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Aqueous ink for ink-jet printing
| Details |
Inventors: Fujii, Tadashi; Murakami, Kakuji; Akutsu, Eiichi; Aruga, Tamotsu;
Assignee: Ricoh Company, Ltd. (Tokyo, JP)
Primary Examiner: Lieberman; Paul
Assistant Examiner: Le; Hoa Van
Attorney, Agent or Firm: Flynn, Thiel, Boutell & Tanis
An aqueous ink for ink-jet printing comprising at least a water-soluble dye, a water-soluble organic solvent, a water-soluble preservative and anti-mold agent, and water, wherein (1) the water-soluble dye is a mixture of dye compounds I and II and/or III, the peak ratio of I/II and/or III of the water-soluble dye measured by liquid chromatography is in the range of 0.9 to 3.0; the total concentration of NaCl and Na.sub.2 SO.sub.4 contained in the water-soluble dye is 3.0 wt. % or less; and the concentration of Ca contained therein is 120 ppm or less; (2) the water-soluble organic solvent is a mixture consisting essentially of glycerin and at least one glycol selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and polyethylene glycol, with the content ratio of (the glycerin:the glycol) being in the range of (1:1) to (1:5) in terms of parts by weight, and the concentration of the water-soluble organic solvent in the aqueous ink is in the range of 10 wt. % to 30 wt. %; and (3) the surface tension of said aqueous ink is 50 dynes/cm or more. |
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The aqueous ink for ink-jet printing according to the present invention comprises as the main components a water-soluble dye, a water-soluble organic solvent, a water-soluble preservative and anti-mold agent, and water with the following particular requirements (1), (2) and (3): (1) The water-soluble dye is a mixture of the following dye compounds I and II and/or III ##STR1## wherein M is an alkali metal.
(a) In the above water-soluble dye, the peak ratio of [I]/[II and/or III] measured by liquid chromatography is in the range of 0.
9 to 3.
0.
(b) With respect to NaCl, Na.
sub.
2 SO.
sub.
4 and Ca contained in the water-soluble dye, the total concentration of NaCl and Na.
sub.
2 SO.
sub.
4 is 3.
0 wt.
% or less, and the concentration of Ca is 120 ppm or less.
(2) The water-soluble organic solvent is a mixture consisting essentially of glycerin and at least one glycol selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol and polyethylene glycol (with an average molecular weight ranging from 200 to 400) with the content ratio of (the glycerin:the glycol) being in the range of (1:1) to (1:5) in terms of parts by weight, and the concentration of the water-soluble organic solvent in the aqueous ink is in the range of 10 wt.
% to 30 wt.
%.
(3) The surface tension of the aqueous ink is 50 dynes/cm or more.
In the aqueous ink according to the present invention, it is an essential condition that the ink is a mixture of the dye compound I and the dye compound II and/or III.
The mixture of those dye compounds can be prepared by synthesizing those dye compounds separately and then by mixing them.
Alternatively, the mixture can be obtained by purifying a commercially available C.
I.
Direct Black 19, using the technique of recrystallization, reprecipitation, extraction or salting-out.
It is preferable that the concentration of the water-soluble dye be in the range of 1.
5 wt.
% to 4.
0 wt.
%.
When the concentration of the water-soluble dye is less than 1
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