The ink jet recording system directly ejects an ink onto a recording paper and is lower in running cost than conventional recording apparatuses and is noticed as a recording method which causes little noise and can easily perform color recording. From the points of safety and printing characteristics, an aqueous ink is used in such recording system. Furthermore, the recording papers used are demanded to have the following characteristics, i.e., they are high in ink absorption and even when ink dots of different color overlap each other, cause no overflow of the ink; spread of ink dots is proper; shape of dots is close to true circle; the dot edge is sharp; and naturally ink dots have a high density and the papers have a sufficiently high ISO whiteness for making distinct the contrast of dot in color recording.
As recording papers used for the ink jet recording system which meet the above conventional demands, it has been proposed to use the exclusive coated papers as disclosed in JP-A-59-35977 and JP-A-1-135682. On the other hand, in the fields of mono-chromatic recording and business color recording, it is desired to use inexpensive and general purpose recording papers, namely, plain papers generally used in the field or electrophotographic recording apparatuses.
When toner transfer papers which are neutral papers and recently becoming main recording papers used in electrophotographic recording apparatuses are used as recording papers for ink jet recording systems, fillers to be used in base papers are restricted, and there are not obtained recording papers which are better in color reproducibility in color recording and higher in ISO whiteness as compared with coated papers exclusively used for full color ink jet recording. Furthermore, the so-called plain paper type ink jet recording papers having no coating of pigments on the recording surface have a principal point in possibility of ink jet recording and are not improved at all in water resistance which is a problem in ink jet recording system.
The object of the present invention is to improve the conventional problems in the above technical field, and it relates to an ink jet recording paper of so-called plain paper type which has no coating of pigment on the recording surface. That is, the object is to provide an ink jet recording paper which is excellent in surface strength and, especially, in water resistance of images recorded thereon and is high in image density of the recorded images and in color reproducibility by enhancing ISO whiteness.