US2174494A

US2174494A - Photographic fixing agent

Info

Publication number: US2174494A
Application number: US264975A
Authority: US
Inventors: Barnes Robert Bowling
Original assignee: American Cyanamid Co
Current assignee: Wyeth Holdings LLC
Priority date: 1939-03-30
Filing date: 1939-03-30
Publication date: 1939-09-26
Anticipated expiration: 1956-09-26

Description

Patented Sept. 26, i93

zen-14,494 rno'roomrmc FIXING AGENT Robert Bowling Barnes, Stamford,

or to American Gyanamid Company,

Gonm; assign; New York,

N. Y., a corporation of Maine No Drawing. Application March 343, 1939,

Serial No. 264,975

8 Claims.

This invention relates to a photographic fixing composition and more particularly, to a photographic fixing and hardening bath.

The standard fixing baths for silver halide sensitized material depend on the solvent action of sodium thiosulfate on silver halide. Commercial solutions usually contain in addition sodium sulfite, suificient acid to bring about the desired pH and, in the case of hardening baths, alum, chrome alum, and the like;

The fixers which are used at the present time have two disadvantages; In the first place, the fixing speed is only moderate and, in the second place; the baths become exhausted very rapidly. In fact, exhaustion takes place when the amount of silver dissolved is only a few-percent of that corresponding to the sodiumthiosulfate present. A serious wastage in chemicals is thus encountered when spent fixing solutions have to be discarded.

According to the present invention, the fixing solution contains an amidine ion and preferably .a guanidine ion in effective amounts. The ion may be introduced into the solution by using the corresponding amidine thiosulfate in place of part or all of the sodium thiosulfate or a salt of the amidine may be added to a fixer bath containing sodium or alkali metal thiosulfate. I do not know in just what form the amidine ion is present but substantially the same results are obtained regardless of whether'the amidine sulfate is first prepared or whether an amidine salt is added to a sodium thiosulfate bath.

The presence of the amidine ion results in a material increase in fixing speed. While this is a characteristic of all of the amidines, they differamong themselves in their effectiveness, guanidine showing the greatest increase in speed. The presence of the amidine ion and particularly the guanidine ion also increases the number of films or paper prints which can be fixed in a given amount .of solution. In the case of guanidine, this increase is most marked. I do not know exactly why the great increase in fixing capacity takes place when the guanidine ion is present in the fixing bath. It is possible that the presence of the guanidine ion permits solution of larger amounts of silver halide before exhaustion and it is also possible that at least part of the effect is due to the precipitation of silver in the metallic form by the presence of the guanidine. Thus, for example, a fixer. containing guanidine thiosulfate after it has become loaded with dissolved silver precipitates out a considerable portion of this" silver on standing.

The present invention is therefore not limited to any particular theory as to why fixing solutions containing the guanidine ion show greatly enhanced fixing capacity.

The present invention contemplates the use of fixing solutions containing any of the simple amidines. The increase in speed of fixing is greatest with guanidine and least with guanyl urea salts, while biguanides are intermediate in their efiect. The guanidine ion has the further advantage that fixing even of highly sensitized material such as panchromatic and orthochromatic film does not produce any noticeable fog.

Some of the other amidines produce a small amount of fog. For this reason, while the present invention broadly includes-the amidine ion, in a more specific aspect guanidine is the preferred amidine ion.

It is an advantage of the present invention that the amidine, and particularly guanidine, ion does not appear to interfere with the other components of the fixing solution. Thus, for example, guanidine thiosulfate may replace sodium thiosulfate in the standard fixing formulae, hardening or non-hardening, and similarly guanidine or other amidine salts may be added to the standard fixing formulae. In the case of guanidine, some care should be taken that the concentration of guanidine thiosulfate, or rather the guanidine ion, does not reach too high a figure. Thus, for

example, if the concentration greatly exceeds that corresponding to 240 parts by weight of guanidine thiosulfate per liter of fixing solution, reticulation may be noticed with certain negative material such as, for example, fast panchromatic film.

Another important advantage of the use of guanidine thiosulfate is its great solubility which permits perparing 50% solutions at 70 C. Highly concentrated liquid fixing baths can therefore be prepared which can then be diluted for use.

Guanidine thiosulfate in the dry form is stable and can be readily incorporated with other components to form a mixed, dry fixing powder which can be dissolved in water to form a fixing solution. Mixtures of guanidine salts and sodium thiosulfate can also be readily made and have satisfactory keeping qualities.

The invention will be described in greater detail in conjunction with the following specific examples which illustrate typical fixing baths according to the present invention.

Example 1 A fixing bath was prepared as follows:

. Parts Water at 52 C 600 Guanidine thiosulfate 240 Sodium sulfite, desiccated" Acetic acid, 28% 48 Boric acid, crystal 7.5 Potassium alum 15 Water at C 400 The solution has a pH of 4.45 and is very stable against sulfurization. The solution clears u'nex-' posed Eastman orthoportrait film in 1% minutes at 24 C. as compared with 3 minutes for a standard Eastman F5 fixing solution in which sodium thiosulfate takes the place of guanidine thiosulfate. The gelatin hardness of the strips was evaluated by melting point tests and showed that the fixer. using guanidine thiosulfate produced slightly harder gelatin having a melting point up to 95 or 96 C. as compared to 93 C. for a standard sodium thiosulfate fixer such as Eastman F5. The fixed films were of satisfactory color, flexibility and showed unreticulated surfaces free from fog. Increased amounts of guanidine thiosulfate causes the bath to fix more rapidly but when the amount is considerably increased there is a tendency to reticulate the film.

When a number of films or other silver halide photographic material have been fixed and the solution is allowed to stand in a glass bottle, metallic silver begins to plate out on the walls of the container whereas with an ordinary sodium thiosulfate fixing solution such as Eastman F5 practically no precipitation takes place until the solution is almost exhausted. Actinic light appears to have some accelerating action on the precipitation of silver from the guanidine thiosulfate fixing bath.

The keeping qualities of the guanidine thiosulfate solution are excellent. A particular solution was prepared and showed 1 minutes clearing time with a pH of 4.45. After 5 months, the clearing time was about the same with a pH of 4.4 and after 10 months, the clearing time was still about 1 minutes with a pH of 4.05. Before the last test, the silver which had precipitated was removed byfiltration, leaving a clear filtrate.

A test was made to determine the limit of exhaustion of the guanidine solution as compared with Eastman F5, in which solution the amount of sodium thiosulfate is the same as that of guanidine thiosulfate in the guanidine thiosul- 3 minutes at 24 fate fixer. A small portion (100 cc.) of each solution was taken and unexposed Eastman orthoportrait films were cleared in both solutions. In the fresh solution the clearing time for the guanidine fixer was 1 minutes and in Eastman F5, C. Clearing times after the solutions had been used were measured and the results of the tests appear in the following table:

Clearing time in minutes Negative material'flxed, square inches 32 Eastman F5 Did not completely clear.

Further use of the guanidine thiosulfate solution did not affect the clearing time even after 625 sq. ins. had been cleared. The longer life of the guanidine thiosulfate fixer is of great practical importance as one of the largest .costsin large scale photographic processing "is .the consumption of fixer as the bath has to be discarded long before its chemicals are exhausteddue to the fact that with sodium thiosulfate after a small amount of-silver has been dissolved the solution no longer shows rapid clearing power.

Ihave not determined definitely the reasons for the extraordinary behaviour of guanidine thiosulfate solutions and do not wish to limit the present invention to any theory of action. I

believe, however, that at least one factor lies in the precipitating action which the guanidine thiosulfate has on the dissolved silver. This appears also more likely from a consideration of the exhaustion curve. It will be noted that the guanidine thiosulfate solution slows up gradually until around 500 sq. ins. is reached and then it remains at a fixed level which makes it seem probable that an equilibrium is being reached between the precipitating action for metallic silver and the additional silver halide dissolved. The fixing action is, however, too complex to permit ready determination of whether this factor is the only one or even whether it is the predominant one and this explanation is advanced merely as a possible one without limitation on the invention.

Example 2 An Eastman F5 fixing solution was prepared and varying amounts of guanidine nitrate were added to successive 200 cc. portions and the clearing times of the resulting solutions with Eastman orthoportrait film were measured. The

An exhaustion test on orthoportrait film was then run with the following results:

Negative material fixed, square inches gg Minutes From the above its appears that the addition of guanidine nitrate produces a fixing bath having essentially similar properties to that in which uanidine thiosulfate itself was added. It is probable that some of the guanidine nitrate reacts with sodium thiosulfate to form guanidine thiosulfate but I do not believe that the presence of guanidine thiosulfate as such is essential, the presence of the guanidine radical or iron being sufiicient. It is interesting to note that even the largest amount of guanidine nitrate added was less than that theoretically required to react with all of the sodium thiosulfate.

Example 3 I A standard F5 fixing solution wasprepared and to separate 200 cc. portions guanidine nitrate, hydrochloride and carbonate were added in the noted that in the case of potassium chrome alum fixers, the fixer frequently does not have as good amounts described in Example 2 (12 gs.) and Example 3. The solutions were then tested in clearing Eastman Panchro Press cut film. The fixing times were as follows:

Fixing time in Firing solution I minutes Eastman F5 4. 25

Eastman F5+guanidine nitrate 2.

Eastman Ffiiguanidine hydrochloride 2. 75

Eastman F5 guanidine carbonate 3. 75

Times for clearing will vary with diflerent films but as is shown above-remain in substantially similar proportions.

Example 5 The Eastman F5 solution was prepared and 5 gs. of biguanide acid sulfate was added to 200 cc. The clearing time for Eastman orthoportrait film was 2.25 minutes. A slight permanent chemical fog was noticed on the film but not sufficient to materially interfere with printing quality.

Example 6 5 gs. of guanyl urea sulfate was added to 200 cc. of Eastman F5. It did not dissolve entirely and the saturated solution produced was used in clearing orthoportrait film. The time was 3.25 minutes and a slight permanent chemical fog was produced somewhat heavier than with the biguanide sulfate.

In the examples the fixing solutions are of the ordinary potassium alum type. The presence of the amidine radicals has the same speed increasing and life increasing properties with fixing solutions which do not contain hardening agents or with those in which potassium chrome alum is used in place of potassium alum. It should be keeping qualities as is the case with potassium alum fixers. The presence of the guanidine radical or iron in every case produces a. bath of high stability but if the composition of the bath is such as to render it of poor keeping qualities, the presence of a guanidine radical or amidine radical will not turn a bath having poor keeping qualities into one having good-keeping qualities.

What I claim is:

1. A silver halide photographic fixing agent of the thiosulfate type containing an amidine salt in amounts efiective to increase the fixing speed.

2. A silver halide photographic fixing agent of the thiosulfate type containin a guanidine salt in amounts effective to increase the fixing speed.

3. A silver containing guanidine thiosulfate as its major silver halide dissolving agent.

- 4. An acid silver halide photographic fixing and hardening agent of the thiosulfate type containing an amidine salt in amounts effective to increase the fixing speed and a hardening agent.

5. An acid silver and hardening agent of the thiosulfate type containing a guanidine salt in amounts effective to increase the fixing speed and a hardening agent. 6. An acid silver halide photographic fixing and hardening agent of the thiosulfate type containing a guanidine salt in amounts eflective to increase the fixing speed and an alum.

I. A silver halide photographic fixing agent of the thiosulfate type containing a biguanide salt halide photographic fixing agent halide photographic fixing in amounts effective to increase the fixing speed. 1

8. A silver halide photographic fixing agent of the thiosulfate type containing a guanyl urea salt in amounts efiective to increase the fixing speed.

ROBERT BOWLING BARNES.