Specific dye set for thermal ink-jet printing on plain and coated papers

Abstract: A specific dye set, comprising Acid Yellow 23, Direct Red 227, and Acid Blue 9, yields true, vivid colors on specially coated paper and transparency, and yields true collors on uncoated or "plain" papers. This dye set, which is intended for 300 dpi thermal ink-jet printers, is a distinct improvement over a prior art dye set.

Description: TECHNICAL FIELD The present invention relates to thermal ink-jet printing, and, in particular, to a specific dye set suitable for use with plain and coated papers in a thermal ink-jet printer provided with a heating means for assisting in drying the print medium. BACKGROUND ART In a commercially available thermal ink-jet printer, yellow, magenta, and cyan colors are provided by inks containing Direct Yellow 86, Acid Red 52, and Acid Blue 9 dyes, respectively. However, this dye set has been observed to yield a rather limited color gamut, that is, a smaller number of colors, on plain paper, although its use with specially coated papers provides high quality color prints. It is desirable to provide a dye set that can be interchangeably used with coated papers, plain papers, and transparencies to provide vivid, true colors. DISCLOSURE OF INVENTION In accordance with the invention, a specifique dye set, comprising Acid Yellow 23, Direct Red 227, and Acid Blue 9 yields true, vivid colors on specially coated paper and transparency film. It also yields true colors on uncoated or "plain" papers. The color print quality on each of these media is superior to the prior art dye set. Specifically, the dye set of the invention provides many colors with higher Munsell chroma (gore vivid colors) and more correct munsell hue (truer colors) than the dye set of the prior art. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a color gamut comparison on Munsell coordinates, comparing the dye set of the invention with the dye set of the prior art on transparency film; and FIG. 2 is a similar plot as FIG. 1, but on special paper and plain paper. BEST MODES FOR CARRYING OUT THE INVENTION The following invention is directed to a specific dye set for use with a 300 dot-per-inch (dpi) (1 inch = 2.54 x 10⁻²m) thermal ink-jet printer. It provides superior results to commercially-available 180 DPI thermal ink-jet printers. As currently contemplated, the best implementation for using the ink formulation of the invention is in a heated printing environment, such as disclosed in co-pending application Serial No. 07/876924, filed 1/5/92 [PD-189404], entitled "Heater Blower System in a Color Ink-Jet Printer", and assigned to the same assignee as the present application. The dye set of the invention comprises inks containing Acid Yellow 23, Direct Red 227, and Acid Blue 9. Black ink is provided by an ink containing Food Black 2 dye. It is often desirable to replace the cation with which the dye is associated (usually, sodium) in order to optimize the performance of the ink for a particular ink-jet printhead. However, it should be noted that the particular ionic form is irrelevant to the practice of the invention. For use with a 300 dpi printhead, the yellow and magenta dyes are first treated to replace the as-supplied sodium counter-ion on the dye with tetramethylammonium cation. The black ink is treated to replace the as-supplied sodium counter-ion on the dye with lithium. This is to prevent crusting of the printhead nozzles by the ink. Acid Yellow 23-Na is purified and ion-exchanged to the tetramethylammonium (TMA) form simultaneously by the method described in U.S. Patent 4,786,327. The use of the TMA cation is described in U.S. Patent 4,761,180. The process of forming the TMA form of the dye and its composition are thus known in the art and form no part of this invention. The Acid Yellow 23-TMA dye is then mixed with deionized (DI) water, diethylene glycol, and a bactericide in the following proportions: Acid Yellow 23-TMA 0.5 to 5 wt%; diethylene glycol 5 to 15 wt%; buffer 0.01 to 0.5 wt%; bactericide 0.1 to 1.0 wt%; and water balance. The pH of the ink is adjusted to a value within the range of 5.5 to 8.5, preferably with KOH. Preferably, the amount of Acid Yellow 23-TMA dye is 2.04 wt% for a 300 dpi printhead and the amount of diethylene glycol is 5.4 wt%. The amount of buffer is preferably 0.078 wt%; KH₂PO₄ is the preferred buffering agent. The preferred pH is 7.5. The bactericide may be any of the well-known bactericides employed in thermal ink-jet inks, such as NUOSEPT 95, avaitable from Hüls America (Piscataway, NJ), PROXEL CRL, available from ICI Americas (Wilmington, DE), and glutaral-dehyde, available from Union Carbide Company (Bound Brook, NJ) under the trade designation UCARCIDE 250. Preferably, 0.3 wt% NUOSEPT 95 is employed with the yellow, magenta, and cyan inks, while 0.08 wt% PROXEL CRL is employed with the black ink. An ink (2.04 wt% dye) made above had the following properties: surface tension 66.2 dyne/cm density 1010 g/l conductivity 4.5 mmho/cm viscosity 1.33 cp Lambda maximum 426 nm dilution factor 5000 absorbance 0.145. Direct Red 227-Na is processed as described above to replace the sodium cations with TMA cations. The ink made from this dye has the following formulation: Direct Red 227-TMA 0.5 to 5 wt%; diethylene glycol 5 to 15 wt%; bactericide 0.1 to 1.0 wt%; and water balance. Preferably, the amount of Direct Red 227-TMA is 2.95 wt% for a 300 dpi printhead and the amount of diethylene glycol is 7.9 wt%. An ink (2.95 wt% dye) made above had the following properties: surface tension 58.8 dyne/cm density 1015 g/l conductivity 3.22 mmho/cm viscosity 1.45 cp Lambda maximum 540 nm dilution factor 5000 absorbance 0.190. Acid Blue 9-Na is purified as above and the dye concentrate is mixed with DI water, diethylene glycol, and a bactericide to form an ink having the formulation Acid Blue 9-Na 0.5 to 5.0 wt%; diethylene glycol 5 to 15 wt%; bactericide 0.1 to 1.0 wt%; and water balance. Preferably, the amount of acid Blue 9-Na is 1.1 wt% for a 300 dpi printhead and the amount of diethylene glycol is 7.9 wt%. An ink (1.1 wt% dye) made above had the following properties: surface tension 62.6 dyne/cm density 1010 g/l conductivity 1.72 mmho/cm viscosity 1.30 cp Lambda maximum 630 nm dilution factor 5000 absorbance 0.193. Using the inks from above on a 300 dpi thermal ink-jet printer, various media were printed on, including plain paper, specially coated paper, and transparency. FIG. 1 shows the color gamut comparison on Munsell coordinates (for printing on transparencies) for the dye set of the prior art (Curve 10) and for the dye set of the invention (Curve 12). The radius measures chroma. It is readily seen that the dye set of the invention can reproduce many new colors. The inks of the invention show a significant improvement in the red (R) and green (G) regions, with comparable performance elsewhere. In this and in FIG. 2, Y is yellow and B is blue. FIG. 2 is a plot similar to that of FIG. 1, but showing printing on special coated paper and on plain paper. Curves 10 and 12 are with respect to the prior art and the invention, respectively, for special paper, while Curve 14 is with respect to the invention for plain paper. With regard to special coated paper, the inks of the invention have a lower chroma in the purple and red purple regions. Fortunately, people are less sensitive to chroma in these regions. They find a "dark" or "navy" blue very acceptable. People are more sensitive to the red and green regions, and the inks of the invention have higher chroma in these regions. With regard to plain paper, the inks of the invention also have lower chroma in the purple and red purple regions, and the comments above relating to special coated paper apply here as well. In the red and green regions, the inks are comparable to the prior art inks. Since the prior art PaintJet printer uses special paper, direct comparison to plain paper is not possible. Indeed, the prior art PaintJet printer cannot print onto plain paper satisfactorily, as excess bleed is obtained. The dye set of the invention is intended for use on 300 dpi thermal ink-jet printers, and will not work on lower resolution printers, such as 180 DPI printers. This is due to the requirement that the dye concentrations in a 180 dpi system needs to be higher than for a 300 dpi system to achieve the same color saturation (e.g., amount of dye per unit area). Indeed, the magenta dye concentration must be so high for Direct Red 227 that severe start-up problems occur. A black ink is used in conjuction with the foregoing color ink set, rather than using composite ink (a combination of the three inks simultaneously to produce black color). For the black ink, Food Black 2-Na is purified and ion-exchanged to the lithium (Li) form simultaneously by the method described in U.S. Patent 4,786,327. The use of the Li cation is described in U.S. Patent 4,994,110. The process of forming the Li form of the dye and its composition are thus known in the art and from no part of this invention. The Food Black 2-Li dye is then mixed with deionized (DI) water, diethylene glycol, and a bactericide in the following proportions: Food Black 2-Li 0.5 to 5 wt%; diethylene glycol 5 to 15 wt%; buffer 0.01 to 0.5 wt%; bactericide 0.05 to 1.0 wt%; and water balance. Preferably, the amount of Food Black 2-Li dye is 2.5 wt% for a 300 dpi printhead and the amount of diethylene glycol is 5.5 wt%. As indicated above, the amount of bactericide is preferably 0.08 wt% PROXEL biocide. The amount of buffer is preferably 0.2 wt%; sodium borate is the preferred buffering agent. INDUSTRIAL APPLICABILITY The specific dye set disclosed herein is expected to find commercial use in thermal ink-jet printers having at least 300 dpi capability. Thus, there has been disclosed a specific dye set and ink set for use with thermal ink-jet printers. It will be readily apparent to those skilled in this art that various changes and modifications of an obvious nature may be made without departing from the spirit of the invention, and all such changes and modification are considered to fall within the scope of this invention, as defined by the appended claims.

Claims: A dye set for use with thermal ink-jet printers having at least 300 dpi print capability consisting essentially of Acid Yellow 23, Direct Red 227, and Acid Blue 9. A dye set for use with thermal ink-jet printers having at least 300 dpi print capability consisting essentially of Acid Yellow 23, Direct Red 227, Acid Blue 9, and Food Black 2. A dye set according to claim 1 or 2 wherein Acid Yellow 23 and Direct Red 227 dye molecules are associated with tetramethylammonium cations. A dye set according to claim 2 wherein Food Black 2 dye molecules are associated with lithium cations. A set of inks containing yellow, magenta, cyan, and black dyes for thermal ink-jet printers having at least 300 dpi print capability, said yellow ink having the formula Acid Yellow 23 0.5 to 5.0 wt% diethylene glycol 5 to 15 wt% buffer 0.01 to 0.5 wt% bactericide 0.1 to 1.0 wt% water balance, the pH of said yellow ink being adjusted to a value within the range of 5.5 to 8.5, said magenta ink having the formula Direct Red 227 0.5 to 5.0 wt% diethylene glycol 5 to 15 wt% bactericide 0.1 to 1.0 wt% water balance, said cyan ink having the formula Acid Blue 9 0.5 to 5.0 wt% diethylene glycol 5 to 15 wt% bactericide 0.1 to 1.0 wt% water balance, and said black ink having the formula Food Black 2 0.5 to 5.0 wt% diethylene glycol 5 to 15 wt% buffer 0.01 to 0.5 wt% bactericide 0.05 to 1.0 wt% water balance. A set of inks according to claim 5, said yellow ink having the formula Acid Yellow 23-TMA 2.04 wt% diethylene glycol 5.4 wt% KH₂PO₄ buffer 0.08 wt% bactericide 0.3 wt% water balance, the pH of said yellow ink being adjusted to a value of 7.5, said magenta ink having the formula Direct Red 227-TMA 2.95 wt% diethylene glycol 7.9 wt% bactericide 0.3 wt% water balance, said cyan ink having the formula Acid Blue 9-Na 1.1 wt% diethylene glycol 7.9 wt% bactericide 0.3 wt% water balance, and said black ink having the formula Food Black 2-Li 2.5 wt% diethylene glycol 5.5 wt% sodium borate buffer 0.2 wt% bactericide 0.08 wt% water balance, where TMA indicates the tetramethylammonium cation associated therewith, Na indicates the sodium cation associated therewith, and Li indicates the lithium cation associated therewith. A method of printing on a thermal ink-jet printer at at least 300 dpi resolution, which comprises printing with an ink having a dye set as claimed in any of claims 1 to 4 or with an ink as claimed in claim 5 or 6.

Inventors: KAPPELE WILLIAM D, KAPPELE, WILLIAM D.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1992
Main classification: C09D11
IPC codes: C09D11, B41M5, C09B67, D21H21