Ink-jet inks for improved print quality

United States Patent [w]

Moffatt et al.

US005935309A [ii] Patent Number: 5,935,309 [45] Date of Patent: Aug. 10,1999

[54] INK-JET INKS FOR IMPROVED PRINT QUALITY

[75] Inventors: John R. Moffatt; Edward T. Bedford;

Hiang P. Lauw, all ol Corvallis, Oreg.

[73] Assignee: Hewlett-Packard Company, Palo Alto, Calif.

4,836,851 6/1989 Pawlowski et al 106/31.43

5,102,459 4/1992 Ritter et al 106/31.36

5.116,409 5/1992 Moffatt 106/31.59

5,145,518 9/1992 Winnik et al 106/31.33

5,342,439 8/1994 Lauw 106/31.59

5,534,052 7/1996 Mennicke et al 106/31.43

5,785,745 7/1998 Lauw et al 106/31.59

5,788,753 8/1998 Pawlowski et al 106/31.59

5,821,283 10/1998 Hesler et al 106/31.59

[21] Appl. No.: 09/063,638 [22] Filed: Apr. 20, 1998

Related U.S. Application Data

[63] Continuation-in-part of application No. 08/742,137, Oct. 31, 1996, Pat. No. 5,785,745.

[51] Int. CI. ( 09D 11/02

[52] U.S. CI 106/31.27; 106/31.43;

106/31.47; 106/31.57; 106/31.58; 106/31.59

[58] Field of Search 106/31.27, 31.43,

106/31.57, 31.58, 31.59

[56] References Cited

U.S. PATENT DOCUMENTS

4,664,708 5/1987 Allen 106/31.43

An ink-jet ink composition for ink-jet printing and a method using the same is disclosed, the ink composition comprising an aqueous liquid vehicle, at least one zwitterionic surfactant; and at least one amphiphilic dye, said at least one amphiphilic dye comprising a plurality of amphiphilic dye molecules, each of said amphiphilic dye molecules consisting essentially of a chromophore and at least one hydrophobic arm attached thereto, said at least amphiphilic dye being present in said ink-jet ink composition in an amount that is at least equal to its critical micelle concentration. The ink compositions of the present invention provide enhanced waterfastness and optical density.

20 Claims, 2 Drawing Sheets

INK-JET INKS FOR IMPROVED PRINT
QUALITY

CROSS REFERENCE TO RELATED

APPLICATIONS 5

The present application is a continuation in part of U.S. application Ser. No. 08/742,137, now U.S. Pat. No. 5,785, 745, by Lauw et al, entitled "Amphiphilic Dyes," filed on Oct. 31, 1996, and assigned to the same assignee as the present invention.

FIELD OF INVENTION

The present invention relates to ink compositions employed in ink-jet printing and, more particularly, to 15 improvement in waterfastness and the reduction of bleed of ink-jet prints employing said inks.

BACKGROUND OF INVENTION

Ink-jet printing is a non-impact printing process in which droplets of ink are deposited on print media, such as paper, transparency film, or textiles. Low cost and high quality of the output, combined with relatively noise-free operation, have made ink-jet printers a popular alternative to other types of printers used with computers. Essentially, ink-jet printing involves the ejection of fine droplets of ink onto print media in response to electrical signals generated by a microprocessor.

There are two basic means currently available for achieving ink droplet ejection in ink-jet printing: thermally and piezoelectrically. In thermal ink-jet printing, the energy for drop ejection is generated by electrically-heated resistor elements, which heat up rapidly in response to electrical signals from a microprocessor to create a vapor bubble, resulting in the expulsion of ink through nozzles associated with the resistor elements. In piezoelectric ink-jet printing, the ink droplets are ejected due to the vibrations of piezoelectric crystals, again, in response to electrical signals generated by the microprocessor. The ejection of ink droplets in a particular order forms alphanumeric characters, area fills, and other patterns on the print medium.

Ink-jet printers offer low cost, high quality printing with relatively noise-free operation. As such, ink-jet printers have become a popular alternative to other types of printers. Notwithstanding their recent success, intensive research and development efforts continue toward improving waterfastness, optical density, print quality, and bleed alleviation of ink-jet images. In general, waterfastness, bleed performance, and optical density of ink-jet images still falls short of that produced by other technologies such as electrophotography or gravure printing. A continued demand in ink-jet printing has resulted in the need to develop reliable printers capable of producing high quality waterfast images at a reasonable cost.

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However, few ink compositions are known that possess all the foregoing desired properties, since an improvement in one property often results in the degradation of another property. Thus, many inks commercially used represent a compromise in an attempt to achieve an ink evidencing at 60 least an adequate response in each of the performance attributes, such as waterfastness and optical density.

DISCLOSURE OF INVENTION

An ink-jet ink composition for ink-jet printing and a 65 method using the same is disclosed, the ink composition comprising an aqueous liquid vehicle, at least one zwitteri

onic surfactant; and at least one amphiphilic dye, said at least one amphiphilic dye comprising a plurality of amphiphilic dye molecules, each of said amphiphilic dye molecules consisting essentially of a chromophore and at least one hydrophobic arm attached thereto, said at least amphiphilic dye being present in said ink-jet ink composition in an amount that is at least equal to its critical micelle concentration. The ink compositions of the present invention provide enhanced waterfastness and optical density.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a plot of % dye transfer versus elapsed time, depicting the enhancement in waterfastness of the printed image using Reactive Black 5-pentylamine derivative and varying concentrations of OOAO.

FIG. 1(b) is a plot of % dye transfer versus elapsed time, depicting the enhancement in waterfastness of the printed image using Reactive Yellow 35-pentylamine derivative and varying concentrations of OOAO.

FIG. 2 is a plot of optical density versus concentrations of OOAO, depicting the enhancement in optical density of the printed image, as a result of the present invention.

DETAILED DESCRIPTION OF THE
INVENTION

The invention described herein is directed to ink-jet inks for printing ink-jet images using commercially available ink-jet printers such as DESKJET® printers, manufactured by Hewlett-Packard Company, of Palo Alto, Calif. The inks enable the production of high-quality printed images having excellent waterfastness, optical density, bleed alleviation, and print quality.

More specifically, the aqueous inks of the present invention comprise at least one water-soluble amphiphilic dye, at least one zwitterionic surfactant; and vehicle. The dye may be any dye having a chromophore and at least one hydrophobic arm attached thereto.

The amphiphilic dye is present at a concentration greater than the critical micelle concentration (cmc) for the dye; in accordance with U.S. Pat. No. 5,116,409, by Moffat, assigned to the same assignee as the present invention, and incorporated herein by reference; such that the micelles are formed that incorporate the dyes therein. Preferably the dye is present at a concentration of about 1.1 times its cmc.

The inks have a pKa greater than the pKa of the surfactant. Specifically, if the pH is excessive, the amphiphilic dye loses its waterfastness. If the pH is too low, the amphiphilic dye is insoluble in the ink vehicle. An organic buffer may be used to adjust the pH of the ink to appropriate levels.

All concentrations herein are in weight percent of total ink composition, unless otherwise indicated. The purity of all components is that employed in normal commercial practice for ink-jet inks.

Inks

Inks made according to the present invention comprise from about 0.01% to about 8% dye, preferably from about 2 to about 6, and most preferably, from about 3 to about 5 wt % dye; from about 0.01 to about 8 wt % surfactant, preferably from about 1 to about 6 , and most preferably, from about 3 to about 5 wt % surfactant.

The amphiphilic dye is present at a concentration greater than the critical micelle concentration (cmc) for the dye; in accordance with U.S. Pat. No. 5,116,409, by Moffat, described above; such that the micelles are formed that incorporate the dyes therein. Preferably the dye is present at