Compositions: coating or plastic – Coating or plastic compositions – Marking
Reexamination Certificate
2002-06-06
2004-04-27
Klemanski, Helene (Department: 1755)
Compositions: coating or plastic
Coating or plastic compositions
Marking
C106S031900, C347S100000
Reexamination Certificate
active
06726758
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a black ink set comprising a plurality of black ink compositions.
2. Background Art
Achromatic color images, in which the gradation changes from black to gray and from gray to white, can be realized by printing by using a plurality of black ink compositions with different black colorant concentrations.
When black images printed by black ink compositions having a very low carbon black concentration are carefully visually inspected, slightly yellowish black is observed. Although genuine black is achromatic (a*=0, b*=0), the printed black is deviated from the achromatic color. It has been pointed out that this phenomenon can be reduced to a considerable extent by increasing the amount of carbon black added while the phenomenon becomes more significant with reducing the amount of the carbon black added.
In order to prevent this phenomenon, Japanese Patent Laid-Open No. 318293/2000 proposes a recording method, wherein, for enhancing the reproduction of black in prints, black is printed, on a recording medium, using a combination of a first black ink with a second black ink having higher black density than the first black ink.
According to experiments conducted by the present inventors, however, when achromatic color images, in which the gradation changes from black to gray and from gray to white, are printed by using a plurality of black ink compositions with different carbon black contents, a light yellow image is found at the boundary between printed colors. For this reason, the present inventors have arrived at a conclusion that there is room for further improvement in reproduction of achromatic color images, particularly gray images.
SUMMARY OF THE INVENTION
The present inventors have now found that an ink set comprising a plurality of black ink compositions, which are different from each other in content of carbon black and contain a magenta pigment and a cyan pigment added in respective amounts such that all the plurality of black ink compositions have specific chroma C* values, can improve the reproduction of achromatic color and consequently can realize good printed images.
Accordingly, it is an object of the present invention to provide a black ink set having excellent reproduction of achromatic color by preventing the formation of a light yellow image at the boundary between colors in an achromatic color image.
According to one aspect of the present invention, there is provided a black ink set comprising a plurality of black ink compositions, wherein
the plurality of black ink compositions each comprise carbon black, a magenta pigment, and a cyan pigment as colorants, and
the plurality of black ink compositions are different from each other in content of carbon black, and the content of the magenta pigment and the content of the cyan pigment are such that all the plurality of black ink compositions have a chroma C* value of not more than 3.
DETAILED DESCRIPTION OF THE INVENTION
Black Ink Set
In the black ink set according to the present invention, black ink compositions constituting the black ink set each comprise carbon black, a magenta pigment, and a cyan pigment as colorants.
Further, the plurality of black ink compositions are different from each other in content of carbon black, and the content of the magenta pigment and the content of the cyan pigment are such that all the plurality of black ink compositions have specific chroma C* values.
Images yielded by the ink set according to the present invention have good reproduction of achromatic color. For example, when the ink set according to the present invention is utilized in prints of black-and-white image specifications where resolution of prints is required (for example, electron photomicrographs and X-ray diffraction images), boundary between colors in the print and a gradational change in achromatic color can be sharply reproduced. According to a preferred embodiment of the present invention, the ink set according to the present invention prefers using a combination of a plurality of ink compositions, i.e., an ink composition having a higher carbon black concentration with an ink composition having a lower carbon black concentration. The ink composition having a higher carbon black concentration can provide sharp shadow in black images, while the ink composition having a lower carbon black concentration can realize black images (particularly highlight black images) having excellent graininess on such a level that dots are not visible. As a result, reproduction and image quality of achromatic color images can be further improved.
1) Chroma C* Value
In the present invention, the plurality of black ink compositions are prepared so that all the plurality of black ink compositions have specific chroma C* values. More specifically, the black ink compositions are prepared so that the chroma C* value is preferably not more than 3, more preferably 0 (zero). To this end, the content of the magenta pigment and the content of the cyan pigment based on the content of carbon black in the black ink composition are properly regulated.
The content of carbon black is in the range of 0.01 to 10% by weight, preferably in the range of 0.1 to 8% by weight, based on the total amount of the black ink composition. According to a preferred embodiment of the present invention, the black ink set comprises a combination of a black ink composition having a carbon black content of not less than 1.0% by weight based on the total amount of the black ink composition with a black ink composition having a carbon black content of less than 1.0% by weight based on the total amount of the black ink composition.
The content of the magenta pigment is in the range of more than 0% by weight to not more than 5% by weight, preferably in the range of more than 0% by weight to not more than 3% by weight, based on the total amount of the black ink composition. The content of the cyan pigment is in the range of more than 0% by weight to not more than 5% by weight, preferably in the range of more than 0% by weight to not more than 3% by weight, based on the total amount of the black ink composition.
In the present invention, the carbon black, the magenta pigment, and the cyan pigment are contained in the above-defined respective ranges so that all the plurality of black ink compositions have desired specific chroma C* values.
2) K Value
According to a preferred embodiment of the present invention, the ink set satisfies a requirement that, in any of all combinations of two black ink compositions of the plurality of black ink compositions, the K value defined by the following equation of the black ink composition having a higher carbon black pigment content is smaller than the K value of the other black ink composition:
K
=
M
+
C
B
k
wherein
Bk represents the content of the carbon black based on the total amount of the black ink composition;
M represents the content of the magenta pigment based on the total amount of the black ink composition; and
C represents the content of the cyan pigment based on the total amount of the black ink composition.
Here, the K value is in the range of approximately 0 to 10, preferably approximately 0 to 5.
3) Pigment
In the black ink composition according to the present invention, carbon black, a magenta pigment, and a cyan pigment are used as colorants.
These pigments are not particularly limited, and any of inorganic and organic pigments may be used. Examples of inorganic pigments include, in addition to titanium oxide and iron oxide, carbon blacks produced by known processes, such as contact, furnace, and thermal processes. Examples of organic pigments include: azo pigments including azo lake, insoluble azo pigment, condensed azo pigment, and chelate azo pigment; polycyclic pigments, for example, phthalocyanine, perylene, perinone, anthraquinone, quinacridone, dioxazine, thioindigo, isoindolinone, and quinophthalone pigments; dye chelates, for example, basic dye chelates and acid dye chelates; nitro pigments; n
Klemanski Helene
Seiko Epson Corporation
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