Patent ID: 7438752

Claim:
An ink composition which comprises: a dye which is represented by formula (1) and has at least one ionic hydrophilic group, wherein the dye has a molecular weight of from 310 to 500 per one ionic hydrophilic group: in formula (1), Z 1 represents an electron attractive group having a Hammett's substituent constant σp value of 0.20 or more; Z 2 represents hydrogen atom, aliphatic group, aromatic group or heterocyclic group; R 1 and R 2 each independently represents hydrogen atom, halogen atom, aliphatic group, aromatic group, heterocyclic group, cyano group, carboxyl group, carbamoyl group, alkoxycarbonyl group, aryloxycarbonyl group, acyl group, hydroxy group, alkoxy group, aryloxy group, silyloxy group, acyloxy group, carbamoyloxy group, heterocyclic ring oxy group, alkoxycarbonyloxy group, aryloxycarbonyloxy group, alkylamino group, arylamino group, heterocyclic amino group, acylamino group, ureido group, sulfamoylamino group, alkoxycarbonylamino group, aryloxycarbonylamino group, alkylsulfonylamino group, arylsulfonylamino group, aryloxycarbonylamino group, nitro group, alkylthio group, arylthio group, alkylsulfonyl group, arylsulfonyl group, alkylsulfinyl group, arylsulfinyl group, sulfamoyl group, sulfo group or heterocyclic thio group, wherein R 1 and R 2 may be bonded together to form a 5- or 6-membered ring; R 3 and R 4 each independently represents hydrogen atom, aliphatic group, aromatic group, heterocyclic group, acyl group, alkoxycarbonyl group, aryloxycarbonyl group, carbamoyl group, alkylsulfonyl group, arylsulfonyl group or sulfamoyl group, wherein R 3 and R 4 maybe bonded together to form a 5- or 6-membered ring; a and e each independently represents alkyl group, alkoxy group or halogen atom, wherein when a and e are both alkyl groups, total of the number of carbon atoms constituting the alkyl groups is 3 or more and each of the alkyl groups may be further substituted, and b, c and d each independently has the same meaning as R 1 and R 2 , wherein a and b may be bonded together to form a condensed ring and e and d may be bonded together form a condensed ring; and Q represents hydrogen atom, aliphatic group, aromatic group or heterocyclic group.