Aqueous ink with water insoluble dyes

Abstract: An Aqueous ink composition having insoluble dye dispersed uniformly throughout by means of a coupling/dispersive agent. The coupling/dispersive agent is characterized by association with insoluble dye molecules as well as by solubilization in a water based carrier medium. The resulting ink is water fast because the coupling/dispersive agent evaporates during drying.

Description: This invention relates to an ink composition according to the first part of claim 1 as known from EP-A-0 273 718. Dyes in some aspects are superior to pigments in ink jet inks for a number of well-known reasons. Pigment particles are about a million times larger than dye molecules. Pigment based inks are, basically, finely ground particles suspended in a transfer medium. The much smaller dye molecules may, under the appropriate conditions, dissolve in a medium as compared with mere physical suspension. It is well known that, owing to its molecular characteristics, dye produces colors spanning a broader range, colors which are truer or otherwise more reproducible, and colors of greater strength. However, water soluble dyes smear and fade after printing. Smearing and fading are, in most applications, highly undesirable characteristics and present severe limitations on the usefulness of dye inks in everyday printer use. What is needed is water insoluble dye dissolved in an aqueous-based ink vehicle. The dye-based ink would enable a greatly expanded range of water-fast, non-smearing, highly saturated colors with high reproduceability and long shelf life. Such an ink composition would be useful in ink jet printing, enabling color consistency over a broad range and suitable, owing to non-smearing and non-fading properties, for archival purposes. The problem of the present invention is to provide an ink composition which has a high water resistance, does not smear even if re-wetted and is suitable for use in many printer types. This problem is solved by claim 1. The invention taught herein provides a homogeneous ink-vehicle system comprising a water insoluble dye, a coupling/dispersive agent, and an aqueous vehicle. The invention further provides a coupling dispersive agent associated at a first molecular site or region with a water insoluble dye, and said agent associated at a second site or region with water. Ink is made by dissolving dye in solvent, then adding the coupling/dispersive agent. The dye interacts with the coupling/dispersive agent. After the dye has interacted with the dispersant, water is added to the dye solution. The coupling/dispersive agent then interacts with water. This association of the coupling/dispersive agent with, as to one functional group or reactive site or region, the dye, and as to another, the water, results in the dissolution of the water-insoluble dye in water. Ink provided by and according to the invention taught herein is suitable for use in many printer types and will adhere upon drying to most cellulose based papers. Once dry upon a medium such as paper, the ink, even if re-wetted, will not smear because the coupling/dispersive agent evaporates as the ink dries and the dried ink, without the coupling/dispersive agent, is insoluble in water. DETAILED DESCRIPTION OF THE INVENTION The invention taught herein provides a homogeneous ink-vehicle system comprising a water insoluble dye, the coupling/dispersive agent as claimed, and water. The invention further provides a water insoluble dye associated with an agent with at least two functional groups or reactive sites or regions, one such group, site or region assisting in water solubility, and another associating with the dye. The insoluble dye may be any of the large variety of dyes known to be insoluble in water. Specific examples are provided below. The aqueous vehicle is largely water, and typically deionized water. Other ingredients, such as isopropyl alcohol, may be included in the aqueous vehicle, depending on desired ink characteristics and also, of course, on the type of printer for which a given ink is formulated and all factors generally considered by ink system designers. Aqueous vehicle also generally includes solvent (diethylene glycol, for example) either incorporated from the solubilization of the solid dye powder, or added in order to accommodate of other factors, including ink system design considerations. Typically the aqueous vehicle is present in the major amount of the ink composition, in the range of 10 to 95 percent, and preferably approximately 50 to 90 percent based on total weight of the ink. The coupling/dispersive agent is selected from the group of compounds that exhibit both the capacity for dye association as well as the characteristic of dissolving in water. While many compounds may be identified as demonstrating these capacities and characteristics, the specific embodiments provided herein are of two basic types. The coupling/dispersive agent comprises a short backbone of between 4 to 6 carbons. Satisfactory compounds include carboxylic and phosphonic acid. It is thought that one end of these acids forms a van der Waals attraction to the insoluble dye molecules. The other end, COOH, easily dissolves with surrounding aqueous vehicle (the major part of which is water, as described hereinabove). The term "end" is used herein to describe the notion that the reactive or functional groups, sites, or regions are either terminal or otherwise somehow spatially distinct; it is not meant to be strictly construed to limit the compounds taught by the invention. Rather, the invention provides for dual functionality the coupling dispersive agent: that of both coupling with the dye and that of dispersing in water. The examples provided herein are believed to form associations on a molecular level, one dye molecule per coupling/dispersive molecule, and this homogeneity facilitates ink performance. The invention taught herein also provides a method for preparing a water-fast composition comprising the steps as listed in claim 4. The preselection of coupling/dispersive agent is from the group of molecules having has at least two functional groups. (The term functional group as used herein means any identifiable site, region or functional structure that contributes to the associative process). The first functional group is pre-selected for dye associative properties, with pi electrons from an aromatic ring, or other electrostatic force enhancing association of the functional group with dye molecules. The second functional group is pre-selected for solubility in water typically arising out of easy formation of ionic or hydrogen bonds and may be selected from a range of carboxylic, phosphonic or other acidic groups. Upon addition, the solubilized dye interacts with the coupling/dispersive agent; most particularly, with a so-called first functional group of the coupling/dispersive agent. After the dye has interacted with the coupling/dispersive agent, the aqueous vehicle is added to the dye/coupling dispersive agent solution. The coupling/dispersive agent then interacts with the molecules in the aqueous vehicle through a second functional group. This association of the coupling/dispersive agent with, as to one functional group, the dye, and as to the other functional group, the water, results in the dissolution of the water-insoluble dye in water. The ink was composed of Orasol Pink (water insoluble) 1.3%; additives to aqueous vehicle 50%; water 33%; Joncryl 61LV, 6.7%; and isopropyl alcohol 9%. The ink has a viscosity of 7.5 cps and was printed with a Deskjet pen. A variety of coupling/dispersive agents with structures similar to the monomer (functional group) of the Joncryl polymer were used. Acids (the COOH terminal group) associate well with dye and provide good solubility in water. Examples: dye: Orasol Pink 1.5 Solvent: Diethlene Glycol 6 coupling/dispersive agent: 4-phenyl butyric acid 5 or 6 phenyl hexanoic acid 5 or 4 bromophenyl acetic acid 5 or 4 bromophenyl boronic acid 5 or 4 amino benzyl phosphonic acid 5 aqueous vehicle: water 87.5 Different colors include: Example 1: Magenta orosol pink 1.3 Diethylene glycol 5.2 Joncryl 682 5.0 Water 88.5 Surface tension 40(Dyne/cm) Viscosity (cps) 2.1 Example 2: Yellow iosol yellow 2 diethylene glycol 8 Joncryl 682 10 water 80.0 Surface tension 36 (Dyne/cm) Viscosity (cps) 2.8 Example 3: Cyan orosol blue 4.0 Joncryl 682 10 diethylene glycol 16 water 70 surface tension 37 Vis (cps) 5.1 Print samples were generated using the HP DeskJet printer. Ink water-fastness was measured by paper chromatography and indicated little or no migration with water. The ink according to the invention taught herein has higher affinity to the paper fiber (cellulose) than to water. The terminal polar group of the coupling/dispersant backbone bonds to the hydroxyl group in the cellulose upon drying; the strength of the bond between the cellulose and the terminal polar group prevents smearing upon rewetting. Alternate embodiments The ink taught herein is not limited to water insoluble dye. The coupling/dispersant agent may be pre-selected for dye in combination with a nonaqueous solvent, such as isopropyl alcohol (IPA). Moreover, rather than paper fiber (cellulose) the substrate affinity replacing solvent bonding may vary widely including metallic surfaces such as aluminum cans and the like. In sum, the invention taught herein provides ink of good transparency. The ink is easy to manufacture because no pigment grinding is required and there are no particle size distribution complications. The ink-vehicle system is flexible accommodating a variety of dye based inks, various coupling/dispersant components as well as wide range of ink-substrate end products. The resulting ink-substrate coupling is non-smearing and water (or solvent) fast. The ink eliminates the problems of dispersing pigment in "ink jet" ink, and, because of adequate binding characteristics, is more robust than systems dependent on or sensitive to the ink vehicle.

Claims: An ink composition comprising a water-insoluble dye, a coupling/dispersive agent, an aqueous vehicle, and a solvent in which said dye is dissolved, wherein the coupling/dispersive agent includes a first and a second functional group, said first functional group interactive with said water-insoluble dye, and said second functional group interactive with said aqueous vehicle, characterized in that the coupling/dispersive agent is selected from compounds wherein said first functional group of said coupling/dispersive agent is selected from nitro groups, and compounds having a backbone of between four and six carbons which are selected from carboxylic acids and phosphonic acids. An ink composition as in claim 1 comprising: a) 1 to 15 parts by weight of the water-insoluble dye of 100 parts by weight of the total composition; b) 1 to 20 parts by weight of the dye solvent of 100 parts by weight of the total composition; c) 1 to 30 parts by weight of the coupling/dispersive agent based on 100 parts by weight of the total composition; d) the remainder of the 100 parts being made up of the aqueous vehicle. A water-fast coloring ink composition as in claim 1 comprising: a) from 1 to 30 parts by weight a combination of water-insoluble dye and solvent; b) from 1 to 30 parts by weight the coupling/dispersive agent; c) remainder of the 100 parts comprised of the aqueous vehicle, said vehicle including water and additives. A method of preparing a water-fast coloring composition according to claim 1 comprising the steps of: a) selecting a water-insoluble dye; b) selecting a solvent; c) dissolving said dye in said solvent to form a dissolved dye; d) selecting a coupling/dispersive agent characterized by two or more functional groups, wherein a first functional group is attractive to said dye and wherein a second functional group is hydrophilic, and wherein the coupling/dispersive agent is selected from compounds wherein said first functional group of said coupling/dispersive agent is selected from nitro groups, and compounds having a backbone of between four and six carbons which are selected from carboxylic acids and phosphonic acids, and e) mixing said solvent dissolved dye with said coupling/dispersive agent; f) selecting an aqueous vehicle; g) combining the product of step e) with said aqueous vehicle.

Inventors: LIM AN-CHUNG ROBERT, TOM HOWARD S, LIM, AN-CHUNG ROBERT, TOM, HOWARD S.
Applicants: HEWLETT PACKARD CO, HEWLETT-PACKARD COMPANY
Application year: 1997
Main classification: C09D11
IPC codes: C09B67, C09D11, B41M5, B41J2