Patent ID: 7674329

Claim:
A water-based ink set comprising a black ink, a yellow ink, a magenta ink and a cyan ink, wherein each of the black ink, the yellow ink, the magenta ink and the cyan ink comprises a polyoxyethylene alkyl ether sulfonate represented by the following general formula (I): R—O—(CH 2 CH 2 O) n —SO 3 M (I), wherein R represents C x H 2x+1 in which x represents a number from 11 to 15; M represents Na, NH 4 or NH(CH 2 CH 2 OH) 3 ; and n represents a number from 2 to 4, wherein the black ink comprises dipropylene glycol propyl ether, wherein each of the yellow ink, the magenta ink and the cyan ink comprises triethylene glycol butyl ether, wherein a dynamic surface tension of the black ink as measured by a maximum bubble pressure method at a measurement temperature of 25° C. is about 35 mN/m or more at a lifetime of 1000 ms and about 45 mN/m or less at a lifetime of 30 ms, and wherein an absolute value of a difference between dynamic surface tensions of each combination of inks selected from the black ink, the yellow ink, the magenta ink and the cyan ink is about 5 mN/m or less at the lifetimes of 30 ms and 1000 ms.