| PATENT ASSIGNEE'S COUNTRY | USA |
| UPDATE | 03.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 14.03.00 |
| PATENT TITLE |
Smear resistant pigmented ink jet inks containing .beta.-diketone or ureido dispersants |
| PATENT ABSTRACT | An ink jet ink composition is provided which contains an aqueous vehicle; a colorant; and a polymeric dispersant comprising 2 to 50% by weight of monomers selected from .beta.-diketone containing monomers and ureido monomers, as well as a combination of such ink with a media having basic groups such as primary or secondary amines and divalent cations |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 31.12.97 |
| PATENT REFERENCES CITED |
Finley, Charles, Printing Paper and Inks, Delmar Publishers, Albany (pp. 76-77), 1997. Leach, R.H. and Pierce, R.J., The Printing ink Manual, Blueprint, London (p. 83), 1993. |
| PATENT CLAIMS |
Monomer: CH2=CX-CO2-(CH2)n-CO-CH2-CO-(CH2)n-H; n = 1-10; X = H,Me |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION This invention relates to aqueous ink jet inks and more particularly, to aqueous ink jet inks containing .beta.-diketone or ureido dispersants to improve smudge and smear resistance of the applied ink. Ink jet printing is a non-impact printing process in which droplets of ink are deposited on a substrate such as paper or transparency film in response to an electronic signal. Low cost and high quality of the output, combined with relatively noise free operation, have made ink jet printers a popular option to other types of printers used with computers. Both dyes and pigments have been used as ink colorants for ink jet printers. The dye-based inks while in general superior in color properties have several disadvantages as compared to pigment based inks. The dyes are usually water soluble and remain so after drying on the substrate. They are easily redissolved by water spills, and the image smears on contact with felt pen markers. In addition, the dyes exhibit poor light stability relative to pigments and are known to fade even under office lighting. Thus, dye-based inks are often unsuitable for use in applications requiring moisture resistance and greater light stability. The pigments are preferred colorants provided the pigment dispersion can be made resistant to flocculation and settling. Water-based pigment dispersions are well known in the art, and have been used commercially for applying films, such as paints, to various substrates. The pigment dispersion is generally stabilized by either a non-ionic or ionic technique. When using the non-ionic technique, the pigment particles are stabilized by a polymer that has a water-soluble, hydrophilic section that extends into the water and provides entropic or steric stabilization. Representative polymers useful for this purpose include polyvinyl alcohol, cellulosics, ethylene oxide modified phenols, and ethylene oxide/propylene oxide polymers. While the non-ionic technique is not sensitive to pH changes or ionic contamination, it has a major disadvantage for many applications in that the final product is water sensitive. Thus, if used in ink applications or the like, the pigment will tend to smear upon exposure to moisture, and mechanical action such as handling. "Highlighting" text with a felt-tip pen which contains translucent ink is particularly damaging to the image, since the solvents in the highlighting ink smear the text, and the mechanical action smudges the print. Also, pigmented ink systems tend to have low chroma versus dye-based ink systems, and are prone to poor pen performance due to ink crusting on the pen orifices, coating of the pen resistors, etc. There exists a need for ink jet inks which have good water resistance, smear fastness and good pen performance. In particular, with pigment based inks there is a need to maintain the stability of the dispersion while improving water and smear fastness. SUMMARY OF THE INVENTION Surprisingly and unexpectedly it was found that inks containing .beta.-diketone polymeric dispersants provided images having improved good water resistance and smear fastness. Accordingly, the present invention provides an inkjet ink comprising: (a) an aqueous vehicle; (b) a colorant; and (c) a polymeric dispersant comprising 2 to 50% by weight of monomers selected from the group consisting of .beta.-diketone monomers having structure (I) and ureido monomers having structure (II): ##STR1## where X.dbd.CH.sub.3 or H; n=1-10; m=0 or 1; and R.dbd.H or an organic moiety ##STR2## where X.dbd.CH.sub.3 or H; n=1-10. The inks of the invention are stable, have low viscosity, exhibit excellent print quality, provide excellent smear resistance after drying and good decap or crusting time. They may be used with a variety of ink jet printers such as continuous, piezoelectric, drop-on-demand and thermal or bubble jet drop-on-demand, and are particularly adapted for use in thermal ink jet printers. These inks may also be useful in air brush printing devices. In another embodiment of the invention and ink/media set is provided comprising an ink as set forth above in combination with a media having thereon primary amine groups, secondary amine groups or divalent cations. DETAILED DESCRIPTION OF THE INVENTION The invention provides an ink jet ink composition which is particularly suited for use in thermal inkjet printers. The inks comprise an aqueous vehicle, a colorant and a .beta.-diketone or ureido containing polymeric dispersant, preferably a structured polymeric dispersant. These inks are stable over long periods, both in storage and in the printer. Aqueous Vehicle The aqueous vehicle is water or a mixture of water and at least one water soluble organic solvent. Selection of a suitable mixture depends on the requirements of the specific application, such as desired surface tension and viscosity, the selected colorant, drying time of the ink, and the type of substrate onto which the ink will be printed. Representative water-soluble organic solvents that may be selected are disclosed in U.S. Pat. No. 5,085,698. A mixture of water and a polyhydric alcohol, such as diethylene glycol, is preferred as the aqueous vehicle in which case the aqueous vehicle usually contains from about 30% to about 95% water with the balance (i.e., 70 to 5%) being the water-soluble solvent. Preferably, the aqueous vehicle is 60-95%, by weight, water. The aqueous vehicle comprises 70 to 99.8%, by weight of the total ink composition, depending on the type of colorant selected. Preferably, the aqueous vehicle comprises 94-99.8% when an organic pigment is selected; 70 to 99.8% when an inorganic pigment is selected; and 80 to 99.8% when a dispersed dye is selected. Colorants The colorant is either a disperse dye or a pigment that is insoluble in the aqueous vehicle. By "pigment" we mean a colorant that is insoluble (i.e., in particulate or crystalline form) throughout the printing process. "Dispersed dyes" are colorants that, while insoluble in the aqueous vehicle, become soluble at some point in the printing process. Pigments are the preferred colorants for use in the ink compositions of this invention. Pigments Useful pigments comprise a wide variety of organic and inorganic pigments, alone or in combination. The pigment particles are sufficiently small to permit free flow of the ink through the ink jet printing device, especially at the ejecting nozzles that usually have a diameter ranging from 10 microns to 50 microns. The particle size also has an influence on the pigment dispersion stability, which is critical throughout the life of the ink. Brownian motion of minute particles will help prevent the particles from settling. It is also desirable to use small particles for maximum color strength. The range of useful particle size is approximately 0.005 micron to 15 microns, preferably 0.005 to 5 microns, and most preferably from 0.01 to 0.3 micron. Representative commercial dry and presscake pigments that may be used in practicing the invention are disclosed in U.S. Pat. No. 5,085,698. In the case of organic pigments, the ink may contain up to approximately 30% pigment by weight, but will generally be in the range of approximately 1 to 15%, preferably approximately 1 to 8%, by weight of the total ink composition for most ink jet printing applications. If an inorganic pigment is selected, the ink will tend to contain higher weight percentages of the pigment than with comparable inks employing organic pigment, and may be as high as approximately 50%, because inorganic pigments generally have a higher specific gravity. Disperse Dyes The color and amount of dye present in the ink composition is largely a function of choice, being primarily dependent upon the desired color of the print achieved with the ink, the purity of the dye and its strength. Low concentrations of dye may not give adequate color vividness whereas high concentrations may result in poor printhead performance or unacceptably dark colors. Generally, the disperse dye will be present in the amount of 0.01 to 20%, preferably 0.05 to 8%, and most preferably 1 to 5%, by weight, based on the total weight of the ink composition. Disperse dyes that may be useful in this invention are known to those in the art and are disclosed in U.S. Pat. Nos. 5,053,495; 5,203,912; and 5,102,448; all of which are incorporated herein by reference. Polymeric Dispersant Polymeric dispersants suitable for practicing the invention include random polymers and structured polymeric dispersants such as block copolymers and branched or graft-type polymers. The polymers may be anionic, cationic, or non-ionic in nature. The .beta.-diketone or ureido containing polymeric dispersants comprise 2-50% by weight of .beta.-diketone monomers having structure (I) or a ureido containing monomer of structure (II) ##STR3## wherein X.dbd.CH.sub.3 or H; n=1-10; m=0 or 1; and R.dbd.H or an organic moiety ##STR4## where X.dbd.CH.sub.3 or H; n=1-10. Some suitable .beta.-diketone or ureido-containing polymeric dispersants include acetoacetoxy ethyl methacrylate, 2-(acetoacetoxy)ethyl acrylate, methacrylamido-ethylacetoxy acetate, hexadione methacrylate, 2-(acetoacetoxy) propyl methacrylate, N-(2-methacryloyloxyethyl)ethylene urea, methacrylamido-ethylethylene urea, etc. Additional monomers that may be used in the preparation of the dispersant are hydrophobic and hydrophilic monomers. Some examples of hydrophobic monomers used in polymeric dispersants are methyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, benzyl methacrylate, 2-phenylethyl methacrylate and the corresponding acrylates, styrene, butadiene, and the like. Some examples of hydrophilic monomers are methacrylic acid, acrylic acid, diemthylamionethyl [meth]acrylate, 2-aminomethylpropane sulfonic acid, styrene sulfonic acid, styrene sulfonate, sulfopropyl acrylate, and vinyl phosphonic acid. The amount of the polymer dispersant present in the ink composition depends on the structure, molecular weight and other properties of the polymer, and on the other components of the ink composition. The polymeric dispersants that are selected in practicing the invention have number average molecular weight of below 40,000, preferably below 20,000, and typically in the range of 2,000 to 10,000. Typically, the polymeric dispersant is present in the amount of 0.1 to 25%, preferably 0.1 to 8% by weight, based on the total weight of the ink composition. If the amount is too high, it will be difficult to maintain the desired ink viscosity. Dispersion stability will be adversely affected if insufficient polymer is present. Other Ingredients The ink may contain other ingredients that are commonly used in the art. For example, surfactants may be used to alter surface tension as well as maximize penetration of the ink into the print media. However, surfactants may destabilize the dispersion, so care must be taken in selecting the appropriate surfactant. In addition, the choice of a specific surfactant is highly dependent on the type of media substrate to be printed. In aqueous inks, the surfactants may be present in the amount of 0.01 to 5% and preferably 0.2 to 2%, based on the total weight of the ink. Biocides, such as Dowicides.RTM. (Dow Chemical, Midland, Mich.), Nuosept.RTM. (Huls America, Inc., Piscataway, N.J.), Omidines.RTM. (Olin Corp., Cheshire, Conn.), Nopcocides.RTM. (Henkel Corp., Ambler, Pa.), Troysans.RTM. (Troy Chemical Corp., Newark, N.J.) and sodium benzoate may be used in the ink compositions to inhibit growth of microorganisms. Sequestering agents such as EDTA may also be included to eliminate deleterious effects of heavy metal impurities. Other known additives, such as humectants, viscosity modifiers and the like made also be added to improve various properties of the ink compositions. Ink Preparation and Properties The inks are prepared by premixing the selected colorant(s) and dispersant and then dispersing or deflocculating the mixture. The dispersing step may be accomplished in a horizontal mini mill, a ball mill, an attritor, a roll mill such as a 2 roll or 3 roll mill, or by passing the mixture through a plurality of nozzles within a liquid jet interaction chamber at a liquid pressure of at least 5000 psi to produce a uniform dispersion in the aqueous vehicle. It is generally desirable to make these inkjet inks in concentrated form. The concentrated ink jet inks are subsequently diluted to the appropriate concentration for use in the ink jet printing system. This technique permits preparation of a greater quantity of ink from the equipment. Prior to use, the concentrate is then diluted to the desired concentration with appropriate solvents which contain the water soluble binder additive. By dilution, the ink is adjusted to the desired viscosity, color, hue, saturation density, and print area coverage for the particular application. Jet velocity, separation length of the droplets, drop size, and stream stability are greatly affected by the surface tension and the viscosity of the ink. Inkjet inks suitable for use with ink jet printing systems should have a surface tension in the range of about 20 dyne/cm to about 70 dyne/cm and, more preferably, in the range 30 dyne/cm to about 70 dyne/cm. Acceptable viscosity is no greater than 20 cP, and preferably in the range of about 1.0 cP to about 10.0 cP. The ink has physical properties compatible with a wide range of ejecting conditions, i.e., driving voltage and pulse width for thermal ink jet printing devices, driving frequency of the piezo element for either a drop-on-demand device or a continuous device, and the shape and size of the nozzle. They may be used with a variety of ink jet printers such as continuous, piezoelectric drop-on-demand and thermal or bubble jet drop-on-demand, and are particularly adapted for use in thermal ink jet printers. The inks have excellent storage stability for a long period and do not clog in an ink jet apparatus. Fixing the ink on the image recording material, such as, paper, fabric, film, etc., can be carried out rapidly and accurately. The printed ink images have clear color tones, high density, excellent water resistance and lightfastness. Furthermore, the ink does not corrode parts of the inkjet printing device it comes in contact with. MEDIA The media (i.e., the ink jet recording sheet) that is particularly useful with these inks has thereon primary amine groups, secondary amine groups or metal cations. These groups may be part of the recording sheet itself or preferably may be present in a coating on the substrate or recording sheet. Some useful substrates include papers such as Gilbert.RTM. bond paper (Mead Corporation, Menasha, Wis.), Champion DataCopy.RTM. (Champion International Corp., Stamford, Conn.), Hammermill Fore.RTM. DP (Hammermill Papers, Erie, Pa.), Weyerhaeuser First Choice.RTM. (Weyerhaeuser Co., Takoma Wash.), transparent films such as polyester, polyethylene, polypropylene, polyamides, etc.; and fabrics or textiles made of cotton, wool, NYLON.RTM., etc. Some useful coatings on the media are selected from the group consisting of aminomethyl propanol, aminoethyl propanol, diethylaminoethanol, diethanol amine, amino ended polyethylene oxide, amino ended polyethylene oxide and mixtures thereof. Particularly preferred as these coatings are the Jeffamine.RTM. brand of polyoxyalkylamines which are commercially available from Texaco Chemical Co. Athens, N.Y. Most preferred are Jeffamine.RTM. T403, T3000, T5000, M-600, M-715, M-1000, M-2005, M-2070, D-230, D-400, D-2000, D-4000, ED-600, ED-900, ED-2001, ED-4000, 6000, EDR-148, EDR-192, and C-346. |
| PATENT EXAMPLES | This data is not available for free |
| PATENT PHOTOCOPY | Available on request |
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