Importance

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Abstract

The present invention provides a method of producing an ink composition for offset printing with use of a crude copper phthalocyanine pigment and/or an active crude copper phthalocyanine pigment and without use of a pigment dispersion resin that requires additional cost, to produce an ink composition which provides a highly tinted and bright image. The method includes the steps of: premixing a premix component through stirring so as to obtain a pigment mixture, the premix component containing a crude copper phthalocyanine pigment and/or an active crude copper phthalocyanine pigment, at least one binder resin selected from the group consisting of a rosin-modified phenolic resin, a rosin-modified maleic acid resin, a petroleum resin, and an alkyd resin, and an oil component; grinding and milling the pigment mixture obtained by the premixing, using a bead mill with grinding media of beads each having a size of 0.1 mm or larger and smaller than 1.5 mm, at a temperature within the range of 0° to 180° C., thereby obtaining a pigment dispersion; and further adding the binder resin and/or the oil component to the pigment dispersion and stirring the resulting dispersion, wherein the method satisfies the conditions that (1) the pigment mixture contains 5 to 40% by mass of the crude copper phthalocyanine pigment and/or the active crude copper phthalocyanine pigment, (2) the pigment mixture contains 5 to 500 parts by mass of the binder resin, for each 100 parts by mass of the crude copper phthalocyanine pigment and/or the active crude copper phthalocyanine pigment, and (3) the pigment mixture has a viscosity of 0.001 to 20 Pa·s at the temperature of the grinding and milling.

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First Claim