EP0378831B1 - Photographic silver halide emulsion - Google Patents

Description

The invention relates to a photographic silver halide emulsion for the production of recording materials for the infrared spectral region.

More recently, image recorders have been developed in which the image is written with a fine light beam generated by a semiconductor laser. The radiation emission of powerful laser diodes lies in the near infrared. There is therefore a need for infrared-sensitive recording materials which are suitable for this type of exposure. It is particularly important to note that the laser beam only exposes each surface element of the recording material during the writing process for a very short time (approximately 100 ns) and that the laser energy is limited. Therefore, materials with high infrared sensitivity for short exposure are primarily required. For easy handling, the lowest possible sensitivity in the visible spectral range is also desirable.

So far, these goals have essentially been pursued in two different ways. On the one hand, attempts were made to provide more effective sensitization of the silver halide for the infrared range by providing new sensitizer dyes. The most important class of dyes for this purpose is, according to the structural formula, that of heptamethine cyanine. On the other hand, special additives to the emulsion have been proposed, by means of which the infrared sensitivity achieved with a particular dye can be increased still further. Triazine derivatives (US 3,695,888 and DE 37 20 138), mercapto compounds (US 3,457,038) and combinations of polyethylacrylate with mercapto compounds or stilbenes (EP 2 03 698) have been described as such additives.

The effect of such so-called super-sensitizing additives is now not uniform, but can vary greatly depending on the type of sensitizing dye and emulsion type. There is therefore still a need for further super-sensitizing compounds for the infrared range. It would also mean a significant technical advance if it were possible to further increase infrared sensitivity. Then the recording could be accelerated with the same light output of the laser.

The object of the present invention is accordingly to provide photographic silver halide emulsions which give infrared recording materials with high sensitivity. Another object is to provide emulsion additives which are super-sensitive to the infrared sensitivity of silver halide materials.

These objects are achieved by an infrared-sensitive silver halide emulsion which contains an aromatic thiosulfonic acid or a salt of such an acid as an emulsion additive.

Such aromatic thiosulfonic acids are known as additives to emulsions for recording materials for the visible spectral range. However, after their action in such emulsions, they are only described as "clearing agents", ie antifoggants in gold sensitization or together with aromatic sulfinic acids (DD 7 376; US 2,394,198). A more recent Japanese patent application (JP 57 176 032; cited from Chem. Abstr. 100: 42996) also describes the use of sodium thiotosylate (compound I-2, see below) in the physical ripening of emulsions, which are then mixed with mono-, tri- or pentaamethine cyanines have been sensitized to visible light. EP 2 93 917 also describes the use of thiosulfonic acids and their salts and esters as clearing agents in color film emulsions. However, it was not previously known that aromatic thiosulfonic acids have a super-sensitizing effect in infrared-sensitized emulsions. Since they were previously only described as antifoggants and stabilizers in emulsions sensitized to visible light, this effect is surprising for the person skilled in the art. It was also found that the effect according to the invention only from the thiosulfonic acids and their salts, but not from others, these compounds structurally related and in the prior art (DE 28 24 082-C2, EP 2 93 917-A2) with those substances commonly described as clarifiers, such as thiosulfonic acid esters. This fact, too, was not to be expected from a person skilled in the art when the prior art was properly assessed.

wiedergegeben. Hier bedeuten R einen ggf. auch zweiwertigen Alkyl-, Aryl- oder Aralkylrest mit 0 bis 10 Kohlenstoffatomen und M ein Kation, vorzugsweise Alkalimetall- oder Ammoniumion, sowie n die Zahlen 1 oder 2.Preferred thiosulfonic acids and salts for the emulsions according to the invention are represented by the general formula (I)

reproduced. Here R is an optionally divalent alkyl, aryl or aralkyl radical with 0 to 10 carbon atoms and M is a cation, preferably an alkali metal or ammonium ion, and n is the number 1 or 2.

Examples of aromatic thiosulfonic acids and their salts according to the invention are

In order to achieve the supersensitization according to the invention, the thiosulfonic acids or their salts must be used in amounts which are considerably higher than those described for the clarifying effect in the prior art. Additions of 0.1 to 5 millimoles per mole of silver halide are generally sufficient. The range between 0.2 and 2 millimoles per mole of silver halide is particularly preferred.

The emulsions according to the invention contain a suitable sensitizing dye for sensitization in the infrared spectral range. In general, cyanine dyes are used that have more than five optionally substituted methine groups (so-called polymethine cyanines). Heptamethine cyanines are preferred because they sensitize to the near infrared range, which is primarily used for recording because of the lower thermal interference radiation and the inexpensive semiconductor lasers.

Hierin bedeuten:
R₁ und R₂, die gleich oder verschieden sein können, jeweils eine Alkylgruppe oder eine substituierte Alkylgruppe;
R₃ und R₄, die gleich oder verschieden sein können, jeweils ein Wasserstoffatom, eine niedere Alkylgruppe, eine niedere Alkoxygruppe, eine Phenylgruppe oder eine Benzylgruppe;
R₅ und R₆ beide jeweils ein Wasserstoffatom oder gemeinsam, miteinander verbunden, eine divalente Alkylengruppe;
R₇ ein Wasserstoffatom, eine niedere Alkylgruppe, eine niedere Alkoxygruppe, eine Phenylgruppe, eine Benzylgruppe oder

worin W₁ und W₂, die gleich oder verschieden sein können, jeweils eine substituierte oder unsubstituierte Alkylgruppe oder eine substituierte oder unsubstituierte Arylgruppe darstellen, mit der Maßgabe, daß W₁ und W₂ miteinander verbunden sein können unter Bildung eines 5gliedrigen oder 6gliedrigen stickstoffhaltigen heterocyclischen Ringes; oder worin R₃ und R₇ miteinander verbunden sein können unter Bildung einer divalenten Alkylengruppe;
Z und Z₁, die gleich oder verschieden sein können, jeweils eine Gruppe von Nichtmetallatomen, die erforderlich ist zur Bildung eines 5gliedrigen oder 6gliedrigen stickstoffhaltigen heterocyclischen Ringes;
X° ein Säureanion; und
m die Zahl 1 oder 2.Particularly preferred sensitizers can be represented by the general formula (II).

Here mean:
R₁ and R₂, which may be the same or different, each represent an alkyl group or a substituted alkyl group;
R₃ and R₄, which may be the same or different, each represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a phenyl group or a benzyl group;
R₅ and R₆ are each a hydrogen atom or together, linked together, a divalent alkylene group;
R₇ represents a hydrogen atom, a lower alkyl group, a lower alkoxy group, a phenyl group, a benzyl group or

wherein W₁ and W₂, which may be the same or different, each represent a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group, with the proviso that W₁ and W₂ may be linked together to form a 5-membered or 6-membered nitrogen-containing heterocyclic ring; or wherein R₃ and R₇ may be linked to form a divalent alkylene group;
Z and Z₁, which may be the same or different, each represent a group of non-metal atoms required to form a 5-membered or 6-membered nitrogen-containing heterocyclic ring;
X ° an acid anion; and
m is the number 1 or 2.

The compounds are examples of suitable infrared sensitizers

The silver halide of the emulsions according to the invention can be silver chlorobromide, silver bromoiodide, silver chloroiodide or silver chlorobromoiodide. Silver chlorobromides with a chloride content of at least 70 mole percent, which may also contain small amounts of iodide, and silver bromoiodides with an iodide content of at most 10 mole percent are preferred. The crystal form can be polyhedral, platelet-shaped, spherical or irregular; the particle size distribution polydisperse or monodisperse. The grains can also have a core-shell structure. In a preferred embodiment, a monodisperse cubic emulsion with a grain size between 0.05 and 1.0 μm is used. Methods for the production of emulsions of certain grain shape, grain size and grain size distribution are known to the person skilled in the art.

Chemical ripening can be carried out using the known methods of sulfur, noble metal or reduction sensitization or else using suitable combinations of these methods. The aromatic thiosulfonic acids according to the invention can be added before, during or after chemical ripening. If they are present in the emulsion during chemical ripening, they also act as clarifiers in the known manner.

The infrared sensitizers are preferably added to the emulsion after chemical ripening or shortly before application to the layer support. However, if they are sufficiently stable, they can also be used in earlier stages of emulsion production.

The emulsions and the recording materials produced therefrom can contain other known agents for adjusting certain properties, for example antifoggants, agents for improving the storage stability, polymer dispersions (for improving the dimensional stability of the recording materials), hardening agents, coating aids, matting agents.

The emulsions of the invention provide photographic materials with superior infrared sensitivity. The gradation of the emulsion is not significantly changed by the addition of the thiosulfonic acid. Suitable thiosulfonic acids or their salts for carrying out the invention are readily available.

The invention can be used in the production of infrared-sensitive photographic recording materials, for example for recordings with a scanning laser beam in reproduction technology or medical diagnosis, and for imagewise photography.
The following exemplary embodiments are intended to explain the invention in more detail. In these examples, all amounts of emulsion additives are based on 1 mol of silver halide; unless otherwise noted, the addition was in dissolved form.

example 1

A monodisperse silver chlorobromide emulsion with a chloride content of 70 mole percent was produced by pAg-regulated two-jet enema. This emulsion had cubic grains with an edge length of 0.22 µm. After removing the soluble salts by flaking and washing, it was subjected to a combined sulfur-gold ripening. Before chemical ripening began, 133 mg of Compound I-1 was added.
The ripening was ended by adding 270 mg of 4-hydroxy-6-methyl-1,3,3a, 7-tetraazaindene. Before application to a polyethylene terephthalate backing provided with an antihalation backing, 1.1 g of saponin and 17 mg of sensitizer II-2 were added to the emulsion. A gelatin protective layer, which contained a hardening agent and further coating aids, was applied at the same time as the emulsion. The recording material thus produced contained 2.6 g of silver and 3.8 g of gelatin per m² on the recording side.

A comparison test was carried out according to the same procedure, but without the addition of compound I-1.
The material obtained in this way was exposed in a sensitometer with an exposure time of 1 ms through interference filters with transmission maxima of 407 and 798 or 830 nm and processed in a X-ray roll developing machine filled with commercially available solutions at a developer temperature of 34 ° C in a total time of 90 s. To assess the sensitivity, the reciprocal of the exposure required for a density of 1.0 above the minimum density (veil + underlay) was determined and related to the value 100 for the comparison test. The test result is shown in Table 1.

Example 2

The experiment according to Example 1 was repeated, but the experimental and the comparative emulsions each containing 200 mg of nonylphenol ethoxylate (10 moles of ethylene oxide per mole of phenol) were added. The result is shown in Table 2.

Example 3

The experiment according to Example 2 was repeated, all samples containing the nonylphenol ethoxylate, but additionally a polyethyl acrylate latex with a solids content of 30% by weight was also introduced. The results are shown in Table 3.

Example 4

A monodisperse silver chlorobromide emulsion with 80 mole percent chloride with cubic grains with an edge length of 0.23 μm was produced by pAg-regulated two-jet inlet. 0.052 mg of rhodium (III) chloride had been added to the precipitation mixture. The emulsion was subjected to a flocculation washing process and a combined gold-sulfur sensitization. Before the digestion, 140 mg of sodium toluenesulfinate and optionally the compound I-2, then 400 mg of 4-hydroxy-6-methyl-1,3,3a, 7-tetraazaindene, 70 mg of benzotriazole, 750 mg of sodium octylphenyldi (oxyethyl) sulfonate, 25 mg of the sensitizer II-1 and, if appropriate, 65 g of the latex of Example 3 were added. The emulsion was applied together with a protective gelatin layer to a support as in Example 1. The recording material thus produced contained 4.3 g of silver and 3.5 g of gelatin per m² on the recording side.

The material was exposed as in Example 1 and processed in a roll developing machine for photoset material with a commercially available rapid developer of the hydroquinone-phenidone type at 34 ° C. in a total time of 120 s. In order to assess the sensitivity, the reciprocal of the exposure required for a density of 3.0 above the minimum density was determined and, for each wavelength, related to the value 100 for the comparison test. The result is shown in Table 4.

Examples 3 and 4 show that the addition of the aromatic thiosulfonate according to the invention increases the sensitivity even in the presence of known supersensitizing additives.

Example 5

Experiments were carried out after the comparative experiment from Example 4, in which the emulsion was sensitized with various sensitizers for the green, red and infrared spectral range with and without the addition of 75 mg of the compound I-1. The sensitivity was determined for each sensitizer at 407 nm and at the sensitization maximum. Table 5 shows the sensitivities of the test films containing the compound I-1 based on the value 100 for the films without this compound with otherwise the same sensitization.

Compound A

Compound B

Compound C

Compound D

It can be seen from these results that the aromatic thiosulfonic acids only increase the sensitivity in the case of infrared-sensitive emulsions, whereas when sensitizing in the visible range the sensitivity is reduced in a known manner, at best stabilized by this compound.

Claims (11)

1. A method for preparation of a photographic silver halide emulsion sensitized for the infrared spectral region,
   characterized in that
   an aromatic thiosulfonic acid or a salt of such acid is added to the emulsion.
2. A method according to claim 1,
   characterized in that
   the aromatic thiosulfonic acid or its salt is represented by the general formula (I)

   

   wherein R is a mono- or divalent alkyl, aryl, or aralkyl radical having 1 to 10 carbon atoms, or hydrogen, and M is a cation, and n is 1 or 2.
3. A method according to claim 1 or 2,
   characterized in that
   the aromatic thiosulfonic acid or its salt is added in an amount of 0,2 to 2 millimol per mol of silver halide.
4. A method according to claim 1 to 3,
   characterized in that
   the emulsion contains a heptamethine cyanine dye as infrared sensitizer.
5. A method according to claim 4,
   characterized in that
   the heptamethine cyanine has the general formula

   

   wherein
   R₁ and R₂, which can be identical or different, signify respectively an alkyl group or a substituted alkyl group;
   R₃ and R₄, which can be identical or different, signify respectively a hydrogen atom, a lower alkyl group, a lower alkoxy group, a phenyl group, or a benzyl group;
   R₅ and R₆ both signify respectively a hydrogen atom, or jointly, being linked together, a divalent alkylene group;
   R₇ signifies a hydrogen atom, a lower alkyl group, a lower alkoxy group, a phenyl group, a benzyl group, or

   

   wherein W₁ and W₂, which can be identical or different, represent respectively a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group, with the proviso that W₁ and W₂ may be linked together forming a 5 or 6 membered heterocyclic ring containing nitrogen; or wherein
   R₃ and R₇ may be linked together forming a divalent alkylene group;
   Z and Z₁, which can be identical or different, signify respectively a group of non-metallic atoms required to form a 5 or 6 membered, nitrogen-containing heterocyclic ring;
   X⁻ signifies an acid anion; and
   m signifies the number 1 or 2.
6. A method according to claim 1 to 5,
   characterized in that
   the silver halide consists to at least 70 mole percent of silver chloride.
7. A method according to claim 1 to 6,
   characterized in that
   the aromatic thiosulfonic acid is p-toluene thiosulfonic acid.
8. A method according to claim 1 to 7,
   characterized in that
   the silver halide is present in the form of cubic grains of uniform size.
9. A method according to claim 1 to 8,
   characterized in that
   the aromatic thiosulfonic acid or the salt of such acid is added to the emulsion before the start of the chemical ripening.
10. Use of a photographic silver halide emulsion prepared by the method according to claim 1 to 9 for preparation of an infrared sensitive recording material.
11. A photographic silver halide emulsion sensitized for the infrared spectral region,
    characterized in that
    it contains an aromatic thiosulfonic acid or a salt of such acid.