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AssigneeAgfa-Gevaert
InventorsHenri Depoorter, Felix Jan Moelants
Estimating the term…
A direct-positive photographic element is described which comprises a support and a spectrally-sensitized light-sensitive silver halide emulsion layer containing fogged silver halide grains wherein the said emulsion is spectrally sensitized by means of a dye containing a pyrrolo[ 2,1-b]thiazole nucleus which may be substituted and carry one or more fused-on rings, the said nucleus being linked by the 5- or 7-carbon atom thereof, directly or through a dimethine chain to another nitrogen containing heterocycle.
A direct-positive photographic element comprising a support and a spectrally-sensitized light-sensitive silver halide emulsion layer containing fogged silver halide grains wherein the said emulsion is spectrally sensitized by means of a dye containing a pyrrolo[2,1-b]thiazole nucleus, the said nucleus being linked by the 5- or 7-carbon atom thereof, directly or through a dimethine chain to another 5- or 6- membered nitrogen containing heterocycle.
Dependencies are inferred from the claim text.
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Characterised by the desensitiser: polymethine dyes
Photosensitive materials for photographic purposes
Term ended 2 Mar 1993 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
The present invention relates to spectrally sensitized direct positive silver halide emulsions.
It is known that direct-positive images can be obtained with certain types of photographic silver halide emulsions without previously forming a negative silver image. For this purpose, the silver halide grains are fogged by an overall-exposure to actinic radiation or by an overall chemical fogging, e.g. by means of reducing agents, before or after they are coated on a support. Upon image-wise exposure of the pre-fogged emulsions the development centres formed by said fogging are destroyed at the exposed areas and remain at the unexposed areas. By subsequent conventional development by means of silver halide developers a direct-positive image is formed.
For the spectral sensitization of negative type silver halide emulsions there is a wide choice of spectrally sensitizing dyes such as mono- and trimethine cyanines, rhodacyanines, hemicyanines, merocyanines, styryl dyes, oxonol dyes, etc. Most of these dyes, however, are unsuitable for the spectral sensitization of direct-positive emulsions.
The following examples illustrate the present invention.
A monodisperse, cubic direct-positive photographic silver bromoiodide emulsion (2.5 mole % of iodide) having an average grain size of about 0.2 micron, was prepared under controlled pH, pAg, and temperature conditions during precipitation of the silver halide. The pH was maintained at about 5.5, the pAg at 8.2 and the temperature at 45.degree.C. After adjustment of the pAg to 10, the emulsion was chill-set, shredded, and washed with cold water.
The emulsion was reduction- and gold-fogged by adjustment of the pAg to 5.3 and the pH to 7, by heating for 90 min. at 60.degree.C and by the addition of 30 mg of chloroaurate per mole of silver halide. Heating was continued for 80 minutes at 60.degree.C whereupon the pAg was adjusted to 8.2 and 35.degree.C.