US3318702A - Silver halide emulsions with increased sensitivity - Google Patents

Description

United States PatentOfiiice 3,3l8,702. Patented May 9, 1967 4 Claims. (61. 96-107 The invention relates to a method of increasing the sensitivity of photographic silver halide emulsions.

Numerous compounds are known which can be used as additives to the emulsion or developer to increase the sensitivity of a photographic layer. Many different terms are used for substances that have this eifect, e.g., chemical sensitizers or activators. The best known class of substances in this field are polyalkylene oxides, in particular polyethylene oxides and water-soluble onium compounds such .as quaternary .ammonium-, phosphoniumand sulphonium salts or combinations thereof or derivatives of thiourea, for example, thiouronium salts.

.The maximum sensitivities obtained in silver halide emulsions by the addition of the above mentioned compounds presupposes that the silver halide emulsions have been activated by treatment with noble metal salts, especially gold salts.

The most commonly used combination for gold sensitization consists of gold-(IID-salts and thiocyanate or thiosulphate, although the solutions of thiocyanate are not very stable and those of thiosulphate are difficult to prepare. Reaction kinetic investigations, e.g., by P-rotass,

Bjirrum and Kirschner (Z. Wiss. Angew. Phot. Kine l, n

455 (1956)) on gold complexes with thiocyanate ions admit of the assumption that sensitization is caused by a controlled, slow decomposition of the Au-(D-complexes in which the thiocyanate ions participate. The mechanism of this sensitization process is not certain since many reaction components are involved, such as metallic gold, Au-(I)-, Au-'(IlI)- and thiocyanate ions, dithiocyanogen and additional sulphur degradation products including thiosulphate and gelatine.

Moreover, a considerable excess of thiocyanate ions is required to stabilize the gold(I) complex and obtain maximum sensitivity of the silver halide emulsions. This method thus has numerous disadvantages. A considerable amount of the gold-(Ill) salts are bound by the gelatin, partly by absorption and partly by complex formation; another amount is reduced to metallic gold and lost for chemical sensitization. In addition the large excess of thiocyanate impairs the stability of the latent image after exposure. a

It has now been found that a combined noble metal sensitization and reduction ripening of silver halide emulsions is obtained, while avoiding the aforesaid disadvant ages, if the after-ripening is performed with salts of noble metals of the VIII group of the periodic systems of the elements having an atomic weight greater than 100 or with salts of gold, in the presence of nit-rilotriacetic acid or its salts.

The nature of the cation of the nitrilotriacetic acid is not critical and can be varied as desired, suitable cations are, for example, those of sodium, potassium, ammonium and the like.

Suitable noble metal salts of the group V111 of the periodic system are platinum, palladium and iridium salts, or mixtures of these salts.

The invention can be used on any photographic silver halide emulsion. The silver halide can consist of silver chloride, silver bromide, silver iodide or of mixtures thereof; however, silver bromoiodide emulsions are pre ferred. These emulsions can be chemically sensitized additionally, for example, with sulfur compounds, with polyalkylene oxides, with water-soluble onium compounds or with combinations of polyethylene oxides and onium compounds. In addition, they can be optically sensitized, e.g., by means of methinecyanine, merocyanine, rhodacyanine dyes and the like.

As stabilizer, it is possible to apply organic mercapto compounds, quaternary benzthiazoles, triazoles, tetraazaindolizines and the like.

An additional advantage of the process according to the invention is that the sensitized emulsion can be used for the production of bl-ack-and-white or color photo,- graphic materials, it being possible in the latter case to incorporate hydrophobic or hydrophilic color couplers into the emulsion layer.

The noble metal salts and the nitrilotriacetic acid salts can be added to the emulsions at any stage of the preparation of the emulsion but before or during the afterripening. The nitrilotriacetic acid can be added in dissolved or in solid form before, during or after adding the noble metal salt. tions of the noble metal salt, for example, gold-III-chloride and of nitrilotriacetic acid. The nitrilotriacetic acid compounds or its salts are used in concentrations of 0.1 g. to 5 g. per 1 kg. of emulsion, advantageously about 0.1-0.5 g./kg. The optimum quantity to be added depends on the nature of the emulsion. It can be deter mined without any diificulty by means of a few tests.

The manner in which the process according to the invention is used is shown by the following examples:

EXAMPLE 1 A silver chloride-bromoiodide-gelatin emulsion with mol percent of silver bromide and 8 mol percent of silver iodide, which contains 50 g. of silver per liter and which further contains potassium bromide and sulfur compounds for chemical ripening is divided, before the after-ripening, into 2 samples:

Sample A serves as comparison sample. Before after ripening, to sample B is added per liter of emulsion a mixture of 5 ml. of a 10% solution of sodium nitrilotriacetate and 0.08% gold-III-chloride.

After the two samples have been after-ripened at a pH=5.86.0 maximum sensitivity is reached, a wetting agent and a stabiliser, e.g., of the tetraazaindolizine type, are added and the emulsion applied onto a paper support.

The two samples are exposed to light and they are developed of the following composition:

It is also possible to add a mixture of solu-,

G. p-Methylaminophenol l Hydroquinone 3 Anhydrous sodium sulphate 13 Anhydrous sodium carbonate 26 Potassium bromide 1 Water to make 1000 ml.

The result is shown in Table I:

TABLE I Increase in Fogging Gamma sensitivity Sample A 0 DIN 0. 02 2. 0 Sample B +4 DIN 0. 04 1.8

As regards the sensitivity data, it is to be pointed out that an increase in the sensitivity of 3 lDIN corresponds to an increase by one aperture.

EXAMPLE 2 A highly sensitive ammonia silver bromide emulsion with 2 mol percent of silver iodide, containing silver halides equivalent to 60 g. of silver per liter, is prepared as in Example 1 and before after-ripening divided into two samples A and B.

Sample A serves as comparison sample. The following mixture is added to sample B per liter before the after-ripening: 5 ml. of a solution of sodium nitrilotriacetate and 1.3 ml. of a 0.08% gold-III-chloride solution.

The samples are after-ripened to maximum sensitivity, at a temperature of about 50 C. and a pH of 6.8. Thereafter a wetting agent and a stabiliser, e.g., of the tetraazaindolinzine type, are added and the samples are cast onto a support of cellulose aceto butyrate.

The samples are exposed to light and they are developed for 5 minutes at C. in an X-ray developer. The result is shown in Table II:

A highly sensitive negative silver bromoiodide gelatin emulsion with 4 mol percent of silver iodide, which contains silver halides equivalent to 55 g. of silver per liter and which further contains bromide, sulfur compounds and the like as chemical sensitizers is divided before after-ripening into three samples A, B and C.

Sample A is the comparison sample. To sample B is added the following mixture per liter: 3 ml. of a 10% solution of sodium nitrilotriacetate and 0.5 ml. of a 0.08% gold-III-chloride solution.

Sample C is prepared as sample B, but only 1 ml. of the 0.08% gold-HI-chloride solution is added.

The samples are after-ripened at a pH of 6.8 and cast onto a film support, as described in Example 2.

The three samples are then exposed to light and they are developed in an usual p-methylaminophenol hydroquinone developer for 10 minutes at 20 C.

The result is shown in Table III.

A silver bromoiodide gelatin emulsion of medium sensitivity with 6 mol percent of silver iodide containing silver halide equivalent to 45 g. of silver per liter is divided before the after-ripening into two samples A and B.

Sample A is the comparison sample. To sample B is added the following mixture per liter of emulsion: 3.5 ml. of a 10% solution of sodium nitrilotriacetate and 1 ml. of a 0.08% gold-III-chloride solution.

The samples are after-ripened at about 55 C. and at a pH of 6.8 and they are cast onto a sheet-like support of polyethyleneterephthalate.

The two samples are exposed to light and developed for 10 minutes at 20 C. in a usual p-methylaminopheuolhydroquinone developer. The result is shown in Table IV.

TABLE IV Increase in Fogging Gamma sensitivity Sample A 0 0.06 005 Sample B +2 DIN 0. 06 0. [:5

It will be clear to those skilled in this art that the practice of the invention lends itself readily to a number of useful modifications in method, material, etc. For example, the noble metal salts are not limited to the previously mentioned, because it is possible to use any suitable salt which is soluble in water or lower alcohols. Such compounds are: gold halides, such as auric chloride, or complex gold halides, such as potassium chloroaurate (KAuOl and sodium chloroaurate (NaAuCl However, gold compounds, such as auric sulfate, are practically as useful as the gold halides. Aurous, as well as auric compounds can be used. Complex gold salts, such as alkali metal aurous thiosulfates, alkali metal aurous sulfites (e.g., sodium or potassium aurous thiosulfate and sodium or potassium aurous thiosulfate and sodium or potassium aurous sulfite). Potassium chloroaurite, potassium bromoaurite, potassium iodoaurite, or the corresponding sodium, calcium, strontium, cadmium or gallium salts can also be used. Pyridinotrichloro-gold, ethylenediaminebis-trichloro gold, diethyl-monobromo-gold and diethyl gold acetone and gold complexes with sulfur compounds such as are commonly present in gelatin, e.g., the gold thiosinamine complexes, can also be used. Suitable salts of noble metals of the VIII group are ammonium or potassium, chloropalladate, ammonium, sodium and potassium chloropl-atinate, ammonium potassium and sodium bromoplatinate, ammonium chlororhodate, ammonium chlororuthenate, ammonium chloroiridate, ammonium, potassium and sodium chloroplatinite, ammonium, potassium and sodium chloropalladite, etc.

The after-ripening of the emulsion with the noble metal salt and the o-hydroxybenxylamine compounds is performed at an appropriate temperature particularly between 30 and 65 C. During after-ripening the pH of the emulsion is advantageously adjusted to the acid side of neutrality preferably between S and 7. Maintenance of the emulsion on the acid side of neutriality during coating of the emulsion is also preferred.

The noble metal salts are employed in an amount below that which produces a substantial fog. In practicing the present invention, a quantity of the noble metal salt is employed, equivalent to between 0.1 and 50 mg. of the noble metal per mol of silver halide in the emulsion. The noble metal compounds are preferably incorporated in the emulsions in the form of their solutions in a suitable solvent such as water, methyl alcohol, ethyl alcohol or the like.

We claim:

1. A process for increasing the sensitivity of silver halide emulsions, characterized by performing the chemical ripening with a mixture of noble metal salts and nitrilotriacetic acid or a mixture or noble metal salts and salts of nitrilotriacetic acid.

2. A process according to claim 1, wherein the noble metal is gold.

3. A process according to claim 2, wherein the emulsions contain additionally as chemical sensitizers sulphur compounds, onium compounds or polyalkylene oxides.

4. A process according to claim 1, wherein tetraazaindolizine stabilizers are added to the emulsions.

No references cited.

NORMAN G. TORCHIN, Primary Examiner.

J. RAUBITSCHEK, Assistant Examiner.

Claims (1)

1. A PROCESS FOR INCREASING THE SENSITIVITY OF SILVER HALIDE EMULSIONS, CHARACTERIZED BY PERFORMING THE CHEMICAL RIPENING WITH A MIXTURE OF NOBLE METAL SALTS AND NITRILOTRIACETIC ACID OR A MIXTURE OR NOBLE METAL SALTS AND SALTS OF NITRILOTRIACETIC ACID.