Abstract This invention relates to the production of a positive-printing lithographic printing plate. The process utilizes an improved stop-bath solution which may be used with a wide variety of emulsions and developer solutions. One of the outstanding features of the invention is that exposure of the plate element to a positive original results in development of the plate element as a photographic negative image which will enable a press to print a positive copy. This is accomplished by treating the photographically developed plate in a stop-bath containing an oxidizing agent, such as potassium dichromate, which is capable of reacting with unoxidized developing agent, such as hydroquinone, in the non-image areas of the plate to make these areas oleophilic through a mechanism akin to polymerization or tanning.
Inventors
👤 V Maffet
👤 A Remesat
Bibliographic Details
Application Number—
JurisdictionUS
Data Sourcegoogle_patents
Last Synchronized2026-11-03 23:14
CPC Classifications
G; G03; G03F; G03F7/00; G03F7/004; G03F7/06
Claims Analysis
Total Claims: 3
Claim 1
Independent Claim
96 words
The method of making a planographic printing plate which method comprises: exposing to light modulated by an original plate element support having a light sensitive gelatinous silver halide emulsion layer thereon, developing the exposed silver halide emulsion layer with a hydroquinone developing agent forming a silver image under alkaline developing conditions, subsequently treating the developed silver halide emulsion layer with an acidic aqueous solution containing acetic acid and dichromate ions that react with the unoxidized hydroquinone left in the non-silver image portions thereby making said portions selectively receptive for a lipophilic ink used in lithographic printing.
Claim 2
Dependent Claim
16 words
The method as claimed in claim 2, wherein the dichromate ions are yielded by potassium dichromate.
Claim 3
Independent Claim
138 words
A method for making planographic prints which method comprises: exposing to light modulated by an original plate element support having a light sensitive gelatinous silver halide emulsion layer thereon, developing the exposed silver halide emulsion layer with a hydroquinone developing agent forming a silver image under alkaline developing conditions, subsequently treating the developed silver halide emulsion layer with an acidic aqueous solution containing acetic acid and dichromate ions that react with the unoxidized hydroquinone left in the non-silver image portions thereby making said portions selectively receptive for a lipophilic ink used in lithographic printing, contacting the thus treated silver halide emulsion layer with a lipophilic planographic printing ink that becomes selectively recepted by tHe non-silver image portions and transferring that recepted ink from said silver halide emulsion layer by contacting with printing stock material used in planographic printing.