Pigmented ink composition

Abstract

A pigmented ink composition comprising a pigment, a resin having an acidic group and an organic solvent having a boiling point of at least 150° C. which is present in an amount of from 50 to 90% by weight based on the whole weight of the ink composition. When this ink composition is subjected to an printed layer-sliding test in which the ink composition is applied on a cationically treated printing medium with a #4 bar coater (available from TOYO SEIKI KOGYO CO., LTD.) and dried and then the printed surface is slid with a cloth on which a weight of 50 g is placed, the printed record is not grazed. This ink composition contains the pigment with a small dispersion particle size and has good water resistance, can be printed on a plain paper sheet without cockling, and suffers from no grazing of printed records when the ink composition is printed on a cationically treated paper sheet.

1 . A pigmented ink composition comprising a pigment, a resin and an organic solvent having a boiling point of at least 150° C. which is present in an amount of from 50 to 90% by weight based on the whole weight of the ink composition;
 wherein said resin has an ether bond and an acid value of 10 to 300 mg-KOH/g.   
     
     
         2 . The pigmented ink composition according to  claim 1  which comprises 0.1 to 20% by weight of the pigment and 0.5 to 30% by weight of the resin based on the whole weight of the ink composition. 
     
     
         3 . The pigmented ink composition according to  claim 1 , wherein said resin has a weight average molecular weight of 1×10 4  to 3×10 5 , and a molecular weight distribution of 1.5 to 10. 
     
     
         4 . The pigmented ink composition according to  claim 1 , wherein said resin is a water-insoluble resin having a hydrophobic group. 
     
     
         5 . The pigmented ink composition according to  claim 1 , wherein said resin is an acrylic resin. 
     
     
         6 . The pigmented ink composition according to  claim 1 , wherein said organic solvent having a boiling point of at least 150° C. is a polar solvent. 
     
     
         7 . The pigmented ink composition according to  claim 1 , wherein said organic solvent having a boiling point of at least 150° C. is an ether solvent. 
     
     
         8 . The pigmented ink composition according to  claim 1 , wherein said organic solvent having a boiling point of at least 150° C. is at least one compound selected from the group consisting of ethylene glycol monoalkyl ether monoalkyl ester, diethylene glycol monoalkyl ether monoalkyl ester, triethylene glycol monoalkyl ether monoalkyl ester, propylene glycol monoalkyl ether monoalkyl ester, dipropylene glycol monoalkyl ether monoalkyl ester, tripropylene glycol monoalkyl ether monoalkyl ester, ethylene glycol dialkyl ester, diethylene glycol dialkyl ester, triethylene glycol dialkyl ester, propyleneglycol dialkyl ester, dipropylene glycol dialkyl ester and tripropylene glycol dialkyl ester. 
     
     
         9 . The pigmented ink composition according to  claim 1 , which is used in an ink-jet printer, wherein said ink composition has a surface tension of at least 25 mN/m at 20° C. and a viscosity of 2 to 30 cp at 20° C., and the pigment has a dispersion average particle size of 0.01 to 0.5 μm.