1. Field of the Invention
The present invention relates to ink for ink jet recording, an ink cartridge, an ink jet recording device, an image forming method, and an image recorded medium.
2. Description of the Background Art
Ink jet recording methods are advantageous in comparison with other recording methods in that the process is simple, full colorization is easy, and quality images can be obtained using a relatively simple mechanical configuration.
Dye-based ink, in which various aqueous soluble dyes are dissolved in water or a mixture of water and an organic solvent, is used as the ink for ink jet recording. Such a dye is excellent for forming vivid color images but tends to fade with prolonged exposure to light.
On the other hand, pigment-based ink, in which carbon black and various organic pigments are dispersed, has been actively researched and developed because it has excellent light resistance relative to the dye-based ink described above, although it tends to clog the printer nozzles. In general, pigment-based inks are prepared by preliminarily dispersing a pigment and a dispersing agent in an aqueous medium such as water and alcohols, conducting dispersion by a media-type dispersing machine such as a sand mill to a certain degree to prepare a liquid dispersion of the pigment, and diluting the liquid dispersion to a predetermined concentration by addition of other materials such as additives. A surface active agent or a water-soluble resin is generally used to disperse the pigment, which is hydrophobic. However, the quality of obtained images is extremely poor.
Adding resin particulates having a film-forming property to ink is known to improve image quality. However, it is difficult to stably disperse multiple particulate components for a long period of time, which leads to an increase of the amount of a dispersing agent such as a surface active agent for stable dispersion. This causes problems such as occurrence of bubbles in an ink tank and an ink head and deterioration of image quality.
In addition, to improve the dispersion property, a method of changing the pigment surface to have a hydrophilic group and a method of using a resin having a hydrophilic group have been studied. These involve a problem that, although they are separately stable, dispersion becomes unstable when different kinds of pigments or resins are mixed, which results in poor stability.
Unexamined Japanese patent application publication no. S56-147871 (JP-S56-147871-A) describes use of polymers. But with advances in contemporary ink jet printers, the ink head, etc. tends to clog with pigments having a particle diameter of from several μm to several hundred μm as described in this application publication, and image quality easily becomes unsatisfactory. In addition, stability is also poor.
JP-H8-283633-A describes a usage of a water-soluble polymer having a molecular weight of from 2,000 to 1,000,000 and JP-2009-241586 describes a usage of resin particles having a molecular weight of from 8,000 to 100,000.
JP-H10-298469-A describes a recording liquid using a polymer agglomerating agent generally having a molecular weight of from about several millions to about ten and several millions with a sole specific example of a methylchloride quaternary salt homopolymer of a methacrylate in Examples.