US2625476A - Photographic silver halide developing solutions containing calcium precipitation inhibitors - Google Patents

Description

Patented Jan. 13, 1953 PHOTOGRAPHIC SILVER HALIDE DEVELOP- ING SOLUTIONS CONTAINING CALCIUM PRECIPITATION INHIBITORS Richard W. Henn, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey No Drawing. Application March 28, 1951, Serial No. 218,073

12 Claims. 1

This invention relates to photography and particularly to methods and materials for preventing precipitation of calcium or other insoluble salts in photographic developers and other solutions.

The precipitation of insoluble calcium salts in water is a problem in many industries and is particularly objectionable in the photographic industry because of its effect on the quality of photographic films and the usability of photographic processing solutions. The use of certain complex phosphates, especially polymerized sodium metaphosphate and sodium or potassium pyrophosphates, in photographic developers to reduce the formation of calcium sulfite scum on the jfilms and calcium precipitates in the developer is known. Upon standing in aqueous solutions, all of these phosphates gradually hydrolyze to the orthophosphates (Na3PO-4, Nan-IP04 or NaH2PO4, depending upon the pH) which not only possess no inhibiting properties but may also precipitate the calcium themselves as the fiocculent calcium orthophosphates. In addition to this difiiculty, the addition of an excess of these inhibitors to alum fixing baths as whencarried over from the developer, causes the precipitation of aluminum phosphate.

If the metaphosphate and pyrophosphate are expressed in terms of the ratio of sodium oxide to phosphorus pentoxide, it will be seen that sodium metaphosphate has the formula NazO-PzOs, and sodium pyrophosphate has the formula 2Na20-P205.

In the copending application, SerialNo. 751,122, filed May 28, 1947, now U. S. Patent 2,541,470, granted February 13, 1951, of whichl am a joint inventor, is disclosed the effect of various polyhydroxycarboxylic acids on calcium precipitation in aqueous solutions.

I have discovered that if diglycolic acid and it alkali metal salts are used alone or in conjunction with a phosphate of the type indicated hereinafter, it is very much more effective in the prevention of calcium precipitation and the precipitation of other insoluble salts than are the polyhydroxy carboxylic acids, or any other acids previously used for this purpose. Moreover, in certain instances in photographic developers, the acid exerts a preservative effect.

It is, therefore, an object of the present invention to provide a method for preventing precipitation of insoluble calcium salts in water. A further object is to provide a method for preventing the precipitation of calcium and the formation of acalcium sulfite scum on photographic films when treated in a developing bath. Other objects will appear from the following description of my invention.

These objects are accomplished by using either diglycolic acid alone or in conjunction with alkali metal phosphates particularly as a calcium precipitation inhibitor. My invention includes aqueous systems, especially developer compositions, containing such compounds both in Wet and dry form.

The phosphates particularly useful in my invention, in conjunction with diglycolic acid, for their sequestering properties, are the water-soluble polyphosphates also known as molecularly dehydrated phosphates having less water in proportion to P205 than orthophosphoric acid. (Schwartz and Munter, Ind. & Eng. Chem., 34, 32: 1942) and (Partridge Chem. & Eng. News, 27, 21411949.) Accordingly, by the term polyphosphate I mean the water-soluble phosphates of the general formula :cM2O-yP2O5, where M20 represents an alkali metal oxide such as sodium, potassium or ammonium oxide, and the ratio of a: to y is from 1 to 2. Included in this group are the following phosphates:

Sodium tripolyphosphate (5:3)

Sodium pyrophosphate (2:1)

Sodium tetraphosphate (3:2)

Sodium metaphosphate (1:1)

Sodium hexametaphosphate (1:1) glass Sodium pentapolyphosphate (6:5)

While the phosphates contemplated as a part of my invention have the property of forming soluble complexes with metal salts such as calcium and magnesium salts to a limited extent, the addition of diglycolic acid and its soluble salts to aqueous systems materially delays the precipitation of insoluble salts and the effect obtained is greater than expected from the behavior of either the phosphate or diglycolic acid used alone, as will be seen from consideration of the data to be subsequently presented. The addition of diglycolic acid to aqueous developing compositions produces the same effect and delays the formation of calcium sludge normally formed when calcium salts are added as an impurity in the water or from the film in processing operations. Presumably, diglycolic acidfor-ms soluble complexes with the calcium salts, as do' other organic acids such as those mentioned in the above copending application. However, the calcium complex of diglycolic acid appears to be more stable than the calcium complexes of the other acids and of the phosphates since a developer composition containing diglycolic acid can be held at the boiling point for from six to seven hours without loss of its sequestering power.

Sodium hexametaphosphate and sodium pyrophosphate and various organic acids have previously been used in photographic developer compositions, and sodium tetraphosphate is disclosed in the mentioned copending invention for the same purpose together with various polyhydroxy acids. Similarly, diglycolic acid and its salts are useful with improved results as can be seen by consideration of the following comparative tests.

Acids such as ethylenediamin tetraacetic acid and triglycin materially accelerate the rate of oxidation of developer solutions particularly in the presence of minute quantities of iron. For example, a developer containing 0.5 per cent of triglycin together with eight parts per million of iron and two parts per million of copper caused very rapid oxidation of the developer when air was bubbled through the solution for two hours. When the developer was formulated with diglycolic acid instead of triglycin, the developer withstood similar aeration for 30 hours.

When sodium tetraphosphate was used alone as a sequestering agent in a developer composition of the type set forth in detail hereinafter at pl-I of 10, it lost 70 per cent of its activity after one hour at 95 C. When diglycolic acid was used in formulating the developer instead of the phopshate, no loss of activity was noted after six hours at 95 C.

These data constitute positive evidence of the improved effectiveness of diglycolic acid as a stabilizing agent for the prevention of calcium precipitation on storage of developer compositions. Diglycolic acid is a stronger sequestering agent than acids such as citric, gluconic and tartaric acids. For example, 50 grams of diglycolio acid incorporated into a liter of developer 'sequestered nine grams of calcium chloride under the conditions of test. At equal concentrations, soduim citrate sequestered two grams; sodium gluconate, 1.5 grams; and sodium potassium tartrate, 1.5 grams of calcium chloride. Similarly, glycolic acid had no effect as a sequestering agent at a concentration at which diglycolic was highly effective.

Diglycolic acid is more elfective in the prevention of calcium precipitation in silver halide developers containing borate salts, than in de- Velopers containing carbonate as the alkaline material; however, very useful results are obtained in either case. Typical developers to which diglycolic acid can be added alone or in conjunction with the phosphates indicated above are the following:

Monomethyl-p-aminophenol sulfate g 2 Hydroquinone g 5 Sodium sulfite desiccated g 100 Borax g 2 Water to liter 1 Monomethyl-p-aminophenol sulfate g 3.1 Hydroquinone g 12 Sodium sulfite, desiccated g 45 Sodium carbonate, desiccated g.. 67.5 Potassium bromide g.. 1.9 Water to liter 1 In addition to protecting the developer against calcium precipitation, the employment of the acid of my invention particularly in conjunction with phosphate, will greatly reduce the tendency for aluminum phosphate to be formed in the fixing bath and will reduce the attendant sludge.

The use of these inhibitors need not be confined to the developer but may be extended to other III IV 0707B"? QTEIYLS Monomethyl-p-aminophenol sulfata 2. 5 2.5 Hydroquinone 2. 5 2. 5 Sodium sulflte (anhydrous). 50.0 50.0 Sodium metaborate. 20. 0 20. 0 Diglycolic acid 50. 0 Sodium hydroxide, 95% 30.0

Developer III was found to precipitate insoluble salt with the addition of 0.15 gram of calcium chloride per liter, while developer IV permitted the addition of 8 grams of calcium chloride per liter without precipitation even after heating and allowing the developer to stand.

The improved results obtained with a carbonate-containing developer are shown by diluting developer II above (one part of developer to two Of water) and then adding 50 grams of diglycolic acid and sufiicient sodium hydroxide to neutralize the acid. As compounded, the developer was protected against addition of 1.5 grams of calcium chloride per liter, whereas without the addition of glycolic acid, insoluble salt was precipitated in the same developer by the addition of less than 0.1 gram of calcium chloride per liter,

In addition to the mentioned instability of phosphate complexes, it is difiicult to prevent the precipitation of the large quantities of calcium introduced into a developer by the film when employing the polyphosphates alone, even in high concentrations. In developers employing metaborate as the alkaline material, optimumsequestering obtainable with polyphosphates still results in the formation of considerable calcium sludge. This sludge is almost completely prevented by the addition of diglycolic acid to supplement the action of the phosphate. In practice, the acid is generally added to the replenisher solution to compensate for the calcium salt be- Developer Replen- Replen V isher A isber B Monomethyl-p-aminophenol sul- Grams Grams Grams fate 2. 5 5. 0 5. 0 Hydroqumone 2. 5 l0. 0 10. 0 Sodium su1fite- 60. O 60. 0 60. 0 Sodium metaborate. 10.0 40. 0 40. 0 Sodium hydroxide 4. 0 8. 5 Sodium tetraphosphate 0.5 l. 0 l. 0 Diglycolic acid 7. 5

A further characteristic of diglycolic acid when used for the prevention of the precipitation of insoluble salts in water is its effectiveness over-a wide range :of pH. For example, sodium hydroxide was added to several one per cent solutions of diglycolic acidto adjust the-pH over the range of 2 to 12. Sodium fluoride was added as an indicator,:and1then as varying quantities of calcium chloride were added, the mixtures were allowed to stand. In the absence of :the diglycolicacid, precipitates were formed with very low concentrations of calcium chloride. Over the pH range of 4 through '10, 0.5 gram of diglycolic acid successfully sequestered 0.1 gram .of calcium ch ride. The sequestering action decreased somewhat at pI-I'values of 2 and 12. A similar but more pronounced effect obtained if a polyphosphate is also present. Accordingly, the use of diglycolic acid as a sequestering agent is not limited to alkaline developer compositions but can be used in acid systems as well, for example, acid photographic fixing baths. Similarly, it has been found that the addition of as little ,as 0.1 per cent of neutral diglycolic acid to ordinary tap water will lar ly prevent the formation of scale usually obtained in heating water, for example, in boiler tubes.

The following examples further illustrate my invention.

EXAMPLE 1 The following compositions are packaged ready for dissolving in one liter of water to make a photographic developing solution:

Compartment A Grams Monomethyl-p-aminophenol sulfate 5 Hydroquinone 2.5

Compartment B Grams Sodium sulfite (anhydrous) 60 Sodium metaborate Diglycolic acid 50 Sodium hydroxide 30 EXAMPLE 2 Compartment A Grams Monomethyl-p-aminophenol sulfate 10 Hydroquinone 5 Sodium tetraphosphate 1 Compartment B Grams Sodium sulfite 60 Sodium metaborate 40 Sodium hydroxide 8.5 Diglycolic acid 7.5

The chemicals are then added to one liter of water.

EXAMPLE 3 If desired, in Example 2, the diglycolic acid can be placed in Compartment A rather than in Compartment B.

EXAMPLE 4 In any of the above solid mixtures containing alkali-metal polyphosphates, the tendency of the polyphosphate to fuse or become tacky on exposure to moist air may be overcome by mixing an inert alkali-metal sulfate, such as anhydrous sodium or potassium sulfate, with the polyphosphate. A mixture of one part of sodium tetraphosphate with two parts of anhydrous sodium sulfate or potassium sulfate was found to remain free flowing upon an exposure to an atmosphere of '70 per cent relative humidity for two weeks. The concentration may vary from one part of 6 polyphosphate in from 2 to :20 :parts .of alkalimetal sulfate.

EXAMPLE 5 Th presence of iron in some po'iyp-hosphates may cause increased development fog. This fog may be controlled by the addition of -antifoggants such as alkali-metal bromides and iodides, or organic antifoggants such as 1,2,3-benzotriazo'1e and 'fi-nitrobenzimidazole. A sample of sodium 'hexametaphosphate containing 0.03 per cent of iron was found to give bad fog when added to developing solutions for high speed negative emulsions. The presence of 0.05 gram of 1,2,3- benzotriazole per gram of sodium hex-ametaphosphate'prevented this fog.

The concentration of antifoggant may vary from 1 part of antifoggant to from 2 to parts of phosphate in the case of potassium iodide, 1,2,3-benzotriazole and 'G-nitrobenzimidazole -nitrate and from 1 part of antifog-gant to from 0.1 to '10 parts of phosphate in the case of potassium bromide. I

In photographic developing solution useful results are obtained by using from about 2 to 100 grams per liter of solution of diglycolic acid or itsalkali metal salts, particularly-in conjunction with from about :05 to 20 grams per liter of polyphosphate. These ranges are particularly useful in conjunction with alkali metal tetraphospha'tes :and'hexametaphosphates.

The other polyphosphates indicated above besides sodium tetraphosphate can be added to any of the above formulas in dry or liquid form.

Diglycolic acid can be added to the hydrazinecontaining developer compositions disclosed in the Ives application, Serial No. 192,380, filed 0ctober 26, 1950, now U. S. Patent No. 2,588,982, granted March 11, 1952, and the Bean et a1. application, Serial No. 218,072, filed concurrently herewith, which are used in making direct positive images. In this case, diglycolic acid is employed especially as a preservative as well as functioning as a sequestering agent.

I claim:

1. An alkaline photographic developing solution comprising a silver halide developer and a compound selected from the class consisting of diglycolic acid and its alkali metal salts.

2. An alkaline photographic developing solution comprising a silver halide developer, a watersoluble alkali metal polyphosphate and a compound selected from the class consisting of diglycolic acid and its alkali metal salts.

3. An alkaline photographic developing solution comprising a silver halide developer, a watersoluble alkali metal polyphosphate having the formula xMzo-yPzOs where M is an alkali metal, and :c and 11 represent numbers in which the ratio of a: to y is from 1 to 2, an alkaline material, and a compound selected from the class consisting of diglycolic acid and its alkali metal salts.

4. An alkaline photographic developing solution comprising a silver halide developer, 2. watersoluble metal salt of tetraphosphoric acid, an alkaline material, and a compound selected from the class consisting of diglycolic acid and its alkali metal salts.

5. An alkaline photographic developing solution comprising a silver halide developer, from .05 to 20 grams per liter of a water-soluble alkali metal polyphosphate, an alkaline material, and from 2 to 100 grams per liter of a compound selected from the class consisting of diglycolic acid and its alkali metal salts.

6. An alkaline photographic developing solution comprising a silver halide developer, from .05 to 20 grams per liter of a water-soluble alkali metal salt of tetraphosphoric acid, and from 2 to 100 grams per liter of a compound selected from the group consisting of diglycolic acid and its alkali metal salts.

7. An alkaline photographic developing solution comprising a silver halide developer, from .05 to 20 grams per liter of a water-soluble alkali metal hexametaphosphate, and from 2 to 100 grams per liter of a compound selected from the class consisting of diglycolic acid and its alkali metal salts.

8. A photographic developer in dry form comprising a silver halide developer, an alkaline material and a compound selected from the group consisting of diglycolic acid and its alkali metal salts.

9. A photographic developer in dry form comprising a silver halide developer, an alkaline material, a compound selected from the group consisting of diglycolic acid and its alkali metal salts, and a water-soluble alkali metal polyphosphate.

10. A photographic developer in dry form comprising a silver halide developer, sufiicient watersoluble alkali metal polyphosphate having the formula mMzO-gPzOa where M is an alkali metal, and a: and 3 represent numbers in which the ratio of x to 1! is from 1 to 2, to produce .05 to 20 grams per liter in solution, a sufficient amount of a compound selected from the class consisting of diglycolic acid and its alkali metal salts to produce 2 to 200 grams per liter in solution, and sufficient alkaline material to produce an alkaline developer solution when the mixture is dissolved in water.

11. A photographic developer in dry form comprising a silver halide developer, sufficient watersoluble alkali metal salt of tetraphosphoric acid to produce .05 to 20 grams per liter in solution, a sufficient amount of a compound selected from the class consisting of diglycolic acid and its alkali metal salts to produce 2 to 200 grams per liter in solution, and sufiicient alkaline material to produce an alkaline developer solution when the mixture is dissolved in water.

12. A photographic developer in dry form comprising a silver halide developer, sufiicient watersoluble alkali metal hexametaphosphate to produce .05 to 20 grams per liter in solution, a sufiicient amount of a compound selected from the class consisting of diglycolic acid and its alkali metal salts to produce 2 to 200 grams per 'liter in solution, and suflicient alkaline material to produce an alkaline developer solution when the mixture is dissolved in water.

RICHARD W. HENN.

No references cited.

Claims (1)

1. AN ALKALINE PHOTOGRAPHIC DEVELOPING SOLUTION COMPRISING A SILVER HALIDE DEVELOPER AND A COMPOUND SELECTED FROM THE CLASS CONSISTING OF DIGLYCOLIC ACID AND ITS ALKALI METAL SALTS.