HK1061694B - Use of cationic surfactant to improve print quality of dyebased inkjet inks - Google Patents

Description

Use of cationic surfactants to improve print quality of dye-based inkjet inks

Technical Field

The present invention relates generally to the field of ink jet printing and, more particularly, to a special ink formulation for improving the print quality of dye-based inks on plain paper, particularly edge raggedness/edge definition.

Background

Ink jet printing is a non-impact printing method in which ink drops are deposited in a specific sequence on a printing substrate to form alphanumeric characters, area fills, and other patterns on the substrate. Ink jet printers are becoming an alternative to other computer-based printers due to their low cost, high hardcopy output quality, and relatively noiseless operation. Despite the current success, there is a continuing search and development to further improve inkjet print quality. The growing interest in the field of ink-jet printing, and especially photographic printing, has led to a need to achieve high quality printing at a reasonable cost. The challenge remains to further improve the print quality of inkjet printing. Ink jet printing for digital photographs is emerging that requires high resolution images with accurate color, that are durable, and that do not show color banding. The present inventors have found that the sharpness of dark areas of an image is improved by the addition of black, and therefore, a black ink is needed to achieve optimum results.

For text quality on plain paper, black pigments are preferred because dye-based inks have a tendency to reduce edge definition by capillary action along the paper fibers. However, black pigments and dye-based colors cannot be used in combination to achieve excellent image quality on photographic substrates. Improving the edge definition/text quality of dye-based black inks enables a black color to be used for both plain paper text and images on photo substrates.

The present invention also relates to a method of improving edge definition of dye-based black inks on plain paper by using a cationic surfactant.

E.g. produced by Hewlett-Packard companyColor ink jet printers such as printers typically use three different color inks: magenta, yellow and cyan, and optionally black. The specific type of colorant such as dye used in the manufacture of the ink is referred to as "primary color dye system". A range of colors, such as secondary colors, can be obtained by combining different primary color dye systems.

In general, a successful color ink jet printing ink set must be compatible with the ink jet pen and the printing system. Some properties that ink-jet inks need to possess include: the ink solution has good stability, proper viscosity, proper surface tension, no harmful reaction with printing head components, high solubility of dye in a medium, safety for consumers and high color saturation. Another desirable high performance of the ink is a high definition character that minimizes wicking on photographic paper and plain paper.

Known inks have one or more of the above properties. However, inks rarely have all of the above properties, as improving one often results in a reduction in another. Thus, most commercial inks are a result of a trade-off that at least properly addresses each of the above factors. For example, inks are known to achieve a gamut comparable to silver halide printing, but only by software manipulation can a sharp and smooth edge topography be obtained that is required for printing well-defined and sharp fonts. Accordingly, there remains a need to develop ink compositions having improved properties without the enhancement of one property at the expense of the other. Accordingly, there is a need in the art to further improve print quality and stability of inkjet printing without sacrificing pen performance and reliability, and to reduce the complexity of printer and software design.

Disclosure of Invention

The invention provides an ink suitable for ink-jet ink and a preparation method thereof. It has been found that a synergistic effect is produced by combining certain anionic dyes using a linear cationic surfactant and a short chain alcohol or glycol. This combination provides a basis for ink formulations that provide excellent printing performance, especially smooth and edge-defined text quality on plain paper (bonded, pure cotton, copy paper) and good ink stability. The ink of the invention can obtain better character quality on the common paper due to the improvement of the edge definition.

The inks of the present invention have significantly higher viscosities (about 5 to about 8cps) due to the addition of the cationic surfactant.

To reduce ink encrustation, alcohols and straight chain alkane diols are often added to the ink vehicle as humectants. However, increasing the humectant alone generally increases the line width and promotes wicking of the resulting ink. Surprisingly, the synergistic effect created between the selected alcohol or alkane diol and the cationic surfactant makes the formulation very stable, allowing the formulator to combine anionic colorants with cationic surfactants without precipitating or "completely separating" (crasing) the colorant from the solution. In the past, it has been common to use an anionic ink and a cationic ink or other solution to control bleed. In this case, when the two fluids contact the printing substrate, the anionic colorant will precipitate, thereby fixing the colorant on the surface of the print. It has now been found that it is possible to formulate a stable solution containing anions and cations without causing precipitation of the colorant. Furthermore, without being bound by any theory, it is believed that the addition of cationic surfactants to anionic colorants increases the viscosity of the ink, which retards dot spread, resulting in sharper edges. This formulation works well on any conventional paper media.

In an embodiment of the present invention, each dye-based aqueous ink comprises from about 0.1 to about 20 weight percent of at least one anionic dye, from about 1 to about 30 weight percent of at least one short chain alcohol or glycol, and from about 0.5 to about 6 weight percent of at least one cationic surfactant in the color ink formulation. Other independently selected ingredients may additionally be added, including buffers, biocides, metal chelators; and the balance water.

The invention is particularly useful for improving the edge definition of text and is also particularly beneficial for dye-based black inks. Although this method is also effective for cyan, magenta, and yellow dyes and any other dyes, edge definition of color text is not currently considered as an important factor.

Detailed Description

While the specification concludes with claims particularly pointing out and distinctly claiming that which is regarded as the present invention, the advantages of this invention may be more readily ascertained from the following detailed description of the invention.

All concentrations herein are in weight percent of the total ink composition, if not specifically stated. The purity of all ingredients is that normally used in commercial practice for ink jet inks.

Those skilled in the art will recognize that other embodiments not specifically disclosed herein are also within the scope of the invention as claimed.

Coloring agent

In an embodiment of the present invention, each dye-based aqueous ink comprises from about 0.1 to about 20 weight percent of at least one anionic dye in the color ink formulation.

Dye:dyes, whether water soluble or non-water soluble, may be used in embodiments of the present invention. Water-soluble dyes are exemplified by sulfonate and carboxylate dyes, particularly those commonly used in inkjet printing. Specific examples thereof include direct black 168, K1334, rhodamine sulfonate (Sulforhodamine) B (sulfonate), acid blue 113 (sulfonate), acid blue 29 (sulfonate), acid red 4 (sulfonate), rose bengal (carboxylate), acid yellow 17 (sulfonate), acid yellow 29 (sulfonate), acid yellow 42 (sulfonate), and acridine yellow G (sulfonate), all of which are available from Aldrich ChemicalsProvided is a method. Specific examples of the water-insoluble dye include azo dyes, xanthene dyes, methine dyes, polymethine dyes and anthraquinone dyes. Specific examples of water insoluble dyes are Ciba-Geigy Orasol blue GN, Ciba-Geigy Orasol powder and Ciba-Geigy Orasol yellow. Any dye available and compatible with the formulation ingredients of the present invention may be used as the colorant.

Medium

The inks of the present invention comprise an aqueous medium containing the following ingredients (in weight% of the total ink composition): about 1 to about 30 wt.%, preferably about 5 to about 20 wt.%, of at least one short chain alcohol or diol. The alcohol or diol preferably has a carbon chain with a number of carbon atoms equal to or less than 7. The alcohol is preferably 3-pyridinemethanol. In addition, the solvent is preferably 2-pyrrolidone. The cationic surfactant is present in the ink formulation in an amount of from about 0.5 to about 6 weight percent, preferably from about 1 to about 5 weight percent. Cationic surfactants having a headgroup carbon number of from about 8 to about 18 are more preferred due to solubility limitations. In addition, other independently selected components may be added, each at a level of up to 3% by weight (0 to about 3%), including buffers, biocides, metal chelators, and the balance water.

Alcohol: any linear or branched mono-or diol having less than 7 carbon atoms may be used, with carbon atoms from about 3 to about 7 being preferred. Two preferred alcohol/glycol solvents used are isopropanol and unbranched glycol ethers.

Cationic surfactant: although any cationic surfactant having a headgroup of about 8 to 18 carbon atoms can be used, preferred surfactants contain the following structure:

R-N(R₁，R₂，R₃)

wherein R has about 8 to 18 carbon atoms, R₁、R₂、R₃The number of carbon atoms may be 1 to 4, and any combination thereof is acceptable.

Buffering agent: the inks of the present invention optionally contain from 0 to about 3 weight percent of a buffering agent. More preferably, the ink contains from about 0.1 to about 0.5 wt% buffer, and most preferably the concentration is from about 0.1 to about 0.3 wt%.

The buffer used to adjust the pH in embodiments of the invention may be an organic biological buffer or an inorganic buffer, preferably an organic biological buffer. In addition, the buffers used in embodiments of the present invention should maintain a pH of from about 3 to about 9, preferably from about 6.5 to about 8, and most preferably from about 7.2 to about 7.8. As a buffer preferably used, Trizma Base, which is supplied by, for example, Aldrich Chemical (Milwaukee, Wis.), 4-morpholinoethanesulfonic acid (MES), b-hydroxy-4-morpholinopropanesulfonic acid (MOPSO), 4-morpholinopropanesulfonic acid (MOPS), is specifically exemplified. Trizma Base is most preferably used in embodiments of the present invention.

Metal chelating agent: the inks of the present invention optionally contain 0 to about 3 weight percent of a metal chelating agent. More preferably, the ink contains from about 0.1 to about 0.5 weight percent of the metal chelating agent, and most preferably at a concentration of from about 0.1 to about 0.3 weight percent.

The metal chelator serves to bind metal ions that may be present in the ink. Specific examples of the metal chelating agent to be preferably used are: ethylenediaminetetraacetic acid (EDTA), diethylenetriaminepentaacetic acid (DTPA), trans-1, 2-diaminocyclohexanetetraacetic acid (CDTA), (ethylenedioxy) diethylenedinitrilotetraacetic acid (EGTA), or other chelating agents capable of binding metal cations. More preferably, EDTA and DTPA are used, and the disodium salt of EDTA is most preferably used in embodiments of the present invention.

Biocide(s): the inks of the present invention optionally contain 0 to about 3 weight percent biocide. More preferably, the ink contains from about 0.1 to about 0.5 weight percent biocide, with a concentration of from about 0.1 to about 0.3 weight percent being most preferred.

Any biocide commonly used in inkjet inks can be used in embodiments of the present invention, such as Nuosept 95, provided by Huls America (Piscataway, n.j.); proxel GXL, supplied by Zeneca (Wilmington, Del.); and glutaraldehyde, available from Union Carbide corporation (Bound Brook, n.j.), under the trade name Ucarcide 250. The biocide Proxel GXL is preferred. The specific ink sets disclosed herein are expected to find commercial use in ink-jet color printing.

Examples

Inks were formulated in embodiments of the present invention and various properties of the formulated inks, namely viscosity and edge definition, were determined in order to evaluate the advantages obtained.

TABLE 1 ink formulations

Composition (I)	1	2	3	4	5	6
							Sodium salt of EDTA	0.1wt％	0.1wt％	0.1wt％	0.1wt％	0.1wt％	0.1wt％
Biocide agent	0.15wt％	0.15wt％	0.15wt％	0.15wt％	0.15wt％	0.15wt％
							Cationic surfactant	0.48wt％	0.5wt％	1.0wt％	0.56wt％	2.0wt％	5.00wt％
1, 6-hexanediol	4wt％	15wt％	24wt％
							Isopropanol (I-propanol)				1wt％	20wt％	28wt％
2-pyrrolidone	4wt％	4wt％	4wt％	4wt％	4wt％	4wt％
							MOPS	0.05wt％	0.05wt％	0.05wt％	0.05wt％	0.05wt％	0.05wt％
3-pyridinemethanol		8wt％				8wt％
							DDI water	Balancing	Balancing	Balancing	Balancing	Balancing	Balancing
Total of	100wt％	100wt％	100wt％	100wt％	100wt％	100wt％

Note: EDTA is ethylene diamine tetraacetic acid;

DDI water is distilled deionized water;

adjusting the pH value of the medium to 7.2-7.3 by KOH;

MOPS is 4-morpholinopropanesulfonic acid;

a plurality of cationic surfactants with head group carbon atoms of 8-18 are used.

Claims (9)

1. An inkjet ink comprising an anionic colorant, a linear cationic surfactant, and a component selected from the group consisting of short chain alcohols, glycols, and combinations thereof, wherein the ink has a viscosity of 5 to 8cps, and the ink comprises 3-pyridinemethanol.

2. The inkjet ink of claim 1, wherein the anionic colorant comprises 0.1 to 20% by weight of the ink composition and is optionally a black dye.

3. The inkjet ink of claim 1 or 2, wherein the cationic surfactant content optionally comprises 0.5 to 6 wt% of the composition, the short chain alcohol or diol content optionally comprises 1 to 30 wt% of the composition, and wherein the ink optionally additionally comprises a buffer, a biocide, a metal chelator, water, or mixtures thereof.

4. The inkjet ink of claim 1, further comprising 2-pyrrolidone.

5. The inkjet ink of claim 1, wherein the short chain alcohol contains 7 carbons or less.

6. The inkjet ink of claim 1, wherein the short chain alcohol is isopropyl alcohol, an unbranched glycol ether, or a mixture thereof.

7. The inkjet ink of claim 1, wherein the cationic surfactant contains a head group having 8 to 18 carbons.

8. The inkjet ink of claim 7, wherein the cationic surfactant structure is:

R-N(R₁，R₂，R₃)

wherein R has 8 to 18 carbon atoms and R₁、R₂、R₃The number of carbon atoms of (a) is independently 1 to 4.

9. A method of making the edges of printed text sharp and smooth comprising printing with the ink of any one of claims 1-8.