US3260605A - Method for preparing light-sensitive silver halide emulsions suitable for print-out recording materials - Google Patents

Description

United States Patent Office 3,260,605 Patented July 12, 1966 3 260,605 METHOD FOR PREPiAlRlNG LIGHT-SENSITIVE SILVER HALIDE EMULSIUNS SUITABLE FOR PRINT-OUT RECORDING MATERIALS Edward Arthur Sutherns, Harrow, Middlesex, England, assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Sept. 5, 1962, Ser. No. 221,428 8 Claims. (Cl. 96108) This invention relates to silver halide photography, and, more particularly, to a method of preparing photographic silver halide emulsions, especially those useful in print-out photography.

Many methods of preparing photographic silver halide emulsions have been previously described and among the most ancient of these methods are those concerned with the preparation of silver halide emulsions exhibiting print-out characteristics. Print-out emulsions are distinguished from developing-out emulsions in that the former produce a visible image merely upon exposure to actinic radiation, whereas developing-out emulsions produce a visible image upon chemical development with a reducing agent, such as hydroquinone.

Print-out materials for recording the path of an oscillograph spot have also been described in the prior art. Print-out papers, known as direct-writing materials, are particularly useful for this purpose since they provide ready access to the recorded information without conventional processing. In general, such oscillograph recording exposures do not ordinarily give a visible image. The record trace is made visible by a photodevelopment technique wherein a subsequent exposure to low intensity lighttusually diffuse) is given.

However, many of these known print-out Papers have one or more of the following defects:

(1) The background where no exposure occurred in the oscillograph may print out to a substantial density, and since the density in the exposed areas may be quite low, there is inadequate discrimination between the trace density and the background density. This may be no more than 0.1 to 0.2 density unit.

(2) Satisfactory discrimination may be only obtained by restricting the intensity of the difiuse low intensity exposure so that the time needed to give an adequate trace density, termed access time, may be a minute or more. Use of higher intensity for the purpose of shortening the access time produces reduced discrimination.

(3) Prolonged exposure, such as may be caused by leaving the paper out in a normal workroom reduces the discrimination either by causing a rise in the density of the background or by reducing the trace density, which may fade completely.

(4) The range of frequencies which can be recorded, even by oscillographs with very powerful light sources, is restricted by emulsion sensitivity, which determines writing speed.

According to my invention, there is provided a method of making a light-sensitive photographic silver halide emulsion exhibiting particularly useful print-out characteristics and. which avoids most or all of the aforementioned defects.

It is, therefore, an object of my invention to provide an improved method of preparing photographic emulsions. Another object is to provide photographic emulsions exhibiting improved print-out characteristics. Still another object is to provide print-out silver halide emulsions exhibiting especially useful stability following the post-latensification exposure. Other objects will become apparent from a consideration of the following description and examples.

The method of my invention comprises precipitating silver halide in an aqueous medium containing a protein peptizer, such as gelatin or a gelatin derivative. The precipitation of the silver halide is most advantageously effected by the double-jet technique wherein an aqueous solution of a water-soluble silver salt and an aqueous solution of a water-soluble halide are simultaneously added to an aqueous solution containing the protein peptizer. Precipitation is effected in an acidic medium and should be effected in the substantial absence of any sulfur-sensitizing compounds. For this reason, I have found that most useful results are obtained using a photographically inert protein peptize-r of the type described by Mees in The Theory of the Photographic Process, Macmillan Company, 1954, page 112. Such inert protein peptizers are also mentioned by Lowe, Jones and Roberts in Fundamental Mechanisms of Photographic Sensitivity, edited by J. W. Mitchel, Butterworth, London, 1951, page 112 (Communication 1311). Most advantageously, the precipitation is effected in the presence of a small amount of a silver halide solvent, such as a water-soluble thiocyanate. The silver halide solvent or ripening agent can be added to the making kettle before adding the soluble silver salt or it may be added with the water-soluble halide, which is run in during the making, or preferably some silver solvent may be present in the making kettle and some in the halide solution.

Rapid stirring is employed during the precipitation and by using the double-jet technique, an exceptionally narrow grain size spread is obtained. A moderate amount of silver halide solvent further facilitates the formation of silver halide grains of substantially uniform grain size. Alkali metal thiocyanates and cyanates have been found to be particularly useful silver halide solvents. By stirring the ingredients of the making kettle and using a silver halide solvent, it is possible to obtain silver halide grains exhibiting particularly useful print-out characteristics and having -a mean grain area between 0.8, and 25,13.

The pH of the precipitation is quite important in obtaining print-out emulsions according to my process, and I have found that the pH should be maintained at no more than about 5.0, and preferably less than this figure. Precipitation is effected in this acidic medium so that the halide ions are always in excess during the precipitation. To achieve this, soluble halide can be added to the aqueous solution containing peptizer before commencing the addition of the silver salt. The actual precipitation time can vary considerably depending upon the grain size desired. Generally 20 to 60 minutes are suflicient to obtain an average grain size in the range desired. The size of the jets admitting the aqueous solutions can be varied, but they are generally similar in size so that the concentrations of the reactants in the making kettle can be accurately controlled.

The amounts of soluble halide and silver salts added can be varied, depending upon the amount of silver halide to be formed. The concentrations of the solutions and the times taken to add them can be varied widely. However, the time taken for the addition of the two solutions and the concentrations of the soluble salts should be sufficient to produce a coarse-grained emulsion by the end of the making period.

The soluble halide employed can be, for example, all bromide or bromide together with a small amount of another halide, such as iodide or a mixture of iodide and chloride. Alkali metal halides, such as sodium or potassium, are particularly useful, although ammonium halides can also be employed. The silver salt is usually silver nitrate, athough other water-soluble silver salts, such as the acetate, etc., can be used.

The amount of soluble silver halide solvent employed may be varied, depending upon the particular grain size materials.

desired, etc. Thiocyanates are particularly useful silver halide solvents and it has been found that good results can be obtained when the thiocyanate used ranges from 0.75 to 7.5 molar percent of the total silver halide formed. If thiocyanate is added With the halide solution, an amount up to 20 mole percent of the silver halide formed can be used.

The temperature of the making kettle is preferably somewhat higher than normally used in making con ventional emulsions, since the higher temperatures facilitate grain growth. I have found that temperatures 'within the range of 65 to 85 C. are particularly useful.

After precipitation has been completed, and further ripening, if necessary, the emulsion is cooled to about 40 to 50 C. and then mixed with more protein peptizer, such as gelatin, and other additives, such as coating aids. The emulsion is then ready for coating, which can be effected without washing the emulsion, although washing with water to remove soluble salts may sometimes be used.

In the emulsions of the present invention, thiocyanates are particularly useful in the precipitation, since they not only function as a ripening agent, but as halogen acceptors. If desired, supplementary halogen acceptors can be used, and where other ripening agents have been employed, it is particularly useful to employ a supplementary halogen acceptor. Typical halogen acceptors which can be employed in my invention include phenylenediamines, hydroquinone, borax, alkali metal hydroxides, 3-pyrazolidones (e.g., 1-phenyl-3-pyrazolidone, etc.), thiosalicylic acid, etc.

In a particularly useful embodiment of the invention, a Water-soluble lead salt can be added to the making kettle, preferably with the soluble silver salt. The lead salt has been found to provide lower background density while exhibiting higher trace density than obtainable with emulsions containing no lead salt. Typical lead salts useful in my invention include lead acetate, lead nitrate, etc.

The process of forming print-out images using the emulsions of my invention comprise exposing a layer of the emulsion to a high intensity actinic light source for a very short period, followed by photodevelopment of the latent image by uniformly exposing the layer for a second or more to diffuse light or relatively low intensity, generally of from about 25 to 1000 ft. candles. The emulsion layer can be exposed to an oscillograph spot or to a rapidly moving galvanometer spot of the type described in Heiland US. Patent 2,580,427, issued January 1, 1952. Upon photodevelopment with diffuse illumination, the recorded image rapidly appears.

Recording materials made according to this invention have satisfactory access time, discrimination, writing speed and stability of trace upon prolonged exposure and show at least one or more of these characteristics to a substantially greater degree than heretofore known recording A particular advantage of my emulsions is that discrimination is much less dependent upon the intensity level of the light used for photodevelopment, thus materially shortening the exposure required to produce an image. Frequently, one second is all that is needed to produce a useful image.

The following examples will serve to illustrate more fully the method of practicing my new invention, although i it is not to be understood that these examples are limittions containing 39 g. of silver nitrate in 200 ml. of water and 29.1 g. of potassium bromide in 200 ml. of water simultaneously to a solution containing 8 g. of inert "gelatin, 0.75 g. of potassium bromide, 3.0 g. of potassium thiocyanate, 5.6 ml. of 1,0 N-sulfuric acid and 113 ml.

of water at 72 C. over a period of 40 minutes. The emulsion was coated on paper and air-dried Without washing.

A sample coating of this emulsion was given an exposure to a Microflash lamp for a period of about 2 microseconds and the image photodeveloped by an exposure to diffuse daylight. It was found to photodevelop rapidly and gave a high trace/ background density ratio, the trace being deep blue and the background light yellow. The exposed and photodeveloped material was held for several hours in daylight. The trace of the material remained clearly visible. The sensitivity of the microflash exposure was high.

Example 2 A silver halide emulsion was prepared by adding solutions containing 39 g. of silver nitrate in 200 ml. of water and 28.6 g. of potassium bromide together with 6 g. of potassium thiocyanate in 200 ml. of Water simultaneously to a solution containing 4 g. of inert gelatin, 0.465 g. of sodium chloride, 5.6 ml. of 1.0 N-sulfuric acid and 115 ml. of Water at 72 C. over a period of 40 minutes.

A sample coating of this emulsion showed photographic properties similar to those described in Example 1.

Example 3 The addition of halogen acceptors, such as thiosalicylic acid to these emulsions of Examples 1 and 2, improved their print-out characteristics by giving 'higher discriminations and shorter access times.

Example 4 An emulsion was prepared according to Examples 1 and 2 except that the silver nitrate solution contained 0.2 g. of lead nitrate. When coated and tested, the material containing the lead salt was found to have a lower background density and a higher trace density than a similar emulsion which contained no lead salt.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scop of the invention as described herein-above and as defined in the appended claims.

What I claim as my invention and desire secured by Letters Patent of the United States is:

1. A method of preparing photographic emulsions comprising simultaneously adding an aqueous solution of a Water-soluble silver salt and an aqueous solution of a water-soluble halide salt, wherein at least 90 mole percent of the halide salt is a bromide salt, to an aqueous solution containing a protein peptizer thereby'precipitating silver halide grains, maintaining the pH of said peptizer solution acidic during said additions and maintaining an excess of halide ions over silver ions by adding said watersoluble silver salt solution at such a rate as to provide said excess of halide ions over said silver ions, said precipitation being effected in the substantial absence of sulfur sensitizers and at least one of said aqueous solutions containing a small amount of an alkali metal thiocyanate silver halide solvent to effect ripening of said silver halide grains.

2. A method as defined in claim 1 wherein a temperature of from 65 to C. is maintained during precipitation.

3. A method as defined in claim 1 wherein the pH is maintained at not more than 5.0 during precipitation of said silver halide.

4-. A method of preparing photographic emulsions comprising simultaneously adding an aqueous solutionof a water-soluble silver salt and an aqueous solution of a Water-soluble halide salt, wherein at least mole percent of the halide salt is a bromide salt, to an aqueous solution containing gelatin thereby precipitating silver halide grains, maintaining the pH of said gelatin solution acidic during said additions and maintaining an excess of halide ions over silver ions by adding said water-soluble silver salt solution at such a rate as to provide said excess of halide ions over said silver ions, said precipitation being effected in the substantial absence of sulfur sensitizers and at least one of said aqueous solutions containing a small amount of an alkali metal thiocyanate silver halide solvent to efiect ripening of said silver halide grains.

5. A method as defined in claim 4 wherein said halide salt consists of an alkali metal bromide.

6. A method of preparing photographic emulsions comprising simultaneously adding an aqueous solution of a water-soluble silver salt and an aqueous solution of a Water-solubl halide salt, wherein at least 90 mole percent of the halide salt is a bromide salt, to an aqueous solution containing gelatin there'by precipitating silver halide grains, maintaining the pH of said gelatin solution acidic during said additions and maintaining an excess of halide ions over silver ions by adding said Water-soluble silver salt solution at such a rate as to provide said excess of halide ions over said silver ions, precipitation being effected in the substantial absence of sulfur sensitizers, at least one of said aqueous solutions containing a small amount of an alkali metal thiocyanate silver halide solvent to effect ripening of said silver halide grains, and at least one of said aqueous solutions containing a small amount of a water-soluble lead salt.

7. A method of precipitating photographic emulsions comprising simultaneously adding an aqueous solution of a water-soluble silver salt and an aqueous solution of a water-soluble halide salt, wherein at least 90 mole percent of the halide salt is a bromide salt, to an aqueous solution containing a protein peptizer and a water-soluble alkali metal bromide, thereby precipitating silver halide grains, maintaining the pH of said peptizer solution acidic during said additions and maintaining an excess of halide ions over silver ions by adding said Water-soluble silver salt solution at such a rate as to provide said excess of halide ions over said silver ions, said precipitation being effected in the substantial absenc of sulfur sensitizers and at least one of said aqueous solutions containing a small amont of an alkali metal thiocyanate silver halide solvent to efiect ripening of said silver halide.

8. A method of preparing photographic emulsions comprising simultaneously adding an aqueous solution of a Water-soluble silver salt and an aqueous solution of a Water-soluble halide salt, wherein at least 90 mole percent of the halide salt is a bromide salt, to an aqueous solution containing gelatin thereby precipitating silver halide grains, maintaining the pH of said gelatin solution acidic during said additions and maintaining an excess of halide ions over silver ions by adding said water-soluble silver salt solution at such a rate as to provide said excess of halide ions over said silver ions, said precipitation being efiected in the substantial absence of sulfur sensitizers and at least one of said aqueous solutions containing a small amount of an alkali metal thiocyanate silver halide solvent to elfect ripening of said silver halide grains, and adding a halogen acceptor to said photographic emulsion prior to coating thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,401,051 5/1946 Crouse et al. 9694 2,584,029 1/1952 Land 96-29 2,618,556 11/1952 Hewitson et al. 9695 2,960,405 11/1960 Dersch 96-94 3,033,682 5/1962 Hunt 96-94 OTHER REFERENCES Ammann-Brass: Chimia (Switzerland), 1956, 10, 173- 188 (abstracted in Chemical Abstracts, 1957, 51, 113, and in The British Journal of Photography, Aug. 2, 1957, page 451 under Analecta).

James et al.: Fundaments of Photographic Theory, 1948, John Wiley & Sons Inc., New York, pp. 21-25.

The Journal of Chemical Education, vol. 8, No. 12, December 1931, pp. 2347-2367.

Wall: Photographic Emulsions, 1929, American Publishing 00., Boston, page -59.

NORMAN G. TORCHIN, Primary Examiner.

A. D. RICCI, Assistant Examiner.

Claims (1)

1. 6. A METHOD OF PREPARING PHOTOGRAPHIC EMULSIONS COMPRISING SIMULTANEOUSLY ADDING AN AQUEOUS SOLUTION OF A WATER-SOLUBLE SILVER SALT AND AN AQUEOUS SOLUTION OF A WATER-SOLUBLE HALIDE SALT, WHEREIN AT LEAST 90 MOLE PERCENT OF THE HALIDE SALT IS A BROMIDE SALT, TO AN AQUEOUS SOLUTION CONTAINING GELTIN THEREBY PRECIPITATING SILVER HALIDE GRAINS, MAINTAIING THE PH OF SAID GELATIN SOLUTION ACIDIC DURING SAID ADDITIONS AND MAINTAINING AN EXCESS OF IONS OVER SILVER IONS BY ADDING SAID WATER-SOLUBLE SILVER SALT SOLUTION AT SUCH A RATE AS TO PROVIDE SAID EXCESS OF HALIDE IONS OVER SAID SILVER IONS, PRECIPITATION BEING EFFECTED IN THE SUBSTANTIAL ABSENCE OF SULFUR SENSITIZERS, AT LEAST ONE OF SAID AQUEOUS SOLUTIONS CONTAINING A SMALL AMOUNT OF AN ALKALI METAL THIOCYANATE SILVER HALIDE SOLVENT TO EFFECT RIPENING OF SAID SILVER HALIDE GRAINS, AND AT LEAST ONE OF SAID AQUEOUS SOLUTIONS CONTAINING A SMALL AMOUNT OF A WATER-SOLUBLE LEAD SALT.