Ink jet recording paper

Details Ink jet recording paper Ink jet recording paper

1999-03-30

2001-04-10

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Including components having same physical characteristic in...

C428S195100, C428S211100, C428S331000

Reexamination Certificate

active

06214449

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a material on which images are recorded with water base ink and, more particularly, to an ink jet recording paper which has high ink absorbency, but generates no cockles, thereby ensuring smooth traveling even in full-color printing and high color developability comparable to that in silver halide photography for the images recorded thereon by full-color printing.
BACKGROUND OF THE INVENTION
As an ink jet recording method comprises jetting fine drops of ink using some of various mechanisms to form images on a recording material, the adoption thereof makes it easy to increase a recording speed and form multicolor images, and further the method requires only inexpensive apparatus. Such being the case, the ink jet recording system has acquired a remarkable popularity in recent years. In particular, recent full-color ink jet printers have achieved great reduction in ink drop size and considerable improvement in ink properties to realize the printing of high quality, including high definition and high gradation comparable to those of silver halide photography.
More specifically, the latest main-current ink jet printers having image reproducibility comparable to that of photography (hereinafter referred to as ink jet printers of photo type) are designed so that, in a highlight section of image, each minute region hitherto reproduced by one concentrated ink drop is depicted by several dilute ink drops to reduce a grainy feeling, thereby increasing their image quality. Accordingly, the amount of ink jetted in such printers is greater than that in conventional printers, so that much higher ink absorbency than before is required for recording paper.
With respect to the ink jet recording paper, on the other hand, various arts of letting the so-called coated paper, or paper having an ink-receiving layer on a base paper, have both ink absorbency and color developability as basic factors of ink jet recording suitability have so far been developed.
For instance, as the coated paper having at least two ink-receiving layers on a substrate, the recording sheet in which the ink absorbing speed of the outermost ink-receiving layer is restricted and the second layer arranged on the inner side has a higher ink absorbing speed than the outermost layer, thereby enabling the ink to penetrate deeply into the sheet, is disclosed in Japanese Tokkai Sho 55-11829 (the term “Tokkai” as used herein means an “unexamined published patent application”), the coated paper having a coating composition coated in a double layer on the same side of a substrate is disclosed in Japanese Tokkai Sho 57-107879, and the coated paper wherein the hole distribution in an ink-receiving layer is localized in specified regions is disclosed in Japanese Tokkai Sho 58-110287.
However, those coated papers provide low image densities when they are subjected to ink jet recording, and are inferior in color developability to sensitized papers for silver halide photography. In particular, the recording on conventional ink jet recording papers with ink jet printers of photo type gives rise to running of ink due to shortage of ink absorbency in those recording papers, and further causes deterioration in traveling properties of the recording papers due to cockles and undulations generated therein after recording by the ink penetrating into their base papers in an increased quantity. In an extreme case, part of the recording paper is scraped with a printing head to leave stains on images printed.
For the purpose of heightening the ink absorbency, the thickness of an ink-receiving layer is generally increased. However, increasing the thickness of an ink-receiving layer results in lowering not only the image density but also surface strength of the ink-receiving layer. Decrease in the surface strength causes problems, e.g., such that the powdery components in the surface region tend to come off. In addition, the cost of production is raised by increasing the thickness. For the purpose of elevating the surface strength, on the other hand, increasing the proportion of an aqueous binder in the ink-receiving layer results in lowering the ink absorbency. Therefore, it is not yet achieved to develop an ink jet recording paper which raises neither ink-bleeding nor ink-overflowing problem, provides highly developed color images comparable to those in silver halide photography and ensures smooth traveling when subjected to printing operations with an ink jet printer of photo type.
SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide an ink jet recording paper which causes neither a traveling trouble nor coming-off of a coated layer, is free from bleeding and overflowing of ink, and can have highly developed color images comparable or superior to those in color photography when it undergoes printing operations using an ink jet printer of photo type.
The above-described object of the present invention is attained by an ink jet recording paper having on at least one side of a base paper at least two ink-receiving layers which each comprise a pigment and a resin as main components; the topmost layer of said ink-receiving layers having a thickness of 5 &mgr;m to less than 25 &mgr;m and a density of 0.4 g/cm
3
to 0.6 g/cm
3
and the ink-receiving layer arranged underneath said topmost layer having a density higher than the density of the topmost layer by 0.05 g/cm
3
to 0.5 g/cm
3
.
DETAILED DESCRIPTION OF THE INVENTION
In the case of ink jet recording, the formation of a thick ink-receiving layer with the intention of elevating the ink absorbency of a recording material generally causes the lowering of image density and deterioration in color developability. A reason why these phenomena are caused can be explained as follows: The ink jetted onto a recording material penetrates vertically into the ink-receiving layer and little causes the spread of each ink dot on the recording material; as a result, the density of an image as a mass of ink dots is lowered. On the other hand, when the ink-receiving layer is reduced in thickness with the intention of heightening the image density, the ink can spread horizontally over the ink-receiving layer surface to increase the diameter of each dot; as a result, though the image density can be heightened, the image quality is lowered because the lines printed are too thick and the solid areas are uneven in density. Therein, as a matter of course, the ink absorbency is lowered.
For the purpose of obtaining recorded images of high quality comparable to that in silver halide photography, it is insufficient to heighten only the so-called apparent density of an image as a mass of ink dots, and so it is necessary to heighten the substantial image density, namely dot density. In heightening the dot density, it is effective to form an ink-receiving layer having high transparency. In general, pigments having a small grain size, such as alumina sol, are employed for the formation of highly transparent ink-receiving layer. However, the small grain size of a pigment is responsible for low ink absorbency to raise ink-bleeding and ink-overflowing problems. The ink absorbency can be improved by heightening the proportion of a pigment used in the ink-receiving layer, but the use of such an expensive pigment in a large quantity is unsuitable for the production of cheap recording papers.
For achieving a high dot density, it is also effective to lower the density of an ink-receiving layer, thereby forming voids for gathering ink. More specifically, when the voids are increased in number by lowering the density of the ink-receiving layer, the ink density per unit volume in the ink-receiving layer can be increased even when synthetic silica as a relatively cheap pigment is employed, resulting in heightening the dot density.
However, if only the ink-receiving layer having a low density and a thickness great enough to meet the ink absorbency requirement is formed on a base paper, decrease in surface strength raises problems, e.g., such that the coated layer

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