Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
1998-05-22
2002-01-29
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031280, C106S031600
Reexamination Certificate
active
06342095
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ink sets for ink-jet recording, which are used in recording black images on a recording medium by using in combination plural inks different in polarity as black inks, and an ink-jet recording method and ink-jet recording instruments using such an ink set, and more particularly to ink sets for ink-jet recording, which permit the provision of clear and high-quality images having a sufficient optical density and of prints having excellent water fastness and light fastness, irrespective of the kind of plain paper, and an ink-jet recording method and ink-jet recording instruments using such an ink set.
The present invention also relates to ink sets for ink-jet recording in which a color image is printed with at least two inks of different colors by ejecting ink droplets on a recording medium, and an ink-jet recording method and ink-jet recording instruments using such an ink set, and more particularly to ink sets, which can prevent bleeding at boundaries between a black ink and color inks (hereinafter referred to “bleeding” simply) and white uneven image disorder (hereinafter referred to “white haze”) occurred in a black image region at a boundary area between a black ink and a color ink even when plain paper is used, and hence permits the provision of clear color images, and an ink-jet recording method and ink-jet recording instruments using such an ink set.
2. Related Background Art
With the spread of ink-jet recording systems, it is advanced to improve the quality and fastness properties of prints. With respect to, for example, water fastness, Japanese Patent Application Laid-Open No. 4-226175 and U.S. Pat. No. 5,053,495 disclose novel black dyes and inks which can provide images having good water fastness.
Black inks using a pigment have been reported to form black images excellent in print quality and fastness properties such as water fastness and light fastness on plain paper.
For example, Japanese Patent Application Laid-Open No. 5-179183 discloses pigment inks stabilized with a block polymer of an AB or BAB type, in which A is a hydrophobic homopolymer or copolymer of an acrylic monomer, and B is a hydrophilic polymer or a salt thereof. Japanese Patent Application Laid-Open No. 6-136311 discloses pigment inks which comprise a block polymer of a hydrophobic polymer having a basic amine functional group and a hydrophilic polymer having a nonionic acidic functional group, can provide prints of excellent quality and have excellent dispersion stability. Japanese Patent Application Laid-Open No. 7-53841 has proposed pigment inks for ink-jet, which comprise a triblock polymer of an ABC type, in which A is a hydrophilic homopolymer, B is a polymer bonded to solid particles, and C is a hydrophilic or hydrophobic polymer different from the block A, have excellent dispersion stability and can provide prints of excellent quality.
On the other hand, with the spread of ink-jet recording systems, it is attempted to improve the quality of color images formed on plain paper.
In order to improve the quality of color images, in particular, it is required that black characters recorded on plain paper have such good quality as they are high in density, sharp and free of any feathering. It has also been reported to reduce bleeding phenomenon caused by contact of plural recording inks of different colors with each other at boundary parts of different colors and white haze occurred in a black image region at a boundary area between a color ink and a black ink. White haze means a phenomenon that an image is disordered white unevenly.
For example, Japanese Patent Application Laid-Open No. 8-193176 discloses inks comprising a penetrating agent and 0.02 to 0.5% by weight of an alginate. Japanese Patent Application Laid-Open No. 6-57192 has proposed black inks containing an anionic dye and yellow inks containing a cationic dye and a polyvalent precipitant. Japanese Patent Application Laid-Open No. 9-118850 has proposed inks in which a first ink is composed of a pigment dispersion, and a second ink comprises an organic acid salt or mineral acid salt. Japanese Patent Application Laid-Open No. 7-314888 has proposed inks comprising a specific fluorine compound.
The methods described in Japanese Patent Application Laid-Open No. 4-226175 and U.S. Pat. No. 5,053,495 feature that one or more carboxylic acids, which are weak acids, are introduced into a dye molecule, thereby developing the water fastness of the resulting print making good use of the dependence of solubility of the dye on pH. However, the water fastness is insufficient, in particular, when using neutralized paper because the surface pH of paper plain varies with the kind of the paper.
The pigment inks disclosed in Japanese Patent Application Laid-Open Nos. 5-179183, 6-136311 and 7-53841 can provide images excellent in fastness properties such as water fastness and light fastness, and improve the print quality in plain paper to some extend. However, these inks have involved such problems as optical density becomes insufficient according to the kind of plain paper, and fixing ability becomes poor in plain paper that sufficient optical density can be attained.
On the other hand, the inks comprising a penetrating agent, 0.02 to 0.5% by weight of an alginate and a solid wetting agent described in Japanese Patent Application Laid-Open No. 8-193176 can prevent bleeding and white haze phenomenon to some extent. However, the wettability of paper is enhanced due to the penetrating agent and solid wetting agent, so that feathering occurs at edge parts of characters printed, resulting in a failure to attain satisfactory character quality.
The inks described in Japanese Patent Application Laid-Open Nos. 6-57192 and 9-118850 cause aggregation of dyes or pigments at boundaries between different colors, so that bleeding can be prevented to some extent, and the quality of black characters is also improved to some extent. However, the aggregation occurs only at boundaries within a black region, so that white haze phenomenon that occurs in the black region cannot be prevented. On the other hand, Japanese Patent Application Laid-Open No. 7-314888 discloses the inks comprising the specific fluorine compound, in which the surface energy of a first ink is adjusted within 15 dyn/cm of the surface energy of a second ink. White haze phenomenon is reduced to some extent by this method. However, it has been insufficient to prevent the white haze phenomenon in the case of high speed recording in which different colors overlap one after other in a short period of time, or according to the kind of plain paper.
SUMMARY OF THE INVENTION
It is therefore the first object of the present invention to provide an ink set for ink-jet, which can attain high optical density for images of black ink and has good fixing ability, irrespective of the kind of plain paper, and a recording method and recording instruments using such an ink set.
The second object of the present invention is to provide an ink set for ink-jet, which can attain high optical density for images of black ink, has good fixing ability and can provide prints excellent in fastness properties such as water fastness and light fastness, irrespective of the kind of plain paper, and a recording method and recording instruments using such an ink set.
The third object of the present invention is to provide an ink set which can provide black characters of high quality, prevent both bleeding and white haze and provide clear color images, irrespective of the kind of plain paper, and a recording method and recording instruments using such an ink set.
The above objects can be achieved by the present invention described below.
According to the first aspect of the present invention, there is provided an ink set comprising two black inks different in polarity from each other as black inks.
The ink set according to the first aspect of the present invention includes the following three embodiments.
(1) An ink set comprising two black inks different in
Osumi Koichi
Takada Yoichi
Takizawa Yoshihisa
Teraoka Hisashi
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