Field of the Invention
The present invention relates to an ink, an ink cartridge, and an ink jet recording method.
Description of the Related Art
The recording speed of ink jet recording apparatuses has been dramatically improved as a result of the technical advance. Such ink jet recording apparatuses have been gradually introduced into the field of business document printing in place of laser recording apparatuses. Ink jet recording apparatuses typically use, as inks for texts to be used for recording images on recording media such as plain paper, aqueous inks containing self-dispersible pigments as a coloring material in consideration of high optical density.
In order to improve the optical density of images to be recorded and image qualities such as character quality, various components have been studied for the aqueous inks containing self-dispersible pigments as a coloring material. For example, an ink enabling recording of high quality images has been disclosed. The ink includes a water-soluble organic solvent that is unlikely to stably disperse a self-dispersible pigment to destabilize the dispersion state of the pigment after evaporation of liquid components (Japanese Patent Application Laid-Open No. 2006-045514). Another ink enabling recording of high quality images has been disclosed. The ink includes a monovalent cation salt to destabilize the dispersion state of a pigment after evaporation of liquid components (Japanese Patent Application Laid-Open No. 2000-198955).
However, the results of studies by the inventors of the present invention have shown that some aqueous inks containing a self-dispersible pigment as a coloring material cannot maintain the storage stability. In particular, as the application field of the ink jet recording method has been rapidly spread, inks are required to have much higher quality and also to have higher storage stability as compared with conventional inks.
An object of the present invention is thus to provide an aqueous ink containing a self-dispersible pigment as a coloring material but having markedly higher storage stability as compared with conventional inks. The present invention is also directed to provide an ink cartridge including the aqueous ink and an ink jet recording method using the aqueous ink.