DE1049230B - Production of direct positive photographic images - Google Patents

Description

Production of direct positive photographic images One can by using known photographic effects, such as the solarization and the Herschel effect, produce direct positive photographic images, d. H. Positives, their production without the mediation of a previously recorded negative can be done.

The solarization effect is a reversal phenomenon that occurs when the overexposure of the photographic material occurs. To be direct positive in this way To produce pictures, a strong overexposure is required, and pure white Parts of the image are still rarely or practically impossible to achieve.

The Herschel effect is based on the destruction of a latent image or a latent haze upon exposure to light of longer wavelength than at the first exposure, mostly with infrared or red rays. Also to achieve this effect requires strong exposure.

When the photographic material is treated with a desensitizer the Herschel effect with light of shorter wavelength, z. B. yellow light, be evoked.

It is known that fogging can be achieved either by exposure to light or by chemical means.

It is also known to use emulsions for direct positive production use that are pre-veiled by a reducing agent, such as. B. by hydrazine, Hydroxylamine, formaldehyde and tin chloride, through salts of gold, platinum, palladium, Iridium, ruthenium and strontium or by sulfur compounds such as sodium thiosulphate and thiosinamine.

When using emulsions with a masking effect However, reducing agents can no longer easily destroy the fog-forming germs so that a very high exposure is required and still none fully pure white parts are achievable.

When using emulsions containing a gold compound, A pre-veil sufficient for the Herschel effect is hardly possible: so that none high-contrast direct positive images can be generated. In addition, the fog-forming germs obtained in this way are likewise only difficult to destroy.

Fog-forming germs, which when using a sulfur-containing Connections are mostly used to create images based on the Herschel effect not suitable.

It is also known to use emulsions in which fogging has been achieved by a reducing agent and a metal compound that is more electropositive than silver is. This method is preferred in high speed photographic applications Emulsions with a soft gradation, but less so with less sensitive emulsions can be used with hard gradation.

It has now been found that very good, direct positive images are obtained, if the emulsions are added with a concealing amount of silane compounds, which contain at least one Si-H group.

It is known that these silane compounds cause an increase in sensitivity the photographic emulsions when added in certain amounts. However, it was not to be expected that the use of silane compounds in concealing amounts on the one hand a fair direct positive production sufficient fogging can be caused, but on the other hand the fogging Germs can be destroyed so easily during exposure that, in contrast to the chemical fogging processes known up to now, even without strong exposure pure white parts are achievable.

The fog-forming agents can be of the invention to be used- Emulsion either in the form of an alcoholic solution or adsorbed on finely divided inert particles such as silica, magnesium silicate and barium sulfate are added will. In an alcoholic solution, the haze-forming agent is more active, so a much smaller amount to cause sufficient fogging the silane compound is required. Suitable amounts are e.g. B. 20 mg to 400 mg alcoholic solution per mole of silver halide or about 75 mg to 1200 mg of the adsorbed Product per mole of halogen silver. The veil-forming means become preferably added in the course of the preparation of the emulsion. For example, the Washed emulsion and increased its? H value. Then you add las to the emulsion fogging agents, after which the emulsion matured for a short time and whose pH value is reduced.

The presence of compounds known in conventional photography as desensitizers in the emulsion, which is necessary for high-contrast imaging during exposure, can be achieved by incorporating these desensitizers into the emulsion either in the course of a bath treatment prior to exposure or in the course of the preparation of the emulsion. Desensitizers particularly suitable for use in direct positive emulsions are e.g. B. the dihydropyrimidine derivatives containing a nitro group according to German Patent 1019 171.

The photographic emulsions fogged according to the invention have does not include the disadvantages commonly associated with the use of formaldehyde are. This addition increases the viscosity of the emulsion before it is poured increased so that the emulsion is not allowed to solidify and melt again after addition can, but must shed immediately. Also arise in the course of the casting process often adverse effects. On the other hand, after the veil according to the invention, it is possible to solidify the emulsion, to store it and to melt it again so that it can be shed at any moment.

The following examples serve to explain the description, without to restrict them in any way. Example 1 In preparing a silver chloride emulsion, which contains 30 g of silver nitrate per kg of emulsion, becomes the emulsion after washing heated to 45 ° C. At this temperature, 10 cm3 of sodium hydroxide are produced per kg of emulsion (1%) and 7 cm3 of methyldichlorosilane solution (0.5% in ethanol) were added. As a result of this In addition, the pH of the emulsion rises to about B. The emulsion becomes a kept at 45 ° C for a further hour, whereupon it was acidified with an aqueous H Cl solution (1%) is brought to pH = 6.

After cooling, 200 cm3 of a 0.5% strength ethyl alcoholic solution of the following desensitizing compound are added added per equivalent of 30g silver nitrate. The emulsion is applied to a paper base and illuminated with minus blue light, e.g. B. through a Gevalor yellow filter L 500 (Gevalor is a registered trademark) exposed. After developing, fixing, washing and drying, a direct positive image with pure whites is obtained.

Example 2 A just washed silver chloride emulsion containing 40 grams of silver nitrate per kg of emulsion is heated to 45 ° C. At this temperature per kg emulsion 12 cm3 sodium hydroxide (1%) and 3 cm3 trichlorosilane solution (0.5 ° / o in Ethanol) added. As a result of this addition, the pH of the emulsion rises to to 8.1. The emulsion is kept at 45 ° C. for 10 minutes, followed by acidification is brought to pH = 6 with an aqueous H Cl solution (1%).

After cooling, 120 cm3 of a 0.5% dioxane solution of the following desensitizing compound are added added per equivalent of 100 g of silver nitrate.

The emulsion is poured onto a film base and passed through a Gevalor Yellow filter L 500 exposed. After developing, fixing, washing and drying a direct positive image with pure whites is obtained.

Claims (1)

Claim: Use of an emulsion containing a desensitizer, which is fogged by the action of a silane compound containing at least one Si-H group, for the production of direct-positive images by exposure to minus blue light. References considered: U.S. Patent Nos. 2694637, 2500110.