1. Field of the Invention
This invention relates to a recording paper useful for ink jet recording, particularly to a recording paper excellent in aqueous-ink absorptivity, resolution of image and color forming characteristic and also to an ink jet recording method by use thereof.
2. Related Background Art
In the prior art, paper for ink jet recording, there have been known:
(1) a recording paper which is prepared by making a paper in general composed mainly of pulp into a sheet with a low sizing degree such as filter paper, blotting paper, etc.;
(2) a recording paper prepared by use of a paper subjected to considerable sizing as the substrate paper, having an ink absorption layer provided thereon by coating of a filler which is porous and large in oil absorption such as silica or zeolite;
(3) a recording paper having a coating layer provided on a substrate paper with low sizing degree as disclosed in Japanese Laid-open Patent Applications Nos. 53012/1977, 11829/1980 and 38087/1984 and U.S. Pat. No. 4,478,910, etc.
In the recording paper (1), although it is excellent in ink absorptivity, ink is penetrates deep into the fibrous layer of the paper and therefore the color forming characteristic of ink is poor. Since the ink is also absorbed along the fibers on the paper surface, there occurs the phenomenon called feathering, whereby there is the drawback that dots become staggered so resolution is lowered to preclude images of good quality.
In the recording paper (2), since the ink absorbing layer is porous and uniform, good dot shapes and resolution can be obtained. However, for imparting sufficient ink absorptivity, the ink absorbing layer must be made thick, and therefore there is also the problem that one coating is insufficient and a plural coatings required.
Further, if the ratio of the pigment to the binder (P/B) in the ink absorbing layer is made too great in order to improve ink absorptivity, the so called powder drop-off by dropping of the pigment may occur, whereby there are involved the drawbacks such that the rollers for paper delivery may slip or that clogging of the ink jet nozzle may occur.
In the recording paper (3), even when a relatively thin coating layer may be provided, there is the advantage that a recording medium with good ink absorptivity and excellent color forming characteristic of the colorant can be obtained as compared with the recording paper (2). However, as a recording system with higher resolution and attachment density of ink is demanded, the ink absorptivity may be sufficient when the recording paper (3) is applied for such a system, but a large amount of ink will penetrate into the substrate paper, whereby color forming characteristic of the colorant and resolution will be lowered. Thus, it is difficult to satisfy both ink absorptivity and these characteristics.
Further, problems called cockling in which pulp fibers are swelled with ink and the printing portion is deformed in wavy form or the so called back-through in which ink reaches the back surface of the paper not only impair quality of recorded image, but cockling will give rise to scraping between the recording paper and the head to impair images, and also back-through may cause back transfer when a recording paper is superposed on another recording paper.
These phenomena are problems inherent in the recording paper (3) which as a whole receives ink, and have appeared particularly as the image with high resolution by ink jet recording is demanded. However, although the above problems are inherent in the recording paper (3), no detailed investigation has been made thereabout.