Radiation imagery chemistry: process – composition – or product th – Nonradiation sensitive image processing compositions or... – Fixer
Reexamination Certificate
2000-01-06
2001-04-24
Le, Hoa Van (Department: 1752)
Radiation imagery chemistry: process, composition, or product th
Nonradiation sensitive image processing compositions or...
Fixer
C430S460000
Reexamination Certificate
active
06221570
ABSTRACT:
This invention relates in general to photographic processing and in particular to compositions and methods of making bleach-fix concentrates. More specifically, this invention describes 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, and if clear colors are to be obtained the silver image must be removed. This can be accomplished by oxidizing the metallic silver with a suitable oxidizing agent, commonly referred to as a bleaching agent. This is followed by dissolving any remaining light-sensitive silver halide 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 and thus it is not generally feasible, from an economic standpoint, to package, transport, and store solutions of working strength, since this would involve the packaging, transport and storage of large amounts of water. As such, the bleaching and fixing solutions are prepared immediately before use by dissolving the necessary ingredients in water. In the alternative a bleach/fix solution may be prepared by mixing bleaching and fixing solutions together that have been prepared separately such as disclosed in U.S. Pat. No. 5,070,004 issued to Yoshihiro Fujita et al. Preparation immediately before use is necessitated by the fact that individual components of the separate solutions can chemically react and quickly decompose and/or oxidize reactive components thereby diminishing the useful life of the working solution.
The prevalence of automatic processing systems used in small photographic service laboratories called “mini labs”, that are supervised by technicians with limited technical background, necessitates the need for providing almost foolproof premixed solutions. However, as stated above, full working solutions that are ready-to-use make shipping more expensive, and further, the 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.
However, because of the serious problem of unwanted chemical reactions that occur between the components, the bleaching and fixing concentrates are usually separated into two or more parts which 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 put together 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 thereby rendering the combined concentrate inactive.
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 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 reference an aqueous solution of an aminopolycarboxylic acid and a thiosulfate ion are mixed along 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
Accordingly, it is a primary object of the present invention to provide one-part bleach-fix liquid concentrates having extended storability while maintaining stability.
It is another object to provide one-part bleach-fix liquid concentrates wherein crystallized precipitates are essentially non-existent after a year of storage.
Yet another object of the present invention is to provide one-part bleach-fix liquid concentrates wherein the polyvalent metal complexed oxidizing agent maintains its oxidizing ability for an extended time.
A further object of the present invention is to provide one-part bleach-fix liquid concentrates that upon dilution will provide working solutions wherefrom silver recovery can be performed electrolytically while reducing the risk of forming toxic hydrogen cyanide gas.
A 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 description.
The inventor of the present invention found that one-part bleach-fix liquid concentrates can be prepared that have an extended shelf life without forming crystallized precipitates therein by combining a bleaching agent with at least a thiocyanate salt used as a fixing agent. Further, after intensive investigations, it has been found that when a thiocyanate salt is used and/or combined in a specific ratio with another fixing agent, the one-part liquid bleach-fix concentrate has increased stability and crystal formation is essentially eliminated. Still further, it is surprising that when the amount by weight of the thiocyanate salt is less than the amount by weight of the other fixing agent the oxidizing ability of the diluted working solution made from the present concentrates is not decreased even after many months of storage.
In accordance with the present invention there is provided a one-part bleach-fix liquid concentrate which comprises:
a) a bleaching agent that oxidizes metallic silver; and
b) a fixing mixture comprising at least a thiocyanate salt, the thiocyanate salt in an effective amount to substantially retard crystal formation in the one-part bleach-fix liquid concentrate thereby extending the shelf-life of the one-part bleach-fix 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 the first fixing agent is a thiocyanate salt and the second fixing agent is selected from the group which includes thiosulfate salts, thioethers compounds, thioureas, 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) c
Ellis Howard M.
Fuierer Marianne
Le Hoa Van
Trebla Chemical Company
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