Silicate-free developer compositions

Abstract

A silicate-free alkaline aqueous developer composition has a pH of at least 12 and comprises a hydroxide alkali agent, a metal cation M 2+ selected from barium, calcium, strontium, and zinc cations, a chelating agent for the metal cation, and an alkali metal salt that is different than the other components. These developer compositions can be used to process imaged positive-working lithographic printing plate precursors to prepare lithographic printing plates.

1 . A silicate-free and sugar-free alkaline aqueous developer composition having a pH of at least 12 and comprising:
 (a) a hydroxide,   (b) a metal cation M 2+  selected from barium, calcium, strontium, and zinc cations,   (c) a chelating agent for the metal cation M 2+ , and   (d) an alkali metal salt different than all of a, b, and c above.   
     
     
         2 . The developer composition of  claim 1  wherein the metal cation M 2+  is calcium or strontium. 
     
     
         3 . The developer composition of  claim 1  that has a pH of at least 12 and up to and including 13.5. 
     
     
         4 . The developer composition of  claim 1  wherein alkali metal salt of component (d) comprises a citrate, acetate, tartrate, nitrate, or oxalate. 
     
     
         5 . The developer composition of  claim 1  wherein the chelating agent of component (c) has a complex formation constant (log K) for the calcium metal cation M 2+  of at least 3.5 and less than or equal to 4.5, and a log K for aluminum ion that is 7 or less. 
     
     
         6 . The developer composition of  claim 5  wherein the chelating agent of component (c) is a phosphono-polycarboxylic acid. 
     
     
         7 . The developer composition of  claim 1  wherein the chelating agent of component (c) is 2-phosphonobutane-1,2,4-tricarboxylic acid. 
     
     
         8 . The developer composition of  claim 1  wherein the metal cation M 2+  is present in an amount of at least 0.001 and up to and including 0.01 gram-atom/kg. 
     
     
         9 . The developer composition of  claim 1  wherein the chelating agent of component (c) is present in an amount of at least 0.01 and up to and including 0.1 mol/liter. 
     
     
         10 . The developer composition of  claim 1  wherein alkali metal salt of component (d) is present in an amount of at least 0.05 mol/liter and up to and including 0.2 mol/liter. 
     
     
         11 . The developer composition of  claim 1  further comprising an anionic surfactant. 
     
     
         12 . The developer composition of  claim 1  further comprising a cationic surfactant or betaine. 
     
     
         13 . The developer composition of  claim 1  having a pH of at least 12 and up to and including 13.5, and comprising:
 a sodium or potassium hydroxide, 
 sodium or potassium citrate, 
 M 2+  is calcium or strontium metal cation, and 
 the chelating agent has a complex formation constant (log K) for the calcium metal cation of at least 3.5 and less than or equal to 4.5, and a log K for aluminum ion that is less than or equal to 7. 
 
     
     
         14 . The developer composition of  claim 13  wherein the chelating agent is 2-phosphonobutane-1,2,4-tricarboxylic acid. 
     
     
         15 . The developer composition of  claim 13  further comprising a cationic surfactant. 
     
     
         16 . A method for providing a lithographic printing plate comprising:
 A) imagewise exposing a positive-working lithographic printing plate precursor having an imageable layer to provide exposed and non-exposed regions, and   B) processing the exposed lithographic printing plate precursor with the developer composition of  claim 1  to remove the exposed regions in the imageable layer.   
     
     
         17 . The method of  claim 16  wherein the positive-working lithographic printing plate precursor has an aluminum-containing substrate and at least one imageable layer disposed on the substrate. 
     
     
         18 . The method of  claim 16  wherein the positive-working lithographic printing plate precursor contains an infrared radiation absorbing compound in the imageable layer, and the imagewise exposure is carried out using infrared radiation. 
     
     
         19 . The method of  claim 16  wherein the positive-working lithographic printing plate precursor has a single positive-working imageable layer disposed on an aluminum-containing substrate. 
     
     
         20 . The method of  claim 19  wherein the single-positive-working imageable layer comprises a polymeric binder comprising recurring units represented by either or both of the following Structures (Ia) and (Ib), in random order: 
       
         
           
           
               
               
           
         
       
       wherein:
 when both Structure (Ia) and (Ib) recurring units are present, the Structure (Ia) recurring units are present in an amount of at least 10 and up to and including 35 mol %, and the Structure (Ib) recurring units are present in an amount of at least 25 and up to and including 60 mol %, all based on total recurring units in the polymeric binder, 
 R is a substituted or unsubstituted hydroxyaryl group, and 
 R 2  is a substituted or unsubstituted hydroxyaryl group in which the hydroxyl group is ortho to the ester linkage. 
 
     
     
         21 . The method of  claim 16  wherein the positive-working lithographic printing plate precursor has a surface imageable layer containing hydroxymandelic acid, an organic compound having at least one amino group and at least one carboxylic acid group directly linked to an aryl group, or both hydroxymandelic acid and at least one of the organic compounds. 
     
     
         22 . The method of  claim 16  wherein the silicate-free and sugar-free developer composition has a pH of at least 12 and up to and including 13.5 and comprises:
 sodium or potassium hydroxide, 
 calcium or strontium ions, 
 sodium or potassium citrate, 
 2-phosphonobutane-1,2,4-tricarboxylic acid, and 
 either or both of an anionic surfactant and a cationic surfactant. 
 
     
     
         23 . The method of  claim 16  that is carried out in a processing apparatus to which the developer composition is supplied as a concentrate that is diluted at least 1.5 times with an aqueous solution for use in step B. 
     
     
         24 . A kit useful for providing lithographic printing plates, the kit comprising:
 a) one or more positive-working lithographic printing plate precursors, each precursor having a substrate and an outermost imageable layer that comprises a polymer binder, and   b) the silicate-free and sugar-free alkaline aqueous developer composition of  claim 1 .