US 3458316 A
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DENS/ TY July 29, 1969 F. v|Ro 3,458,316
LIGHT SENSITIVE SILVER HALIDE EMULSIONS Filed May 26, 1966 2 Sheets-Sheet 1 FIG.
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RELATIVE LOG EXPOSURE 8-- E0714 JUST BEFORE DRYING United States Patent l 3,458,316 LIGHT SENSITIVE SILVER HALHDE EMULSIGNS Felix Viro, Apalachin, N.Y., assignor to GAF Corporation, New York, NY, a corporation of Delaware Filed May 26, 1966, Ser. No. 553,082 lint. Cl. G03c 1/10 US. Cl. 96-94 2 Claims ABSTRACT OF THE DISCLOSURE Addition to a light-sensitive colloid-silver halide emulsion, prior to precipitation of the silver halide, of nitrilotriacetic acid or an alkali metal or ammonium salt thereof, in an amount from about 0.1 to 3 grams per 150 grams of silver.
This invention relates to photography and, more particularly, to light-sensitive silver halide emulsions having increased sensitivity to actinic light. More specifically, it relates to light sensitive emulsions which contain small amounts of nitrogen-containing acetic acid derivatives or other specified compounds which exhibit chelating and/ or reducing properties.
It has been suggested in US. Patent 2,666,700 that the light-sensitivity of colloid-silver halide emulsions can be improved by the presence of tetracarboxyethylenediamine, also known as ethylenediamine tetraacetic acid (EDTA) or its alkali metal or ammonium salt in restricted proportions during the emulsion digestion period of precipitated silver halide emulsion. I have found that improved light sensitivity can be obtained by adding EDTA or its salt at an earlier stage of emulsion preparation. Certain other chelating agents may also be employed; nitrilotriacetic acid and its water-soluble salts have been found better than EDTA in sensitizing silver halide emulsions. The emulsions prepared according to my invention by adding the chelating agents prior to precipitation have been found to retain their improved sensitivity longer than those prepared by adding the chelating agents during ripening.
Photographic silver halide gelatin emulsions are conveniently prepared by first swelling a part of the gelatin required for the emulsion formulation in water, heating the mixture to complete its solution and then adding a water-soluble halide salt. Such halide salts may be the alkali metal or ammonium chlorides, bromides or iodides, or mixtures thereof.
To the resulting solution, silver nitrate is added in the desired concentration with the rate of addition, temperature, and so on being dependent on the particular emulsion product to be desired. The precipitated halide emulsion is then heated to carry out the first physical or Oswald ripening step. The ripened emulsion is then precipitated and washed by a coagulation-wash technique employing generally organic Wetting agenttype materials, such as polystyrene sulfonate, in which the gelatin is loosely coagulated and separated for washing, or by a precipitation technique generally using inorganic salts, such as ammonium sulfate, in which the gelatin is precipitated as relatively large particles suitable for Washing. In both these latter techniques relatively dilute gelatin solutions are employed.
After washing, the emulsion generally is reconstituted by the addition of further gelatin and water with mild agitation and heating. The reconstituted emulsion is now chemically ripened by digesting it for a period of from 30 to 90 minutes at a temperature of from 45 C. to 75 C. Other ripening agents needed for chemical sensitization, stabilization pAg and pH adjustment etc. are added.
3,458,3l6 Patented July 29, 1969 Just before coating onto the photographic support certain coating finals such as wetting agents, additional stabilizers and optical sensitizers may be added.
As mentioned earlier, this invention is based on the discovery that the addition of certain chelating agents to the gelatin solution containing the alkali metal or ammonium halide before silver halide precipitation, provides a further improvement in the light sensitivity to the finished photographic silver halide emulsion. In addition to optimized sensitization, any excess of the special chelating agent is removed during the washing step and thus sensitization will depend less on the original concentration of the chelating agent. This technique offers the big advantage of making it possible to reproduce consistently the emulsion characteristics.
In addition to the advantages listed above, it has been discovered that, by adding the chelating agent before the silver halide precipitation, a Wider range of other chelating compounds may be employed. Thus, it was discovered that the following compounds effectively increased light sensitivity of silver halide emulsions if present during the precipitation step.
Speed in crease In the examples given below, about 1 g. of the test compound was used per g. of silver nitrate employed in the precipitation of the silver halide. However, it is to be understood that widely varied concentrations can be used, depending on the compound in question and the emulsion preparation procedure. It should also be understood that alkali metal salts or ammonium salts of these chelating compounds can be used and indeed are often more advantageous with certain emulsions. Emulsions prepared by the procedure of this invention retain their increased sensitivity in optically sensitized regions and thus can be sensitized either orthochromatically or panchromatically, and can equally well be used in color negatives or color reversal products. Indeed this sensitivity can be additional to noble metal sensitization, such as known to the art of emulsion making.
It has been found that EDTA may cause increased fog in certain emulsions and in many cases loss of speed and gradation on aging. These shortcomings are not exhibited by nitrilotriacetic acid, particularly when the nitrilotriacetic acid is and its ammonium or alkali-metal salts are added prior to the precipitation of the silver halide.
The invention will be further illustrated but is not intended to be limited by the following examples:
Example I A mixed silver halide boil type emulsion is prepared by adding silver nitrate solution to a solution of alkali metal halides (2.2 mole percent of iodide and 97.8 percent of bromide ions) in the presence of a colloid such as gelatin, as known in the art of emulsion making. At the end of the addition, ten mole percent excess of most soluble halide is retained. The formed silver halide emulsion is digested for 3 min. at 65 C., the digested emulsion is then precipitated by the addition of an aqueous ammonium sulfate solution. The supernatant liquid is decanted and the precipitated silver halide gelating residue is Washed until all soluble salts are effectively removed. The emulsion is then reconstituted in known manner with gelatin and water, digested for 15 minutes at 40 C., and then after-ripened at 55 C. In the latter step, agents to adjust pH and pBr to the desired levels (pH=6; pBr=3.3) gold sensitizer and a stabilizer are added. The emulsion is then coated on a film support, after necessary coating finals, such as a wetting agent, have been added. After exposure in a sensitometer, the coating is developed for 10 minutes in an Ansco A-47 developer, fixed in a commercial hypo solution, washed, and dried.
Example 11 An emulsion is made according to the exact procedure used in Example I, but 1.0 g. of nitriloacetic acid is added to the alkali halide solution before silver addition.
Example III An emulsion is made according to the exact procedure used in Example I, but 1.8 g. of S-quinolinol is added to the alkali halide solution before silver addition.
Example IV An emulsion is made according to the exact procedure used in Example I, but 1.0 g. of glycine is added to the alkali halide solution before silver addition.
Example V An emulsion is made according to the exact procedure used in Example I, but 1.0 g. of hexamethylenetetramine is added to the alkali solution before silver addition.
Example VI An emulsion is made according to the exact procedure used in Example I, but 1.0 g. of EDTA is added to the alkali halide solution before silver addition.
Example VII An emulsion is made according to the procedure described in Example I of U.S. Patent 2,666,700. To a washed gelatino silver iodobromide emulsion, in which the silver halide consists of 2.2 mol percent of silver iodide and 97.8 mol percent of silver bromide, there is added at the start of the digestion process 0.94 gram of the sodium salt of tetracarboxymethylenediamine based on 485 grams of silver (0.29 g. of EDTA/ 150 g. silver). An orthochromatic sensitizing dye, chrome alum, potassium bromide and saponin are added in amounts and in a manner known to the art. The emulsion is then coated on a cellulose acetate fiurnl support and dried in the usual manner.
Examples VIII-IX The procedure of Example II was followed but using 0.5 gram and 1.0 gram respectively of EDTA per 150 grams of silver.
Example X The procedure of Example VI was employed using 0.5 gram of EDTA per 150 grams of silver.
The improvements obtained due to the use of this invention are illustrated in the accompany drawings, in which FIGURE 1 is a graph comparing the results obtained when varying amounts of EDTA were added to the emulsion at different stages of preparation. Thus the unspecified line is a blank; the line determined by solid dots is that of samples made by the procedure of Example IX; the
line determined by the small circles is that of samples made by the procedure of Example VIII; the line determined by the triangles is that of samples made by the procedure of Example VI while the line determined by the crosses is that of samples made by the procedure of Example X. It will be observed that in the samples where EDTA is added during precipitation, the photographic materials develop a suitable density with a far shorter exposure time.
FIGURE 2 is a graph comparing the results obtained when nitriloacetic acid is added during precipitation to those obtained when EDTA is added just before ripening or when no chelating agent is employed. These samples once more demontrate that the process of this invention provides photographic materials which can be exposed to suitable density in a shorter time period.
FIGURE 3 shows the effects resulting from the addition of various chelating agents prior to silver halide precipitations as described in Examples I to V1.
In addition, it was found that EDTA causes some aging stability deterioration which consequent speed loss on a standard 6 day oven test. The same effect is exhibited by the sodium salt of EDTA. Nitrilotriacetic acids does not show this ill effect and no such speed loss is observed.
In conclusion, it is possible to obtain up to 1 /2 stops of speed increase with fine-grain emulsions in addition to gold sensitization by adding nitrilotriacetic acid to the emulsion components before the first precipitation. This extra sensitivity obtained by this method does not deteriorate upon aging; also, the sensitization is not so highly dependent on exact amounts of adjuvant used.
What is claimed is:
1. In a process for preparing a light sensitive colloidsilver halide emulsion including precipitation, digestion, washing and ripening periods, the step which comprises adding to the emulsion, before the precipitation step, about 0.1 to 3.0 grams, per grams of silver in the emulsion, of an adjuvant selected from the group consisting of nitrilotriacetic acid, and its alkali metal and ammonium salts.
2. The process of claim 1 in which the adjuvant is supplied in the amount of about 1.0 grams per 150 grams of silver.
"l References Cited UNITED STATES PATENTS 2,666,700 1/1954 Baldsiefen 96--l07 NORMAN G. TORCHIN, Primary Examiner M. KELLEY, Assistant Examiner