US2382683A - Concentrated selenium toner and process of making - Google Patents

Description

Patented Aug. 14, 1945 CONCENTRATED SELENIUM TONER'AND raooass OF MAKING Walter V. Wadman and Lionel D. Butcher, Rochester, N. Y., asslgnors to Eastman Kodak Company, Rochester, N. Y.,

Jersey a corporation of New No Drawing. Application June 30, 1942, Serial No. 449,182

7 Claims.

This invention relates to, a concentrated selenium toner adapted to be diluted with water for use and process of making the same.

Selenium toners are well known in the photographic art. However, selenium toners heretofore used have been prepared immediately prior to use and have been in the form of dilute photographic baths. Such dilute solutions can not be marketed. As the result of numerous experiments we have found that the preparation of concentrated selenium toners presents many difliculties. Selenium is.a peculiar material insofar as its toning properties are concerned. It is difficult to get into solution, particularly in high concentrations, and it may be easily converted into selenium compounds having no toning properties. Also, it may be precipitated by the presence of other materials, particularly in high concentration. Selenium is quite similar to sulfur and it will be realized that its incorporation in toning solutions in high concentration along with the large amounts of other necessary ingredients of a satisfactory selenium toner is a diflicult problem.

This invention has for its object to provide a selenium toner in concentrated aqueous solution adapted to be diluted with water to form a satisfactory selenium toning bath. A further object is to provide a concentrated selenium toner containing the selenium compound -'in stable condition and in solution. A still further object is to provide a concentrated selenium toner adapted to be diluted for use and in diluted condition adapted to form a rapid toning bath. Other objects will appear hereinafter.

These and other objects are accomplished by our invention which includes an aqueous concentrated selenium toning solution adapted to be diluted with water to form a photographic toning bath, said concentrate containing a thiosulfate of a nitrogen compound and having a pH range of about 6.5 to 8.5.

We have found that the selenium compound having a toning action may be incorporated in the necessary high concentration when in the presence of the nitrogen-containing thiosulphate and at the pH value mentioned without precipitation of the selenium compound, or destruction of its toning properties. The selenium compound is also preserved so that it will exert its full tonin effect even if the concentrate is stored for a long period of time, as customarily takes place between its passage from the manufacturer to the consumer. The nitrogen-containing thiosulfate also contributes to the concentrated toner in otherways. It greatly increases the speed of toning and also prevents toning of the white portions of the.picture.

In the following description we have given several of the preferred embodiments of our invention but it is to be understood that these are set forth for the purpose of illustration and not in limitation thereof.

The selenium compound present in the concentrated toner is preferably an alkali metal selenite such as sodium selenite. This material can be added as such to the concentrate but it is preferred to form it therein. Thus, metallic selenium may be added to the concentrate in which case sodium sulfite is also present. A reaction takes place between the selenium and the sodium sulfite to form sodium selenite. It is desirable that an excess of sodium sulfite be present in the concentrated toner to act as a stabilizer, or preservative. Selenic acid, selenium dioxide and other selenium compounds may be used in the concentrate instead of the sodium selenite mentioned. When these materials are used the reaction mentioned in connection with the selenium may take place, al-' though this cannot be stated definitely since there are numerous substances present making possible several reactions.

The pH of the toning concentrate is important. If the pH of the concentrated toner is below about 6.5, the rate of toning is rapidly decreased and the tone qualities are inferior. If the concentrated toner has a pH of above about 8.5,. it will function satisfactorily as a toner. However, such a solution has the objectionable odor of ammonia and is unstable. The pH can headjusted by the addition of acidic materials such as sodium bisulfite or other alkali metal bisulfite. The acidic material should preferably have a high pH of about 4 to 6. An acid such as aqueous sulfurous acid could be used but sulfur dioxide should not be run into the mixture in order to acidify it since this will precipitate the selenium. We prefer to use sodium bisulfite for this purpose since it will not only adjust the pH to the desired value, but also form sodium sulfite which acts as a protecting agent.

In some cases the specific nitrogen-containing thiosulfate selected will not have th power of increasing the toning speed of the selenium; in this case there may also be added to the concentrate an ammonium compound having this property, such as ammonia, ammonium chloride, urea, thiourea, etc. Examples of nitrogen-containing thiosulfates are ammonium thiosulfate, uanidine thiosulfate and ethanolamine thiosulfate.

The necessary. constituents of the toner concentrate are present in such high concentration that the concentrate can be diluted with water to several times its original volume to form a satisfactorily active toning bath. The amount of selenium present preferably should be about 1% to 1.5%; the thiosulfate should preferably be present in amounts of 30% to 45%, and the sulfite or preservative preferably in amounts of about 5 to although somewhat larger or smaller amounts of these materials can be used.

Example 30 grams of sodium selenite are dissolved in 300 cc. of water (125 F.); 500 grams of ammonium thiosulfate, '75 grams sodium sulfite and 100 grams sodium bisulfite wer dissolved in another quantity of water amounting to 500 cc. The sodium selenite solution was then added with constant stirring to the second solution. The volume was adjusted to make one liter and the pH of the mixture was then adjusted to 6.98 by the addition of sodium bisulfite. This concentrated solution precipitated none of its constituents during keeping over a substantial period of time. For use it is diluted with three parts of water at about 70 F. and will satisfactorily tone in the very short time of two to five minutes. Washing with water should follow the toning.

The concentrated toner can be used for the same purpose as selenium toners heretofore prepared, thus it may be employed to tone photographic papers of various types such as Velox, Azo, Portrait proof, and other photographic papers containing silver chloride, silver bromide, or mixtures of such light sensitive substances which have been exposed and developed. Toning treatment is preferably applied to the developed image immediately after fixing and before drying of the prints. However, it may be applied to dry prints or photographic images in other stages of preparation.

What we claim is:

1. An aqueous concentrated selenium toning solution adapted to be diluted with water to many times its original volume to form a photographic toning bath, said concentrate including an aqueous'solution of a selenium compound hav ing a toning action, and a nitrogen-containing thiosulfate, and having suflicient acidic substance present to give a pH range of about 6.5 to 8.5, the selenium compound being present in an amount suflicient to give between about 1 and 1.5% selenium content, the nitrogen-containing thiosulfate in an amount between about 30 and 45% and all of the constituents being substantially completely dissolved in the water and being present in such high concentration that the concentrate can be diluted with water equal to many times its volume to form a satisfactory toning bath.

2. An aqueous concentrated selenium toning solution adapted to be diluted with water to ma y times its original volume to form a photographic toning bath, said cancentrate including an aqueous solution of a selenium compound having a toning action, a preservative, a nitrogencontaining thiosulfate, and an alkali metal bisulfite, and having sufficient acidic substance present to give a pH range of 6.5 to 8.5, the selenium compound being present in an amount suflicient to give a selenium content of between about 1 and 1.5%, the nitrogen-containing thiosulfate in an amount between about 30 and 45% and all of the constituents being substantially completely dissolved in the water and being present in such high concentration that the concentrate can be diluted with water equal to at least three times its volume to form a satisfactory toning bath.

3. An aqueous concentrated selenium toning solution adapted to be diluted with water to form a photographic toning bath, 'said concentrate containing about 1 to 1.5% selenium, about 30 to 45% of a nitrogen-containing thiosulfate and about 5 to 10% of a soluble sulfite, and having sufficient acidic substance present to give a pH range of about 6.5 to 8.5 the constituents being substantially completely dissolved in the water.

4. An aqueous concentrated selenium toning solution adapted to be diluted with water to many times its original volume to form a photographic toning bath, said concentrate including an aqueous solution of an alkali metal selenite, an alkali metal sulfite, an alkali metal bi-sulfite, and a nitrogen-containing thiosulfate and and having sufficient acidic substance present to give a pH range of 6.5 to 8.5, the alkali metal selenite being present in an amount sufiicient to give between 1 and 1.5% selenium content, the nitrogen-containing thiosulfate in an amount between about 30 and 45% and all of the constituents being substantially completely dissolved in the water and being present in such high concentration that the concentrate can be diluted with water equal to at least three times its volume to form a satisfactory toning bath.

5-An aqueous concentrated selenium toning solution adapted to be diluted with water to many times its original volume to form a photographic toning bath, said concentrate including an aqueous solution of a selenium compound having a toning action, an alkali metal sulfite, an alkali metal bisulfite, and ammonium thiosulfate, and having sufficient acidic substance present to give a pH range of 6.5 to 8.5, the selenium compound being resent in an amount sufiicient to give between about 1 and 1.5% selenium content, the ammonium thiosulfate in an amount between about 30 and 45% and all of the constituents being substantially completely dissolved in the water and being present in such high concentration that the concentrate can be diluted .with water equal to at least three times its volume to form a satisfactory toning bath.

6. An aqueous concentrated selenium toning solution adapted to be diluted with water to form a photographic toning bath, said concentrate including as initial constituents an aqueous solution of about 30 grams of sodium selenite, 7 grams of sodium sulfite, grams of sodium bi-sulfite and 500 grams of a member of the group consisting of ammonium and guanidine thiosulfate, and having a pH of about '7, said constituents being contained in 1 liter of solution in the amounts indicated and being substantially completely dissolved therein.

7. The method of preparing a concentrated selenium toner which comprises dissolving a selenium compound having a toning action in water to form a first solution, dissolving a nitrogen containing thiosulfate, a soluble sulfite and a bisulfite in water to form a second solution, adding the first solution to the second with stirring and adiusting the pH of the mixture to between about 6.5 and 8.5 by incorporation of an acidic substance the selenium compound being present in the final mixture in an amount sufficient to give a selenium content of between about 1 and 1.5% and the nitrogen-containing tgiosulfate in an amount between about 30 and 4 WALTER V. WADMAN. LIONEL D. BUTCHER.