Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2001-06-19
2002-12-17
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S100000, C347S101000
Reexamination Certificate
active
06494569
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an ink-jet printing method and, more particularly, it relates to an ink-jet printing method for printing characters and images on a sheet of printing paper, OHP paper or the like, using an ink containing a coloring material and a liquid for insolubilizing the coloring material contained in the ink (to be referred to as treatment liquid hereinafter).
2. Related Background Art
The ink-jet printing system has various advantages including a low noise emission level, low running cost, the potential for high speed printing and down-sizing, the ease of color printing and so on and hence It is currently widely used in various printers and copying machines. With a printer using an ink-jet printing system, ink is generally selected from the viewpoint of ink ejection performance, printing characteristics including fixability and printing quality including blurring of printed images, optical reflection density and color development properties. Meanwhile, it is well known that there are two types of ink in terms of the coloring material contained therein. They are dye ink and pigment ink.
Pigment ink is advantageous to dye ink from the viewpoint of water-resistance and light-resistance and can print characters clearly to achieve high quality printing. On the other hand, pigment ink takes more time than dye ink for fixation on a printing medium and is not satisfactory in terms of abrasion resistance of the image after fixation if compared with dye ink. Additionally, each ink dot of pigment ink formed on a printing medium by a single ink-ejecting operation of a nozzle is relatively small when compared with that of dye ink. The pigment contained in the pigment ink can be reliably and stably dispersed in the ink by means of the electric repulsion of a polymeric dispersant so as to overcome the intermolecular force which acts between the pigment particles to cause aggregation. Therefore, it is preferable to add a polymeric dispersant to pigment ink depends on the pigment content of pigment ink.
When a sheet of plain paper is printed with pigment ink by means of an ink-jet recording method, the pigment particles contained in the ink aggregate as the solvent of ink, such as water, penetrates into the paper and evaporates into the air. Then, in terms of the behavior of the ink on the sheet of paper, the aggregational force of the ink becomes stronger when the polymeric dispersant is contained in the ink in a higher content. As a result, each ink dot formed on the printing medium by an ink having a predetermined volume ejected from an ink-jet head tends to minimize its diameter and keep a distorted profile produced as a result of the collision of the ink with the surf ace of the sheet of paper. Therefore, in order to obtain ink dots having a recording density necessary for forming an image on the sheet of paper and having a dot diameter necessary for forming an image without generating white stripes, some regulating measures should be taken to have a rather large volume of ink ejected from the ink-jet head. However, even with such regulating measures, the fixation of ink to the printing medium can take a long time and the scratch resistance of the recorded image can be reduced, because of the strong aggregational force of the pigment particles adsorbed by the polymeric dispersant and the resultant poor permeation of ink into the sheet of paper.
The use of a penetrant may be conceivable to improve the ink permeability of the printing medium in order to increase the ink dot diameter and improve the fixation of ink to the printing medium. However, the use of a penetrant can be accompanied by a problem of a degraded ink dot profile (a degraded circumferential profile of each ink dot such as feathering) and that of permeation of ink to the rear surface of the sheet of paper (so-called back-through) that are undesirable for producing high quality recorded images. Additionally, if the ink dot diameter is relatively large, the OD (optical density) of the ink dot may not be raised because the coloring material of the ink can penetrate into the printing medium. Still additionally, there is a problem that a higher printing speed will be required to ink-jet printers in business applications where the demand for ink-jet printers is expected to rise dramatically. If fixation of ink to the recording medium is not enough in a process of successively discharging printed sheets of paper from an ink-jet printer and sequentially laying them one on the other, a second sheet of paper discharged from the ink-jet printer may be laid on the first sheet of paper while the ink on the surface of the first sheet of paper is not fixed enough, so that there may arise a problem that the image on the first sheet of paper becomes blurred and/or the ink on the first sheet of paper sticks to the rear surface of the second sheet of paper.
Meanwhile, an ink containing a self-dispersion type pigment has been proposed. With such ink, the ink dots formed on a sheet of paper give an increased dot diameter probably because the pigment contained in the ink has an aggregational force weaker than that of ordinary ink pigment that is dispersed by a polymeric dispersant, when applied onto the surface of paper. However, the increased dot diameter is still not satisfactory.
As pointed out above, the currently available ink-jet printing methods still have much room for improvement in various aspects relating to the quality of the recorded image that include fixation of ink, enlargement of ink dot diameter, uniformity of density of each ink dot and high optical density of ink dots.
On the other hand, in the field of ink-jet printing technology, methods of applying ink and treatment liquid that reacts with the applied ink have been proposed In order to improve the quality of printed characters and images (e.g., in terms of water resistance and optical density of the image formed on a printing medium) by causing the applied ink and the treatment liquid to favorably react each other on the printing medium. Some of such methods have found practical applications.
SUMMARY OF THE INVENTION
Under the above identified circumstances, the inventors of the present invention have paid intensive research efforts for developing the ink-jet recording technology of using in combination a pigment ink and a treatment liquid that destroys the dispersibility of the pigment ink at the time of recording. In the course of the researches, the inventors experimented a recording process of applying a treatment liquid onto the surface of a printing medium and subsequently applying a pigment ink in such a way that the latter is mixed with the treatment liquid in a liquid state on the printing medium. As a result, it was found that some of the obtained images showed an image quality that is far from satisfactory and is sometimes even worse than the quality of images formed by using only pigment ink. More specifically, in the case of a combination of a pigment ink containing a pigment dispersed in an aqueous medium by means of a polymeric dispersant and a treatment liquid capable of reacting with such ink, the produced ink dots had a low optical density (OD) probably because of a small area factor of the ink dots. Although why such a phenomenon occurred is not clear, the inventors presume that the aggregation of pigment in the ink was greatly accelerated by the treatment liquid on the printing medium.
The area factor may be raised to enhance the OD by increasing the shot-in quantity of the pigment ink. Then, however, the fixation of ink can sometimes be worsened. In the case of a combination of a pigment ink containing a self-dispersion type pigment and a treatment liquid capable of reacting with such pigment ink, the dots formed on the printing medium showed the phenomenon of so-called exudation or haze along the circumferences thereof to blur the profiles of the dots.
FIG. 1
of the accompanying drawings schematically illustrates a dot showing such exudation or haze As shown in
FIG. 1
, the pheno
Fujimoto Yasunori
Koitabashi Noribumi
Tsuboi Hitoshi
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Shah Manish S
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