Abstract:
An aqueous ink composition having insoluble dye dispersed uniformly throughout by means of a coupling/dispersive (dual function) 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 probably evaporates during drying or migrates away.

Description:
Continuation-in-part (CIP) of prior application Ser. No. 08/676,707 filed on Jul. 8, 1996 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to inks, and in particular aqueous inks comprising water insoluble dyes. 
     2. Description of Related Art 
     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 still needed is one or more water insoluble dyes dissolved in an aqueous-based ink vehicle. This dye-based ink would enable a greatly expanded range of water-fast, non-smearing, highly saturated colors with high reproduceability and long shelf life. The ink composition of the present invention is 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. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention taught herein provides a homogeneous ink-vehicle system comprising a water insoluble dye, a coupling/dispersive agent (CDA), and an aqueous vehicle. The invention further provides a coupling - dispersive agent associated at a first molecular site or a region with a water insoluble dye, and said agent is 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 first with the coupling/dispersive agent. After the dye has interacted with the dispersant, water is added to the dye solution. The coupling/dispersive agent having a hydrophilic molecular site or region 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 or organic polymer, the ink, even if re-wetted, will not smear possibly because the coupling/dispersive agent evaporates or migrates away as the ink dries and the dried ink, without the coupling/dispersive agent, is insoluble in water. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a schematic representation of the method of solubilizing the insoluble ink using the agent, and drying of the printed ink. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The invention taught herein provides a homogeneous ink-vehicle system comprising a water insoluble dye, a coupling/dispersive agent, and water. The coupling/dispersive agent is a compound having at least 2 different reactive or interactive sites or more sites. It can therefore be described as a multifunctional (i.e. dual) compound since it has at least 2 functional groups. The invention further provides a water insoluble dye associated with an coupling/dispersive agent by coupling/dispersive agent is meant a compound 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 dye and coupling/dispersive agent were associated through Van Der Weal&#39;s forces. 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. The 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 characteristics 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. 
     One embodiment includes a coupling/dispersive agent comprising a short backbone of fewer than several dozen carbons in a chain, with the preferred length being 4 to 6 carbons. Satisfactory compounds include a carboxylic acid or a phosphonic acid. It is thought that one end of these phenyl groups 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 situation that the reactive or functional groups, sites, or regions are either terminal groups 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 functionally 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 second eligible coupling/dispersive agent provided by the invention is a much larger molecule generally in the range of 15-25 monomer units, and typically an acrylic. The preferred embodiment provided herein teaches the use of a short acrylic commercially known as JONCRYL &#39;682. Joncryl is a low molecular weight (1700) acrylic resin available from SC Johnson Polymer of Racine, Wis. 
     The invention taught herein provides a method for making an improved ink composition. The method of ink according to the present invention includes the steps of: selecting a dye; selecting a solvent; and dissolving the dye in the solvent. Adding a preselected coupling/dispersive agent to the solution of dye dissolved in solvent. The preselection of coupling/dispersive agent is from the group of molecules having 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, such as ionic forces, 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 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. 
     In preferred embodiment, the coupling/dispersive agent selected was an acrylic resin solution commercially available as JONCRYL 61LV, (composed in large part of JONCRYL &#39;678, a low molecular weight acrylic resin) or a solution of JONCRYL &#39;682 (a low molecular weight styrenated acrylic resin supplied in flake form). These polymers are estimated to have about 15 to 20 monomer units. It is thought that because the polymer is not long enough to wrap around the dye molecule, it associates with the dye by Van der Waals forces. The other end of the polymer has a water soluble ionic group such as an acid. In preferred embodiment, an ink solution with a roughly one-to-one ratio of polymer to dye (where the dye has a molecular weight of about 800) was used and printed using an HP DeskJet printer. 
     The ink was composed of ORASOL Pink (water in soluble) 1.3%; aqueous vehicle 83%; 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. 
     Phenyl groups associate well with dye and acid groups provide good solubility in water. 
     
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 Examples: 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 dye: 
                 ORASOL Pink 1.5 
                   
               
               
                 Solvent: 
                 Diethylene 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 Ink 
               
               
                 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 Ink 
               
               
                 IOSOL yellow 2 
               
               
                 diethylene glycol 8 
               
               
                 JONCRYL 682 10 
               
               
                 water 80.0 
               
               
                 Surface tension 36 (Dyne/cm) 
               
               
                 Viscosity (cps) 2.8 
               
               
                 Example 3 
               
               
                 Cyan Ink 
               
               
                 ORASOL 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 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. 
     Referring now to FIG. 1 is shown the method of solubilization and the water-fast qualities of the dried ink on the substrate. The coupling/dispersive agent (CDA)  11  (having a hydrophilic region or portion  11 A and a hydrophobic region or portion  11 B connected by an organic linking group  11 C) is first dissolved in an organic solvent. This solution is then contacted with water insoluble dye  12  (usually in an organic solvent). Dye  12  interacts with a suitable portion  11 B of the agent producing an associated moiety  13 . Water is then added and the agent bonded to the water-insoluble dye as moiety  13  remains in the aqueous solution. The aqueous solution of the ink is sprayed (printed) onto a substrate such as paper. 
     The water and solvent evaporates quickly and the agent  11  bonds to the substrate  15 . Since the agent  11  is now bonded to the substrate with agent  11  and dye  12  are both water insoluble, the printed ink is now water fast on the substrate  15 . 
     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 non-aqueous solvent, such as isopropyl alcohol (IPA). Moreover, rather than paper fiber (cellulose) the substrate affinity replacing solvent bonding may vary widely polar forces are useful in bonding the dye to many surfaces 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. 
     While only a few embodiments of the present invention have been shown and described herein, it is apparent to those skilled in the art that various modifications and changes can be made in the novel components of this water-fast ink jet ink and the method to produce water-fast inkjet print without departing from the spirit and scope of the present invention. All such modifications and changes coming within the scope of the appended claims are intended to be covered thereby.