a member, such as, a bond, an alkylene group having from 1 to 6 carbon atoms (e.g., methylene, ethylene, propylene, isopropylene, hexylene, hydroxyethylene, hydroxypropylene, dihydroxyethylene, dihydroxypropylene, methoxyethylene, ethoxyethylene, carboxylmethylene, carboxyethylene, carboxyh'ydroxymethyl, carboxymethoxyethyl, carboxyethoxyethyl, carboxybutoxypropyl, etc); a vinylene group (e.g. vinylene); a phenylene group (e.g., phenylene, chlorophenylene, methylphenylene, etc.); all organic carboxylic acid having the formula:

a cyclohexylene group, a phenylene group and a it; R6 Ra Rio N -group I I I l R5 R1 L Rn u CEL -C0011 R2, R3, R4, R5, R5, R7, R3, R9, R10 and R11 CaCh represent the same or ditferent member, such as, hydrogen, hydroxyl, an amino group, nitro halogen a lower alkyl group having from 1 to 6 carbon atoms (e.g. methyl, ethyl, propyl, etc.) and a lower alkoxy group having from 1 to 6 carbon atoms (e.g., methoxy, ethoxy, propoxy, etc.) so that no single carbon atom in the structure containing said groups R through R contains more than one hydroxyl group, more than one amino group, and more than one nitro group; p represents an integer of from 2 to 4; and q represents an integer of from 1 to 4; and an organic sulfonic acid having the formula:

(V R12SO3H wherein R represents a group, such as, a lower alkyl group having from 1 to 7 carbon atoms (e.g., methyl, ethyl, propyl, etc.) and a phenyl group (e.g., phenyl, tolyl, etc.).

My preferred stabilizer compositions are non-polluting and use acids (when needed) other than phosphoric or boric.

My alkali metal aldehyde bisulfite addition complexes are advantageously made by reacting an alkali metal bisulfite (e.g., sodium, potassium, lithium, etc. salt of the bisulfite ion) with an aldehyde having from 1 to 5 carbon atoms, including the carbon atoms in from 1 to 3 carbonyl groups, at least one of which is part of a formyl group. Useful aldehydes include, formaldehyde, acetaldehyde, propionaldehyde, malonaldehyde, succinaldehyde, glutaraldehyde, glyoxylic acid, propane 3-al carboxylic acid, etc. The last two aldehydes listed also contain a carboxy group.

Typical aldehyde addition complexes used to advantage include the following:

sodium formaldehyde bisulfite potassium formaldehyde bisulfite sodium glutaraldehyde bisulfite potassium succinaldehyde bisulfite sodium malonaldehyde bisulfite sodium propionaldehyde bisulfite sodium furfuraldehyde bisulfite sodium isobutyraldehyde bisulfite potassium 3-hydroxypropionaldehyde bisulfite sodium methoxybutyraldehyde bisulfite disodium glyoxal dibisulfite disodium glyoxylic acid bisulfite disodium propane 3-a1 carboxylic acid bisulfite Acids used to advantage according to my invention include the following:

sulfuric acid nitric acid phosphoric acid hydrochloric acid formic acid acetic acid propionic acid benzoic acid phenyl acetic acid tartaric acid succinic acid maleic acid malonic acid malic acid fumaric acid citric acid pyruvic acid lactic acid oxalic acid monomethyl oxalate monoethyl succinate dimethyl citrate 2-methoxypropanoic acid Z-methoxy-l,2,3-propanetricarboxylic acid succinamic acid l-aminosuccinamic acid (asparagine) alanine N-methylalanine phenylalanine phthalic acid ethylene diamine tetraacetic acid diethylene triamine pentaacetic acid 1,3-diaminopropanol-N,N,N',N'-tetraacetic acid nitrilotriacetic acid itaconic acid u-hydroxyphenylacetic acid benzenesulfonic aicd toluenesulfonic acid methanesulfonic acid ethanesulfonic acid My stabilizer compositions are advantageously packaged in kit form, either in dry form without water or in a liquid concentrate, for ease in storing, shipping and using, so that the user simply dissolves the components in the appropriate amount of water or dilutes the liquid concentrate with the proper amount of water for use in a photographic process. The components of my stabilizer compositions are well suited for use in prepackaged kits since the alkali metal aldehyde bisulfite addition complexes are solids and since a number of the acids are also solids.

In addition to the aldehyde bisulfite addition complex and the acid, other addenda are advantageously included in my compositions, e.g., antioxidants (e.g., glucose, galactose, sorbitol, mannitol, etc.), any water-soluble optical brighteners that are commercially available, any commercial wetting agents that are used to prevent the formation of drying spots, etc.

My stabilizer compositions will stabilizer a color photographic image regardless of the method which is used to form the dyes. Any dye image formed by reaction of an oxidized p-phenylenediamine developing agent with a coupler is advantageously stabilized. It is believed that dyes are stabilized by virtue of the mild reducing properties of the aldehyde bisulfite addition complex, while the residual unreacted coupler, if present, is prevented from yellowing by having reacted at the active site with the aldehyde.

Any color photographic elements are advantageously used in my invention, including those described in patent references, such as, Mannes et al., U.S. Pat. 2,252,718; Froehlich et al., U.S. Pat. 2,376,679; Vittum et al., (US. Pat. 2,322,027; Fierke et al., US. Pat. 2,801,171; Godowsky, US. Pat. 2,698,794; Barr et al., US. Pat. 3,227,554; Graham, US. Pat. 3,046,129; Martinez, US. Pat. 2,284,- 877 and Wolf et al., US. patent application Ser. No. 634,- 104, now Pat. No. 3,516,831, filed Apr. 27, 1967.

Any of the photographic silver halide emulsions, e.g., silver bromide, silver bromoiodide, silver chloride, silver chlorobromide, silver bromochloroiodide, etc., used in photography can be used to advantage in photographic materials used according to my invention. Silver halide emulsions including coarse grain or fine grain prepared by well-known procedures are used. The emulsions advantageously contain any of the known chemical sensitizers, spectral sensitizers, antifoggants, stabilizers, coating aids and other addenda used in photographic elements. The silver halide emulsions advantageously contain any of the various hydrophilic colloids, such as, naturally-occurring substances, e.g., proteins, for example, gelatin, gelatin derivatives, cellulose derivatives, polysaccharides such as dextrose, gum arabic, etc. and synthetic polymeric substances, such as, soluble polyvinyl compounds like poly (vinylpyrrolidone) acrylamide polymers, etc. Any of the known Z-equivalent and 4-equivalent nondififusible colorforming couplers known in the art are advantageously used in emulsions that contain incorporated couplers. The phenolic and naphtholic couplers are advantageously used as cyan-dye-formers; the S-pyrazolone couplers are advantageously used as magenta-dye formers and the openchain ketomethylene couplers are advantageously used as yellow-dye-formers. Included among the nondiffusible couplers used to advantage are those described in column 4 through 10 of Wolf et al., US. patent application Ser. No. 634,104, now Pat. No. 3,516,831, filed Apr. 27, 1967. The light-sensitive layers of photographic elements, used according to my invention, are advantageously coated on a wide variety of photographic supports including cellulose nitrate film, cellulose acetate film, polyacetal film, polystyrene film, polyterephthalate film, polyethylene film and related films of resinous materials as well as paper, glass and others.

Following light image exposure, color photographic elements, such as those described above, are usually color processed according to one or" the following process cycles:

(1) Color develop, stop-fix, bleach, hardener-fix, stabilize and dry (2) Color develop, bleach-fix, stabilize and dry (3) Develop, stop, color develop, stop, bleach, fix, stabilize and dry (4) Develop, stop, color develop, bleach-fix, stabilize and dry (5) Preharden, neutralize, develop, stop, color develop,

bleach-fix, stabilize and dry In these process cycles, water washes are inserted between each step as needed, but preferably no wash is used after the stabilization step because it is essential that the imbibed stabilizer solution remain in the layers of the processed photographic element containing the residual colorforming couplers and the dye images. The support or base side of a photographic element that has been treated with my stabilizer composition, however, can be washed if desired or, alternatively, either or both sides of the stabilized photographic element is squeegeed with a wiper blade or air knife to remove water droplets before the drying step. Alternatively, and less desirably, a rapid jet rinse or dip rinse of the emulsion surface of the photographic element is possible, provided that it is not sufficient to Wash the stabilizing compound out of the dye-containing layers. The drying step is usually carried out at elevated temperatures that drive off free aldehyde, such as, formaldehyde that is used as a stabilizing agent in some prior art stabilizers. Loss of the free aldehyde from the element during the drying step following stabilization with a prior art formaldehyde stabilizer represents a substantial loss in the active stabilizing agent from the photographic element with the accompanying loss in stabilization of the color image.

The use of an alkaline solution of sodium formaldehyde bisulfite as a color photographic stabilizer is dis closed in US. Pat. 2,647,057. This patent discloses the stabilization of dyes to conditions of high humidity. Treatment times of from to minutes are required for adequate protection.

My invention gives improved light stability at very low treatment times in addition to the advantages of the stabilizer of the prior art. The maximum treatment times for my stabilizer treatments are 4 minutes at 24 C., 3 minutes at 29 C. and 1 minute at 38 C. while the pre ferred treatment times are 2 minutes at 24 C., 1 minute at 29 C. and 30 seconds at 38 C. The time required to optimize stabilization is independent of stabilizer concentration but the maximum degree of stabilization is dependent upon concentration.

The use of formaldehyde and formaldehyde-bisulfite as a hardening agent in prehardener solutions used in color processing is not to be confused with my invention. The prehardening step where used is the first step of a color process and essentially all of the formaldehyde and formaldehyde-bisulfite complex is removed from the photographic element before the developer step, so obviously there would be no formaldehyde or its bisulfite addition complex left in the photographic element following the 4 to 7 additional process steps (including washes) preceding the stabilization step.

Sulfite or bisulfite ions are not generally used in a final bath in color photographic processing because these ions have been known to destroy cyan dyes made from conventional cyan-dye-for ming couplers. Sometimes, as in the stabilization process of Wrisley et al., U.S. Pat. 3,335,004, sulfite and bisulfite ions are used in a stabilization bath to preserve retained hypo and color developing agent.

The following examples are included for a further understanding of my invention:

EXAMPLE 1 A stabilizer composition is prepared by dissolving sodium formaldehyde bisulfite addition complex in water with sulfuric acid or sodium hydroxide to produce a solution of 5 g./l. of sodium formaldehyde bisulfite complex having a pH of 7. Two unexposed samples of a conventional multilayer color-forming coupler incorporated photographic paper coated on one side in succession with a gelatin blue-sensitive silver chlorobromide emulsion layer containing an incorporated nondiffusible open-chain ketomethylene yellow-dye-image-forming coupler, a gelatin green-sensitized silver chlorobromide emulsion layer containing an incorporated nondiffusible S-pyrazolone magenta-dye-image-forming coupler, and a gelatin red-sensitized silver chlorobromide emulsion layer containing an incorporated nondiifusible phenolic cyan-dyeimage-forming coupler are developed at 29 'C. for 3% minutes in a color developer similar to that described in Bard et al., US. Pat. 3,189,452 in column 8, lines 8 through 27, then bleach-fixed for 1 /2 minutes with a conventional blix bath comprising sodium ferric ethylene diamine tetraacetate and sodium thiosulfate. These samples are then treated as follows:

Strip No.: Process steps 1 Wash 3 minutes and dry. 2 Wash 2 minutes, stabilize 1 minute in a bath containing 5 g./1. of sodium formaldehyde bisulfite addition complex and enough sulfuric acid and/or sodium hydroxide to adjust the pH to 7, and dry.

The samples are equally white at the end of the process. They are then subjected to 14 days treatment in an oven held at C./% relative humidity and the stain increase is measured at 420 nm. The stain increases are as follows:

Strip No.: Stain density increase 1 +.09 2 +.05

My stabilizer composition is seen to be an effective agent in retarding stain growth due to decomposition of couplers and other components in a color processed color photographic element.

EXAMPLE 2 Example 1 is repeated three times, but the samples are image exposed respectively to red, green and blue light, and the dye loss is measured after the test is complete. There are no deleterious effects due to the stabilizer. This shows that the sulfite and bisulfite ions are so constituted in the addition compound that they do not harm the dyes.

EXAMPLE 3 Example 1 is repeated, but using as the stabilizer a solution comprising 5 g./l. of sodium formaldehyde bisulfite, 1 g./l. of concentrated sulfuric acid and enough of a 40% solution of sodium hydroxide to adjust the solution to a pH of 4.5. The results are substantially the same as obtained in Example 1, with effective retardation of stain growth being provided by my stabilizer composition.

EXAMPLE 4 Example 2 is repeated, using the stabilizer solution described in Example 3. The results are substantially the same as described in Example 2, i.e., no detrimental elfect from sulfite and bisulfite upon image dye.

EXAMPLE 5 Strip No: Process steps 1 Wash 3 min. and dry. 2 Wash 2 min., stabilize 1 min. (5 g./l.

SFB and dry. 3.. -i Wash 2 min., stabilize l min. (10 g./l.

SFB*) and dry.

* SFB=sod1um formaldehyde bisulfite addition complex.

The magenta dye loss at peak wavelength is now measured after two week treatment in the oven as described in 10 stabilizer solution used in Example 1, the stabilizer described hereinabove.

Example 1 above. The dye losses are as follows: Strip No; Strip No Magenta dye loss, percent 1 Wash 3 min.

1 -11 2 Wash 2 min., stabilize 1 min. 2 -8 (Solution X outside invention). 3 -4 3 Wash 2 min., stabilize 1 min. The data show that my stabilizer bath with 5 g./l. con- (SolutlonAof my mventlon) centration level of sodium formaldehyde bisulfite addi- At the end of the process, the strips are dried on a comtion complex produces a substantial decrease in magenta mercial ferrotype drum at 82 C. Strip No. 2 turns vivid dye loss; however, at the 10 g./l. concentration of my pink due to rapid reaction of the succinaldehyde with addition complex, there is more than a 50% reduction compounds in the photographic element. Strips No. 1 and inma-genta dye loss. No. 3 are unchanged by this drying step. This example EXAMPLE 6 shows that stabilizer Solution A of my invention in a processed photographic element does not produce the pink SHIPS of a color photggraghlg i g lelement stain produced by stabilizer Solution B outside my inmate on paper s upport as escnbe m Xamp e 1 are vention in another piece of the processed photographic exposed as follows element when these are drum dried at 82 C. Strip No.: Exposure 1a, 1b, 1c Red light exposure. EXAMPLE 9 2a, 2b, 2c Green light exposure, Stabilizer compositions B, C and D of my invention and 3a, 3b, 3c Blue light exposure, stabilizer composition Y outside my invention are made containing the following ingredients. These are processed as described in Example 1 through the blix step, then given two minutes water washing, one Stabilize Acid minute stabilizing in the indicated stabilizer and dried. Stabilizer Amn, mt, composition Name g. Name g.

Strip Nos. Stabilizer Y Formaldehyde (37%) 0.8 Citric acid 6 B Sodium formaldehyde 3.5 do 5 1a, 2a, 3a 1 10 ml./l. of 37% formaldehyde. 3O bisulfite. 1b, 2b, 8b 2 2 m1./l. of 37% formaldehyde. 0 do 10.5 do 5 1c, 2c,3c 3 5 g./l. or sodium formaldehyde bisulfite ad- D do 35.0 do 5 dition complex.

Se arate one-liter a ueous solu io ar All i Smps are Sub]ected.t.2000 hours 9 uradlatlon th: above compositions. Each so l ijtior l i s ii e r d a t i to a simulated source of artificial north skylight (SANS)1 PH of by adding the amount of 40% Sodium hydroxide at 500 f candle hours The dya losses records solution found necessary. Four unexposed samples of a as follows multilayer color photographic material on a paper support as described in Example 1 are processed as described in Example 1 through the blix step, then are washed for g sgagag gg ggg ggg 40 two minutes and then each strip is treated for one minute 3 M ma Yellow in a diiferent stabilizer Solution Y, B, C or D described Stabilizer i g dye above. Each strip is arbitrarily identified according to the 1 identification of the stabilizer solution used to treat it. :111:11: g After drying the strips, the stain in the D of each strip 3 5 is measured. The strips are then treated for six days in an oven at 49 C./90% RH. The density changes are measured and recorded in the following table: This clearly shows the effectiveness of the aldehyde-bisulfite addition product. Formaldehyde alone is not as ef- Changein density tofight of fective and the solution has a very objectionable odor. 50 indicated 6010: This example demonstrates the unexpected advantage of Strip and Stabilizer Red Green sulfite or bisulfite ion in the stabilizer bath. Y (outside invention) 025 030 B (of my invention)- 0. 00 0.00 EXAMPLE 7 C (of my invention). 0, 0 I D (of my invention) 010 .005 .005 Three strips of a photographic element similar to that described in Example 1 are processed i a conventional It can be seen that the sodium formaldehyde bisulfite is bleach then fi process as described b d et 1 Us, effective in preventing stain increases and, at higher conp 139 45 columns 7 and 8, Process C, up to b centrations, actually causes some lowering of stain. not including the buffer step and are treated in stabilizers as described in Example 1 after the 3-minute final wash. EXAMPLE 10 The results after wet oven treatment show that my sta- Example 9 is repeated with exposed strips, and the dye bilizer is very eifective in reducing stain formation. Examlosses are measured and found to be lower than those ple 2 is also repeated, but using the bleach then fix proc- With the plain formaldehyde. eis 2and the results are substantially identical to Exam- EXAMPLE 11 e p EXAMPLE 8 Example 9 is repeated, but the samples are exposed to 1,000 hours at 500 foot candles sans illumination. The A Stabilizer Composition A of my invention is made samples treated with the sodium formaldehyde bisulfite y dissolving 40 of Sodium succinaldehyde bisulfite addition product are equal or superior for dye stability to addition complex and hydrochloric acid in water to make h coating treated i f ld h d l one liter of stabilizer Solution A, there being enough hy- EXAMPLE 12 drochloric acid to give a pH of 3.0. A stabilizer Solution X, outside my invention, is made by dissolving 40 g. of Example 1 is repeated, using a stabilizer solution consuccinaldehyde in one liter of Water and adjusting the pH taining 5 g./l. of sodium formaldehyde bisulfite, 1 g./l. of to 3.0. Example 7 is repeated, but using in place of the concentrated sulfuric acid and enough of a 40% solution 1 1 of sodium hydroxide to adjust the solution to a pH of 4.8. As in Example 1, my stabilizer is shown to be an effective agent in retarding stain growth due to decomposition of couplers and other components in a color processed color photographic element.

EXAMPLE 13 Example 12 is repeated, using 1 g./l. of concentrated hydrochloric acid in place of sulfuric acid. The results are comparable to those obtained in Examples 1 and 12.

EXAMPLE 14 Example 2 is repeated, using the stabilizer described in Examples 12 and 13. As in Example 2, the sulfite and bisulfite ions are so constituted in the addition complex of my stabilizer solution that there is no change in dyes.

EXAMPLE 15 Example 9 is repeated, but instead of using g./l. of citric acid in the stabilizer solution, 18 g./l. of citric and 1 g./l. of benzoic acid, 5 g./l. of acetic acid, 5 g./l. of ethylenediamine tetraacetic acid, 10 g./l. of tartaric acid, 10 g./l. of succinic or g./l. of malic acid, is used. A sufficient amount of 40% sodium hydroxide solution is added to each of the compositions to buffer the pH at a pH of 4.5 Substantially the same results are obtained in this example that were obtained in Example 9, i.e., that these stabilizer compositions of my invention are also effective in preventing stain increases and, at the higher concentrations, actually cause some decrease in stain.

EXAMPLE 16 Example 1 is repeated, using 5 g./l. of sodium succinaldehyde bisulfite addition complex instead of sodium formaldehyde bisulfite addition complex. Substantially the same effective retardation of stain growth is obtained in the immediate example as is obtained in Example 1.

EXAMPLE 17 Example 1 is repeated, using 5 g./l. of sodium propionaldehyde bisulfite addition complex. The results again show the effectiveness of my stabilizers in retarding stain formation.

EXAMPLE 18 Example 2 is repeated, using 5 g./l. of sodium succinaldehyde bisulfite and then 5 g. l. of sodium propionaldehyde in place of the sodium formaldehyde bisulfite. The results obtained are substantially the same as obtained in Example 2, with no detrimental effect produced by sulfite or bisulfite ions on image dye stability.

EXAMPLE 19 Examples 1 and 2 are repeated using 5 g./l. of sodium glutaraldehyde bisulfite addition complex in place of sodium formaldehyde bisulfite addition complex. The results show that the immediate stabilizing composition is effective in reducing stain formation in processed color photographs and that the immediate composition has no deleterious effect on dye images.

EXAMPLE 20 Examples 1 and 2 are repeated, using 5 g./l. of sodium malonaldehyde bisulfite addition complex in place of sodium formaldehyde bisulfite addition complex. This example again demonstrates that the immediate element is effectively stabilized against strain growth and that the addition complex is not detrimental to image dyes.

EXAMPLE 21 Example 9 is repeated, using potassium formaldehyde bisulfite at 3.5 g./l., 10.5 g./l. and 35 g./l. concentrations in place of the sodium formaldehyde bisulfite. Substantially the same results are obtained as are described in Example 9.

12 EXAMPLE 22 Example 15 is repeated, but with the solution buffered at pHs of 3.0, 4.0, 5.0, 6.0 and 7.0 by adding the necessary amount of 40% sodium hydroxide solution. In each instance, the sodium formaldehyde bisulfite is shown to be effective in improving dye stability when comparisons are made with 37% formaldehyde at a pH of 3.0, 4.0, 5.0, 6.0 and 7.0.

EXAMPLE 23 Examples 1 through 7 are repeated, but using pHs of 3.0, 4.0, 5.0 and 6.0 in place of the pH of 7, used in Examples 1 through 7. Example 8 is repeated, but with the pHs of 4.0, 5.0, 6.0 and 7.0, instead of a pH of 3 used in Example 8. In each instance, "a comparison of the results obtained in an example at a given pH show the superiority of my stabilizer over the stabilizer outside my invention.

Similarly, it can be shown that my stabilizer compositions, having the alkali metal aldehyde bisulfite addition complexes illustrated in the preceding examples, as well as the other alkali metal aldehyde bisulfite addition complexes of my invention, are used to advantage at concerntration levels in the range of from about 0.5 g./l. to about g./l. at pHs in the range of from 3 to 7. My stabilizer compositions advantageously contain the acids illustrated in the preceding examples, as well as the other acids of my invention, for adjusting the pHs below 7. In my preferred stabilizer compositions that are buffered at a pH in the range of from 3 to 7, my acids are advantageously used in the concentration range of from about 0.5 g./l. to about 25 g./l. with sufiicient alkali metal hydroxide being added to buffer the solution at the desired pH.

My stabilizer compositions are advantageously prepackaged without water or with enough water to dissolve one or more of the necessary chemicals in one or more concentrated solutions for dilutioin to the working concentration level for use in a processing machine.

My stabilizer compositions are particularly valuable because they are not only very effective in preventing or minimizing the formation of unwanted stain in processed color photographs, but does this without giving ofl? toxic vapors that are characteristic of many of the stabilizers used previously. The stabilizing effect of my compositions persist over a substantially longer period of time than most prior art stabilizers after processing and drying, even at elevated temperatures, because the aldehyde is retained in the photographic element as the addition complex which only very slowly releases aldehyde and bisulfite ion. It is not obvious that the bisulfite ion released would protect the dyes to light fading; however, the data presented in the preceding examples, especially in Examples 2, 4, 14, 18 and 19, show that my stabilizer compositions do protect the image dyes. Use of my stabilizer compositions provide valuable technical advances that are illustrated and discussed herein.

The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

I claim:

1. A composition for use in stabilizing a processed color photographic element that contains dye images, said composition comprising:

( 1) a sufficient amount of at least one water-soluble complex of an alkali metal bisulfite and an aldehyde containing from 1 to 6 carbon atoms and from 1 to 3 carbonyl groups, at least one of said carbonyl groups being part of an aldehyde group, to give a concentration of said complex in the range of from about 0.5 g./l. to about l00 g./l. when dissolved in water, and

(2) a sufficient amount of at least one member selected from the group consisting of alkali metal hydroxides and acids selected from the class consisting of sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrochloric acid, organic carboxylic acids and organic sulfonic acids to adjust the pH of an aqueous solution of said composition in a pH range of from 3 to 7.

2. A composition for use in stabilizing a processed color aldehyde containing from 1 to 6 carbon atoms and from 1 to 3 carbonyl groups, at least one of said carbonyl groups being part of an aldehyde group, to provide when dissolved in water with (2) and (3), an aqueous stabilizer solution having a concentraphotographic element that contains dye images and re- 5 sidual color-forming coupler, said composition comprising:

tion of said addition complex in the range of from about 0.5 g./l. to about 100 g./l.;

(2) a sufiicient amount of an acid to provide, when dissolved in water with (l) and (3), an aqueous stabilizer solution having a concentration of said acid in the range of from about 0.5 g./l. to about 2.5 g./l.; and

(3) a suflicient amount of an alkali metal hydroxide to provide, when dissolved in Water with (1) and (2), an aqueous stabilizer solution buffered at a pH in the range of from 3 to 7.

4. A composition for use in stabilizing a processed color photographic element that contains dye images and residual color-forming coupler, said composition comprising:

said composition to a pH in the range of from 3 to 7, said acids being selected from those having the formulas:

(1) a suflicient amount of a water-soluble addition complex of an alkali metal bisulfite and an aldehyde having the formulas:

RC HOOCG-'*NG?COOH H and 11125031; and

0 0 wherein R represents a member selected from the class consisting of hydrogen, lower alkyl group, a

carbonyl group and a phenyl group; L represents a member selected from the class consisting of a bond, a lower alkylene group vinylene and a phenylene group; G represents a group selected from the class consisting of an alkylene group, a phenylene group and a heterocyclene group; G represents a group selected from the class consisting of a lower alkylene group, a phenylene group and a heterocyclene group; G represents a group selected from the class consisting of a lower alkylene group, a phenylene group and a heterocyclene group; Z represents a group selected from the class consisting of a cycloacid, P P Q C id, ydrochloric acid, an organic hexylene group, a phenylene group, a carboxylic acld and an organic sulfonic acid to provide, when dissolved in water with 1) and (3), an R2 group aqueous stabilizer solution having a concentration of said acid in the range of from about 0.5 g./l. to about 25 g./l.; and

p (3) a sufiicient amount of an alkali metal hydroxide to and a provide, when dissolved in water with 1) and (2), an aqueous stabilizer solution bufiered at a H in 154 I sa 8 R10 group the range of from 3 to 7. p 5. A composition for use in stabilizing a processed R5 R1 0 R11 color photographic element that contains dye images and (CHDQCOOH residual color-forming coupler, said composition comprising:

2 3, 4, 5 6, 7 8 9 10 and 11 each represent a member selected from the class consisting of hydrogen, hydroxyl, amino, nitro, a halogen atom, a lower alkyl group and a lower alkoxy group so that no single carbon atom in the structure con- 0 taining said R group contains more than one nitro U and l)n-1 group; p represents an integer of from 2 to 4; q H

represents an integer of from 1 to 4 and R represents a group selected from the class consisting o a lower alkyl group and a phenyl group.

3. A composition for use in stabilizing a processed color photographic element that contains dye images and residual color-forming coupler, said composition compris- (l) a sufficient amount of at least one water-soluble addition complex of an alkali metal bisulfite and an wherein R is a member selected from the class con- 70 sisting of hydrogen, a lower alkyl group and fury], and n represents an integer of from 1 to 5, to provide, when dissolved in water with (2) and (3 an aqueous stabilizer solution having a concentration of said addition complex in the range of from about 0.5 g./l. to about g./l.;

(2) a sufiicient amount of an acid selected from those having the formulas:

RrCOOH HO O CL--C O OH wherein R represents a member selected from the class consisting of hydrogen, a lower alkyl group, a carbonyl group and a phenyl group; L represents a member selected from the class consisting of a bond, a lower alkylene group, vinylene and a phenylene group; G represents a group selected from the class consisting of an alkylene group, a phenylene group and a hetero cyclone group; G represents a group selected from the class consisting of a lower alkylene group, a phenylene group and a heterocyclene group; G represents a group selected from the class consisting of a lower alkyleue group, a phenylene group and a heterocyclene group; G represents a group selected from the class consisting of a lower alkylene group, a phenylene group and a heterocyclene group; Z represents a group selected from the class consistof a cyclohexylene group, a phenylene group, a

s group Ra n represent a member selected from the class consisting of hydrogen, hydroxyl, amino, nitro, a halogen atom, a lower alkyl group and a lower alkoxy group so that no single carbon atom in the structure containing said R group contains more than one hydroxyl group, more than one amino group and more than one nitro group; p represents an integer of from 2 to 4; q represents an integer of from 1 to 4 and R represents a group selected from the class consisting of a lower alkyl group and a phenyl group to provide, when dissolved in water with (1) and (3), an aqueous stabilizer solution having a concentration of said acid in the range of from about 0.5 g./l. to about 25 g./l.; and

(3) a sufiicient amount of an alkali metal hydroxide to provide, when dissolved in water with (l) and (2) an aqueous stabilizer solution buttered at a pH in the range of from 3 to 7.

6. A composition of claim 5 in which said addition complex is a complex of an alkali metal bisulfite and formaldehyde.

7. A composition of claim 5 in which said addition complex is a complex of an alkali metal bisulfite and succinaldehyde.

8. A composition of claim 5 in which said addition complex is a complex of an alkali metal bisulfite and propionaldehyde.

9. A composition of claim 5 in which said addition complex is a complex of an alkali metal bisulfite and glutaraldehyde.

10. A composition of claim 5 in which said addition complex is a complex of an alkali metal bisulfite and malonaldehyde.

11. An aqueous solution for use in stabilizing a processed color photographic element, said solution comprismg:

(1) at least one water-soluble complex of an alkali metal bisulfite and an aldehyde containing from 1 to 6 carbon atoms and from 1 to 3 carbonyl groups,

at least one of said carbonyl groups being part of an aldehyde group, said solution containing said complex at a concentration in the range of from about 0.5 g./l. to about g./l., and

(2) a sufficient amount of at least one member selected from the group or alkali metal hydroxides and acids selected from the class consisting of sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrochloric acid, organic carboxylic acids and organic sulfonic acids to adjust the pH of an aqueous solution of said composition in a pH range of from 3 to 7.

12. An aqueous solution for stabilizing a processed color photographic element, said solution comprising:

(1) sodium formaldehyde bisulfite at a concentration in the range of from about 0.5 g./l. to about 100 g./l.;

(2) an acid selected from the class consisting of sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrochloric acid, acetic acid, benzoic acid, tartaric acid, succinic acid, maleic acid, malonic acid, malic acid, citric acid, phthalic acid, ethylene diamine tetraacetic acid, diethylene triamine pentaacetic acid, 1,3- diaminopropanol-N,N,N,N-tetraacetic acid and nitriloacetic acid at a concentration in the range of from about 0.5 g./l. to about 25. g./l.; and

(3) a sutficient amount of sodium hydroxide to buffer said solution at a pH in the range of from 3 to 7.

13. An aqueous stabilizer solution for stabilizing a processed color photographic element, said solution comprising:

(2) at least one of citric acid and benzoic acid so that the total concentration of acid is in the range of from about 0.5 g./l. to about 25 g./l.; and

(3) a suflicient amount of sodium hydroxide to bufier said solution at a pH in the range of from 3 to 7.

14. An aqueous stabilizer solution for stabilizing a processed color photographic element, said solution comprising:

(1) sodium succinaldehyde bisulfite at a concentration in the range of from about 0.5 g./l. to about 100 g./l.;

(2) an acid selected from the class consisting of sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrochloric acid, acetic acid, benzoic acid, tartaric acid, succinic acid, maleic acid, malonic acid, malic acid, citric acid, phthalic acid, ethylene diamine tetraacetic acid, diethylene triamine pentaacetic acid, 1,3- diaminopropanol-N,N,N',N-tetraacetic acid and nitrilotriacetic acid at a concentration in the range of from about 0.5 g./l. to about 25 g./l.; and

(3) a sufiicient amount of sodium hydroxide to butter said solution at a pH in the range of from 3 to 7.

15. An aqueous stabilizer solution for stabilizing a processed color photographic element, said solution comprismg:

(2) at least one member selected from the group consisting of citric acid and benzoic acid so that the total concentration of acid is in the range of from about 0.5 g./l. to about 25 g./l.; and

(3) a sufficient amount of sodium hydroxide to buffer said solution at a pH in the range of from 3 to 7.

16. In the color processing of a color photographic element containing incorporated color-forming couplers in which a latent image is color developed, silver and residual silver halide are removed, the color image is stabilized and the processed photographic element is dried, the improvement comprising stabilization with an aqueous stabilizer solution containing an addition complex of an alkali metal bisulfite and an aldehyde containing from 1 to 6 carbon atoms and from 1 to 3 carbonyl groups, at least one of which is part of a formyl group at a concentration in the range of from about 0.5 g./l. to about 100 g./ 1., said stabilizer solution having a pH in the range of from 3 to 7.

17. In the color processing of a colorphotographic element containing incorporated color-forming couplers in which a latent image is color developed, silver and residual silver halide are removed, the color image is stabilized and the processed photographic element is dried, the improvement comprising stabilization with an aqueous stabilizer solution containing a water-soluble addition complex of an alkali metal bisulfite and an aldehyde having the formulas:

wherein R is a member selected from the class consisting of hydrogen, a lower alkyl group and the furyl group; n represents an integer of from 1 to 5 at a concentration in the range of from about 0.5 g./l. to about 100 g./1., said stabilizer solution having a pH in the range of from 3 to 7.

18. In the color processing of a color photographic element containing incorporated color-forming couplers in which a latent image is color developed, silver and residual silver halide are removed, the color image is stabilized and the processed photographic element is dried, the improvement comprising stabilization with an aqueous stabilizer solution containing:

(1) a water-soluble complex of an alkali metal bisulfite and an aldehyde having the formulas:

0 o and C-(CHZ)nI-C wherein R is a member selected from the class consisting of hydrogen, a lower alkyl group and furyl, and n represents an integer of from 1 to said addition complex having a concentration in the range of from about 0.5 g./l. to about 100 g./l. in said solution; (2) an acid selected from those having the formulas:

R1COOH HOOCL-COOH HOOC-G-lTl-(h-C OOH i HO0CG3-NG=-COOH and R118 03H wherein R represents a member selected from the class consisting of hydrogen, a lower alkyl group, a carbonyl group and a phenyl group; L represents a member selected from the class consisting of a bond, a lower alkylene group and a phenylene group; G represents a group selected from the class consisting of an alkylene group, a phenylene group, a heterocyclene group; G represents a group selected from the class consisting of a lower alkylene group, a phenylene group and a heterocyclene group; G represents a group selected from the class consisting of a lower alkylene group, a phenylene group and a from the class consisting of a lower alkylene group, a phenylene group and a heterocyclene group; Z represents a group selected from the class consisting of a cyclohexylene group, a phenylene group, a

and a R2, R3 R4! R5 R61 R7! R8 R9 R10 and R11 each represent a member selected from the class consisting of hydrogen, hydroxyl, amino, nitro, a halogen atom, a lower alkyl group and a lower alkoxy group so that no single carbon atom in the structure containing said R group contains more than one hydroxyl group, more than one amino group and more than one nitro group; p represents an integer of from 2 to 4; q represents an integer of from 1 to 4; R represents a group selected from the class consisting of a lower alkyl group and a phenyl group; said acid having a concentration in the range of from about 0.5 g./l. to about 25 g./l. in said solution; and

(3) a sufficient amount of sodium hydroxide to buffer,

said solution at a pH in the range of from 3 to 7.

19. In the color processing of a color photographic element containing incorporated color-forming couplers in which a latent image is color developed, silver and residual silver halide are removed, the color image is stabilized and the processed photographic element is dried, the improvement comprising stabilization with an aqueous stabilizer solution containing:

,( 1) sodium formaldehyde bisulfite at a concentration in the range of from about 0.5 g./l. to about 100 g./l.;

(2) at least one acid selected from the class consisting of sulfuric acid, nitric acid, phosphoric acid, boric acid, hydrochloric acid, acetic acid, benzoic acid, tartaric acid, succinic acid, maleic acid, malonic acid, malic acid, citric acid, phthalic acid, ethylene diamine tetraacetic acid, diethylene triamine pentaacetic acid, l,3-diaminopropanol-N,N,N, '-tetraacetic acid and nitrilotriacetic acid so that said solution contains a total concentration of acid in the range of from about 0.5 g./l. to about 25 g./l.; and

20. In the color processing of a color photographic element containing incorporated color-forming couplers in which a latent image is color developed, silver and residual silver halide are removed, the color image is stabilized and the processed photographic element is dried, the improvement comprising stabilization with an aqueous stabilizer solution comprising:

(1) sodium formaldehyde bisulfite at a concentration in the range of from about 0.5 g./1. to about 100 g./l.;

(2) at least one member selected from the class consisting of citric acid and benzoic acid so that the total concentration of acid is in the range of from about 0.5 g./l. to about 25 g./l. in said solution; and

21. In the color processing of a color photographic element containing incorporated color-forming couplers in which a latent image is color developed, silver and reheterocyclene group; G represents a group selected sidual silver halide are removed, the color image is 19 2O stabilized and the processed photographic element is dried, I References Cited the improvement comprising stabilization with an aqueous UNITED STATES PATENTS Stabilizer solution Containing 2,134,053 12 1939 Muehler 5 g (1) sodium succinaldehyde bisulfite at a concentration 5 2,515,122 7/1950 Harsh 96 -56 in the range of from about 0.5 g./l. to about 100 2,647,057 7/1953 'y gJL; 2,657,139 10/1953 Bates 96-56 (2) at least one acid selected from the class consisting of sulfuric acid, nitric acid, phosphoric acid, boric 10 3,212,395 10 19 5 Barbie; 1 acid, hydrochloric acid, acetic acid, benzoic acid, 3,424,583 1/ 1969 Seiter 96-56 tartaric acid, succinic acid, maleic acid, malonic acid, 9 i Y FOREIGN PATENTS malic acid, citric acid, phthalic acid, ethylene diamine 1,137,801 12/1968 Great Britain. 96 50 tetraacetic acid, diethylene triamine pentaacetic acid, I

1,3-diaminopropano1-N,N,N,N'-tetraacetic acid and 15 NORMAN TORCHIN, Pflmary Examiner nitrilotriacetic acid so that the total concentration I. R. HIGHTOWER, Assistant Examiner of acid in said solution is in the range of from about US. Cl- XR- 0.5 g./l. to about 25 g./l.; and 66 4 (3) a sufficient amount of sodium hydroxide to buffer said solution at a pH in the range of from 3 to 7;