| 摘要 |
PURPOSE: To obtain an ink containing an amphoteric polymer having both an anionic group and a cationic group, and capable of giving a water-resistant picture image having a high quality to plain paper in a high picture image concentration without bleeding. CONSTITUTION: This ink contains a coloring agent, a liquid medium for dissolving or dispersing the coloring agent, and an amphoteric polymer having both an anionic group (preferably a carboxyl group or a sulfonyl group) and a cationic group (preferably either of an amino group, an imino group, a pyrrolidone ring and an imidazole ring). The polymer is the copolymer of a monomer having an anionic group in the molecule (e.g. acrylic acid) with a monomer containing a cationic group in the molecule (e.g. 2-vinyl-pyrrolidone), and has an isoelectric point in a pH range of 3-10 and a weight-average mol.wt. of 1,000-1,000,000, concretely preferably allylamine-maleic acid copolymer, etc. |
