Radiation imagery chemistry: process – composition – or product th – Nonradiation sensitive image processing compositions or... – Fixer
Reexamination Certificate
2000-11-17
2002-09-24
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Nonradiation sensitive image processing compositions or...
Fixer
C430S403000
Reexamination Certificate
active
06455236
ABSTRACT:
FIELD OF THE INVENTION
This invention relates in general to photographic processing, and in particular to compositions and methods of making bleach-fix concentrates. More specifically, this invention relates to one-part bleach-fix liquid concentrates that remain free of crystallized precipitates and retain optimal oxidizing capability during extended storage.
BACKGROUND OF THE INVENTION
Color developers produce a combined silver and dye image, however, to obtain clear colors the silver image must be removed. This is accomplished by oxidizing the metallic silver with a suitable oxidizing agent, commonly referred to as a bleaching agent. Any remaining light-sensitive silver halide is then dissolved in a silver halide solvent, commonly referred to as a fixing agent. These bleaching and fixing processes may be performed sequentially in two separate solutions, or in the alternative, the bleaching agent and fixing agents can be combined into a single bleaching-fixing solution.
The form in which the bleaching and fixing agents are typically employed is a dilute aqueous solution. Thus, it is not generally feasible from an economic standpoint to package, transport, and store solutions of working strength because this would involve the packaging, transport, and storage of large amounts of water. Therefore, the bleaching and fixing solutions are prepared immediately before use by dissolving the necessary ingredients in water.
The prevalence of small photographic service laboratories using automatic processing systems that are supervised by technicians who have limited technical background requires nearly foolproof premixed solutions. However, as stated above, full working ready-to-use solutions are expensive to ship, and further, the bulky containers take up valuable storage space. To overcome these disadvantages, there has been a trend to reduce the size of packaging, and thus, provide a savings in shipping costs. One way to achieve this goal is to make either all-powder or liquid bleaching, fixing, and/or bleach fixing concentrates. These concentrates merely have to be dissolved in or diluted with water to form a working solution.
DESCRIPTION OF THE RELATED ART
A bleach/fix solution that is prepared by mixing pre-prepared bleaching and fixing solutions is disclosed in U.S. Pat. No. 5,070,004 issued to Yoshihiro Fujita et al. Preparation immediately before use is necessary because the individual components of the separate solutions chemically react and quickly decompose and/or oxidize reactive components thereby diminishing the useful life of the working solution.
Because of the serious problem of unwanted chemical reactions occurring between the components, the bleaching and fixing concentrates are usually separated into two or more parts that are subsequently combined to form a working solution. For instance, a two-part bleach-fixing liquid concentrate is disclosed in U.S. Pat. No. 4,956,268 issued to Kiyoshi Nakazyo et al, wherein a first concentrate comprises a silver halide solvent and the second concentrate contains an oxidizing agent. The components are packaged separately from each other to prevent chemical reactions that form undesirable reaction products, such as crystallized precipitates. For instance, when a bleaching concentrate containing a ferric ion solution is combined with a fixing concentrate containing a thiosulfate solution the concentrate will have a very short shelf life because the ferric ion can be reduced to a ferrous ion and the thiosulfate can sulphurize to inactivate the concentrate.
While the higher degree of concentration will reduce some of the volume of water the two separate concentrates are still not sufficiently compact to substantially reduce the cost of shipping and/or the necessary storage space.
In an attempt to provide a one-part concentrate, U.S. Pat. No. 5,310,633, issued to Yoshida et al., discloses a one-part powdery bleach-fixing composition. Powdered components tend to solve the disadvantages of shipping and storing separate liquid concentrates, but lumping or caking of the dry components, especially of the thiosulfate, can occur during shipping and/or storage thereby making it difficult to provide a homogenous solution upon dilution.
U.S. Pat. No. 3,751,251 provides for a one-part liquid bleach-fix concentrated regenerator. As described in this patent an aqueous solution of an aminopolycarboxylic acid and a thiosulfate ion are mixed with a sufficient amount of a sulfite ion, in the form of gaseous sulfur dioxide, to adjust the pH of the solution to between 5.4 and 6.0. However, this product still has a limited shelf life due to undesirable crystal formation in the concentrate.
Accordingly, there is a need for improved one-part bleach-fix liquid concentrates which can be shipped economically, require minimal storage space, eliminate the need for mixing several different components, retain oxidizing ability, and prevent crystals from forming in the concentrate.
SUMMARY OF INVENTION
It is, therefore, a primary object of the present invention to provide one-part bleach-fix liquid concentrates having stability for extended storability.
It is another object to provide one-part bleach-fix liquid concentrates wherein crystallized precipitates are essentially non-existent after a year or more of storage.
It is yet another object of the invention to provide one-part bleach-fix liquid concentrates wherein the polyvalent metal complexed oxidizing agent maintains its oxidizing ability for an extended time period.
A further object of the present invention is to provide stable one-part bleach-fix liquid concentrates that upon dilution provide working strength solutions from which silver can be recovered with reduced risk of toxic hydrogen cyanide gas formation.
A yet still further object of the present invention is to provide one-part liquid beach-fix concentrates that reduce transportation and packaging costs.
These and other objects of the present invention will be clear from the following, more detailed, description.
This inventor found that one-part bleach-fix liquid concentrates suitable for dilution to working strength solutions can be formulated to have an extended shelf life without forming crystallized precipitates by combining a bleaching agent with a thiocyanate salt fixing agent. After further investigation, it was found that when a thiocyanate salt is used and/or combined in a specific ratio with another fixing agent, crystal formation is essentially eliminated thus increasing the stability of the one-part liquid bleach-fix concentrate. Surprisingly, it was found that when the amount of the thiocyanate salt is less than the amount of the other fixing agent the oxidizing ability of the diluted working solution is not decreased even after many months of storage.
In accordance with the present invention there is provided one-part bleach-fix liquid concentrates which comprise:
a) a bleaching agent for oxidizing metallic silver; and
b) a fixing mixture comprising at least a thiocyanate salt in an amount to substantially inhibit crystal formation for extending the stability and shelf-life of the liquid concentrate. The concentrate remains essentially free of crystallized precipitates during the extended shelf life.
More preferably, there is provided a first and second fixing agent wherein one fixing agent is a thiocyanate salt and the other fixing agent is selected from the group which includes thiosulfate salts, thioethers compounds, thiourea, thioglycolic acid, and the like.
The bleaching agent may be selected from the group consisting of compounds of polyvalent metals such as iron, (III), cobalt (III), chromium (VI), and copper (II); peracids; quinones; nitro compounds and mixtures thereof The compounds of the polyvalent metals may include iron (III) compounds such as ferric chloride; ferricyanide; bichromates; and organic complexes with aminopolycarboxylic acids, aminopolyphosphonic acids and organic phosphonic acids.
It was found that the polyvalent metal oxidizing agent does not precipitate out of the concentrate when a thiocyanate fixing a
Ellis Howard M.
Le Hoa Van
Trebla Chemical Company
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