Abstract Non-ferrous lithographic printing plates, and especially those in which the hydrophobic image areas are constituted by photosensitive polymers, are desensitized by application to the metal surface of the developed plate of an aqueous desensitizing solution comprising a phosphate glass such as sodium hexametaphosphate, preferably in admixture with a fluoride salt, such as sodium fluoride. The aqueous composition is maintained at a pH in the range of pH 5-7 by a water-soluble phosphorus acid, such as phosphoric acid. The treatment can be performed at room temperature and permits the hydrophylic areas of the printing plate to be maintained upon storage without special protection. The treatment can also be used as a fountain solution in a press fountain.
Inventors
👤 James E Harper
Bibliographic Details
Application Number—
JurisdictionUS
Data Sourcegoogle_patents
Last Synchronized2026-11-01 23:17
CPC Classifications
B; B41; B41N; B41N3/00; B41N3/08
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
18 words
A process as recited in claim 1 in which said aqueous desensitizing solution further comprises a fluoride salt.
Claim 2
Dependent Claim
33 words
A process as recited in claim 2 in which said aqueous solution is slightly acidic to provide a pH in the range of from pH 5 up to but less than pH 7.
Claim 3
Dependent Claim
23 words
A process as recited in claim 3 in which the acidity of said solution is provided by including therein an acid of phosphorus.
Claim 4
Dependent Claim
19 words
A process as recited in claim 2 in which said fluoride salt is an alkali metal or ammonium fluoride.
Claim 5
Dependent Claim
19 words
A process as recited in claim 2 in which said fluoride salt is an alkali metal or ammonium bifluoride.
Claim 6
Dependent Claim
142 words
A process for desensitizing a developed aluminum lithographic printing plate comprising applying to the developed surface of said plate for coaction with the surface thereof in the non-image areas of said surface of said developed plate a slightly acidic aqueous desensitizing solution comprising an alkali metal phosphate glass present in the amount of 75 - 300 grams per 1,000 c.c. of water, a fluoride salt present in the amount of 20 - 150 grams per 1,000 c.c. of water, and an acid of phosphorous providing a pH in the range of from pH5 up to but less than 7, said solution being applied to said developed plate at about room temperature to about 150* F. for a period of time which is directly related to the concentration and the acidity of said solution and no less than a few seconds at pH5.