1. Field of the Invention
The present invention relates to an ink composition, an ink set, and an image forming method.
2. Description of the Related Art
In recent years, various materials have been used as ink jet recording media, and in addition to ink jet-specific paper, printing media such as, for example, commercially available plain paper, fine paper, coated paper, and art paper have been used. High image quality is sought when recording on any of the materials.
Even in a case where plain paper or a printing medium is used or the like, pigments are preferable as the ink coloring material that can form an image with high robustness in terms of water resistance, light resistance, and the like. Among inks that include pigments, water-based pigment inks are gathering attention from the viewpoints of cost effectiveness, safety in terms of global environment, work environment, and the like. Among such inks, a quinacridone-based pigment is preferably used as a magenta pigment for ink jets.
As a water-based ink for ink jet recording, water dispersions of water-insoluble vinyl polymer particles that contain a quinacridone-based pigment such as one or both of C.I. Pigment Red 122 and C.I. Pigment Violet 19 and a pigment derivative with a quinacridone skeleton in which an acidic group is introduced to an organic pigment have been disclosed (for example, refer to JP2006-176623A). However, with such a configuration, since the ink cannot be maintained stably when the ink is used after being kept for an extended period or at high temperature, there are problems in which density unevenness and streak unevenness occur.
In view of the problem described above, a water-based ink for ink jet recording that contains coloring particles in which a quinacridone-based pigment, a synergist including a basic group, and a predetermined high-molecular weight vinyl polymer are included in an aqueous liquid medium has been proposed (for example, refer to JP2009-227719A). The water-based ink has excellent discharge stability.
Further, a water-based active energy beam curable ink that contains a water-soluble photopolymerization material that radically polymerizes, a specific water-soluble photopolymerization initiator, and an anionic water-based pigment dispersing element have been disclosed (for example, refer to JP2009-102454A). Further, a water-based ink composition including a water-soluble polymerizable compound, a photopolymerization initiator, and a water-insoluble coloring material has been disclosed (for example, refer to JP2011-105826A), and a quinacridone solid solution pigment is exemplified as the water-insoluble coloring material.