Radiation imagery chemistry: process – composition – or product th – Nonradiation sensitive image processing compositions or... – Fixer
Patent
1992-07-16
1993-09-14
Le, Hoa Van
Radiation imagery chemistry: process, composition, or product th
Nonradiation sensitive image processing compositions or...
Fixer
430393, 430419, 430456, B03C 538
Patent
active
052447782
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to thiosulphate fixing solutions. The use of thiosulphate as a fixing agent is well known in the photographic art. It is usually combined with a low concentration of a soluble sulphite as a stabilizer.
These traditional high concentration thiosulphate fixers can be used with low coating weight silver photographic materials, but the thiosulphate is not used efficiently, and large concentrations of uncomplexed thiosulphate go to waste and constitute an unnecessary burden on sewage treatment plants as measured by BOD(5), or COD.
The present invention has addressed this problem, particularly with colour photographic materials coated low weights of silver by providing a stabilized thiosulphate fixer solution having concentrations of less than 1/10 of the conventional values (e.g. 100 gpl) and wherein the soluble sulphite stabilizer is in an excess.
U.S. Pat. No. 2,397,016 reveals alkaline fixers having a narrow range of utility in between pH 8.3 and pH 9.0 and utilizing a substantial excess of alkaline metal sulphite as a stabilizer for the thiosulphate. Such fixers cannot operate under acid conditions.
In U.S. Pat. No. 3,008,828 there is dislosed an acid photographic hardner fixer bath comprising a hardening agent, a soluble thiosulphate, such as sodium thiosulphate and/or ammonium thiosulphate; an acid such as acetic acid, and a soluble sulphite or bisulphite such as sodium sulphite and/or sodium bisulphite. The bisulphite has an activity ratio of 2:1 and hence is slightly more effective than the sulphite, however it is acidic and for some fixes it is better to use sulphites as they provide some buffering against changes in acidity.
In this disclosure the alkali metal sulphite is disclosed as being utilized in the bath in an excess by weight of up to twice that of the alkali metal thiosulphate. This improves the wash out characteristics.
We have now found that photographic fixing agents, particularly when utilized with photographic colour materials coated with low rates of silver can be effectively fixed by means of a fixing solution comprising a significant excess of the soluble sulphite material. This has both economic and environmental advantages.
According to the present invention therefore there is provided an acid photographic fixing agent adapted for colour photography utilizing silver coating rates of up to 2.1 mg/dm.sup.2 whereby stabilized thiosulfate fixer solution has a concentration of less than 10 gpl of ammonium thiosulphate or its chemical equivalent, comprising a solution of an alkali metal thiosulphate or an ammonium thiosulphate or a mixture thereof stabilized by a soluble sulphite or bisulphite; characterised in that the ratio by weight of the soluble sulphite to the thiosulphate is greater than 1.2:1 or greater than 1.44:1 if the bisulphite is used; thereby to preferentially maintain the thiosulfate in use.
The soluble sulphite is approximately twice as efficacious as the bisulphite and ratios should be considered accordingly.
The soluble sulphite may be selected from an alkaline metal sulphite such as sodium or potassium sulphite and may be present in a weight ratio of 1.2:1 to 2.5 or even 3:1; preferably about 2:1.
The thiosulphate may be utilized in any convenient effective form such as an organic or inorganic thiosulphate salt. Usually sodium or potassium thiosulphate is utilized.
The fixer solution is particularly efficacious for the removal of silver halides from photographic colour materials coated with low weights of silver for example up to 2.1 mg/dm.sup.2 and generally operate best at an acid pH of down to pH4.
In particular it has been found that silver chloride and bromide photographic materials (containing up to 5% of iodide) which are coated with a total silver coating weights of up to 2.1 mg/dm.sup.2 can be fixed efficiently with a dilute solution of either an alkali metal or ammonium thiosulphate or a mixture of thiosulphates. This is stabilized by the addition of an excess of sulphite in sufficient quantity to overcome oxidation
REFERENCES:
patent: 2397016 (1944-07-01), King
patent: 3008828 (1961-11-01), Henn
patent: 3261685 (1966-07-01), Haer et al.
patent: 3674490 (1972-07-01), Matejec
G. Haist: "Modern Photographic Processing", 1979, John Wiley & Sons, New York, see p. 598, line 29-p. 599, line 13.
Chemical Patents Index, Basic Abstracts Journal Week 8932,20 Sep. 1989, No. 89/233474/32, Derwent Publications Ltd., London, G.B. & SU-A-1456926 (Phys Che Problems) Jul. 2, 1989.
Eastman Kodak Company
Le Hoa Van
LandOfFree
Thiosulphate fixing solutions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Thiosulphate fixing solutions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thiosulphate fixing solutions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2025791