DE1572140B2 - Process for the preparation of a direct positive silver halide emulsion - Google Patents

Description

The invention relates to a process for the preparation of a direct positive silver halide emulsion which after silver halide formation by adding 0.33 mg to 12 g of an aminoborane compound is chemically obscured per mole of silver halide.

Direct positive images can be made in a number of ways using silver halide emulsions produce. For example, one can use a silver halide emulsion with a short overall exposure exposure to high intensity radiation and then taking a prolonged imagewise exposure Connect radiation with lower intensity. A direct positive image is then obtained during development. Another method is imagewise exposing and developing, followed by flash exposure and reverse engineering. Another way of working is instead of a solarizing one Exposure via the fogging of the silver halide grains by chemical means, for example with Formaldehyde, hydrazine, sodium arsenate, silver ions and other non-sulphidic fogging agents. at the imagewise exposure and development of a material chemically fogged in this way then a positive image. In the direct positive photographic used for this latter process Materials usually have incorporated therein a desensitizing compound, generally a desensitizing agent Dye.

All of the emulsions listed above have disadvantages such as B. low inversion density, impractical long exposure times, undesirable, due to the desensitizing dyes Spots and disturbing contrasts. If more than one exposure step is used, additional steps are required Operations required, which adds to the complex nature of the process. the Use of formaldehyde as a chemical fogging agent is undesirable as it continues has a hardening effect on the gelatin, which is already sufficiently hardened in itself.

DT-PS 10 48 778 describes a process for the production of direct positive photographic emulsions or layers with precipitation of silver halide and using a soluble salt of a Metal from group 8 of the periodic table. This procedure requires that during the entire Production and processing of the silver halide emulsions always worked in the pH range above 7 will.

DT-OS 15 72 125 describes a photographic material which consists of a support and at least one layer applied to it of a photographic silver halide emulsion capable of producing direct positive images. The emulsion is distinguished by the fact that it contains at least one aminoborane as a chemical fogging agent in an amount of 0.00033 to 12 g / mol of silver halide. The direct positive photographic materials described in this patent are extremely sensitive compared to the prior art direct positive materials. In addition, they do not have the disadvantages of long exposure times, undesirable spots due to the desensitizing dyes and undesirable contrasts. They also do not require multiple exposure and treatment processes.
However, the last two materials mentioned are extremely susceptible to kinking. This kink sensitivity has long been recognized as a problem in emulsion layers for highly sensitive negatives and X-rays. So far, however, it has never had a disturbing effect on emulsion layers for the production of direct positive images, probably because of the low sensitivity of these layers. However, for the particularly effective materials described in the references cited above, kinking has become a problem which is manifested in the fact that kinked areas bleach more quickly than unfolded areas during exposure.

The object of the invention is therefore to provide highly sensitive images capable of producing direct positive images To provide silver halide emulsions, which compared to the prior art in terms of their sensitivity to kinking are improved.

The invention is based on a process for the preparation of a direct positive silver halide emulsion, after silver halide formation by adding 0.3 mg to 12 g of an aminoborane compound is chemically obscured per mole of silver halide. It is characterized by the formation of silver halide in an acidic medium and in the presence of 1.5 to 325 mg of a water-soluble rhodium or iridium salt occurs per mole of silver halide.

The emulsion is preferably a gelatin silver halide emulsion, in which the silver halide is a mixture of silver bromide and silver chloride with 80 to 90 weight percent silver bromide. Additionally up to 6 percent by weight of silver iodide can be present in addition to the two halides.

Rhodium chloride, rhodium nitrate and iridium tetrachloride have proven particularly useful. The optimal one Concentration of a particular rhodium or iridium salt can be determined by looking at the Changes in density observed in a kink area when the material of the usual bleaching Exposure is exposed and these density changes are compared with those of the unfolded areas. The crease procedure used for testing is to strip a film strip prior to exposure by about 90 ° over a small curvature

radius to bend and the ratio between the minimum density in the kinked area and the Determine density in the unfolded area.

The amino borane chemical fogging agents are intended to match the emulsions in those listed above Amounts are added, preferably they are used in amounts of 0.013 to 1.3 g per mole of silver halide. They are either set in a fixed form or as a solution in a suitable solvent. The effectiveness of the aminoborane compound in the Fogging of a silver halide emulsion is affected by the pH of the system. The higher the pH value, the greater the masking effect for a given amount of borane compound. Of course, when equivalent amounts are used, certain borane compounds are more effective than others. The fogging effect created by the borane compound is due to exposure before the Develop bleachable. All alkaline photographic developer solutions customary in practice which are used for conventional direct positive image treatment of emulsions containing no aminoborane compounds are in use can also be applied here. Although the mechanism of the process is not completely clear, it can be assumed that the light-bleaching effect on a solarization going back. It is also not clear why soluble rhodium or iridium salts, such as Rhodium chloride or iridium tetrachloride, prevent faster bleaching in the kinked areas, while on the other hand they do not affect the unfolded areas. Although the aminoborane compounds The solarizing seems to lead to a chemical obscuration of all types of emulsions Effect occurs especially in silver chlorobromide emulsions.

The aminoborane compounds that have proven themselves as chemical fogging agents include following:

A. Alkylaminoboranes

Typical aminoboranes of this type correspond to the formula

I.

R ₁ - N: BH ₃

R ₃

where R _{1 is} an alkyl radical having 1 to 20 carbon atoms and R ₂ and R _{3 are} either equal to R ₁ or equal to hydrogen. Examples of such boranes:

3. Dimethyldodecylaminoborane
CH ₃

C ₁₂ H ₂₅ N: BH ₃
CH ₃

4. Dimethyloctadecylaminoborane CH ₃

C ₁₈ H ₃₇ - N: BH ₃
CH ₃

5. Diisooctylaminoborane

CH,

CH (CH ₂ ) ₅

HN :. BRA,

CH ₃

6. Tricaprylaminoborane

QH ₁₇

C ₃ H ₁₇ - N: BH ₃
QH ₁₇

B. Heterocyclic Aminoboranes 1. Pyridineborane

N: bra,

2. Picoline borane and isomeric mixtures of the three isomers

! Trimethylaminoborane
CH ₃

CH ₃ -N: BH ₃
CH ₃

2. tert-butylaminoborane
CH ₃ H

CH ₃ -CN: BH ₃
CH ₃ H

55

60 N: BH ₃

3. Morpholine borane
CH ₂ -CH,

NH: BH,

CH ₇ CHo

65 The greatest possible fogging effect is preferably achieved when the aminoborane compounds are added to the silver halide emulsion after it has been physically ripened and washed to remove the excess of soluble salts resulting from the precipitation of the silver halides. Usually the aminoborane compounds are then added immediately before or during the

maturation period added. The pH of the emulsion is set to values between 5 and 9, preferably between 8.0 and 8.5, adjusted and kept at this level during the entire digestion process. After digestion, the pH is lowered to 5 to 6 and the usual coating aids are used added. The emulsion is then applied and dried in a manner known per se.

In addition to the described bending of test film strips for the purpose of determining the kinking effect sensitometric data of the emulsions producing direct positive images can be obtained by treating Determine test strips with applied layers as follows:

In each of the following examples, a test strip was fixed out in a conventional photographic fixing bath in order to have a basis for determining the minimum density (D _mi ") . The test strips are exposed in an intensity scale sensitometer (described on page 616 in M ees, The Theories of the Photographic Process, MacMillan Company, New York, 1942), with exposure units corresponding to a ^ 2 step wedge and a log of exposure of 5, 92 were applied. The exposed strip was then developed for 1.5 minutes at 15 ° C in a developer with the following composition:

Water 750 cm ³

N-methyl-p-aminophenol hydrogen

sulfate 1.5 g

Sodium sulfite, anhydrous 19.5 g

Hydroquinone 6.0 g

Sodium carbonate, anhydrous 24.0 g

Potassium bromide 0.8 g

Made up to 1.01 with water

The developed strip was immersed in a conventional break bath for 5 to 10 seconds and Fixed in a conventional fixing bath for 3 minutes, followed by washing and drying.

When evaluating the treated strips, the lowest density above the density of the fully fixed strip is regarded as the minimum density (D _{mi ").} The maximum density (D _max ) is the highest density above D _mi ". The entire scale is given in units of the log £ range and is equal to the difference between log E (exposure) at 0.01 above D _min and log £ at 3.5 above D _mi “. No overall ranges are given where in the following examples D _{max is above 3.5.} The sensitivity of a typical commercial direct positive material, measured in units of 100 / £ ^10-15 , is 10.3; the common material has a D _mi "value of 0.02, a D _max value of 3.5 and a full scale range of 0.40.

As can be seen from the sensitometric data, when compared to the data of a typical commercially available direct positive material, the photographic materials of the invention direct positive Images with extremely low minimum and extremely high maximum densities. Besides, they are opposite the known direct positive images delivering materials extremely sensitive, but show at the same time a reduced sensitivity to kinking. You can use the new materials in all common developer solutions develop in a known manner. Variations in the developer solutions often have an effect in the same way as when developing irreversible emulsions. When applying the new Materials eliminates the need for pre-exposure or the use of special auxiliary measures. It is also unnecessary to use desensitizing dyes, which can sometimes cause stains, or introduce other desensitizing substances into the emulsion. As chemical fogging agents are the Boranes are superior to formaldehyde, which is mainly known as a masking agent, since they do not contain any have a hardening effect on the gelatin layer.

In addition, the kinking problem is eliminated by the new emulsions.

The emulsions are generally applied to the support in such amounts that one Layer weight of 50 to 75 mg silver halide per square decimeter of the substrate surface is present.

Good prints pass through the materials coated with the emulsion of the invention Make contact printing using either carbon arc lamps or tungsten flood lamps as Light sources used. The materials are suitable for reproducing negatives with continuous gradual tonal values, raster negatives, line copies and machine drawings. The direct positive materials can also be used in color photography use. Furthermore, the production of washable, direct positive relief printing forms is under Use of a hardening developer is possible with the invention.

The following examples illustrate the invention. Unless otherwise stated, all are Quantities are to be regarded as weight information.

example 1

In each case 11 up to a pH value of 2.0

40. Acidified, aqueous, 1.95% strength gelatin solutions, each of which contained 1 mole of potassium chloride and the amounts of rhodium chloride listed in the table below (chemical formula RhCl ₃ -3H ₂ O), 11 aqueous solutions were quickly added, each Contained 1 mole of silver nitrate. 0.4 mol of potassium bromide dissolved in 1.33 ml of water was added to each of the resulting mixtures, and the emulsions were then allowed to physically mature by heating at 71 ° C. for 10 minutes. Finally, 0.6 mol of potassium bromide, dissolved in 200 ml of water, was added to each of the emulsions and the emulsions were left to physically ripen ^{at 71 ° C. for a further 10 minutes.}

The emulsions obtained were then cooled and flocculated as described in US Pat. No. 2,772,165, washed and redispersed. The temperature of the redispersed emulsions was brought to 55 ° C and then 87 g of gelatin was added to each dispersion, after which the pH was adjusted to 8.2 with borax became. It was then according to the subsequent

60th standing table, morpholine borane was added and the emulsions were digested at 55 ° C. for 40 minutes. The pH was lowered to 7.0 with citric acid and the usual coating aids included a gelatin hardener added, after which the emulsions coated on a photographic support and in have been dried in the usual way.

The sensitometric evaluation resulted in the following data:

mg RhCl ₃
3H ₂ O
ever Mon!
AgNO ₃

mg morpholine
borane
per mole
AgNO ₃

Reciprocal 100 / £ D

Kinking sensation
possibility *)
(Ratio of
minimal
Density in
the kinked
Areas
to density
in the
not kinked
Areas)

-10 " ⁵
sensitivity

(Control sample)
1.34
4.0
12th
36
108
325

1.7

1.7
1.7
1.7
4.0
4.0
4.0

0.33

0.58
0.83
0.87
0.90
0.89
0.94

1660 4.00 0.04

1060

1410

1820

457

123

229

3.83
3.35
3.65
3.75
4.00
3.96

0.05
0.03
0.02
0.02
0.10
0.12

*) Ideally, the reciprocal kink sensitivity should be the same
be.

Example 2 ■

1 l of an aqueous 1.95% gelatin solution containing 1 mol of potassium chloride and 12 mg of rhodium chloride (RhCl ₃ · 3 H _{2 O), acidified to a pH of 2.0, was added 1 l of an aqueous 1} Moles of silver nitrate-containing solution given. 0.4 mol of potassium bromide dissolved in 1.33 ml of water was added to the mixture obtained. The emulsion was then physically ripened ^{by heating to 71 ° C. for 10 minutes.} This was followed by a second addition of 0.6 mol of potassium bromide, dissolved in 200 ml of water, after which it was again allowed to physically ripen ^{at 71 ° C. for 10 minutes.} The emulsion obtained was cooled and, as in Example 1, flocculated, washed and redispersed. The temperature of the redispersed emulsion was then raised to 55 ° C., 87 g of gelatin were then added and the pH was adjusted to 8.2 with borax. The emulsion was divided into two parts and tertiary butylaminoborane was added to part (A) in such amounts that 0.84 mg of borane were present per mole of silver halide. 3.3 mg of trimethylaminoborane per mole of silver nitrate were added to the other portion (B). The pH of the emulsions was lowered to 7.0 with citric acid and the usual

Coating auxiliaries including a gelatin hardener added, after which the emulsions on photographic Carriers were coated and dried in the usual way.

The sensitometric evaluation resulted in the following data:

emulsion

Reciprocal 100 /, EI (T ⁵ D _max
Kink sensitivity

Control sample of the
Example 1

0.33

0.80
0.80

1660

994
367

Example 3

4.00 0.04

4.00
4.00

0.01
0.01

For two 1 l each acidified to a pH of 2.0, aqueous 1.95% gelatin solutions (A) and (B), each of which contained 1 mole of potassium chloride, were for (A) 6.2 mg of iridium tetrachloride and for (B) 24 mg of the iridium salt were added. Each of these solutions quickly became 1 1 of an aqueous, 1 mol Silver nitrate containing solution was added and then 0.4 mol of potassium bromide, dissolved in 1.33 ml of water, added. The emulsions were then physically ripened by heating at 7 ° C. for 10 minutes. A second addition of 0.6 mol of potassium bromide, dissolved in 200 ml of water, was made to each emulsion, which then were further physically ripened for 10 minutes at 71 ° C. The emulsions obtained were then further processed as described in example 1 including the addition of 1.7 mg morpholine borane, the following sensitometric data were obtained:

4 ° emulsion Reciprocal 100 / E · ΙΟ " ⁵ 4.00 0.04 Kink temp Sensation delicacy opportunity Control 0.33 1660 3.88 0.01 ⁴⁵ sample of the 4.00 0.01 Example 1 (A) 0.78 1060 (B) 0.96 969

As can be seen from Example 1, 12 mg of rhodium chloride appear to be the optimum for emulsions, which contain morpholine borane as a chemical fogging agent. Iridium salts are likely to have a be effective in a wider range of quantities.

509 532/17

Claims (2)

Patent claims: 1. A process for the preparation of a direct positive silver halide emulsion which is prepared after Silver halide formation by adding 0.33 mg to 12 g of an aminoborane compound is chemically fogged per mole of silver halide, characterized in that the silver halide formation in an acidic medium and in the presence of 1.5 to 325 mg of a water-soluble rhodium or iridium salt per mole of silver halide. 2. The method according to claim 1, characterized in that the silver halide consists of silver bromide chloride consists of 80 to 90 percent by weight of silver bromide.