OFFSET INK COMPOSITION

PROBLEM TO BE SOLVED: To provide a permeation drying type printing ink which can reproduce a wide RGB color reproduction region expressed by four yellow, red, indigo and black ink process colors. SOLUTION: This offset ink composition comprises a yellow process ink, a red process ink, an indigo process ink, and a black process ink. The three colors of (a) the yellow ink, (b) the red ink, and (c) the indigo ink have the following spectral reflection factors, when the maximum reflection factor in a wavelength region of 400 to 700 nm is 100%. In (a) the yellow ink, a reflection in a wavelength region of 400 to 480 nm is 1 to 20%, and a reflection in a wavelength region of 530 to 700 nm is 90 to 100%. In (b) the red ink, the maximum reflection factor in a wavelength region of 400 to 500 nm is 50 to 100%, and the reflection factors of wavelength regions 500 to 560 nm and 630 to 700 nm are 1 to 20% and 90 to 100%, respectively. In (c) the indigo ink, a reflection in a wavelength region of 400 to 530 nm is 50 to 100%, and a reflection in a wavelength region of 600 to 700 nm is 1 to 30%. COPYRIGHT: (C)2008,JPO&INPIT