Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means
Reexamination Certificate
2002-03-22
2003-06-17
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Fluid or fluid source handling means
C106S031850
Reexamination Certificate
active
06578958
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an inkjet recording method and apparatus and ink therefor.
2. Discussion of the Background
Recently, inkjet recording methods in which a liquid ink is discharged from a nozzle to form an image on a receiving material have rapidly been in widespread use for printers which output images prepared by computers or the like because of having the following advantages:
(1) images can be formed on plain papers;
(2) color images can be easily produced;
(3) printers can produce images at low noise; and
(4) power consumption of the inkjet recording apparatus is relatively low.
Recently, as the inkjet recording techniques have been improved, color images as good as photographs can be produced by inkjet recording methods. With the rapid progress of the inkjet recording methods, the following needs exist for the inkjet recording methods:
(1) to produce images having good water and light resistance;
(2) to produce images having good durability; and
(3) to stably discharge ink drops at a high speed.
Currently, water-soluble dyes are typically used as the colorant of inkjet inks. When a water soluble dye is used as the colorant, the resultant images have poor light resistance because water-soluble dyes typically have a poor light resistance. In addition, the resultant images tend to have a poor water resistance.
In attempting to solve the light and water resistance of ink images, aqueous inks including a pigment have been proposed because pigments have better light and water resistance than water-soluble dyes. Images recorded by pigment inks have better light and water resistance than those recorded by dye inks. However, color tone and saturation of images recorded by pigment inks are inferior to those of images recorded by dye inks. Namely, color reproducibility of the full color images formed by pigment inks is inferior to that of the images formed by dye inks. In addition, since images recorded by pigment inks have low transparency, the projected images of the images formed on an OHP (overhead projection) sheet by pigment inks has a drawback of being unclear.
For the above-mentioned reasons, pigment inks have been used only for the application in which images are formed on a special paper to produce images having good light and water resistance. Namely, pigment inks cannot record high quality images on a plain paper at a high speed.
Inkjet inks are required to have a property such that drops of the inks are stably discharged from fine nozzles of an inkjet recording head. In other words, it is needed for inkjet inks that the ink present at the exit of a nozzle does not thicken or solidify due to the evaporation of the solvent therein. With respect to the thickening and solidification, pigment inks are inferior to dye inks. In addition, the solidified pigment inks cannot be easily re-dispersed in the inks. Therefore, a clogging problem in that a nozzle of an inkjet recording head is clogged with a material such as solidified inks included in an ink tends to occur when printing is suspended for a long period of time. When printing is suspended for a while or printing a document having a long blank area, pigment inks tend to thicken due to evaporation of the solvent therein, and thereby ink drops are discharged to an undesired direction, resulting in formation of undesired images (hereinafter this problem is sometimes referred to as poor periodic discharge stability) In addition, when a pigment ink is discharged from a nozzle which has suspended to discharge the ink for a while, a problem (hereinafter referred to as a paled image problem) occurs such that the resultant images have a low density or pale color tone because the pigment content of the ink drops decreases due to deposition of the pigment.
In order to stably discharge drops of a pigment ink, the dispersibility of the pigment needs to be improved. Therefore, various surfactants and polymer dispersants have been investigated to determine whether such materials can be used as dispersants for pigment inks. In addition, self-dispersion pigments in which a hydrophilic group is incorporated on the surface of a pigment have been proposed in attempting to prepare pigment inks without a dispersant (for example, Japanese Laid-Open Patent Publications Nos (hereinafter JOPs) 10-195360 and 10-330665).
However, the periodic discharge stability of such pigment inks is not satisfactory, although the clogging problem can be fairly solved. In particular, when such pigment inks are discharged from nozzles having a small diameter, problems such that the ink discharging direction often changes and the ink discharging speed decreases occur. In addition, these inks never solve the paled image problem.
In attempting to improve the periodic discharge stability of a pigment ink, JOP 11-80639 discloses a combination technique in which an ink including a carbon black on which a hydrophilic group is grafted by a physical or chemical treatment, and one of acetylene glycol to which ethylene oxide or propylene oxide is added, polyoxyethylene alkyl ether or polyoxyethylene polyoxypropylene alkyl ether is used for a recording method in which a piezoelectric element is moved such that the ink drop is not discharged from a nozzle. However, the evaluation results of the periodic discharge stability of the ink in the system are not described therein and therefore it is not clear that the graft carbon is effective for improving the periodical discharge stability. In addition, the details of the graft carbon are not described therein. Further, whether or not the ink causes the paled image problem is not described therein.
JOP 10-95941 discloses an inkjet recording method in which an ink including a pigment capable of being dispersed without a dispersant and a specific glycol ether is contacted with a reaction liquid to form an image without blurring on a recycled paper. JOP 10-95941 also discloses a technique in which a piezoelectric element is moved (hereinafter referred to as non-discharge driving) such that the ink is not discharged to agitate the ink and to prevent the ink from thickening. However, the effect of moving the piezoelectric element is unknown judging from the examples described in JOP 10-95941.
In general, pigment inks dry and thicken such that the inks exhibit non-Newtonian flow when the pigment inks are contained in open nozzles from which drops of the inks are not discharged for a while. Namely, it is needed to always apply a driving voltage to nozzles to improve the periodic discharge stability of pigment inks, however this measure shortens the life of the recording head. In addition, JOP 10-95941 does not describe the paled image problem and therefore measures against the paled image problem are not disclosed.
With respect to the paled image problem of pigment inks, Japanese Laid-Open Ko-hyo Patent Publication 08-501330 (i.e. WO94-03546) describes that as a volatile solvent in an ink present in the vicinity of the tip edge of a nozzle evaporates, condensed products of the ink (i.e., the colorant and low volatile materials) are built up at the tip edge. Subsequently, the pigment moves toward the inside of the nozzle because the pigment has a better affinity for the ink present therein. WO94-03546 only describes that by using such an ink, the clogging problem can be solved. Namely, the paled image problem is not discussed therein.
JOP 10-279869 discloses that by using an ink having a property such that phase separation occurs at a meniscus portion of the ink in a nozzle, reliability of the inkjet apparatus can be improved. JOP 11-91096 discloses that by using such an ink and in addition by disposing of the paled ink in a nozzle in a proper amount before recording images, formation of undesired images can be prevented. However, when disposing of the paled ink, the carriage having a recording head has to be moved to a non-image forming position under which a receiving material is not present. Therefore this technique is not suitable for high speed recording. In particula
Bannai Akiko
Gotoh Akihiko
Barlow John
Brooke Michel S
Ricoh & Company, Ltd.
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