DE977335C - Process for reducing the blue sensitivity of photographic silver halide emulsions - Google Patents

Description

ISSUED DECEMBER 16, 1965

A 17626 IXa I 57 b

To reduce the blue sensitivity or inherent sensitivity of photographic silver halide emulsions Numerous desensitizers have already been specified that meet the requirements to be placed on them more or less corresponded. A good desensitizer must meet a number of conditions fulfill. First and foremost, this includes reducing the sensitivity without affecting the latent image to influence and without creating a noticeable veil. Furthermore, it should be as colorless as possible, can be soaked out easily and leave practically no noticeable layer staining. In the end the desensitizing effect should as far as possible not be impaired by the developer.

It has now been found that to reduce the blue or intrinsic sensitivity of photographic Halogen silver emulsions used to produce negative and direct positive images serve, especially compounds of the general formula

NX-CH ₅

suitable, where Y = members of a heterocyclic six-membered ring to which a further benzene ring is attached can be, and X = halogens or any other acid radicals and R = nitro groups.

Compounds of this type are, for example, 2-, 3- or 4-nitrobenzylpyridinium halides, 2-, 3- or 4-nitrobenzylquinolinium halides. These connections are characterized by very good solubility and very easy rinsing. Because they are practical are colorless, there is no staining of the layers

509 734/4

instead of. A particularly good effect is achieved with compounds which have a in the m-position of the benzyl radical Wear nitro group.

The effect of the desensitizers can be increased significantly by the presence of small amounts of compounds of metals of the first subgroup of the periodic table.

The desensitizers can be added to the photographic emulsions at any point in time Production - in quantities of up to 10 g per liter of emulsion • - ■ can be added, or they can be added to the finished product Emulsion layer are incorporated in the bath process. If necessary, these desensitizers can also can be added to the photographic developer.

The method according to the invention can be used in all cases where a reduction is required the inherent sensitivity of the halogen silver emulsions. In more recent times have Process for the production of direct positives with the help of the Herschel effect of particular practical importance attained. Halogen silver emulsions with the above-mentioned desensitizers are suitable for such a process, especially in connection with small amounts of metal salts of the I. subgroup of the periodic table particularly suitable. For this purpose, an emulsion is made with a Nitrobenzylpyridinium chloride or with a nitrobenzylquinolinium chloride and with a low Amount of a copper salt added. The emulsion layer produced therefrom becomes a general one Subject to pre-exposure up to the apex of their blackening. After an exposure under an original with yellow light and development, a positive image is obtained.

Example ι

5 g of o-nitrobenzylpyridinium chloride are added to a silver halide emulsion to 11 emulsion, 5 to 200 mg of 2-mercaptobenzothiazole and 10 mg of copper sulfate were added. The emulsion layer cast therefrom is exposed and processed in the usual way.

Example 2

4 g of o-nitrobenzylquinodium chloride are added to a silver halide emulsion on the emulsion, 5 to 200 mg of 2-mercaptobenzothiazpl and 10 mg of copper sulfate were added. The emulsion layer cast therefrom is exposed and processed in the usual way.

Example 3

The 5 g of o-nitrobenzylpyridinium chloride in Example 1 are replaced by the appropriate amount of p-nitrobenzyl-2-methylpyridinium chloride replaced.

Example 4

Instead of o-nitrobenzylpyridinium chloride (Example 1), m-nitrobenzylpyridinium chloride is used Use.

Example 5

6 g of o-nitrobenzylpyridinium chloride are added to a silver halide emulsion with at least 60% silver chloride on 11 emulsion and 10 to 250 mg benzimidazole added and processed as in Example 1.

Example 6

3 g of m-nitrobenzylpyridinium chloride are added to a silver halide emulsion to 11 emulsion, 100 mg benzimidazole and 50 mg copper sulfate added. the The emulsion layer obtained therefrom is exposed and processed in the usual manner.

Example 7

An insensitive, steeply working chlorine overemulsion, the per liter of emulsion mass 28 g of chlorine silver and contains 70 g of gelatin, is used once without any additional pouring additives and, on the other hand, after adding 3 g of o-Nitrobenzylchinohniumchlorid poured. Both samples are then blackened up to 1.2 with short-wave, intense light, e.g. B. with the light of a high pressure mercury lamp or a strobe, pre-exposed. The sensitometry is then carried out using a yellow filter. No positive step wedge is obtained with the sample without addition, with the sample with the addition of a desensitizer a well graded positive wedge with good whites and good blacks.

Claims (3)

PATENT CLAIMS: i. Process for reducing the blue sensitivity of photographic silver halide emulsions which are used to produce negative and direct-positive images, characterized in that the desensitizers used are compounds of the general formula N — X — CH, used, where Y = members of a heterocyclic six-membered ring to which a further benzene ring is attached can be, and X = halogens or any acid radicals and R = nitro groups. 2. The method according to claim 1, characterized in that that one uses nitrobenzylpyridinium or nitrobenzylchinolinium compounds, 3. The method according to claim 1 or 2, characterized in that in addition to the desensitizers Traces of metal salts of the I. subgroup of the periodic system used. References considered: U.S. Patent No. 2,541,472. © 509 577/258 10.55 (509 734/4 12.65)