Radiation imagery chemistry: process – composition – or product th – Color imaging process – Using identified radiation sensitive composition in the...
Reexamination Certificate
2001-08-01
2004-11-30
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Color imaging process
Using identified radiation sensitive composition in the...
C430S430000
Reexamination Certificate
active
06824965
ABSTRACT:
This invention relates to a bleach or bleach/fixing solution for processing photographic silver halide materials which, relative to the silver halide content of the unprocessed material, exhibit prior to the bleaching step a content of silver arising from development of at least 65 mol %, in particular to a bleach or bleach/fixing solution for processing colour reversal materials and to a process for the processing colour reversal materials using such a solution.
It is known to use iron(III) complexes of aminopolycarboxylic acids for bleaching photographic materials, i.e. for oxidising the metallic silver formed during development, for which purpose numerous complexing agents have been proposed (c.f. for example Research Discl., Vol. 240, Item 24023, DE 2 321 400, DE 3 743 783, DE 3 800 270, U.S. Pat. Nos. 3,241,966, 3,615,508, 5,238,791, 5,885,757). In practice, colour reversal materials are usually processed using the iron(III) complex with ethylenediaminetetraacetic acid (EDTA) at a concentration of at least 0.30 mol/l as the complexing agent for bleach baths. While other substances, such as for example propylenediaminetetraacetic acid (PDTA), &bgr;-alaninediacetic acid (ADA), methyliminodiacetic acid (MIDA), diethylenetriaminepentaacetic acid (DTPA), iminosuccinic acid propionate (ISP), racemic and (S,S)-ethylenediaminedisuccinic acid (EDDS), are indeed stated as suitable iron(III) complexing agents for bleaching photographic materials and have successfully been used for processing colour negative materials, suitability for the specific requirements of colour reversal processing has not been described.
The content of complexing agents is excessively high in known bleach baths for colour reversal materials. Apart from entailing material costs, this content is in particular associated with an unwanted environmental impact as the complexing agents used are sparingly biodegradable. The elevated concentration is used in order to meet the very stringent requirements which reversal materials place on a bleaching bath. In reversal processing, the majority of the silver halide is in fact reduced to silver, namely in the first development initially the proportion of crystals exposed with the image, which generally amounts to less than 30 mol %, and then the unexposed crystals on secondary development after the reversal bath, such that, relative to the total silver content of the material, at least 65 mol % of Ag
0
, frequently at least 80 mol % and often even at least 90 mol % of Ag
0
must be bleached, whereas in negative materials this proportion of Ag
0
originates only from the exposed crystals and is accordingly conventionally distinctly below 30 mol %. This difference with colour reversal films is manifested particularly seriously in materials having a total silver content, stated as silver nitrate, of at least 6.0 g/m
2
, in particular of at least 7.5 g/m
2
. Unless indicated to the contrary, all absolute quantities of silver are stated hereinafter as g of silver nitrate; 1 mol of silver is accordingly stated as 170 g of silver, irrespective of whether it is metallic or chemically bound silver.
When processing colour reversal films, at least 3.9 g of silver, frequently at least 5.6 g of silver and often even at least 6.3 g of silver must be bleached per m
2
.
Another problem of known bleach baths is the stability of the bath with regard to chemical precipitation. U.S. Pat. No. 4,933,266 accordingly discloses that when an iron/PDTA bleaching bath is used, it is necessary to use another complexing agent, such as for example diaminopropanoltetraacetic acid (DPTA) in order to counteract precipitation, for example due to entrained phosphate. Such additional complexing agents constitute an additional chemical load in the bleach baths and are accordingly unwanted both on cost grounds and due to the associated environmental impact.
Moreover, it is not possible according to the prior art simultaneously to achieve in colour reversal processing both a very good bleaching action, discernible from a very low residual silver content, and a very low bleaching fog value, discernible from a low value of yellow minimum density. Both requirements are particularly critical in reversal materials since, on the one hand, as described above, an elevated proportion of reduced silver must be bleached and, on the other, both the residual silver, which is usually coloured, and the bleaching fog give rise to colour casts and an elevated minimum density, which have a severely disruptive effect for example when projecting reversal films and, unlike with negative films, cannot be corrected by the enlargement process in the printer.
Known bleach baths for reversal materials exhibit further environmental and economic disadvantages as they cannot sensibly be reprocessed. Due to the required elevated active substance content, such a large volume of fresh concentrate would have to be added to the used solution that the resultant increase in volume would make recycling uneconomic. The increase in volume also results in increased quantities of waste.
The object underlying the invention is accordingly to provide a bleach or bleach/-fixing bath which is particularly suitable for processing photographic silver halide materials having an elevated proportion of silver to be bleached and in particular is suitable for processing colour reversal materials, and to provide a process for processing colour reversal materials, wherein the least possible quantity of complexing agent should be used, a low residual silver content and simultaneously a low bleaching fog value of the processed materials should be achieved and the bleach or bleach/fixing bath should also be resistant to precipitation without stabilising additives.
It has now surprisingly been found that this may be achieved if the iron/PDTA or iron/ADA complex is used in the ready-to-use bleach or bleach/fixing bath in a concentration range of from 0.045 to 0.25 mol/l. Particularly surprisingly it is consequently possible to manage with only little bleaching agent, despite the elevated proportion of silver to be bleached.
The present invention accordingly provides a bleach or bleach/fixing solution for processing photographic silver halide materials which, relative to the silver halide content of the unprocessed material, exhibit prior to the bleaching step a content of silver arising from development (bleaching proportion) of at least 65 mol %, characterised in that the solution contains at least one iron complex of propylenediaminetetraacetic acid or of &bgr;-alaninediacetic acid or a mixture of these complexes and the total concentration of the stated iron complexes in the solution is at least 0.045 and at most 0.25 mol/l.
The iron complex of PDTA is conventionally used as a sodium, potassium or ammonium salt, but any other cations may also be used.
In a preferred embodiment, the bleach bath used contains no ammonium ions.
The bleaching proportion may readily be determined by, contrary to conventional practice, only fixing the developed material and then determining the silver content, for example by using the X-ray fluorescence method. This value is then related to the corresponding result for the unprocessed material.
The present invention also provides a bleach or bleach/fixing solution for processing colour reversal silver halide materials, characterised in that the solution contains at least one iron complex of propylenediaminetetraacetic acid or of &bgr;-alaninediacetic acid or a mixture of these complexes and the total concentration of the stated iron complexes in the solution is at least 0.045 and at most 0.25 mol/l.
The bleach baths according to the invention are advantageously used for materials having a bleaching proportion of at least 80 mol %, in particular of at least 90 mol %.
The bleach baths according to the invention are preferably used for materials with negative-working emulsions. These may, in rare cases, comprise special negative materials in which an unusually large proportion of the silver halide crystals is exposed and thus reduced to sil
Hübsch Thomas
Stetzer Thomas
Wichmann Ralf
AGFA-Gevaert
Connolly Bove & Lodge & Hutz LLP
Le Hoa Van
LandOfFree
Bleach bath does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Bleach bath, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Bleach bath will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3310364