Recording sheets

Details Recording sheets Recording sheets

1998-06-30

2001-05-29

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Composite

C428S195100, C428S500000, C428S522000

Reexamination Certificate

active

06238797

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to recording sheets for use in recording with ink. More specifically, it relates to recording sheets which can provide high-quality printed images even in multicolor printing and which is also suitable for a transparency for OHP.
PRIOR ART
Ink-jet printers are widely used in the art because of their clear images and reasonable prices.
With such ink-jet printers, recording takes place by generating small droplets of ink by various operating mechanisms incorporated in the printers so that these small droplets are received on an ink-receiving layer of a recording sheet.
Ink-jet printers normally use water-based ink from the viewpoint of safety or avoidance of clogging. Thus, the ink-receiving layer of the recording sheet is made from a water-soluble resin or a water-absorbing resin which readily takes up water-based ink.
Recently, it has become common to convert an image datum captured by a digital camera into a printing signal with a data processing apparatus such as a personal computer to form a printed image on a recording sheet by an ink-jet printer.
Such a technique eliminates the necessity of developing a film and remarkably reduces costs, as compared with conventional so-called silver salt photography using an optical camera and a photosensitive film.
Since the resulting printed images are to be compared with photographic images, they are required to have high quality in terms of sharpness and colorfulness.
Conventional recording sheets however have not been thoroughly examined with respect to obtaining colorful printed images of high quality.
Generally, three inks with different colors, i.e. yellow, magenta, and cyan, or four inks including black in addition to said three colors are required for obtaining colorful printed images.
In order to obtain high quality printed images, the resolution must be increased and distances between inks with different colors as described above have been reduced.
Conventional recording sheets had the problem or so-called “repelling” which means that inks with different colors as described above printed in close proximity repel each other to leave unprinted portions. This problem of repelling was frequently observed in recording sheets based on water-soluble resins.
The above problem of repelling occurs less frequently in conventional recording sheets based on water-absorbing resins, but they had another problem of so-called “blurring” which means that inks of printed images diffuses into the receiving layer with the lapse of time to make the outlines of printed images unclear.
The recording sheets also had the problem that they are unsuitable for a transparency for OHP (overhead projector) because the ink-receiving layer itself is highly phototransmissive but printed images formed on the ink-receiving layer are not phototransmissive enough.
Accordingly, it is the first object of the present invention to provide a recording sheet which can produce colorful printed images of high quality without causing either problem of repelling of ink even in multicolor printing or blurring of printed images after a lapse of time.
In addition to said first object, it is the second object of the present invention to provide a recording sheet which can produce highly phototransmissive printed images on the ink-receiving layer so that it is suitable for a transparency for OHP.
SUMMARY OF THE INVENTION
In order to solve the problems mentioned above, the present invention provides a recording sheet having an ink-receiving layer formed on at least one surface of a substrate, characterized in that said ink-receiving layer is formed by applying a resin solution comprising a resin (a) containing a component (
1
) presenting water-solubility in its molecules and a component (
2
) containing a functional group forming a crosslinking point in its molecules and presenting water-solubility before a crosslinking point is formed, and a water-soluble resin (b) on the substrate, and thereafter forming a crosslinking point, as defined in claim
1
.
The component (
1
) presenting water-solubility of the resin (a) here include polyalkylene oxides, as defined in claims
1
to
2
.
The component (
2
) containing a functional group forming a crosslinking point of the resin (a) include a component containing an isocyanate group which is protected against reaction with water by a protecting group, as defined in claims
3
to
4
.
The water-soluble resin (b) include polyvinyl alcohols, as defined in claims
5
to
8
.
In a recording sheet, the ratio between the resin (a) and the water-soluble resin (b) in the ink-receiving layer in % by weight include in the range from 5:95 to 30:70, as defined in claims
9
to
16
.
Furthermore, a recording sheet can also be mentioned wherein the ratio between the resin (a) and the water-soluble resin (b) in the ink-receiving layer in % by weight is in the range from 5:95 to 20:80, as defined in claims
17
to
24
.
Careful investigations of conventional recording sheets led us to the following findings.
Water-soluble resins have a good affinity for water-based inks used in ink-jet printers. Namely, when a water-soluble resin is used for the ink-receiving layer, the in readily spreads over the surface of the receiving layer to facilitate mutual contact between adjacent ink portions before it is absorbed into the receiving layer.
If a multicolored printed image is to be formed, inks with different colors are required which normally vary in surface tension, drying characteristics and absorption characteristics for the receiving layer or other characteristics depend on the difference in the ingredients of their coloring materials (dyes and pigments) or dispersants for dispersing their coloring materials. When these inks with different properties come into contact with each other, repelling occurs due to low affinity for each other.
On the other hand, water-absorbing resins are highly absorptive and unsoluble in water.
Therefore, when a water-absorbing resin is used for the ink-receiving layer, the problem of repelling as described above is less likely to occur because ink is absorbed into the receiving layer without spreading over the surface of the receiving layer.
However, because of the high water absorbing property, water in the ink is to be taken up in the receiving layer without evaporating into the air. As a result, ink may readily diffuse into the receiving layer even after a printed image is produced, whereby blurring occurs to make the outline of the printed image unclear. In addition, water-absorbing resins are swollen with ink absorbed therein to lower the phototransmission of printed images.
In order to solve the problems as described above, a recording sheet having an ink-receiving layer comprising a water-soluble resin and a water-absorbing resin in an appropriate ratio to control the ability of absorbing ink or other properties is contemplated from the prior art.
However, it is difficult to prepare such a recording sheet. Namely, water-absorbing resins are not soluble in water and can not be homogeneously mixed with water-soluble resins if water is used as a solvent for dissolving both resins.
Even if an alcoholic solvent capable of dissolving both resins is selected, the ink-receiving layer prepared from such a mixed solution whitens to lower the phototransmission because the solubility of water-soluble reins become lower.
As a result of long-term study, we developed a recording sheet having an ink-receiving layer formed by applying a resin solution comprising a resin (a) containing a component presenting water-solubility and a component containing a functional group forming a crosslinking point in its molecules and presenting water-solubility before a crosslinking point is formed, and a water-soluble resin (b) on a substrate, and thereafter forming a crosslinking point. Namely, the resin (a) of the present invention can be homogeneously mixed with the water-soluble resin as desired because it shows water-solubility before a crosslinking point is formed. As a result, the contradict

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