Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Finishing or perfecting composition or product
Patent
1993-04-20
1994-05-03
Van Le, Hoa
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Finishing or perfecting composition or product
430205, 430302, G03C 500
Patent
active
053087461
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method of bleaching silver images and to solutions therefor.
The photographic silver salt diffusion transfer image forming process is well known. It is also well known that lithographic printing plates can be formed by this process and such printing plates can be formed on a metal, polymeric film or paper base. Sometimes it is desirable to retouch the silver image formed thereby and, specifically, it is sometimes desired to remove parts of the image such as unwanted cut lines and spots.
It is known, for example from British specification 2 107 889 that a thickened solution containing, for example, iodine and an iodide can achieve the desired result. When such a deletion solution is used with a litho plate that has been treated with a litho plate conditioner which contains phenyl-mercapto-tetrazole and cetyl-trimethyl-ammonium bromide the results are unsatisfactory.
The present invention provides a method of removing silver images while avoiding the problem noted above.
According to the present invention there is provided a deletion fluid for lithographic printing plates comprising a silver image formed by the silver salt diffusion transfer process comprising an aqueous solution containing iodine and an iodide salt characterized in that it contains from 1 to 10% by weight of a surfactant which comprises both polyalkylenoxy units and a quaternary ammonium group.
The silver image to be treated may be on an imagewise exposed and processed printing plate made by the photographic silver salt diffusion transfer process. Such materials are described in Research Disclosure Item 308119, December 1989 published by Kenneth Mason Publications, Emsworth, Hants, United Kingdom.
The deletion fluid may be applied to the silver image either before or after the image has been treated with a conditioner to make the silver oleophilic. Preferably it is applied before the conditioner because if it is applied afterwards, it will usually be necessary to wipe the plate with a conditioner-dampened pad to achieve the best deletion effect.
The alkyleneoxy groups may, for example, be ethyleneoxy or propyleneoxy groups. The surfactant molecule may comprise one or more ethyleneoxy chains having a total of 5 to 25 units, preferably 10 to 20 units. The quaternary ammonium group may have one or more alkyl substitutents having from 1 to 18 carbon atoms, typically such groups being derived from natural products are a mixture.
The surfactant preferably has the general formula: ##STR1##
wherein x+y =from 10 to 20, and
R is an alkyl group having from 10 to 18 carbon atoms or represents a mixture thereof. The preferred compounds have groups R having predominantly 12 and/or 15 carbon atoms.
An example of such a surfactant is ETHOQUAD C25 (Trademark of Akzo Chemie).
The deletion solution preferably contains a mixture of water and butyrolactone. The ratio of aqueous to organic solvent is optimized to provide sufficient water for rapid penetration of the solute into the gelatin layer (if present) on the image-bearing material, together with sufficient butyrolactone to obtain high complexing power for silver iodide so that the image is removed in a conveniently quick time. It may also contain other solvents used alone or in combination including alcohols eg ethyl or butyl alcohol.
The iodide may be provided by an ammonium or alkali metal iodide, eg sodium or potassium iodide.
The deletion solution preferably contains from 2 to 50 g, especially from 2 g to 20 g, of iodine and from 50 g to 250 g, especially from 150 g to 200 g, of iodide ions per liter of solution. The solvent preferably comprises from 10 to 60% by weight of water.
Preferably the solution also contains an acid, for example acetic acid, preferably in an amount of from 10 to 30, preferably 15 to 25, g/1 of 90% acetic acid.
The following Example is included for a better understanding of the invention. The words KODAK, PMT, IMAGEMAKER, IMAGEMATE, ROTAPRINT, KLUCEL and SURFONYL are trademarks.
EXAMPLE
The following deletion solution was made up:
_____________
REFERENCES:
patent: 4258122 (1981-03-01), Uchida et al.
patent: 4746597 (1988-05-01), Zellmer et al.
patent: 4837122 (1989-06-01), Kondo et al.
Baker Julie
Barnett Anthony M.
Gray Colin J.
Green Jeffrey K.
Hallbery David A.
Eastman Kodak Company
Le Hoa Van
Lorenzo Alfred P.
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