DE2301280C3 - Process for preparing a photosensitive silver halide emulsion - Google Patents

Description

-0-CH ₂ CH ₂ -S-

used

4. The method according to claim 3, characterized in that the thioether-silver halide solvent 1,8-dihydroxy-3,6-dithiaoctane or 1,10-dithia-4,7,13,16-tetraoxacyclooctadecane used

5. The method according to claim 1 to 4, characterized in that the pH value during the Mixing is adjusted to below 7 and the pAg is maintained between 7 and 9.8.

35

The invention relates to a method for preparing a photosensitive silver halide emulsion with internally fogged silver halide grains by mixing a silver salt solution with a halide solution in a liquid reaction medium containing at least 0.5 g of a thioether silver halide solvent contains per mole of silver halide to be formed

It is known, for example from US-PS 29 96 382, internally fogged photosensitive silver halide emulsions by preparing the silver halide grains obtained in the silver halide precipitation exposed and thus photolytically an inner veil under the surface of the silver halide grains It is also known e.g. B. from US-PS 20 15 070 and 32 06 313, internally veiled to produce light-sensitive silver halide emulsions by the so-called core-shell process, in which chemically fogged silver halide grains with an unveiled silver halide shell to be covered.

It is also known e.g. B. from DT-OS 19 04 148, monodisperse ones suitable for the production of direct positive photographic recording materials Preparing silver halide emulsions by the silver halide precipitation in the presence of a organic thioether silver halide solvent and the precipitated silver halide grains subsequently veiled

The use of thioether silver halide solvents in the preparation of silver halide emulsions is also z. B. from US-PS 32 71 157 and is known to be 74 628.

From GB-PS 11 50 013 it is finally known for the production of highly sensitive negative recording materials To use silver halosenide emulsions for their preparation silver nitrate solutions be used, which before the reaction with a gelatin solution containing soluble halides with relatively small amounts of potassium iodide were moved. . ....

The object of the invention is to provide a compared to the known processes for the preparation of internally fogged silver halide emulsions for the preparation of an internally fogged photosensitive silver halide emulsion to specify the photosensitive Silver halide grains are internally fogged and practically no surface fog

exhibit. . . ,,

The invention is a method for Preparation of a photosensitive silver halide emulsion having internally fogged silver halide grains by mixing a silver salt solution with a halide solution in a liquid reaction medium, that is, at least 0.5 g of a thioether silver halide solvent per mole of silver halide to be formed contains which is characterized in that one Silver salt solution is used that is per mole of silver salt 05 to 7.0 mol% iodide in the form of a soluble silver iodide complex

One which can be produced by the method according to the invention light-sensitive silver halide emulsion can be used for the production of direct positive or negative Recording materials are used. That which can be produced by the method of the invention Emulsions can be incorporated into surprisingly high concentrations of sensitizing dyes, without desensitization taking place

Any suitable water-soluble iodide compound can be used to carry out the process according to the invention be used. Examples of typical suitable iodide compounds are ammonium, potassium, Lithium, sodium, cadmium and / or strontium iodide compounds. When carrying out the inventive method, the iodide compound is in the Silver salt solution in a concentration of 03 to 7.0 Mole% iodide per mole of silver salt used Dissolving potassium iodide e.g. or another suitable iodide compound is usually easier and better if concentrated silver salt solutions, for example, concentrated silver nitrate solutions can be used. For example, allow aqueous Silver nitrate solutions that are more than 2.0 molar allow the potassium iodide to dissolve more easily.

When a water-soluble iodide compound is added to a silver nitrate solution, silver iodide is known to form first, but in the presence of excess silver ions it forms a soluble complex that probably _{corresponds to the formula AgI · 2 AgNO 3.} In this context, reference is made to A. Seidell, »Solubilities of Inorganic and Metal Organic Compounds ", 4th edition, editor: American Chemical Society, Washington D. C, USA, 1958, page 94.

It has been shown that internally fogged silver halide emulsions of the desired properties are not obtained if one works without a thioether-silver halide solvent or without a silver iodide complex, as can be seen from the examples _below

To carry out the folding according to the invention

23 Oi

η various organic thioether silver ^{er> 5} ^ !!! solvents can be used. Suitable ^lJoB ih _e organic thioether Silberhalogenidlö solcne _ind ^ B ^ _{e greater} solubility for Silberhalo- "ngs ¹¹¹¹¹¹ ^ 'gjiberchiorid having as water. Prejudice. ? · * _Crden jhioether silver halide solution - ", sometimes ^ ^. - _Their use in aqueous

medium usable _{concentration at 60} o _{C more}

Solving solutions _"Gewichtsme length silver *" i _s water at 60 ° C.

^kÖ Um process of the invention verwenflüssiEen reaction medium is it ^det? "Jrwetee an aqueous solution of a polymethyl ^ pSisierinittels. For example, an aqueous ^reindeer, ·. '' ine The liquid reaction medium, eg. as ^Gela ßrte gelatin solution is often also ^e f So ung "called the liquid reaction ^{>> Ke} Msum is it usually a uonstneaiun _unschten case but can also

Sri ^W ^ e LöLngsmittel as ⁰¹ Sr are used ethanol, for example methanol. ^Un r? The concentration of the thioether silicate solvent used can be varied within a wide range depending on the liquid thioether, the silver equivalent to be produced, the concentration of the iodide used and the type of reaction medium. The mixing of the silver salt solution with a halide solution is carried out in the presence of at least 0.5 g of a thioether-silver halide solvent per mole of silver salt, for example in the presence of 0.5 to 10 g of the thioether-silver halide solvent per mole of silver salt.

Typical thioether silver halide organic solvents useful in practicing the process of the invention contain at least one radical in which oxygen and sulfur atoms are replaced by a Ethylene radical are separated from each other, for. B. a residue of the formula

(-O-CH2CH2-S-)

In general, the aforesaid thioether silver halide solvents 1 to 3 thioether-like bonded sulfur atoms, although also silver halide solvents with more than 3 such sulfur atoms can be used. Suitable thioether / superhalide solvents are known for example from US-PS 32 71 157 and 35 74 628

Examples of suitable thioether-silver halide organic solvents are those of the general formulas

IS

Q - [(CH ₂ ) _r -CH ₂ -S- (CH ₂ ) ₂ -X- (R) _p - (CH ₂ ) ₂ - (R ') _ii -S-CH ₂ - (CH ₂ ) _ro - Z] _n and Q- (CH ₂ ) _m -CH ₂ -S- (CH ₂ ) _r -S-CH ₂ - (CH ₂ ) _r -Z

aeut-roughly _S 0 to _{4, nlbi S} 4, _P and carbon atoms, preferably the ethylene radical, _ 0 to i X an oxygen or sulfur atom be jutene. ^^. ^ ^^ _Embodiment a carbamyl _{process of the} invention is considered organic

Thioether silver halide solvent is a cyclic one Thioether of the following formula used:

Il
—C-

NH-

Carbonyl

(R ² -O) ₁ -R ²

or oxycarbonyl radical

\ —C — O — j

R and R ¹ each represent an ethylene oxide radical (—O - CH ₂ - CH ₂ -)

and Q and Z each represent a hydroxy, carboxy or alkoxy radical (- O - alkyl) having 1 to 5 carbon atoms in the alkyl group or one of the radicals indicated for X to form a cyclic compound.

According to a preferred embodiment of the method of the invention, the organic thioether silver halide solvent is used a straight-chain thioether, for example one of the following formulas used:

HO (--R ² - S) _x R ² OH

or

HO (- R ² - S - R ² - O - R ² ) ₂ O

wherein s 1 to 3 and R ^{2 is} an alkylene radical with 1 to

(R ² - O), - R ²

in which t = 1 or 2 and R ^{2 has} the meaning given above

The light-sensitive silver halides can consist of any light-sensitive silver halides, e.g. from silver bromide, silver iodide, silver chloride, Silver chlorobromide, silver bromide iodide and silver chlorobromide iodide. The silver halide grains which can be produced by the process according to the invention have usually an average grain diameter, i. H. an average grain size of 0.1 to 2 microns, preferably from 0.25 to 1 micron. The mean grain diameter, i.e. the average grain size, can be determined by conventional methods. The silver halide emulsions which can be prepared according to the invention can be prepared by conventional emulsion preparation processes, i.e. according to the Single inlet and the double inlet method, furthermore using methods in which one automatic quantity metering to maintain certain pAg and pH values takes place and below Use of methods with increasing flow rates and methods like them e.g. in BE-PS 7 63 040 and DT-OS 21 12 765.

23 Ol 280

Advantageously, the process of the invention can be used to prepare monodisperse silver halide emulsions, that is, silver halide emulsions having silver halide grains of practically uniform diameter. In general, not more than 5% by weight of the silver hook soften in aeolian emulsions; _t 'enide grains by more than 40% from the mean grain diameter. Preferred silver halide emulsions which are produced by the process according to the invention contain silver halide grains of which at least 92% by weight have a diameter which is within 30% of the mean grain diameter. Silver halide emulsions containing silver halide grains having a narrow size distribution can be obtained by monitoring the conditions under which the silver halide grains are precipitated by the double jet method. In this method, an aqueous solution of a water-soluble silver salt, for example silver nitrate, which contains the iodide compound described, and an aqueous solution of a water-soluble halide, for example an alkali metal halide, such as potassium bromide, are allowed to simultaneously with vigorous stirring in an aqueous solution of a silver halide peptizer, preferably of gelatin, a gelatin derivative or some other protein pepizer. The pH and pAg values used in this method must be coordinated with one another.

The applied when carrying out the method of the invention Tenperatur is generally from 30 to 90 ⁰ C, the applied pH is up to 9, preferably less than 7, such as 4 to 7, and ρ Ag-value is between 7 and 9.8.

Process for preparing silver halide emulsion with uniform particle size are, for example, from "The Journal of Photographic Science", volume 12, 1964, pages 242-251, ibid., Vol. 13, 1965, pages 85 to 89, ibid. Volume 13, 1965, pages 98-103 and ibid. Volume 13, 1965, pages 104-107

A wide variety of silver halide peptizers can be used to carry out the process of the invention, e.g. B. gelatin, gelatin derivatives or other peptizers! protein-based and other silver halide peptizers, such as cellulose derivatives, polysaccharides and synthetic polymers, e.g. B. vinyl polymers, as they are known from US-PS 30 62 674 and 23 11 059 and BE-PS 7 27 604 are known. The concentration of the peptizer in the peptizer solution is generally from 10 to g peptizer per liter of solvent, generally water.

The emulsions which can be prepared by the process of the invention are suitable, inter alia, for the preparation of Recording materials for the colloid transfer process such as disclosed in US Pat 16 059 is known for the silver salt diffusion transfer process, the color image transfer process, As for example from US-PS 30 87 817, 567, 29 83 606, 32 53 915, 32 27 550, 32 27 551, 27 552, 34 15 644, 34 15 645 and 34 15 646 as well as BE-PS 7 57 959 and 7 57 960 is known and for the Induction transfer method. The emulsions are also suitable for the production of recording materials for color photography, for example for the production of recording materials, the color couplers contain, as for example from US-PS 76 679, 23 22 027, 28 01 171, 26 98 794, 32 27 554 and 30 46 129 are known for the production of Aufzeichnunfesmatcrialien, which contain in color couplers Solutions are developed, such as those from US Pat. No. 2,252,758.25 92,243 and 29 50 970 5 are known, as well as for making wrong sensitized color recording materials, such as them for example from US-PS 27 63 549 are known.

The süberhalide emulsions which can be prepared by the process of the invention can contain electron acceptors, which are often also referred to as desensitizers, are added. The concentrations of the Depending on the silver halide composition, electron acceptors can the average grain size and the grain size distribution be different ι s Particularly advantageous results are often obtained when the electron acceptors the monodisperse silver halide emulsions in concentrations from 10 to 500 mg, preferably 50 to 200 mg per month! Silver salt can be added.

The electron acceptors or desensitizers are generally compounds that have a reduction potential! or have a cathodic half-wave potential (E ₀ ) that is more positive than -1.0 V. Particularly suitable enAtron acceptors are also those with an anodic half-wave potential that is more positive than +0.90 V, preferably + 1.0 V. .

The electrochemical potential measurements can be carried out according to methods such. B. from the the following literature references are known: D e 1 a h a y ■ "New Instrumental Methods in Electrochemistry", Interscience Publishers, New York, New York, 1954 J K ο 11 h ο f f and L i η g a η e: »Polarography«, 2. Edition, Interscience Pubiishers, New York, New York, 1952 and Adams: "Electrochemistry at Solid Electrodes", Marcel Dekker, Inc, New York New York, 1969.

Electron acceptors used with preference are methine dyes, both monomethine and also polymethine dyes. These methine dyes include those that are found in direct positive silver halide emulsions can be used as electron acceptors. Polymethine dyes used with preference are those that contain at least one core with a desensitizing effect. The one used here The term "desensitizing nucleus" refers to those nuclei that, after being converted into a symmetrical Carbocyanine dye and when added to a 40 mol% chloride and 60 mol% bromide containing Gelatin silver chlorobromide emulsion in one concentration from 0.01 to 2.0 g of dye per mole of silver halide due to electron capture loss of the Cause the emulsion to have a blue sensitivity of at least 80% if the emulsion is exposed sensitometrically and for three minutes in a developer of the composition given in Example 1 at room temperature to be developed. The desensitizing cores are preferably those after conversion to a symmetrical carbocyanine dye and the above the test described practically completely desensitize the test emulsion to blue radiation (i.e. to lead to a loss of sensitivity to blue radiation of more than 90 to 95%). A particularly suitable class of electron acceptors that can be produced in accordance with the invention photographic silver halide emulsions are used kfinnpn hpet ^ ht α ,, «· r \," ":., r u _« _ rr

23 Ol 280

in particular imidazoquinoxaline dyes, as is known, for example, from US Pat. No. 3,431,111. very good results are obtained with cyanine dyes which are aromatically substituted in the 2-position contain indolers, e.g. B. with cyanine dyes of the type known from US-PS 33 14 796. A suitable one Class of spectral sensitizing electron acceptors are also the bis- (l-alkyi-2-phenylindole) -trimethine cyanines, as they are known from US-PS 29 30 694. Other suitable cyanine dyes are, for. B. off the GB-PS 9 70 601 and 7 23 019 known The above-described spectral sensitizing Electron acceptors can also be used to produce reversal images.

The electron acceptors can be used in various concentrations. Preferably they are used in concentrations of 50 to 800 mg per mole of silver halide. Specific examples for suitable electron acceptors are:

l, r-dibutyl-4,4'-dipyridinium chloride,

Phenosafranine and

related halogenated dyes,

as they are known from US-PS 35 01 309,

e.g.

l, l'33'-tetramethyl-2,2'-cyanine iodide · NBS,

3,3'-Diethylthiacyaninjodid · NBS, 9-ethyl-3,3'-dimethyl-4,5,4 ', 5'-dibenzthia-

carbocyanine chloride · NBS and

1,1'-dimethyl-2 ^ '-cyanine iodide,

where NBS stands for N-bromosuccinimide.

The silver halide grains producible according to the invention have practically no surface veil. The emulsions contain only minimal developables Surface veil centers. those with 5 minutes of development at 27 ° C. in a conventional developer following composition:

Water (50 ° C) 500 ml N-methyl-p-aminophenol sulfate 2.5 g Sodium sulfite, dehydrated 30.0 g Hydroquinone 2.5 g Balancing alkali 10.0 g Potassium bromide 0.5 g topped up with water 1 liter

various exposure and development processes can be used. So according to the invention produced emulsions in the form of layers on a support imagewise exposed and then in a Inner grain type silver halide developers are developed. A typical internal grain developer has that the following composition:

give a density of less than 0.4 and preferably less than 0.25. The surface of the invention however, produced silver halide grains may be chemically sensitized.

A “chemical sensitization” here means a sensitization as described by A. H a u t o t and H. Saubenier in Science et Industries Photographiques. Volume XXVIH, January 1957, pages 1 through 23 and January 1957, pages 57-65. This chemical sensitization includes three main types, namely the noble metal or especially gold sensitization, the sulfur sensitization, for example by means of a compound having a labile sulfur atom and the reduction sensitization, d. H. the treatment of the Silver halide with a reducing agent, which does not noticeably obscure the silver halide, however, introduces small specks of metallic silver into the silver halide grain

For producing negative and positive images using those produced according to the invention photosensitive silver halide emulsions can

ί, ο

Water (50 ° C) 500 ml N-methyl-p-aminophenol sulfate 2.0 g Sodium sulfite 90.0 g Hydroquinone 8.0 g Sodium carbonate monohydrate 52.5 g Potassium bromide 5.0 g Callium iodide 0.5 g topped up with water 1 liter

In certain cases, when using emulsions prepared according to the invention, it is also possible under Use surface developers to develop images.

A "surface developer" is to be understood as meaning those developers who have the latent Make the surface image visible on a silver halide grain, but the latent inner image of an inner grain emulsion under the conditions generally used for developing a surface-sensitive silver halide emulsion are practically invisible.

Examples of typical silver halide developing agents which can be used for developing in accordance with the invention Suitable emulsions are hydroquinones, pyrocatechols, aminophenols, 3-pyrazolidones, ascorbic acid and their derivatives, reductones, phenylenediamines, and combinations thereof. The developer connections can optionally contain the photographic emulsions prepared according to the invention Recording materials are incorporated. As a rule, however, they are preferably used in a developing solution used.

The emulsions which can be prepared according to the invention are generally unsensitized Silver halide emulsions, which are therefore practically free from chemically induced sensitivity to the Surface of the grain are.

In order to give the silver halide emulsions an additional sensitivity, conventional spectral sensitizing dyes are added. For example, an additional spectral sensitization can be achieved achieve by that the emulsion with a solution of a sensitizing dye in a Treated organic solvent or adding the dye in the form of a dispersion as it is from the GB-PS 11 54 781 is known. To achieve optimal results, the dye can either be in the emulsion at the final stage or at any earlier stage. Sensitizing dyes that are for sensitizing such emulsions for negative images are, for example, from the US-PS 25 26 632, 25 03 776, 24 93 748 and 33 84 486 known examples of spectral sensitizers, which can be used are cyanine, merocyanine, complex (3- or 4-ring) merocyanine, complex (3- or 4-nuclear) cyanine, holopolar: f, s cyanine, styryl, hemicyanine (e.g. enamine hemicyanine), Oxonol and hemioxonol dyes.

If necessary, combinations of spectral sensitizing dyes can also be used.

709 652/247

23 Ol

10

the. In addition, supersensitizing additives, which do not even absorb visible light can be added, e.g. B. ascorbic acid derivatives, azaindenes, Cadmium salts and organic sulfonic acids, such as those from US Pat. No. 2,933,390 and 2,937,089 are known

The emulsions which can be prepared by the process of the invention can contain surprisingly high concentrations to be added to sensitizing dyes, e.g. B. 50 to 800 mg of dye per mole of silver halide The use of spectral sensitizing dyes in these unusually high concentrations does not result in any loss of the fogging properties of the silver halide.

The following examples are intended to explain the invention in more detail.

example 1

This example illustrates the preparation of particularly advantageous emulsions.

Silver bromide iodide gelatin emulsions with an average grain size of about 1.0 micron were prepared by adding an aqueous solution of potassium bromide and an aqueous solution at the same time Silver nitrate solution containing potassium iodide as a soluble silver iodide complex in the table I below given concentration contained, with vigorous stirring to a gelatin solution, also as a kettle solution The gelatin solution contained a thioether silver halide solvent in the concentration given in Table 1 below. The addition took place at a temperature of 50 ° C. over a period of 40 minutes at a pAg value of 83- The silver halide emulsions thus obtained

Table I.

were washed and applied to cellulose acetate support. The recording materials obtained in this way were then developed using one of the following methods:

1.) Development at 20 ^° C. for 6 minutes

in a surface developer

of the following composition:

Water (50 ° C) 500 ml of N-methyl-p-aminophenol sulfate (Elon) 2.0 g

Sodium sulfite 90.0 g

Hydroquinone 8.0 g

Sodium carbonate monohydrate 52-5 g

Potassium bromide 5.0 g

made up to 1 liter with water or

2.) (a) Immersion at 20 ^° C. for 5 minutes

in a surface bleach bath of the following composition:

Glacial acetic acid 1.8 ml

Sodium hydroxide 0.8 g

Potassium ferricyanide 3.18 g

made up to 1 liter with water

(b) Development at 20 ^° C. for 6 minutes

in an internal grain developer made from the

specified surface developer by adding

0.5 g potassium iodide per liter of solution.

In each case, the treated recording material was fixed, washed and dried

The results obtained are summarized in Table 1 below

Emulsion no. In the AgNOs- Thioether in the Veil values (2)! Fine grain Solution dissolved Kj Boiler solution developer MoI% (g / mole) (1) surface 0.70 developer 2.18 IA 1.49 I (03) 0.04 2.08 IB 1.49 I (2.0) 0.06 2.00 IC !, 49 I (2.0) 0.06 0.03 ID 0.75 II (1.1) 0.05 0.03 IE 1.49 - 0.03 IF 1.49 - 0.04

In the case of the emulsion IC, the potassium iodide became the Silver nitrate solution added under red safety light. It was stirred until the first formed Precipitate was dissolved. In the case of the other emulsions, this process step became white Light carried out The thioether marked with the number I was -; I was 1,8-dihydroxy-3,6-dithiaoctane, in the case of the thioether marked with the number II around U

oxacyclooctadecane.

From the results obtained, it can be seen that mar according to the method of the invention when used Potassium iodide and a thioether give an inner grain emulsion which has practically no surface surface haze on the silver halide grains

has the development of a latent surface image would allow.

Example 2

This example illustrates the usefulness of emulsions made by the process of the invention for the production of negative and direct positive recording materials.

At various proportions of an internally fogged silver halide emulsion, which, as described in Example 1, had been prepared, dyes A and B were listed in the following Table II Concentrations added. After ten minutes

60 of the Silberhaiogenidemulsionen Center at 40 ⁰ C, the emulsions were exposed coated on cellulose acetate support and long each developed at 2O ⁰ C in either 6 minutes a surface developer or 6 minutes ir an inner grain developer of being give in Example 1 NEN Composition The obtained results are the following in the Table II compiled

11th

23 Ol 280

Table II

emulsion
No.

dye

(mg / Mol / AgX)

Relative sensitivity D _mm (negative sensitivity, measured at 0.3 above the haze) after surface development, internal grain development (reverse development)

Relative reversal sensitivity Dmin D _m

opportunity, measured by one
Point accordingly

2 0.70 0.70 0.04 219 0.04 0.44 '0.04 186 0.04 0.22 0.04 309 0.04 0.55 0.04 269 0.04 0.45 0.04 - 2.08 2.08 0.06 83 0.17 1.02 0.04 105 0.12 1.46 0.04 112 0.18 1.90 0.05 126 0.13 1.14 0.06 _ 2.18 2.18 0.06 83 0.16 2.20 0.06 174 0.15 2.00 0.06 2.00 2.00 0.05 525 0.22 0.90 0.07 363 0.20 0.60 0.07 457 0.14 1.38 0.07 525 0.12 1.26 0.07

100 148

155 41

A (IOO) A (200) B (IOO) B (200)

A (50) A (IOO) B (IOO) B (200)

A (50) A (IOO)

A (IOO) A (500) B (IOO) B (200)

The dyes A and B had the following appearance:

Dye A

CH = C

NO ₂

C —Ν —Η

r * < -

Dye B

CH ₂ CH = CH ₂ CH ₃

CH = CH-C

35

45

CH ₂ CH = CH ₂ J ^ From the results obtained it follows that the internally fogged silver halide emulsions prepared by the process of the invention can be used advantageously with a dye acting as an electron acceptor and that by developing the emulsions applied to a layer support in one Inner grain developer receives usable reversal images

Example 3
(Comparative example)

This example shows that an iodide is present in the silver salt solution used in accordance with the invention must in order to achieve the desired goal.

The procedure described in Example 1 was repeated, but this time using a silver nitrate solution was used without potassium iodide. After the development carried out as described in Example 1 the following results were obtained:

Table UI K | in the
Solution in AgNCb-
Mol% Children
Solution in Boiler-
Mol% Children
solution in Halide
Mol% Schleicrwerte
Surface
development Inner grain
development Thioether (1) in the
Kitchen solution
(g / mole) 1.49 2.48 2.48 0.05
0.06
0.06 0.20
0.08
2.18 2.0
2.0
in

Claims (3)

23 Ol K's claims: 1. Method of making a photosensitive Silver halide emulsion having internally fogged silver halide grains by mixing one Silver salt solution with a halide solution in a liquid reaction medium containing at least 0.5 g contains a thioether silver halide solvent per mole of silver halide to be formed, that ι ο characterized in that a silver salt solution is used which per mole of silver salt 0.5 to 7.0 mol% iodide in the form of a soluble silver iodide contains complex 2. The method according to claim 1, characterized in that 0.5 to 2.0 thioether silver halide solvent used per mole of silver halide to be formed 3. Process according to Claims 1 and 2, characterized in that there is a thioether-silver halide solvent with at least one grouping of the formula