The present invention relates to ink-jet inks employed in ink-jet printing. In particular, this invention relates to an ink system that utilizes the addition of specific polymers to the pigment-based ink. These polymers reduce, and in some cases even eliminate, color bleed and halo problems typically associated with ink-jet printing.
Ink-jet printers offer a low cost, high quality, and comparatively noise-free option to other types of printers commonly used with computers. Such printers employ a resistor element in a chamber provided with an egress for ink to enter from a plenum. The plenum is connected to a reservoir for storing the ink. A plurality of such resistor elements are arranged in a particular pattern, called a primitive, in a printhead. Each resistor element is associated with a nozzle in a nozzle plate, through which ink is expelled toward a print medium. The entire assembly of printhead and reservoir comprise an ink-jet pen.
In operation, each resistor element is connected via a conductive trace to a microprocessor, where current-carrying signals cause one or more selected elements to heat up. The heating creates a bubble of ink in the chamber, which expels ink through the nozzle toward the print medium. In this way, firing of a plurality of such resistor elements in a particular order in a given primitive forms alphanumeric characters, performs area-fill, and provides other print capabilities on the medium.
Many ink-jet inks, when printed in various colors on bond paper, copier paper, and other media, can lead to bleed and halo. Bleed and halo occur as colors mix both on the surface of the paper being printed on and in the paper. The terms “bleed” and “halo”, as used herein, are defined as follows: When inks of two different colors are printed next to each other, it is desired that the border between the two colors be clean and free from the invasion of one color into the other. When one color does invade into the other, the border between the two colors becomes ragged, and this is called bleed. This is in contradistinction to uses of the term “bleed” in the prior art, which often defines “bleed” in the context of ink of a single color following the fibers of the paper. When dye-based inks are printed adjacent to pigment- based inks, the dye-based ink may invade the pigmented ink causing a whitish edge to form in the pigmented ink. This is known as halo, and is most often observed when dye-based color inks are printed adjacent to pigment-based black inks.
Prior solutions to bleed have largely involved the use of heated platens or other heat sources and/or special paper. Heated platens add cost to the printer. Special paper limits the user to a single paper, which is of a higher cost than a plain paper. Another way to reduce bleed involves increasing the penetration rate of the ink into the paper. However, increasing the penetration rate reduces the edge acuity (lowers the print quality of the ink). Nevertheless, this method is acceptable for printing color ink because of the lesser importance of color text quality. However, print quality is important for black ink. And hence, alternate bleed control mechanisms are needed.
U.S. Pat. No. 5,428,383 teaches a method to control bleed in multicolor ink-jet printing involving the use of multi-valent metal salts as precipitation agents in a first ink composition. The precipitation agent is designed to react with the coloring agent in a second ink composition.
A solution to the specific problem of black to yellow color bleed is disclosed in U.S. Pat. No. 5,198,023 wherein multivalent cations such as calcium chloride and magnesium chloride are added at concentrations ranging from about 1 to about 10 wt % to yellow cationic inks to prevent bleed between yellow and black inks. However, it has been determined that the addition of large amounts of multivalent cations to thermal ink-jet ink compositions may induce precipitation of dye salts, requiring further adjustments in the ink composition. U.S. Pat. No. 5,518,534 teaches the use of a first ink having a pigment dispersion and the second ink containing a salt of an organic acid or mineral acid wherein said salt reacts with said first ink to alleviate bleed between the inks. However, in this case, the pigment requires the presence of a dispersing agent, and both inks must have the same ionic character.
A method to control bleed is also disclosed by U.S. Pat. No. 5,730,790. The ink-jet ink is formulated to comprise at least one dye-based ink composition and at least one pigment-based ink. The dye-base ink also contains a cationic surfactant, and the pigment-base ink contains a negatively charged dispersant.
Another method of reducing bleed between ink-jet inks involves the use of pH-sensitive dyes as disclosed in U.S. Pat. No. 5,181,045. It discloses an ink having a pH- sensitive dye to prevent bleeding to an adjacent ink having an appropriate pH. Migration of the ink having the pH-sensitive dye is prevented by rendering the dye insoluble on the page by contact with the pH of the adjacent ink. This method requires a pH differential of about 4 or 5 units to completely control bleed. Accordingly, a pH not exceeding 4 would be required to effectively eliminate bleed from a pH-sensitive ink having a typical pH of about 8.
U.S. Patent 5,679,143 builds upon the '045 case referenced above, but an organic acid component is added to the so-called target ink-jet ink composition, as opposed to the pH-sensitive ink composition. The organic acid component reduces the pH differential required to control bleed to about 3 units or less.
While each of the above has produced varying degrees of success, a need still remains for ink compositions for use in ink-jet printing which do not evidence bleed or halo, as defined herein, when printed on plain papers, and yet which posses relatively long shelf life and other desirable properties of such inks.
DISCLOSURE OF INVENTION
In accordance with the invention, an ink set is provided in which certain pigment-based inks, especially inks comprising self-dispersing pigments, contain polymers which become insoluble under either specific and well defined pH conditions or when contacted with incompatible ionic substances. By forcing the polymers present to become insoluble on the page, migration of the colorant is inhibited, thereby helping to reduce bleed and halo between different colors. Rendering the polymers insoluble is achieved by making the polymer come out of solution or to precipitate; this is done by contacting the polymer with another ink having an appropriate pH or one which contains ions that are incompatible with the polymers, or both.
BEST MODES FOR CARRYING OUT THE INVENTION
While it is known that certain colorant classes, including dyes and dispersed pigments, become insoluble under specific and well defined pH conditions or in the presence of incompatible ions, the use of specific polymers found to precipitate under certain pH conditions and in the presence of certain ions allows the use of a broader class of pigments, particularly self-dispersing pigments, which have not been previously associated with good bleed control. Use of these specific polymers also allows formulation flexibility because these polymers do not contribute to the dispersion or water-solubility of the colorants, so new classes of polymers can be utilized for bleed control without concern of their ability to disperse. For example, traditional water based pigment inks consists of a pigment material that is essentially insoluble. These pigments were rendered effectively soluble through the use of a dispersant, usually having a hydrophobic portion and a hydrophilic portion. By utilizing self-dispersing pigments, the polymers of this invention can be designed to be pH and ion/or sensitive yet have little dispersing ability.
Polymers that have acidic groups, such as carboxylate groups, are pH sensitive. These carboxylated, or otherwise acidified, polymers will either be in solution or precipitate based on their pH-dependant solubility. As the pH is lowered and the carboxylate groups become protonated, the solubility of the polymer decreases. At some point, the polymer will begin to become unstable and will effectively drop out of solution. Typical polymers for use herein include those having at least one and preferably multiple carboxyl groups, which commonly consist of acrylic monomers and polymers known in the art. Hydrophobic moieties are also required to aid in the precipitation of the polymer and induce flocculation of the pigment in an aqueous based ink. When the polymer carries a net anionic charge, the pigment must also carry a net anionic or nonionic charge.
Without subscribing to any particular theory, the Applicants believe that by forcing a polymer contained in an ink to become insoluble on the page, then migration of the colorant in the ink will be inhibited, thereby helping to reduce bleed between the inks. The “force” used to make the polymer come out of solution or to precipitate is to contact the polymer containing ink with another ink having an appropriate pH or containing incompatible ions.
The polymers of this invention can be random or block copolymers. The polymers are selected to precipitate with a change of pH or in the presence of certain ions or both. In general, polymers which precipitate with a change from higher to lower pH will comprise monomers containing an acidic group and a hydrophobic group; polymers which precipitate with a change from lower to high pH will comprise monomers containing amine functionality and hydrophobic moieties. The structure for the polymers of this invention is:
wherein R1 are independently selected from H or a C1-C18 substituted or unsubstituted, branched or unbranched, alkyl, aromatic, or cyclic chain and may contain halogen, ester, ether, amine or amide functionalities, and is preferably H, CH3, a halogen or a halogenated methyl group; and R2 is a group containing either a carboxylic acid group having a pKa of from about 5 to about 7.5, or a primary, secondary, or tertiary amine functionality. R3 is a C1-C18 substituted or unsubstituted, branched or unbranched, alkyl, aromatic, or cyclic chain, which may contain ester, ether, amine or amide functionalities. Examples of monomers of type X that contain carboxylic acids that are useful in the invention include, but are not limited to; acrylic acid, methacrylic acid, crontonic acid, 2-trifluoromethylacrylic acid and 2-bromoacrylic acid. Typically, polymers containing acidic R2 monomers will be present in the ink as acid salts of Na, K, Li, triethanolamine, 2-amino-2-methyl-1propanol and the like. Examples of monomers of type X that contain primary, secondary, and tertiary amines that are useful in the invention include, but are not limited to; 2-(diethylamino)ethyl acrylate, 2-(dimethylamino)ethyl acrylate, 3-(dimethylamino)propyl acrylate, butylaminoethyl methacrylate, 2-aminoethyl methacrylate and N-[3-(dimethylamino)propyl]acrylamide. Typically, polymers containing primary secondary, and/or tertiary amine R2 monomers alone will be present in the ink as salts of Cl, Br, I, sulfate, nitrate, and the like. Hydrophobic monomers of type Y that are useful in the invention include, but are not limited to; methyl and ethyl esters of acrylic and methacrylic acids, ethyl-2-(bromomethyl) acrylate, propyl acrylates and methacrylates, butyl a acrylates and methacrylates, isoamyl acrylate, hexyl acrylates and methacrylates, cyclohexyl acrylates and methacrylates and their alkyl derivatives, ethylhexyl acrylates and methacrylates, trimethylhexyl acrylate, isooctyl acrylate, isodecyl acrylate, dodecyl acrylate, tridecyl methacrylate, octadecyl acrylate, isobomyl acrylate and methacrylate, phenyl methacrylate, benzyl methacrylate, 2-butoxyethyl acrylate and methacrylate, 2-ethoxyethyl acrylate, neopentyl glycol acrylate benzoate, ethylene glycol phenyl ether acrylate, hydroxybutyl acrylate, alkyl esters of crotonic acid, N,N-dimethylacrylamide, N-isopropylacrylamide and methacrylamide, N-octylacrylamide, N-(butoxymethyl)acrylamide, N-(isobutoxymethyl)acrylamide, methyl-2-acrylamido-2-methoxyacetate, vinyl acetate, vinyl neodecanoate, cyclohexyl vinyl ether, 2-ethylhexyl vinyl ether and styrene. Polymers of this invention may contain more than one X-type or Y-type monomer.
The average molecular weight of the polymers of this invention ranges from about 1,000 to about 20,000, preferably from about 1,000 to about 12,000; more preferably from about 3,000 to about 10,000. The above monomers are provided in sufficient amounts to provide a polymer that will be stable when solubilized in water yet will effectively precipitate and flocculate the pigment upon the change in pH or contact with the appropriate ions. Thus, polymers may be selected which comprise other monomers as long as an effective amount of the above monomers comprise part of the polymer chain. Polymers of this invention may contain monomers of more than one X-type, Y-type, or both, in addition to other monomers chosen by the formulator.
In a preferred embodiment, R2
is a carboxylic acid moiety, thus having the structure:
wherein R1 are independently selected from H or a C1-C18 substituted or unsubstituted, branched or unbranched, alkyl, aromatic, or cyclic chain and may contain ester, ether, amine or amide functionalities, and is preferably H, CH3, a halogen or a halogenated methyl group; and n is from 0 to 15, preferably 0 to about 3, so as long as the group has pKa of from about 5 to about 7.5. R3 is a C1-C18, substituted or unsubstituted, branched or unbranched, alkyl, aromatic, or cyclic chain, which may contain ester, ether, amine or amide functionalities.
The acidity, measured by the acid number, of these polymers are in the range of 55-400 mg KOH/g of polymer; preferably from 80-350 mg KOH/g of polymer; more preferably from 80-200 mg KOH/g of polymer. When the polymers have X-type monomers without acidic groups and the R2 groups contain primary, secondary, and/or tertiary amine functionality, the amount of basic nitrogen in the polymer, measured as the meq of basic nitrogen per gram, ranges from between about 1 to about 7 meq/g, preferably about 1.5 to about 6.2 meq/g and even more preferably between about 1.5 to about 3.5 meq/g.
The following examples of polymers that are useful in this invention are not intended to limit the scope of the invention. Monomer ratios are given in weight percent. Molecular weights conform to the ranges given above. Examples; a) 8:92 acrylic acid:butyl acrylate, acid number 62 mg KOH/g; b) 10:90 methacrylic acid:butyl acrylate, acid number 65 mg KOH/g; c) 12:88 acrylic acid:ethyl acrylate, acid number 93 mg KOH/g; d) 14:86 methacrylic acid:ethyl acrylate, acid number 91mg KOH/g; e) 16:60:24 acrylic acid:methyl methacrylate:hexyl acrylate, acid number 125 mg KOH/g; f) 16:5:15:64 acrylic acid:butylaminoethyl methacrylate:octylacrylamide:methylmethacrylate, acid number 125 mg KOH/g; g) 19:40:41 methacrylic acid:ethyl acrylate:methyl methacrylate, acid number 124 mg KOH/g; h) 30:30:30 methacrylic acid:methyl methacrylate:benzyl methacrylate, acid number 195 mg KOH/g; and i) 44:56 acrylic acid:ethyl acrylate, acid number 325 mg KOH/g. Other combinations could also be made. Some modifications could be made by those skilled in the art and still be within the spirit of the invention.
The use of pH sensitive polymers should not be confused with the use of pH changes on paper, which lead to improved waterfastness. First, waterfastness issues involve the ability of the ink to resist smearing when water is dripped across a printed line of ink, while bleed resistance is the ability of the ink to resist mixing of one color with another when both are printed in close succession. Having solved one problem does not imply a solution to the other.
Solving waterfastness in other systems has involved the use of a single ink. This is in contrast to the present invention in which a second ink is used to bring about the desired effect, i.e., reduction of bleed and halo.
In addition, the present invention involves what is essentially a border effect, i.e., the drastic pH conditions of the two inks in question or the presence of incompatible ions in one of the inks bring about the desired effect at the border of the two inks. This differs with the mode in which other dye-based inks achieve waterfastness, i.e., an entire dot of black ink is subjected to paper which lowers the pH slightly and brings about insolubility (and thus waterfastness); see, e.g., U.S. Pat. No. 4,963,189.
Finally, it should be mentioned that using a second ink with a pH of, for example, 4 will have a much greater effect on the solubility of the pH-sensitive polymer than will any pH change caused by the paper. Paper-induced pH changes in the ink are small compared to contact with a fluid that is buffered at a pH of 4. Thus, while it is thought that the pH of the paper itself contributes to an improvement of waterfastness, in the present application, a second ink, having a pH low enough to bring about insolubility of polymers in the first ink or the presence of specific polymer-incompatible ions, is used to bring about the desired effect, i.e., bleed and halo reduction.
The method of the invention eliminates the requirement of a heater or heated platen in order to reduce bleed and halo from an ink of one color into an ink of another color, and the need for special paper to control bleed and halo between inks that otherwise would bleed or show signs of halo on plain types of paper.
While the specific example given is directed to the use of an ink having a lower pH than the first ink, it is also possible to employ an ink having a higher pH than the initial ink. In this case, the pH-sensitive ink would have the property that it precipitates as the pH is increased. For example, if the polymer is soluble at a low pH by carrying a positive charge through protonation of an amine group on the polymer, it is possible to precipitate the polymer by contacting it with a second ink that is buffered at a high pH causing deprotonation of the polymer. This system would work in conjunction with pigments that are either dispersed by nonionic or with a cationic charged moieties or with self-dispersing pigments that have been modified to carry a net positive charge.
The effect on bleed may be seen at a pH difference of about 1 to 3 units. Further and near complete control of bleed results when the pH difference is further increased, to about 4 to 5 units. However, these values do not preclude the use of a polymer which is more sensitive to pH than those disclosed herein; with more sensitive pH-polymers, near complete control of bleed could result with only a small difference in pH, considerably less than 4 units.
In one embodiment herein, the polymers of this invention interact with incompatible multi-valent (inorganic or organic) salts in the second ink. These salts must be soluble in the ink in the concentration employed. Suitably-employed cations for the multi-valent salt include alkaline earth metals of group 2A of the periodic table (e.g., magnesium and calcium); the transition metals of group 3B of the periodic table (e.g., lanthanum); cations from group 3A of the periodic table (e.g., aluminum); and lanthanides (e.g., neodymium). Preferably, calcium and magnesium are employed as cations in the practice of this invention. Suitably employed anions associated with calcium or magnesium include nitrate, chloride, acetate, benzoate, formate, and thiocynate. Salts preferably employed in this invention are nitrate, chloride, and acetate salts of calcium and magnesium. If used, the salt should be present in the second ink in an amount ranging from about 1% to about 10%, preferably from about 1.5% to about 7%, more preferably from about 2% to about 6% by weight of the ink.
Examples of organic acids which may be included in the second ink to aid in the pH and buffering capabilities of the second ink include, but are not limited to, mono-, di-, and polyfunctional organic acids. In general, it is contemplated that any soluble organic acid having a pKa equal to or less than that of the pH-sensitive polymer of concern may be suitably employed. Preferably, one of the following classes of organic acids is employed: polyacrylic, acetic, glycolic, malonic, malic, maleic, ascorbic, succinic, glutaric, fumaric, citric, tartaric, lactic, sulfonic, and ortho-phosphoric acid, derivatives thereof, and mixtures thereof. If used, the organic acid should be present in the second ink in an amount ranging from about 1% to about 10%, preferably from about 2% to about 7%, more preferably from about 3% to about 6% by weight of the ink.
In one approach, the pigment employed in the ink is a self-dispersing pigment. Such pigments suitable for use herein include all chemically modified water-dispersible, pigments known for use in ink-jet printing. These chemical modifications impart water-dispersiblity to the pigment precursors that encompass all organic pigments.
For self-dispersibility or water solubility, the pigments herein are modified by the addition of one or more organic groups comprising at least one aromatic group or a C1-C12 alkyl group and at least one ionic group or ionizable group. The ionizable group is one that forms its ionic groups in the aqueous medium. The ionic group may be anionic or cationic. The aromatic groups may be further substituted or unsubstituted. Examples include phenyl or napthyl groups and the ionic group is sulfonic acid, sulfinic acid, phosphonic acid, carboxylic acid, ammonium, quaternary ammonium, or phosphonium group.
Depending on the process selected, the pigment can either be anionic or cationic in character. As commercially available, the anionic chromophores are usually associated with sodium or potassium cations, and the cation chromophores are usually associated with chloride or sulfate anions.
For modification, one preferred method is treatment of the carbon black pigment with aryl diazonium salts containing at least one acidic functional group. Examples of aryl diazonium salts include those prepared from sulfanilic acid, 4-aminobenzoic acid, 4-aminosalicylic acid, 7-amino-4-hydroxy-2-naphthlenesulfonic acid, aminophenylboronic acid, aminophenylphosphonic acid and metanilic acid.
Ammonium, quaternary ammonium groups, quaternary phosphonium groups, and protonated amine groups represent examples of cationic groups that can be attached to the same organic groups discussed above.
See U.S. Pat. Nos. 5,707,432; 5,630,868; 5,571,311; and 5,554,739 for a discussion of modified carbon black pigments and methods of attaching the functionalized groups.
The following pigments are useful in the practice of this invention; however, this listing is not intended to limit the invention. The following pigments are available from Cabot: Monarch® 1400, Monarch® 1300, Monarch® 1100, Monarch® 1000, Monarch® 900, Monarch® 880, Monarch® 800, and Monarch® 700, Cab-O-Jet® 200 and Cab-O-Jet® 300. The following pigments are available from Columbian: Raven 7000, Raven 5750, Raven 5250, Raven 5000, and Raven 3500. The following pigments are available from Degussa: Color Black FW 200, Color Black FW 2, Color Black FW 2V, Color Black FW 1, Color Black FW 18, Color Black S 160, Color Black FW S 170, Special Black 6, Special Black 5, Special Black 4A, Special Black 4, Printex U, Printex 140U, Printex V, and Printex 140V. Tipure® R-101 is available from DuPont.
All concentrations herein are in weight percent, unless otherwise indicated. The purity of all components is that employed in normal commercial practice for ink-jet inks. All references are hereby incorporated by reference.
Ink-jet Ink Vehicle—The ink compositions of this invention comprise the colorants, a bleed and halo controlling polymer(s), and the ink vehicle. For a discussion of inks and their properties, see The Printing Manual, 5th ed. Leach et al. (Chapman and Hall, 1993). See also U.S, Pat. Nos. 2,833,736; 3,607,813; 4,104,061; 4,770,706; and 5,026,755.
A typical formulation for an ink useful in the practice of the invention includes the colorant (about 0.001% to 10 wt%), one or more cosolvents (0.01 to about 50 wt%), one or more water-soluble surfactants/amphiphiles (0 to about 40, preferably about 0.1 to about 5 wt %), one or more high molecular weight colloids (0 to about 3 wt %), and water (balance). Of course, one or more of the inks in the ink-set will contain the bleed and halo controlling polymer(s), present in a amount of from about 0.1 to about 10 % by wt of the ink composition, preferably from 0.1 to about 3%.
One or more cosolvents may be added to the vehicle in the formulation of the ink. Classes of cosolvents employed in the practice of this invention include, but are not limited to, aliphatic alcohols, aromatic alcohols, diols, glycol ethers, poly(glycol) ethers, caprolactams, lactones, formamides, acetamides, and long chain alcohols. Examples of compounds employed in the practice of this invention include, but are not limited to, primary aliphatic alcohols of 30 carbons or less, primary aromatic alcohols of 30 carbons or less, secondary aliphatic alcohols of 30 carbons or less, secondary aromatic alcohols of 30 carbons or less, 1,2-alcohols of 30 carbons or less, 1,3-alcohols of 30 carbons or less, 1,5-alcohols of 30 carbons or less, ethylene glycol alkyl ethers, propylene glycol alkyl ethers, poly(ethylene glycol) alkyl ethers, higher homologues of poly(ethylene glycol) alkyl ethers, poly(propylene glycol) alkyl ethers, higher homologues of poly(propylene glycol) alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, substituted formamides, unsubstituted formamides, substituted acetamides, and unsubstituted acetamides. Specific examples of cosolvents that are preferably employed in the practice of this invention include, but are not limited to, 1,5-pentanediol, 2-pyrrolidone, 2-ethyl-2-hydroxymethyl-1,3-propanediol, diethylene glycol, 3-methoxybutanol, and 1,3-dimethyl-2-imidazolidinone. The cosolvent concentration may range from about 0.01 to about 50 wt %, with about 0.1 to 20 wt % being preferred.
Water-soluble surfactants may be employed in the formulation of the vehicle of the ink. These surfactants are added as free components to the ink formulation and are not otherwise associated or intended to become part of the polymers described herein. For convenience, examples of surfactants are divided into two categories: (1) non-ionic and amphoteric and (2) ionic. The former class includes: TERGITOLs, which are alkyl polyethylene oxides available from Union Carbide; TRITONs, which are alkyl phenyl polyethylene oxide surfactants available from Rohm & Haas Co.; BRIJs; PLURONICs (polyethylene oxide block copolymers); and SURFYNOLs (acetylenic polyethylene oxides available from Air Products); POE (polyethylene oxide) esters; POE diesters; POE amines; POE amides; and dimethicone copolyols. Amphoteric surfactants such as substituted amine oxides are useful in the practice of this invention. Cationic surfactants such as protonated POE amines may also be used. U.S. Pat. No. 5,106,416, discloses more fully most of the surfactants listed above. The non-ionic amphiphiles/surfactants are more preferred than the ionic surfactants. Specific examples of amphiphiles/surfactants that are preferably employed in the practice of this invention include iso-hexadecyl ethylene oxide 20, SURFYNOL CT-111, TERGITOL 15-S-7, and amine oxides, such as N,N-dimethyl-N-dodecyl amine oxide, N,N-dimethyl-N-tetradecyl amine oxide, N,N-dimethyl-N-hexadecyl amine oxide, N,N-dimethyl-N-octadecyl amine oxide, N,N-dimethyl-N-(Z-9-octadecenyl)-N-amine oxide. The concentration of the amphiphile/surfactants may range from 0 to 40 wt %, preferably from about 0.1% to 3 wt %.
To further improve optical density, between 0 and about 3 wt % of a high molecular weight colloid derived from natural or synthetic sources may optionally be added to the ink formulation. Addition of a high molecular weight colloid improves print quality. Example of high molecular weight colloids employed in the practice of this invention include alginates, mannuronic acid, carageenan, guar gum, xanthan gum, dextran, chitin, chitosan, carboxymethylcellulose, nitromethylcellulose, and all derivatives thereof. These colloids are disclosed in U.S. Pat. No. 5,133,803, “High Molecular Weight Colloids for Bleed Control.” The preferred concentration of the high molecular weight component colloid in the inks of this invention is from about 0.1% to about 0.75 wt %.
Consistent with the requirements for this invention, various types of additives may be employed in the ink to optimize the properties of the ink composition for specific applications. For example, as is well-known to those skilled in the art, biocides may be used in the ink composition to inhibit growth of microorganisms. Preferred examples of biocides include Urarcide™ and Proxel™, and NuoCept™. Sequestering agents such as EDTA may be included to eliminate deleterious effects of heavy metal impurities, and buffer solutions may be used to control the pH of the ink. Other known additives such as viscosity modifiers and other acrylic or non-acrylic polymers may be added to improve various properties of the ink compositions as desired.
The inks are formulated by combining the various components of the vehicle and mixing them with the colorants and polymers disclosed herein. The viscosity of the final ink composition is from about 0.8 to about 8 cPs, preferably from about 0.9 to about 4 cPs.
A method of ink-jet printing is also disclosed herein. The inks of this invention may be used in any conventional ink-jet or bubble-jet or piezoelectric printer. Preferably the inks are used in thermal ink-jet printers. The ink is typically charged into a printer cartridge and printed on any medium. Examples of suitable media for printing includes paper, textiles, 10 wood, and plastic.