Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
1999-10-26
2002-07-02
Pham, Hai (Department: 2861)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C347S095000
Reexamination Certificate
active
06412937
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an ink composition for electrostatic attraction (suction) ink jet and to an electrostatic attraction ink jet recording process using the ink composition.
BACKGROUND OF THE INVENTION
Ink jet recording process allows high speed printing with low noise and has recently spread rapidly.
An ink jet printer is adapted to jet a liquid ink having a high fluidity through a fine nozzle onto a recording paper to perform recording. The ink jet printer operates either in an on-demand (voluntary jetting) process or continuous jetting process. As such continuous jetting processes there are known electrostatic jetting processes (e.g., Sweet type, Hertz type). As such on-demand jetting processes there are known piezoelectric process, thermal ink jet process and electrostatic acceleration process.
As the on-demand ink jetting processes using electrostatic force there is known a process so-called electrostatic acceleration ink jet process or slit jet process as disclosed in Susumu Ichinose and Yuji Oba, “Bulletin of Society of Electronic Communications of Japan”, vol. J66-C (No. 1), page 47, 1983, Tadayoshi Ono, Ei Mizuguchi, “Bulletin of Society of Image Electronics of Japan”, vol. 10, (No. 3), page 157, 1981, etc. Specific examples of these type processes are disclosed in JP-A-56-170 (The term “JP-A” as used herein means an “unexamined published Japanese patent application”), JP-A-56-4467, and JP-A-57-151374.
In this type of ink jet printer, an ink is supplied from an ink tank into a slit ink nozzle or the like comprising a slit ink retaining portion having many electrodes disposed inside thereof, while a high voltage is selectively applied to these electrodes, to thereby jet the ink in the vicinity of the electrodes onto a recording paper disposed closely opposed to the slit.
As one of other types of ink jet recording processes free of slit recording head there is disclosed in JP-A-61-211048 a process which comprises filling pores in a film-like ink support having a plurality of micropores with an ink while a voltage is selectively applied from multi-needle electrodes, to thereby transfer the ink in the pores to a recording paper.
Explaining the mechanism of ink flying, it is interpreted that the high voltage applied to the electrodes disposed causes electric charge to be injected into the ink in contact with these electrodes to thereby electrostatically charge the ink in the vicinity of these electrodes, and hence an electrostatic force is caused to jet the ink. Accordingly, the ink is normally not electrostatically charged. Only when a voltage is applied to these electrodes, the ink is electrostatically charged in the vicinity of these electrodes by energizing, thus obtaining a jetting force. The ink for use in these ink jet recording processes has an electrical resistance of from about 10
5
to 10
6
&OHgr;·cm. Since water has a low electrical resistance, an ink obtained by dispersing a coloring agent such as dye in an oily solvent with a dispersing aid such as surface active agent for adjusting the electrical resistance thereof is generally used.
Referring to the oily ink for use in this type of ink jet recording process, there have been proposed a process which comprises controlling the viscosity and specific resistivity of the oily ink (as disclosed in JP-B-52-13127 (The term “JP-B” as used herein means an “examined Japanese patent publication”)), a process which comprises controlling the dielectric constant of the dispersion medium to be incorporated in the ink and the specific resistivity of the ink (as disclosed in JP-A-53-29808), a process which comprises changing the kind of the dispersion medium to be incorporated in the oily ink or allowing a specific compound to be incorporated in the oily ink as an ink composition (as disclosed in JP-A-3-79677, JP-A-3-64377, JP-A-4-202386, JP-A-7-109431), etc.
However, the conventional techniques leave something to be desired. For example, the oily ink used in these conventional techniques leaves something to be desired storage stability, reproducibility of recorded image upon repeated use, resistance to ink feathering on transfer material, anti-clogging property in nozzle and ink supply passage, stability in ink jetting, etc. Further improvement in these properties has been desired.
On the other hand, another electrostatic suction ink jet technique is disclosed in WO93/11866. This process involves the supply of an ink obtained by dispersing, in an insulating liquid, charged particles or particles which are rendered electrostatically chargeable under the application of electric field into the ink jetting apparatus. Under the application of electric field, a continuous process is effected comprising the steps of (i) forming an ink meniscus at the forward end of a jetting electrode for jetting ink, (ii) allowing the electrostatically chargeable particles in the ink meniscus to be electrophoretically migrated to cause agglomeration (concentration), and (iii) forming an electric field between a counter electrode on which a recording medium is placed and the jetting electrode, to thereby jet the electrostatically chargeable particles thus agglomerated.
Unlike the conventional types of ink jet recording process, this type of ink jet recording process requires no ink nozzle structure. Thus, this type of ink jet recording process can jet an ink comprising dispersed particles of pigment, etc. in the form of fine droplet having a size of about several micrometers. Further, a high concentration droplet as the result of the agglomeration of dispersed particles can be jetted. Moreover, by controlling the jet signal, the size of droplet can be changed, making it possible to change the size of dots in the image.
Accordingly, in accordance with this type of ink jet recording process, an image based on light-resistant and water-resistant pigments and an image comprising a continuous dot gradation can be sharply formed with a high resolution and a high density.
As the oily ink to be used in this type of ink jet recording process WO95/1404 and WO96/10055 disclose an oily ink comprising insoluble and electrostatically chargeable particles and a charging agent each incorporated in an insulating liquid having an electrical resistance of not less than 10
9
&OHgr;·cm.
Further, an oily ink comprising electrostatically chargeable particles having a specified chargeability or specified average particle diameter has been proposed (as disclosed in JP-A-9-193389, JP-A-8-291267). Moreover, an oily ink which exhibits specified thermal properties when dried has been proposed (as disclosed in JP-A-9-137094).
However, these proposed oily inks are disadvantageous in that they leave something to be desired in jettability in ink jet recording. For example, they cause portions where the oily inks cannot be jetted upon application of a voltage corresponding to the jet signal. Further, these oily inks are occasionally jetted with its dispersed particles being insufficiently agglomerated, causing feathering or lack in density on dots printed on the transfer material. Moreover, in case of changing the application time of pulse voltage during jetting to change the size of dots thus printed to thereby form a continuous gradation, these proposed oily inks cannot be jetted at an efficiency of 100% when the pulse time is reduced to print small dots, making it impossible to form a high resolution image.
On the other hand, with the recent development of office machines and office automation, an offset lithographic printing process has spread in the art of light printing which comprises plate-making or forming an image by various methods on a lithographic printing plate precursor comprising an image-receiving layer provided on a water-resistant support to prepare a printing plate. As one of these plate-making processes there is also practiced an ink jet recording process.
When the foregoing oily ink is printed on such a lithographic printing plate precursor using the foregoing electrostatic suction ink jet recording process, several hundr
Kato Eiichi
Nakazawa Yusuke
Fuji Photo Film Co. , Ltd.
Pham Hai
Reed Smith LLP
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