US1521840A

US1521840A - Acid-fixing bath

Info

Publication number: US1521840A
Application number: US467308A
Authority: US
Inventors: Samuel E Sheppard
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1921-05-06
Filing date: 1921-05-06
Publication date: 1925-01-06
Anticipated expiration: 1942-01-06

Description

Patented Jan. 6, 1925,

ATENT osrics.

SAMUEL E. SHEPPARD, OF ROCHESTER, NEW YORK, ASSIGNOR TO EASTMAN KODAK COMPANY, OF ROCHESTER, NEW YORK, A CORPORATION OF NEW YORK.

AoIiJ-FIXING BATH.

No Drawing. Application filed May 6,

To all whom it may concern:

Be it known that I, SAMUEL E. SHEPPARD, a subject of the King of Great Britain, residing at Rochester, in the county of M911- roe and State of New York, have invented certain new and useful Improvements in Acid-Fixing Baths, of which the following is a full, clear, and exact specification.

This invention relates to photographic acid fixing baths. One object is toinclude in such a bath only materials which will not inhibitthe action of any hardener that may be present, nor form objectionable com-. pounds or 'precipitates'with any of the materials present. Another object of this in vention is to provide such baths made from constituents which may be prepared in the form of a single dry powder, which will not deteriorate under ordinary conditions or within areasonable time. Another object is to provide such a powder which will not contain'an acid, as such, but which will when dissolved produce an acid through the decomposition of the substances. Another object is to provide in such a bath a buffer material, of the nature of'those described and claimed in the patent of Felix A. Elliott, No. 1,411,687, granted Apr. 4, 1922, by which the acidity of the bath is main tained within desired limits. As there pointed out, the fixing bath should have an acidity or hydrogen ion concentration not greater than pH=4 and not less than pH:6.5 or, preferably, pI-I:6.

These and other objects, and the manner in which they are attained, will be more fully set forth in the following specification and claims. In order to make the invention clear, I will first mention a few well known characteristics of such baths and then point out the principles of myinvention.

The basis of practically all fixing baths is sodium thiosulfate or hypo, the best known solvent .for photographic silver salts. In operation, there is brought over from the developing bath a considerable amountof alkaline developer, 'and as a preservativeto prevent the harmful oxidation of the de veloper, a sulfite, usually sodium sulfite, is

customarily added to the fixing bath. To the reversible equations connecting these 100 1921. Serial No. 467,308.

increase the preservative action and also to neutralize the alkali, an acid is also usually added. Hypo has a tendency in an acid solu tion to decompose into sulfurous acid and sulfur, but this is prevented if there ,is enough sulfite present to maintain the bath in equilibrium. Sometimes an acid bisulfite, such as sodium bisulfite, N aHsO or potassium metabisulfite,;K S,O is used as a preservative in a fixing bath. .-It is also organic acids, which are solid at all ordinary temperatures It has not been possible to furnish an acetic acid bath in powder form because of the low melting point of this acid. It has been unsatisfactory, moreover, to mix in a single powder all the ingredients including hypo and an acid, because when these in finely divided form are intimately mixed the hypo is decomposed. It has been customary therefore, to furnish two separate powders.

I have discovered that the acid asa separate ingredient may be omitted entirely from such'a, mixed powder, by the substitution, in place of sulfite and an acid, of a bisulfite and the salt of an organic acid, which when dissolved produce a bath containing bisulfite, sulfite,sulfurous acid, an organic acid and a buffer salt of the organic acid. If, for instance, sodium bisulfite and sodium acetate are dissolved, the resulting bath contains sodium bisulfite, sodium sulfite, sulfurous acid, sodium acetate, and acetic acid.- For purposes of illustration and without committing myself to an exact statement of reactions that would occuris a fixing bath,

v substances only may be assumed to be as follows:

' within certain limits as described in the above identified Elliott patent.

This action may, of course, be attained by the use of many other salts such as fol-mates, citrates, tartrates, etc.

The dissociation necessary is attained only when the salts are in true solution as distinguished from suspension or so-called colloidal solution, and obviously, only such salts are suitable as enter into a true'solution in water. 7

When the bisulfite and-salt are dissolved together with hypo, the reaction is, of course, more complicated, butthe nature of the reaction is apparent from the above explanatory remarks.

The reaction is still more complicated when a hardener is also introduced. It has long been known that alum has a hardening effect and that the alum bath should be acid. It has been generally assumed that many acids, particularly organic acids, could be a used with equally satisfactory results; but

I have discovered that the presence in appreciable quantities of polybasic and hydroxy-organic acids, such as citric, tartaric, lact1c, ma-lic, maleic, salicylic, etc., acids or their salts inhibits the hardening action of alum upon the gelatine of photographic emulsions. This is due to the fact that theseaacids, or rather their anions, form stable complexes with aluminium, chromium and iron (the latter being frequently present as an impurity in commercial alums) whereby the combination of the hydrous oxides with the gelatlne 1s prevented. The" monobasic fatty acids and their alkali metal salts and partlcularly formic and acetic acids and their alkali metal salts, do not form complexes w1th aluminium of sufficient stability to inhibit hardening, but they do stabilize sufficlently to prevent the precipitation of aluminium hydroxide. For this reason, where, as is usually the case, an alum is present, a formate or acetate is very much preferable to salts-of acids of the classes specified above. When I refer to the alkali metalsI intend to include ammonium.

I have further discovered that sodium bisulfite or commercial potassium metabisulfite, which hitherto could notbe used satisfactorily with an alum containing an aluminium compound because of the formatlon of insoluble basic aluminium c mpounds, can'be used with such alums if an acetate or formate is also present. A typical formula is the following, the dry powdered salts being mixed in the order given,-

. Grams. Sodium thiosulfate 240 Sodium acetate 55 Sodium bisulfite 30 Potassium alum 8 of the bisulfite and the acetate or other salt; so that these constitute substantially the only source of acid.

Where I have referred to the materials as in the form of a powder, I donot mean to limit myself to any particular degree of fineness of the particles and rather coarse crystals or lumps of material may be used. These if desired may be mixed in an inert binding material such as gum arabic and formed into tablets or a paste.

The use of such gums appear to be especially desirable where commercial salts are used, containing impurities. The gum tends to keep any precipitates in a harmless suspended form. At the same time small amounts of alkali citrates or tartrates, or/a-nd salts of the corresponding acids may be included replacing acetate and bisulfite to improve pro rata the clarity of the bath, but the quantity of these must be small if the hardening action of the alum is not to be greatly reduced.

It is apparent that numerous modifications and equivalents are possible, and I contemplate these as within the scope of my invention as defined in the appended claims.

Having thus described my invention,

what I claim. as new and desire to secure by Letters Patent, is: 1. Powdered material adapted'when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a bisulfite of an alkali metal, and a alkali metal salt of a carboxylic acid, said salt having the property of entering into a true solution in water.

2. Powdered material adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a

bisulfite of an alkali metal, and an alkali metal salt of a carboxylic acid, said salt having the properties of entering into a true solution in water and, when in true aqueous solution in equilibrium with the bisulfite of acidfying the bath and of maintaining the hydrogen ion concentration of the bath at a predetermined strength greater than pH:6.5.

3. Powdered material adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a bisulfite of -an alkali metal and an alkali metal salt of a carboxylic acid having not over nine carbon atoms.

4:. Powdered material adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a bisulfite of an alkali metal and an ,alkali metal salt of a monobasic carboxylic acid having not over nine carbon atoms.

5. Powdered material adapted when dissolved to constitute a photographic fixing bath and'comprising sodium thiosulfate, a bisulfite of an alkali metal and an alkali metal salt of a monobasic carboxylic acid, said salt having the property of entering into a true solution with water.

6. Powdered material adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a bisulfite of an alkali metal and an alkali metal salt of a mon'obasic carboxylic acid, said salt having the properties of entering into a true-solution with water and, when in true aqueous solution in equilibrium with the bisulfite, of acidifying the bath and of maintalnlng the hydrogen lon concentration of the bath at a predetermined strength greater than pH:6.5.

7. Powdered material adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a bisulfite of an alkali metal and an alkali metal salt of a lower fatty acid.

8. Powdered material adapted when-dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a bisulfite of an alkali metal and an, alkali metal salt of an acid of the aliphatic series having not over two carbon atoms.

9. Material in the form of a single powder adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a bisulfite, of an alkali metal and an acetate of an alkali metal.

10. Powdered material adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a hardener and an alkali metal salt of a carboxylic acid, said salt having the property of entering into 'a true solution in water.

11. Powdered material adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a hardener and an alkali metal salt of a monobasic carboxylic acid, said salt having the property of entering into a true solution with water.

12. Powdered material adapted when dissolved to constitute a photographic fixing bath and comprising sodium thiosulfate, a hardener and an alkali metal salt of a monobasic carboxylic acid, said salt having the properties of entering into a true solution with water and, when in true aqueous solution in equilibrium with the bisulfite, of acidifying the bath and of maintaining the hydrogen ion concentration of the bath at v a predetermined strength greater than pH=6. t

13. Powdered material in a single mixture adapted to constitute when dissolved a photographic acid fixingbath and comprising sodium thiosulfate, a hardener, a bisulfite of an alkali metal, and an alkali metal salt of a lower fatty acid.

14. Material'in the form of a single powder adapted to constitute when dissolved a photographic acid fixing bath and comprising sodium thiosulfate, a hardener, a bisulfite of an alkali metal, and an alkali metal salt of a fatty acid containing not over two carbon atoms.

15. Powdered material in the form of a single mixture adapted to constitute when. dissolved a photographic. acid fixing bath and comprising sodium thiosulfate, a hard ener, a bisulfite of an alkali metal and an acetate of an alkali metal.

16. Powdered material in the form of a single mixture adapted when dissolved to constitute a photographic acid fixing bath, and comprising sodium thiosulfate, an alum, a bisulfite of an alkalimetal, and an alkali salt of a lower fatty acid.

17. Material in the form of a single powder adapted when dissolved to constitute a photographic acid fixing bath, and comprising sodium thiosulfate, an alum containing an aluminium compound. a bisulfite of an alkali metal, and an alkali metal salt of a fatty acid containing not over two carbon atoms.

18. Material in the form of a single powder adapted when dissolved to constitute a photographic acid fixing bath, and comprising sodium thiosulfate, an alum, a bisulfite of an alkali metal, and an acetate of an alkali metal, said acetate having the property of entering into a true solution in water. i

19. Material in the form of a single powder adapted in aqueous solution to constitute a photographic acid fixing bath and comprising sodium thiosulfate, an alum, a bisulfite of an alkali metal and an acetate of an alkali metal, the powder being substantially free from free acid.

20. Material in the form of a single powder adapted when dissolved to constitute a photographic acid fixing bath, and comprising sodium thiosulfate, alum, a bisulfite of an alkali metal and an acetate of an alkali metal.

21. Material in the form of a single powder adapted when dissolved to constitute a,

photographic acid fixing bath and consisting of sodium thiosulfate, a hardener, a bisulfite of an alkali metal, and an acetate of an alkali metal. 1

Signed at Rochester, New York, this 3rd day of May, 1921.

SAMUEL E. SHEPPARD.