Abstract Planographic printing plates sensitized with a benzene diazonium salt are converted into offset printing forms by imagewise exposure and subsequent development with an aqueous phloroglucinol solution buffered to a pH between 4 and 8 and containing 1-10 percent by volume of water-miscible organic solvent having a molecular weight greater than 50. The organic solvent avoids or greatly reduces a problem of initial prints being blemished by ink held on blank (background) areas of the printing forms. Especially effective solvents, such as propyl glycol, acetonyl acetone, diacetone alcohol, and Nmethylpyrrolidone-2, having boiling points above 90* C. A high salt content in the developing solution inhibits any bleeding of the azo-dyestuff during development.
THE ORGANIC SOLVENT AVOIDS OR GREATLY REDUCES A PROBLEM OF INITIAL PRINTS BEING BLEMISHED BY INK HELD ON BLANK (BACKGROUND) AREAS OF THE PRINTING FORMS. ESPECIALLY EFFECTIVE SOLVENTS, SUCH AS PROPYL GLYCOL, ACETONYL ACETONE, DIACETONE ALCOHOL, AND N-METHYLPYRROLIDONE-2, HAVING BOILING POINTS ABOVE 90*C. A HIGH SALT CONTENT IN THE DEVELOPING SOLUTION INHIBITS ANY BLEEDING OF THE AZO-DYESTUFF DURING DEVELOPMENT.
Claim 2
Dependent Claim
19 words
A process according to claim 1, wherein said solvent is one also having a boiling point above 90* C.
Claim 3
Dependent Claim
22 words
A process according to claim 1, said solvent being selected from the group consisting of n-propylgylcol, acetonyl acetone, diacetone alcohol and N-methylpyrrolidone-2.
Claim 4
Dependent Claim
56 words
A process according to claim 1, further characterized in that said solution contains as buffering salt at least one alkaline-reacting salt of weak acid and in addition contains 1-10 percent by weight of at least one water-soluble inorganic salt of a strong acid, which salts do not react together to form a precipitate in said solution.
Claim 5
Dependent Claim
63 words
A composition for developing into an oleophilic azo-dyestuff image an imagewise exposed, light-sensitive planographic printing surface sensitized with a benzene diazoniUm compound, comprising an aqueous solution of phloroglucinol containing buffering salt giving the solution a pH between 4 and 8 and containing 1-10 percent by volume of water-miscible organic solvent selected from the group consisting of n-propylglycol, acetonyl acetone, diacetone alcohol and N-methylpyrrolidone-2.
Claim 6
Dependent Claim
51 words
A composition according to claim 5, said buffering salt comprising at least one alkaline-reacting salt of a weak acid, said solution also containing 1-10 percent by weight of at least one water-soluble inorganic salt of a strong acid, which salts do not react together to form a precipitate in said solution.