Compositions: coating or plastic – Materials or ingredients – Pigment – filler – or aggregate compositions – e.g. – stone,...
Reexamination Certificate
2002-02-26
2004-03-09
Green, Anthony J. (Department: 1755)
Compositions: coating or plastic
Materials or ingredients
Pigment, filler, or aggregate compositions, e.g., stone,...
C106S031860, C106S503000, C523S160000, C523S161000, C524S553000, C524S554000, C524S585000
Reexamination Certificate
active
06702889
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the priority benefit of Japanese application serial no. 2001-052720, filed Feb. 27, 2001.
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a pigment dispersing liquid having improved discharge stability, liquid-phase stability and stability in pigment grain size and being capable of improving light stability and color visibility of printed images, an ink composition for ink jet using the pigment dispersing liquid, and a method for forming images with the ink composition.
2. Description of Related Art
The ink jet printing method has many advantages over other printing methods because it is simpler in process and can be configured easily for full-color printing, and allows the use of a simple apparatus to obtain a high resolution picture. The ink compositions for ink jet include dye-system ink compositions, which are usually fabricated by dissolving various water-soluble dyes in water or in a mixture of water and a water-soluble organic solvent, as described in the official gazettes of Japanese Patent Applications Laid Open No. Sho 63-51485, Sho 63-56575 and Hei 1-198671. The dye-system ink has improved color visibility but has poor light stability and poor water resistance for printed matters.
On the other hand, the pigment-system ink with carbon black or various organic pigments dispersed therein is widely studied now since it has higher light stability and better water resistance over the dye-system ink, as described in the official gazettes of Japanese Patent Applications Laid Open No. Sho 57-10660, Sho 57-10661, Hei 2-255875 and Hei 2-276876, and in Japanese Patent Publication No. Hei 1-15542. The causes of high light stability and high water resistance of the pigment-system ink are explained as follows.
When a pigment-system ink composition dries on a printed material, the pigment left as a coloring agent does not dissolve in water like a dye does and therefore will not effuse.
On other hand, since the light reactivity of a pigment is lower than that of a dye, the light stability of a pigment is higher than that of a dye.
The pigment-system ink is prepared by dispersing a mixture consisting of a pigment, a liquid medium and dispersing agents with a dispersing apparatus, such as a ball mill or a sand mill. However, the pigment-system ink easily causes a nozzle jam and to its detriment provides a narrower color gamut as compared with the dye-system ink. In order to prevent a nozzle jam and to broaden the color gamut, the pigment grains in the pigment dispersing liquid, used as a component of the ink for ink jet recording, usually have a size smaller than 200 nm, preferably smaller than 150 nm. This also ensures the visibility of the images printed with the ink and the secondary color reproducibility and the transparency of the ink. Therefore, it is necessary to atomize the pigment grains in the pigment dispersing liquid and to promote the long-time stability in mean grain size. The atomization of the pigment grains needs to be finished in a short period in order to reduce the price for industrial production.
Moreover, it is required that the pigment grain size in the pigment dispersing liquid be maintained even after a long period and/or under a high temperature or a low temperature, so as to prevent a nozzle jam of the printer.
Moreover, in order to atomize the pigment particles in a short period and to reduce the variation of the pigment grain size after a long period, the pigment dispersing agent is preferably used together with some additives.
Nevertheless, the ink compositions for ink jet currently used have the drawbacks of larger mean grain size, low stability in mean grain size and low discharge stability. Such ink compositions include those using styrene-acryl copolymer, styrene-maleic acid copolymer (Japanese Patent Applications Laid Open No. Sho 56-147863) and sodium naphthalenesulfonate/formalin condensate (Japanese Patent Applications Laid Open No. Sho 61-083267) as polymer pigment dispersing agents, and using polyethylene glycol alkylphenyl ether (Japanese Patent Applications Laid Open No. Hei 5-105837), polyethylene glycol alkylphenyl ether sulfate (Japanese Patent Applications Laid Open No. Hei 10-168367) and polyethylene glycol alkylphenyl ether phosphate (Japanese Patent Applications Laid Open No. Hei 10-88050) as surfactants.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems, this invention provides a pigment dispersing liquid and an ink composition for ink jet that has a small mean pigment grain size, high stability in mean grain size and high discharge stability. Meanwhile, the pigment grains can be atomized in a short period during the preparation of the pigment dispersing liquid and the size variation over a long time of the pigment grains in the pigment dispersing liquid or in the ink can be reduced.
After studying the above-mentioned problems, the inventor provides an ink composition that contains a dispersing agent expressed by formula (1a) or (1b) below and preferably further contains specific additives including at least one of the compounds expressed by formulae (2), (3) and (4), respectively.
wherein
R
1
is H, a C
1
-C
20
alkyl, allyl or aralkyl group, phenyl, substituted phenyl or naphthyl;
k is an integer of 0-7;
A
1
is oxyethylene, oxypropylene or a blend of oxyethylene and oxypropylene;
A
2
is oxyethylene, oxypropylene or a blend of oxyethylene and oxypropylene;
i, j≧0 and (i+j) range from 30 to 100;
M
1
is selected from the group consisting of H, Li, Na, K and N
+
R
2
R
3
R
4
R
5
, wherein each of R
2
, R
3
, R
4
, and R
5
is either H, methyl, ethyl, 2-hydroxyethyl or 3-hydroxypropyl;
p, q≧1 and (p+q)=3.
The group R
1
with a carbon number exceeding 20 will lower the dispersion stability and increase the viscosity of the colorant dispersing liquid. The value of (i+j) preferably ranges from 30 to 100, more preferably from 30 to 80. When (i+j) is larger than 100, the viscosity of the dispersing liquid or the ink increases and the stability in mean grain size becomes lower. In addition, p and q can be set as a combination of p=1 and q=2, or as another combination of p=2 and q=1.
The formulae (2), (3) and (4) are as follows.
R
6
—(A
3
)
m
—OH (2)
R
12
O—(A
4
)
x
—CH
2
COOM
3
(4)
wherein
In formula (2), R
6
is C
8
-C
14
alkyl, A
3
is oxyethylene, oxypropylene, or a blend of oxyethylene and oxypropylene, and m is an integer of 3-16;
In formula (3), M
2
is selected from the group consisting of H, Li, Na, K and N
+
R
8
R
9
R
10
R
11
, wherein each of R
8
, R
9
, R
10
, and R
11
is either H, methyl, ethyl, 2-hydroxyethyl, or 3-hydroxypropyl, and R
7
is C
1
-C
20
alkyl; and
In formula (4), R
12
is C
1
-C
20
alkyl; A
4
is oxyethylene, oxypropylene, or a blend of oxyethylene and oxypropylene; x is an integer of 1-12; and M
3
is selected from the group consisting of H, Li, Na, K and N
+
R
13
R
14
R
16
, wherein each of R
13
, R
14
, R
15
, and R
16
is either H, methyl, ethyl, 2-hydroxyethyl or 3-hydroxypropyl.
The group R
6
in the compound of formula (2) is preferably an alkyl group having from 8 to 14 carbon atoms. When the carbon number is less than 8 or larger than 14, the stability in mean grain size is lowered. In addition, m is preferably an integer ranging from 3 to 16. When m is less than 3 or larger than 16, the stabilizing effect for the grain size becomes weaker. The group R
7
in the compound of formula (3) is preferably an alkyl group having from 1 to 20 carbon atoms. When R
7
is H or its carbon number exceeds 20, the stability in the mean grain size is lowered. Moreover, when the group R
12
in the compound of formula (4) is H or its carbon number exceeds 20, the stabilizing effect for the colorant grain size in the colorant dispersing liquid becomes weaker. In addition, A
4
is suitably oxyethylene, oxypropylene or a blend of oxyethylene and oxypropylene, and x is preferably an integer from 1 to
Keishi Taniguchi
Shigeo Hatada
Green Anthony J.
Ricoh & Company, Ltd.
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