Recording liquid, inkjet recording method and recording...

Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means

Reexamination Certificate

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C347S095000, C347S096000

Reexamination Certificate

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06688737

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an aqueous recording liquid suitable for inkjet recording, particularly, to a composition of a recording liquid featuring excellent characteristics in the case of using so-called plain paper, and also to a recording method and a composition suitable for the recording liquid. The present invention may be applied as aqueous ink compositions for aqueous writing instruments, recording instruments, and pen plotters.
2. Description of the Related Art
Various researches with inkjet printers have in recent years, been envisaged in order to improve printing properties and fastness of printing on plain paper being used. Particularly, color images on plain paper have been improved with a view for decreasing the blurring of printed letters and inter-colors bleeding.
Furthermore, researches have extensively been conducted in order to improve problems of waterproofing and of light fading or degrading. Particularly, while inkjet printers and plotters using ink employing pigments as coloring materials have been now available, they however still have more problems in reliability than those using dye ink, by occurrence of clogging or the like. In addition, while ink containing particles being colored by dyes or pigments has been investigated in order to prevent color bleeding, there still remains problem of clogging, caused by attaching of the ink to a nozzle portion.
An attempt for yielding higher quality of images has been carried out by use of dot density modulation art using inks more dense and lesser dense, in combination with area modulation art, in order to substitute silver emulsion photography by inkjet printing. As a result, high quality images being compatible to those given by silver emulsion photography are now reproducible on brightened paper. However, the resistibility for light fading is still insufficient, and the image quality on plain paper with regard to both density and chroma is poorer than those by electrophotography.
In order to improve the light resistibility, it has been attempted to add an ultraviolet absorbent or an antioxidant to inks. For example, Japanese Unexamined Patent Publication (Tokkai) No. 4-227773 discloses to add an ultraviolet absorbent having hydrophilic groups. However, the ultraviolet absorbent in aqueous ink is so readily crystallized that clogging is likely to occur.
Other attempts for adding dye-chelated compound into ink have been carried out to prevent fading. For example, suppression of fading has been designed by adding &bgr;-cyclodextrin into a light purple-magenta ink, but, it leads to a significant increase of viscosity. Therefore if an ink being concentrated enough is used, adding of the &bgr;-cyclodextrin into the ink of high density sufficient to make it possible chelating will be suffered from a difficulty to eject ink, due to an increased viscosity.
It also has been attempted to improve the reliability by forming chelated compounds of cyclodextrin with coloring material, in order to prepare insoluble and highly water-resistant colors. Japanese Patent No. 2612661 discloses an ink obtained by forming a chalated compound of cyclodextrin or polycyclodextrin including an alcohol-soluble or oil-soluble dye, and dissolving the chelated compound in the ink. However, for some types of dye, sufficient reliability in reproducing dense enough images cannot be attained.
Moreover, Japanese Unexamined Patent Publication (Tokkai) No. 11-506800 discloses an attempt to ensure the reliability and to improve light resistibility by bonding an ultraviolet absorbent with cyclodextrin. However, for some types of dye, sufficient effects also cannot be attained.
On the other hand, for the purpose of suppressing the bleeding in the boundary of colors, efforts to find out compounds to be used in ink have been made, according to which a compound is added to precipitate at least one coloring material in the ink. For example, Japanese Unexamined Patent Publication (Tokkai) No. 10-219160 discloses an ink set using color ink containing a water-soluble calcium salt or magnesium salt, together with a comparatively highly water-soluble dye as coloring material, thereby suppressing the bleeding on boundary of printings is made. The cited Publication also says that the bleeding may often be countered by use of black ink having a slow permeability. Japanese Unexamined Patent Publication (Tokkai) No. 11-323225 discloses an ink set using ink containing a quaternary ammonium salt and/or a water-soluble polyvalent metal salt, to suppress the bleeding on the boundary of printings. Which may be happened in case of self-dispersion of carbon ink having a slow permeability is used. However, the water resistibility of such color inks is not sufficient, because of there are only limited varieties in combination of dyes capable of adding salts therein are investigated.
For the purpose of improving the suitability of ink for plain paper various attempts to modify the ink using pigment, colored particles or the like as a coloring material from a view of improving reliability, have been researched to improve the reliability of ink using pigment. For example, Japanese Unexamined Patent Publication (Tokkai) No. 10-330665 discloses pigments ink using self-dispersible carbon particles and using urea or urea derivatives. The cited also discloses inks having resinous particles being colored by dyes or pigments, and showing improved reliability by adding urea or the like.
While those types of inks are preferable in recording with recording head having a high ejection pressure and utilizing thermal energy, its ejection characteristics in the case of actuator driven by piezoelectricity or electrostatic force may however be affected by ammonia or carbon dioxide generated by decomposing of the urea. In the case of using thermal energy too, the reliability may often be deteriorated in the head being contacted with ink, depending on head material.
In addition to the influence of carbon dioxide from atmosphere, acidic substance being eluted into ink, which makes lowered the pH of ink, may occur especially during high temperature storage, to make deteriorating of components being contacted with the ink. This phenomenon is particularly noticeable in the case of inks having some types of dyes or self-dispersing carbon particles.
SUMMARY OF THE INVENTION
It is the first object of the present invention to provide a recording liquid and an ink for inkjet recording which satisfy various characteristics and show an excellent coloring property on plain paper, with high durability of image in storage such as light fastness and the like, and improved reliability.
It is the second object of the present invention to provide more preferable scheme of compound salts to be added the recording liquid for the purpose of improving the above-mentioned properties.
It is the third object of the present invention to provide more preferable and defined mode of above-mentioned compound salts.
It is the fourth and the fifth objects of the present invention to provide more preferable and defined mode achievable excellent safety of the compound salts.
It is the sixth object of the present invention to provide a recording liquid and an ink for inkjet recording which make them capable of suppressing the bleeding on the boundary of colors, and capable of improving light stability and the water resistibility.
It is the seventh object of the present invention to provide an additive preferably used without affecting color tone of images.
It is the eighth object of the present invention to provide a recording liquid and an ink for inkjet recording which show preferable color reproducibility on plain paper, with improved light stability.
It is the ninth object of the present invention to provide a recording liquid and an ink for inkjet recording which show an improved light stability, a balanced color tone with a water resistibility on plain paper.
It is the tenth object of the present invention to provide a recording liquid and a pigment ink for inkj

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