1.  Field of the Invention
The present invention relates to an ink suitable for ink jet recording, and an ink cartridge and an ink jet recording method each using the ink. 
2.  Description of the Related Art
In recent years, the advance of an ink jet recording technology has started to enable easy, low-cost recording of such high-definition images each having high glossiness as realized in a silver halide photography and offset printing even in ordinary households.  The term “glossiness” as used herein refers to the following state of the reflected light of illumination or the like, which is reflected in an image recorded on any one of the recording media each having a glossy surface (so-called glossy papers), on the image.  In the image, “glare” due to the reflected light is suppressed and the reflected light is vividly observed. 
When a dye ink containing a dye as a coloring material is used for realizing high glossiness, a good image free of graininess is obtained.  On the other hand, the following problem arises.  The image is poor in fastness properties.  In view of the foregoing, an ink containing a pigment as a coloring material has started to be used in recent years.  An ink obtained by dispersing the pigment with a water-soluble resin has started to be widely used as such ink for the purposes of additionally improving, for example, the fixability of the pigment to a recording medium and the abrasion resistance of an image. 
However, the following problem arises.  The color developability of an image recorded with the pigment ink is generally insufficient as compared with that in the case of the dye ink.  In addition, the following problem arises owing to the fact that the pigment is a particle.  The glossiness of an image recorded on a recording medium having gloss on its surface is particularly insufficient as compared with that in the case of the dye ink.  Those problems remarkably occur particularly when glossy paper is used.  Accordingly, improvements in the color developability and glossiness of an image such as a photograph recorded with the pigment ink have been strongly requested in recording the image. 
Particularly in the case of a monochromatic image recorded with the pigment ink, the internal scattering of light occurs owing to voids in a pigment layer, and light thus generated is observed as the reflected light of the image.  As a result, an apparent black density remarkably reduces as compared with that of a monochromatic image recorded with the dye ink.  In addition, carbon black having a relatively high refractive index among pigments is used in a black type ink.  Accordingly, an image recorded with the ink is apt to glare and its glossiness is insufficient. 
Various attempts have heretofore been made to solve such problem as described above, i.e., an improvement in the performance of the monochromatic image recorded with the pigment ink.  For example, a proposal concerning the following has been made (see Japanese Patent Application Laid-Open No.  2004-225037).  In order that the glare of an image recorded with a pale black ink may be suppressed, the content of a resin emulsion in the ink is made twice or more as large as the content of carbon black.  In addition, a proposal concerning the following has been made (see Japanese Patent Application Laid-Open No.  2000-072991).  Resin fine particles each having a multilayer structure or microdomain structure formed of two or more kinds of resins having different refractive indices are incorporated into an ink for improving color developability.  Further, a proposal concerning the following has been made (see Japanese Patent Application Laid-Open No.  2004-331946).  Carbon black to which resin fine particles are stuck and the resin fine particles are incorporated into an ink for improving color developability and glossiness.