Incremental printing of symbolic information – Ink jet – Medium and processing means
Reexamination Certificate
2001-03-09
2003-03-04
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Medium and processing means
C347S100000, C347S096000
Reexamination Certificate
active
06527385
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ink-jet printing method, more specifically, relates to an ink-jet printing method for carrying out printing of characters, images, or the like on a recording medium such as printing paper, OHP paper using an ink and a liquid which makes a coloring material in the ink insoluble (hereafter referred to as a treating liquid).
2. Related Background Art
The ink-jet printing method has various advantages including low noise operation, low running cost, high-speed printing, and easy adaptation for down-sizing and for color printing. Thus, ink-jet printing is widely employed for printers, copying machines, or the like. In general, the ink employed for printers is selected in consideration of its printing properties such as ejecting properties and fixing properties and print qualities such as bleeding, optical reflection density, and coloring of the printed images. As is well known, inks are divided into two types according to the coloring material contained in the ink, i.e., the dye ink and the pigment ink.
The pigment ink has various advantages in comparison with the dye ink, such as superior water resistance and light fastness, and clear character printing. On the other hand, in comparison with the dye-based ink, it takes time to fix the pigment-based ink on a recording medium, the rub-off resistance of the fixed images is not sufficient sometimes, and the size of the ink dot formed on the recording medium by one ejection from the nozzle tends to be small. That is, the pigment in a pigment ink is generally stably dispersed in the ink by the electric repulsion force of the polymer dispersant which destroys the agglomeration of the pigment particles due to intermolecular force. Therefore, it is preferable to add a polymer dispersant to an ink in an amount according to the amount of the pigment. When such a pigment-based ink is applied onto a recording medium such as plain paper by an ink-jet recording process for printing characters, the solvent, e.g. water, of the ink penetrates into the paper and evaporates into the ambient air, and the pigment particles agglomerate. At that time, the more a polymer dispersant is added, the stronger the agglomeration force of the ink on the paper becomes. Thus, when an ink dot is formed on a paper sheet with a prescribed volume of the ink ejected from an ink-jet head, the diameter of the dot is small and the dot shape remains irregular due to the impact of landing on the paper. Therefore, in order to obtain an ink dot having a sufficient recording density and a diameter necessary for forming a recording image without white stripes or other similar defects, the ejection volume of an ink from an ink jet head must be adjusted rather high. Even with such an adjustment, the presence of a polymer dispersant in a pigment ink, in combination with the penetrability decrease of the ink due to the strong agglomeration force of the pigment particles adsorbed on the dispersant, may delay the fixation of a pigment ink on a recording medium or lower the rub-off resistance of the recorded image.
In order to make the dot diameter larger and to improve the fixation properties, a penetrant may be added to a pigment ink to enhance penetration of the ink into a recording medium. However, use of a penetrant may cause undesirable phenomena such as the irregular peripheral shape of the dot (feathering), and penetration of the ink to the back of the recording medium (back-through), which are undesirable for the high quality recorded image. Further, since the coloring material penetrates into the recording medium, it often occurs that the optical density (OD) of the ink dot is not so much increased as the dot diameter increases. In business use application of the ink-jet printers, which will be developed intensively, more improvement will be required in printing speed. In that case, insufficient fixation of the ink onto the recording medium may cause following phenomena: when printed recording medium such as paper sheets are continuously output from the ink-jet printer to be piled one after another, the image on a paper sheet may be disturbed or the set off of the image may occur.
To solve such problems, inks containing a self-dispersing pigment have been proposed. Such an ink can provide dots of a larger diameter, since the pigment agglomeration force on the paper is weaker than that in conventional pigment inks in which the pigment is dispersed by a dispersant. It, however, is not sufficient yet.
As mentioned above, there are still much room for study and development in the printing method to satisfy various factors determining the quality of printing such as fixability of the ink, enlargement of the ink dot diameter, uniform density in an ink dot, and high optical density of the ink itself.
Meanwhile, in order to further improve printing quality by the ink-jet printing process such as water fastness and optical density of the print on a recording medium, there has been proposed and practically used a method to provide onto a recording medium an ink and a treating liquid which is reactive with the ink so as to make them react on the recording medium.
In purpose of solving the above-mentioned problems of the pigment ink but still maintaining the advantages of the pigment ink, the inventors of the present invention have been studying the above-mentioned ink-jet printing technology using a pigment-based ink and a treating liquid which breaks the pigment dispersion state of the ink by reaction. As a part of the study, the inventors have carried out a recording process, in which a pigment ink is applied after a treating liquid was applied onto the recording medium so as to be mixed with the pigment ink in a liquid state. The quality of the resultant image was not necessarily satisfactory and in some cases the quality was rather inferior to that formed using the pigment ink only. Specifically, when a pigment ink containing a pigment dispersed in an aqueous medium by a polymer dispersant was used in combination with a treating liquid reactive with the pigment ink, sometimes OD reduction due to the low area factor of the obtained ink dot was observed. The reason why such a phenomenon occurs is not clear, but probably because the agglomeration of the pigment of the ink on the recording medium is promoted to a large extent by the treating liquid. Thus, to increase the optical density, the area factor may be increased by increasing the amount of the ink ejection, but sometimes leading to the inferior fixability. Also, when a combination of a pigment ink containing a self-dispersing pigment and a treating liquid reactive with the ink is used, a phenomenon called “oozing” or “haze” is sometimes observed at the peripheral part of the ink dot formed on a recording medium interfering with clear dot formation.
FIG. 1
is a schematic plan view of a dot to which this oozing or haze phenomenon has occurred, where a haze part
7
is present due to the oozing around a reaction area of a pigment ink
7
and a treating liquid
6
.
FIGS. 2A
,
2
B, and
2
C illustrate the assumed mechanism of occurrence of this phenomenon.
When a treating liquid S is applied to a recording medium P (especially plain paper) (
FIG. 2A
) and then a pigment ink I
p
containing a self-dispersing pigment but not containing a polymer dispersant (hereinafter referred to as “dispersant-free pigment ink”) is applied thereon as shown in
FIG. 2B
, a reaction product
9
starts to be formed. As the reaction proceeds, radial “oozing” occurs from an approximately circular dot of the reaction product as illustrated in
FIG. 2C
surrounding the dot with “haze”. Such “oozing” or “haze” is recognized as the same as the known feathering in appearance, deteriorating the printing quality.
Above described “oozing” or “haze” is assumed to be a chemical reaction or, in a micro-scale, a following phenomenon. A dispersant-free pigment ink reacts with the treating liquid at a relatively high reaction rate, so that immediately the dispersion break dow
Koitabashi Noribumi
Tsuboi Hitoshi
Barlow John
Shah Manish S
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