Ink Compositions for Thermal Ink Jet Printing

The present invention is directed to ink compositions and to processes for the preparation and use thereof. More specifically, the present invention is directed to compositions suitable for use in ink jet printing processes. One embodiment of the present invention is directed to an ink composition which comprises water, a dye selected from the group consisting of Direct Blue 199, Direct Yellow 132, Acid Yellow 17, Reactive Red 180, Acid Red 52, and mixtures thereof, and a material of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20, wherein the ink is substantially free of imidazole.

Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.

Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.

The other type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.

The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.

U.S. Pat. No. 5,019,166 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses a thermal ink jet printing composition comprising a dye, a liquid medium, and a surfactant selected from the group consisting of polyoxyalkylated ethers, anionic bitail fluorothio alkyls, alkyl aryl sulfonates, alkyl amine quaternary salts, and mixtures thereof. Also disclosed is a process for generating images which comprises causing the ink compositions disclosed herein to be ejected from a thermal ink jet printer in imagewise fashion onto a substrate.

U.S. Pat. No. 5,401,303 (Stoffel et al.), the disclosure of which is totally incorporated herein by reference, discloses a process wherein the halo effect seen at the interface between a first ink, exhibiting sharp edge acuity, and a second ink, having low surface energy, is addressed by adding certain fluorocarbon compounds to the first ink. Edge acuity of the first ink is maintained.

U.S. Pat. No. 5,540,765 (Gundlach et al.), the disclosure of which is totally incorporated herein by reference, discloses a thermal ink jet printing composition which contains a surfactant comprising an alkylsulfoxide having an alkyl group of 4 to 6 carbon atoms. Preferably, the composition contains a betaine zwitterionic base and dibutylsulfoxide.

U.S. Pat. No. 5,531,815 (Gundlach et al.), the disclosure of which is totally incorporated herein by reference, discloses a thermal ink jet printing composition contains a betaine zwitterionic base and a quasisurfactant penetrant.

U.S. Pat. No. 5,389,133 (Gundlach et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for preparing an aqueous ink composition which comprises adjusting the pH of the ink with phosphorous acid or phosphite salts. Also disclosed are ink compositions prepared by this process. In certain preferred embodiments, the ink compositions can also contain betaine, sulfolone, dimethyl sulfoxide, or N,N'-bis(3-aminopropyl)-1,2-ethylenediamine, as well as mixtures thereof. In other preferred embodiments, the ink composition comprises an organic component selected from the group consisting of sulfolane, dimethyl sulfoxide, and mixtures thereof, and anions selected from the group consisting of phosphite, hypophosphite, phosphate, polyphosphate, sulfate, hexafluorophosphate, glycolate, acetate, ethylenediaminetetroacetate, formate, borate, sulfite, sulfamate, and mixtures thereof.

Copending application U.S. Ser. No. 08/961,335, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach, Richard L. Colt, and Edward J. Radigan, Jr., the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, a colorant, betaine, a tertiary amine, and a material of the formula ›(F.sub.2n+1 C.sub.n CH.sub.2 S).sub.2 (CH.sub.3)C--CH.sub.2 CH.sub.2 COO.sup.- !›B.sup.+ !, wherein n is an integer of from about 8 to about 20 and B is a cation. In one specific embodiment, n is 10 and B is (HO--CH.sub.2 CH.sub.2).sub.2 NH.sub.3 +. In another specific embodiment, the tertiary amine is 1-methylimidazole. In yet another specific embodiment of the present invention, the colorant is an anionic dye with carboxylate groups, sulfonate groups, or both carboxylate and sulfonate groups. Also disclosed is a process for preparing the aforementioned ink composition wherein a liquid containing the material of the formula ›(F.sub.2n+1 C.sub.n CH.sub.2 S).sub.2 (CH.sub.3)C--CH.sub.2 CH.sub.2 COO.sup.- !›B.sup.+ ! is subjected to centrifugation. Also disclosed are ink jet printing processes employing the aforementioned ink.

Copending application U.S. Ser. No. 08/961,435, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach, Luis A. Sanchez, Cheryl A. Hanzlik, Kathy-Jo Brodsky, Richard L. Colt, Aileen M. Montes, and Edward J. Radigan, Jr., the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises (a) water, (b) a colorant, (c) a fluorinated material selected from: (1) those of the formula ›(F.sub.2n+1 C.sub.n CH.sub.2 S).sub.2 (CH.sub.3)C--CH.sub.2 CH.sub.2 COO.sup.- !›B.sup.+ !, wherein n is an integer of from about 8 to about 20 and B is a cation, (2) those of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20, and (3) mixtures thereof, and (d) a monomeric compound having at least two carboxylic acid functional groups. Also disclosed is a process for preparing said ink composition which comprises (i) admixing the ink ingredients, and (ii) subjecting the mixture thus formed to ultrasonification, thereby reducing the average particle diameter of liposomes of the fluorinated material in the ink. Further disclosed is a process which entails (i) incorporating into an ink jet printing apparatus the aforementioned ink composition, and (ii) causing droplets of the ink composition to be ejected in an imagewise pattern onto a substrate. In a preferred embodiment, the printing apparatus employs a thermal ink jet process wherein the ink in the nozzles is selectively heated in an imagewise pattern, thereby causing droplets of the ink to be ejected in imagewise pattern.

Copending application U.S. Ser. No. 08/961,118, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach, Luis A. Sanchez, Cheryl A. Hanzlik, Kathy-Jo Brodsky, Richard L. Colt, Aileen M. Montes, Danielle Avolio, and Rachael L. McGrath, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises (a) water, (b) a colorant, and (c) a material of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20. Also disclosed are processes for preparing the ink composition and ink jet printing processes with the ink composition.

Copending application U.S. Ser. No. 08/961,461, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach and Walter F. Wafler, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, a colorant, a nonionic surfactant, and a fluorinated material selected from the group consisting of (a) those of the formula ›(F.sub.2n+1 C.sub.n CH.sub.2 S).sub.2 (CH.sub.3)C--CH.sub.2 CH.sub.2 COO.sup.- !›B.sup.+ !, wherein n is an integer of from about 8 to about 20 and B is a cation, and (b) those of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation. Also disclosed are ink jet printing processes employing the aforementioned ink.

Copending application U.S. Ser. No. 08/961,637, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach, Luis A. Sanchez, Cheryl A. Hanzlik, Kathy-Jo Brodsky, Richard L. Colt, and Aileen M. Montes, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, an anionic dye having at least one anionic functional group and having a cationic counterion associated with each anionic functional group, and a material of the formula ›(F.sub.2n+1 C.sub.n CH.sub.2 S).sub.2 (CH.sub.3)C--CH.sub.2 CH.sub.2 COO.sup.- !›B.sup.+ !, wherein n is an integer of from about 8 to about 20 and B is a cation, said ink composition containing alkali metal cations in an amount of no more than about 1.times.10.sup.-3 moles per liter. Also disclosed are ink jet printing processes employing the aforementioned ink.

Copending application U.S. Ser. No. 08/961,173, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach, Luis A. Sanchez, Richard L. Colt, and Rachael L. McGrath, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, a colorant, a bisquaternary ammonium compound, and a material of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20. Also disclosed are ink jet printing processes employing the aforementioned ink.

Copending application U.S. Ser. No. 08/961,393, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach, Richard L. Colt, Luis A. Sanchez, and Danielle Avolio, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, a colorant, 1,4-diazabicyclo(2.2.2)octane, and a fluorinated material selected from the group consisting of (a) those of the formula ›(F.sub.2n+1 C.sub.n CH.sub.2 S).sub.2 (CH.sub.3)C--CH.sub.2 CH.sub.2 COO.sup.- !›B.sup.+ !, wherein n is an integer of from about 8 to about 20 and B is a cation, and (b) those of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20. Also disclosed are processes for preparing the aforementioned ink and ink jet printing processes employing the aforementioned ink.

Copending application U.S. Ser. No. 08/960,792, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach, Luis A. Sanchez, Richard L. Colt, and Danielle Avolio, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises (a) water, (b) a colorant selected from the group consisting of Acid Yellow 23, Acid Yellow 17, Reactive Red 180, Direct Blue 199, Acid Blue 9, and mixtures thereof, (c) imidazole, (d) an additive selected from the group consisting of betaine, polyethylene oxide, and mixtures thereof, and (e) a material of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20. Also disclosed are ink jet printing processes employing the aforementioned ink.

Copending application U.S. Ser. No. 08/961,334, filed concurrently herewith, entitled "Improved Ink Compositions for Thermal Ink Jet Printing," with the named inventors Kurt B. Gundlach, Luis A. Sanchez, Danielle Avolio, Maura A. Sweeney, and Richard L. Colt, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises (1) water, (2) a colorant, (3) a material of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20, (4) a polymer selected from the group consisting of (a) tetrafunctional block copolymers derived from the addition of propylene oxide and ethylene oxide to ethylenediamine; (b) polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymers; (c) polypropylene oxide-polyethylene oxide-polypropylene oxide triblock copolymers; (d) ethoxylated 2-naphthol polymers; and (e) mixtures thereof; and (5) an additive selected from the group consisting of (i) diethylene glycol; (ii) glycerol; (iii) trimethylol propane; (iv) urea; (v) n-methyl pyrrolidone; (vi) sulfolane; (vii) 1,4 diazabicyclo(2.2.2)octane; (viii) cyclohexylpyrrolidone; and (ix) mixtures thereof. Also disclosed are ink jet printing processes employing the aforementioned ink.

While known compositions and processes are suitable for their intended purposes, a need remains for ink compositions with improved characteristics. In addition, a need remains for ink compositions which exhibit reduced or no intercolor bleed when printed adjacent to other inks of different colors. Further, a need remains for ink compositions which exhibit good shelf stability. Additionally, a need remains for ink compositions having improved colorimetry. There is also a need for ink compositions which exhibit reduced intercolor bleed in combination with improved shelf stability and improved colorimetry. In addition, there is a need for ink compositions with good lightfastness characteristics. Further, there is a need for ink compositions which exhibit good waterfastness characteristics. Additionally, there is a need for ink compositions which enable the generation of prints with excellent optical density. A need also remains for ink compositions having dye colorants which exhibit reduced intercolor bleed with ink compositions having pigment colorants, whether or not the pigmented ink compositions contain a fluorinated material. In addition, a need remains for ink compositions with improved color gamut. Further, a need remains for ink compositions which exhibit reduced showthrough when printed on paper substrates. Additionally, a need remains for ink compositions suitable for printing onto a wide variety of substrates. There is also a need for ink compositions which are relatively benign with respect to any tendency to cause degradation of common thermal ink jet printhead materials. In addition, there is a need for ink compositions which enable the generation of prints on various papers with reduced or eliminated curling of the paper.

It is an object of the present invention to provide ink compositions with the above noted advantages.

It is another object of the present invention to provide ink compositions with improved characteristics.

It is yet another object of the present invention to provide ink compositions which exhibit reduced or no intercolor bleed when printed adjacent to other inks of different colors.

It is still another object of the present invention to provide ink compositions which exhibit good shelf stability.

Another object of the present invention is to provide ink compositions having improved colorimetry.

Yet another object of the present invention is to provide ink compositions which exhibit reduced intercolor bleed in combination with improved shelf stability and improved colorimetry.

Still another object of the present invention is to provide ink compositions with good lighffastness characteristics.

It is another object of the present invention to provide ink compositions which exhibit good waterfastness characteristics.

It is yet another object of the present invention to provide ink compositions which enable the generation of prints with excellent optical density.

Another object of the present invention is to provide ink compositions having dye colorants which exhibit reduced intercolor bleed with ink compositions having pigment colorants, whether or not the pigmented ink compositions contain a fluorinated material.

Yet another object of the present invention is to provide ink compositions with improved color gamut.

Still another object of the present invention is to provide ink compositions which exhibit reduced showthrough when printed on paper substrates.

It is another object of the present invention to provide ink compositions suitable for printing onto a wide variety of substrates.

It is yet another object of the present invention to provide ink compositions which are relatively benign with respect to any tendency to cause degradation of common thermal ink jet printhead materials.

It is still another object of the present invention to provide ink compositions which enable the generation of prints on various papers with reduced or eliminated curling of the paper.

These and other objects of the present invention (or specific embodiments thereof) can be achieved by providing an ink composition which comprises water, a dye selected from the group consisting of Direct Blue 199, Direct Yellow 132, Acid Yellow 17, Reactive Red 180, Acid Red 52, and mixtures thereof, and a material of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20, wherein the ink is substantially free of imidazole.

Inks of the present invention contain an aqueous liquid vehicle, a dye selected from the group consisting of Direct Blue 199, Direct Yellow 132, Acid Yellow 17, Reactive Red 180, Acid Red 52, and mixtures thereof, and a material of the formula ›(F.sub.3 C(F.sub.2 C).sub.n CH.dbd.CHCH.sub.2 OCH(OH)CH.sub.2).sub.2 NCH.sub.2 COO.sup.- !›X.sup.+ !, wherein X is a cation and n is an integer of from about 3 to about 20, wherein the ink is substantially free of imidazole. The liquid vehicle can consist solely of water, or it can comprise a mixture of water and a water soluble or water miscible organic component, such as ethylene glycol, propylene glycol, diethylene glycols, glycerine, dipropylene glycols, polyethylene glycols, polypropylene glycols, tripropylene glycol monomethyl ether, amides, ethers, urea, substituted ureas, ethers, carboxylic acids and their salts, esters, alcohols, organosulfides, organosulfoxides, sulfones (such as sulfolane), alcohol derivatives, carbitol, butyl carbitol, cellusolve, ether derivatives, amino alcohols, ketones, N-methylpyrrolidinone, 2-pyrrolidinone, cyclohexylpyrrolidone, hydroxyethers, amides, sulfoxides, lactones, polyelectrolytes, methyl sulfonylethanol, imidazole, and other water soluble or water miscible materials, as well as mixtures thereof. When mixtures of water and water soluble or miscible organic liquids are selected as the liquid vehicle, the water to organic ratio typically ranges from about 100:0 to about 30:70, and preferably from about 97:3 to about 40:60. The non-water component of the liquid vehicle generally serves as a humectant which has a boiling point higher than that of water (100.degree. C.). In the ink compositions of the present invention, the liquid vehicle is typically present in an amount of from about 60 to about 95 percent by weight of the ink, and preferably from about 70 to about 90 percent by weight of the ink, although the amount can be outside these ranges.

In one specific embodiment, the liquid vehicle contains a penetrant material selected from betaine, cyclohexyl pyrrolidinone, butyl carbitol (diethylene glycol monobutyl ether), tripropylene glycol monomethyl ether, or mixtures thereof. The penetrant material is present in any effective or desired amount, typically from about 0.1 to about 20 percent by weight, and preferably from about 3 to about 15 percent by weight, although the amount can be outside these ranges. Inks of this specific embodiment are preferred over those containing a surfactant because of frequently reduced viscosity.

Also contained in the ink is a material of the formula ##STR1## wherein X+ is a cation and n is an integer of from about 3 to about 20, preferably from about 4 to about 15, and more preferably from about 5 to about 11. Examples of suitable cations include (HO--CH.sub.2 CH.sub.2).sub.2 NH.sub.2 +, (HO--CH.sub.2 CH.sub.2).sub.3 NH+, an imidazolium cation such as imidozolium, N-methyl imidazolium, or N-butyl imidazolium, tris(hydroxymethyl)aminomethane hydrochloride, tris(hydroxymethyl)aminomethane hydrocitrate, protonated 1,4-diazabicyclo(2.2.2)octane, and the like. Materials of this formula are available from, for example, Ciba-Geigy, Ardsley, New York (Greensboro, N.C.) as LODYNE P-502, containing a mixture of compounds wherein n has varying values and has an average value of about 9. The material of this formula is present in the ink in any effective or desired amount; typically, the amount ranges from about 0.1 to about 10 percent by weight of the ink, preferably from about 0.25 to about 6 percent by weight of the ink, more preferably from about 0.5 to about 5 percent by weight of the ink, and even more preferably from about 1 to about 4 percent by weight of the ink, although the amount can be outside these ranges.

In one preferred embodiment of the present invention, the fluorinated material is of the formula ##STR2## wherein n is 5. This material is available from, for example, Ciba-Geigy, Ardsley, New York (Greensboro, N.C.) as LODYNE P-502L, containing the fluorocarbon wherein substantially all of the material has exactly 6 carbon atoms in each of the fluorinated hydrocarbon chains. Inks containing this material exhibit improved shelf stability, even when the fluorocarbon and/or the ink are not subjected to ultrasonification or high shear mixing. These materials also exhibit good shelf stability with a wide variety of dyes, whereas inks containing mixtures of fluorocarbons of the above formula wherein n has varying values may be compatible with some dyes and may exhibit reduced shelf stability with other dyes. The ink fabrication process is accordingly simplified, with no need for procedures other than simple mixing of the ingredients to obtain optimal performance.

Also contained in the ink composition of the present invention is a dye. The dye is selected from the group consisting of Direct Blue 199 (commercially available as, for example, PROJET CYAN 1 from Zeneca Colors, Dighton, Mass.), Direct Yellow 132 (commercially available as, for example, PROJET YELLOW 1G from Zeneca Colors, Dighton, Mass.), Acid Yellow 17 (commercially available from, for example Tricon Colors, Elmwood Park, N.J.), Reactive Red 180 (commercially available as, for example, PROJET MAGENTA 1T from Zeneca Colors, Dighton, Mass.), Acid Red 52 (commercially available from, for example Tricon Colors, Elmwood Park, N.J.), and mixtures thereof. The dye is present in the ink composition in any effective amount, typically from about 0.5 to about 15 percent by weight of the ink, preferably from about 0.5 to about 8 percent by weight of the ink, more preferably from about 1 to about 10 percent by weight of the ink, and even more preferably from about 1 to about 6 percent by weight of the ink, although the amount can be outside of these ranges.

Inks of the present invention containing the fluorinated material and one or more of the above dye compositions exhibit excellent shelf stability as a result of the compatibility of these dyes with the fluorinated material. In addition, the inks exhibit good compatibility with printhead hardware, improved waterfastness and lightfastness, excellent optical density, and good color quality.

Optionally, 1,4-diazabicyclo(2.2.2)octane is also contained in the ink. This material is of the formula ##STR3## The 1,4-diazabicyclo(2.2.2)octane acts as a buffer in the ink composition, maintaining the ink containing the fluorinated material additive at a desirable pH in the event of acid contamination. In addition, the 1,4-diazabicyclo(2.2.2)octane is highly efficient as a buffer, with relatively small amounts being required in the ink to enable the buffering function. Typically, the 1,4-diazabicyclo(2.2.2)octane is present in an amount from about 0.1 to about 6 percent by weight of the ink, preferably from about 0.5 to about 4 percent by weight of the ink, and more preferably from about 1 to about 3 percent by weight of the ink, although the amount can be outside these ranges. Further, the presence of the 1,4-diazabicyclo(2.2.2)octane enables buffered ink compositions containing the fluorinated material without undesirable increase in viscosity, particularly when the ink is heated or subjected to changes in pH.

Optionally, ink compositions contain a bisquaternary ammonium compound. Bisquaternary ammonium compounds suitable for the present invention include (but are not limited to) those of the general formula ##STR4## wherein each of R.sub.1, R.sub.2, R.sub.3, R.sub.4, R.sub.5, and R.sub.6, independently of the others, is an alkyl group, preferably with from 1 to about 6 carbon atoms (and wherein the alkyl group can be substituted with, for example, hydroxide groups, halide groups, or the like, R.sub.7 is an alkylene group, preferably with from about 2 to about 10 carbon atoms (and wherein the alkylene group can be substituted with, for example, hydroxide groups, halide groups, or the like), and wherein A is an anion. Examples of suitable anions include (but are not limited to) hydroxide, halide, citrate, ethylene diamine tetraacetate, phosphite, and the like. Examples of suitable bisquaternary ammonium compounds include N, N'-hexamethylenebis(tributyl ammonium) compounds, N, N'-hexamethylenebis(trimethyl ammonium) compounds, and the like. Specific examples of suitable bisquaternary ammonium compounds include N,N'-hexamethylenebis(tributyl ammonium hydroxide), of the formula ##STR5## N,N'-hexamethylenebis(trimethyl ammonium bromide) (also called hexamethonium bromide), of the formula ##STR6## and the like. The bisquaternary ammonium compound is present in the ink in any desired or effective amount, typically in a stoichiometric amount of from about 0.1 to about 4 moles of bisquaternary ammonium compound per one mole of fluorinated material, preferably in a stoichiometric amount of from about 0.25 to about 2 moles of bisquaternary ammonium compound per one mole of fluorinated material, and more preferably in a stoichiometric amount of from about 0.5 to about 1 moles of bisquaternary ammonium compound per one mole of fluorinated material, although the relative amounts can be outside these ranges. The bisquaternary ammonium compound typically is present in the ink in an amount of from about 0.1 to about 10 percent by weight of the ink, and preferably from about 0.5 to about 4 percent by weight of the ink, although the amount can be outside these ranges.

While not being limited to any particular theory, it is believed that the bisquaternary ammonium compound becomes associated with the fluorinated material (which has a carboxylic acid substituent) and imparts shelf stability to the ink. It is further hypothesized that the bisquaternary ammonium compound associated with the fluorinated material may reduce liposome lattice energy through ionic complexation, thereby arresting liposome growth and inhibiting phase separation in the ink composition. Additionally, it is hypothesized that the bisquaternary ammonium compound associated with the fluorinated material may increase the liposome radius of curvature, thereby stabilizing small liposomes relative to large liposomes (which may undesirably increase ink viscosity).

Optionally, betaine can also be present in the inks of the present invention. Betaine is commercially available from, for example, Finnsugar Biomedical, Helsinki, Finland. Betaine is present in the ink in any effective or desired amount; typically, the amount ranges from about 5 to about 25 percent by weight of the ink, and preferably from about 10 to about 20 percent by weight of the ink, although the amount can be outside these ranges. In one embodiment of the present invention, betaine is present in the ink compositions in combination with dipropylene glycol. In this embodiment, the dipropylene glycol typically is present in the ink in an amount of up to about 20 percent by weight of the ink, preferably from about 5 to about 15 percent by weight of the ink, and more preferably from about 5 to about 10 percent by weight of the ink, although the amount can be outside these ranges. In another preferred embodiment of the present invention, betaine is present in the ink compositions in combination with butyl carbitol. In this embodiment, the butyl carbitol typically is present in the ink in an amount of up to about 15 percent by weight of the ink, preferably from about 2 to about 10 percent by weight of the ink, and more preferably from about 2 to about 5 percent by weight, although the amount can be outside these ranges.

Optionally, a monomeric compound having at least two carboxylic acid functional groups is also contained in the inks of the present invention. Examples of suitable multifunctional acids include ethylenediamine tetraacetic acid, aspartic acid, citric acid, malic acid, glutaric acid, adipic acid, oxalic acid, malonic acid, maleic acid, alpha keto glutaric acid, and the like. The multifunctional acid is present in the ink in any effective or desired amount, typically from about 0.05 to about 5 percent by weight of the ink, preferably from about 0.2 to about 3 percent by weight of the ink, and more preferably from about 1 to about 2 percent by weight of the ink, although the amount can be outside these ranges. Additional examples of multifunctional acids include those disclosed in columns 19 to 22 of U.S. Pat. No. 5,589,277, the disclosure of which is totally incorporated herein by reference. While not being limited to any particular theory, it is believed that the presence of the multifunctional acid in combination with the fluorocarbon material enhances the shelf stability of the inks of the present invention. The fluorocarbon material in an ink in the absence of a multifunctional acid may exhibit a tendency to salt out of the ink, particularly when the colorant is an anionic dye. It is believed that hydrogen bonding occurs between the polar carboxyl groups of the fluorocarbon material and the carboxyl groups of the multifunctional acid, thereby stabilizing the liposome structure of the fluorocarbon material in the ink. The stabilized ink also exhibits improved jetting characteristics and improved viscosity stability with respect to pH and temperature. It is believed that the stabilized liposome structure renders the liposomes resistant to coalescence, thereby improving resistance to viscosity build.

The ink compositions of the present invention contain substantially no imidazole. Imidazole can be used in ink compositions containing fluorinated materials such as those contained in the inks of the present invention to enhance the shelf stability of the ink. Since imidazole can cause degradation of many materials commonly used to fabricate thermal ink jet printheads, however, inks of the present invention are particularly benign with respect to ink jet printhead materials.

In another preferred embodiment, the ink compositions of the present invention contain tripropylene glycol monomethyl ether. When present, the tripropylene glycol monomethyl ether is present in any desired or effective amount, typically up to about 15 percent by weight of the ink, and preferably up to about 10 percent by weight of the ink, although the amount can be outside these ranges. This material is believed to function as a penetrant and also imparts shelf stability to the ink.

Other additives can also be present in the inks. For example, one or more surfactants or wetting agents can be added to the ink. These additives may be of the cationic, anionic, or nonionic types. Suitable surfactants and wetting agents include sodium lauryl sulfate, TAMOL.RTM. SN, TAMOL.RTM. LG, those of the TRITON.RTM. series available from Rohm and Haas Company, those of the MARASPERSE.RTM. series, those of the IGEPAL.RTM. series available from GAF Company, those of the TERGITOL.RTM. series, SURFYNOL.RTM. GA available from Air Products and Chemicals Co., and other commercially available surfactants. These surfactants and wetting agents are present in effective amounts, generally from 0 to about 10 percent by weight, and preferably from about 0.01 to about 4 percent by weight, although the amount can be outside of this range.

In one specific embodiment the ink contains a nonionic surfactant. Any suitable or desired nonionic surfactant may be employed. Examples of suitable nonionic surfactants include octylphenoxy polyethoxy ethanols, such as TRITON X-100, available from Union Carbide Co., Danbury, Conn., acetylenic diols such as 2,4,7,9-tetramethyl-5-decyn-4,7-diol and the like, such as SURFYNOL GA and SURFYNOL CT-136, available from Air Products & Chemicals Co., Allentown, Pa., trimethyl nonylpolyethylene-glycol ethers, such as TERGITOL TMN-10 (containing 10 oxyethylene units, believed to be of the formula C.sub.12 H.sub.25 O(C.sub.2 H.sub.4 O).sub.5 H), available from Union Carbide Co., Danbury, Conn., non-ionic esters of ethylene oxide, such as MERPOL SH (believed to be of the formula CH.sub.3 (CH.sub.2).sub.12 (OC.sub.2 H.sub.4).sub.8 OH), available from E. I. Du Pont de Nemours & Co., Wilmington, Del., non-ionic esters of ethylene oxide and propylene oxide, such as MERPOL LFH (believed to be of the formula CH.sub.3 (CH.sub.2),(OC.sub.2 H.sub.4).sub.8 (OC.sub.3 H.sub.6).sub.8 OH where n is an integer from about 12 to about 16), available from E. I. Du Pont de Nemours & Co., Wilmington, Del., and the like, as well as mixtures thereof. The nonionic surfactant is present in the ink in any suitable or desired amount, typically from about 0.1 to about 5 percent by weight of the ink, and preferably from about 0.5 to about 2 percent by weight of the ink, although the amount can be outside of these ranges.

Polymeric additives can also be added to the inks to enhance the viscosity and the stability of the ink. Water soluble polymers such as Gum Arabic, polyacrylate salts, polymethacrylate salts, polyvinyl alcohols, hydroxy propylcellulose, hydroxyethylcellulose, polyvinylpyrrolidinone, polyvinylether, starch, polysaccharides, polyethylene oxide, block copolymers of polyethylene oxide and polypropylene oxide, polyvinylpyridine, polyethyleneimine, polyhydroxyethyl ethyleneimine, polyquaternary salts, and the like are typical polymeric additives. Polymeric additives can be present in the ink of the present invention in amounts of from 0 to about 10 percent by weight, and preferably from about 0.01 to about 5 percent by weight, although the amount can be outside this range.

One example of an additive to the inks is a polymeric additive consisting of two polyalkylene oxide chains bound to a central bisphenol-A-type moiety. This additive is of the formula ##STR7## wherein R.sup.1 and R.sup.2 are independently selected from the group consisting of hydrogen, alkyl groups with from 1 to about 8 carbon atoms, such as methyl, ethyl, propyl, and the like, and alkoxy groups with from 1 to about 8 carbon atoms, such as methoxy, ethoxy, butoxy, and the like, R.sup.3 and R.sup.4 are independently selected from the group consisting of alkyl groups with from 1 to about 4 carbon atoms, and x and y are each independently a number of from about 100 to about 400, and preferably from about 100 to about 200. Generally, the molecular weight of the polyalkylene oxide polymer is from about 14,000 to about 22,000, and preferably from about 15,000 to about 20,000, although the molecular weight can be outside this range. Materials of this formula are commercially available; for example, Carbowax M20, a polyethylene oxide/bisphenol-A polymer of the above formula with a molecular weight of about 18,000, available from Union Carbide Corporation, Danbury, Conn., is a suitable polymeric additive for the inks of the present invention. In addition, compounds of the above formula can be prepared by the methods disclosed in Polyethers, N. G. Gaylord, John Wiley & Sons, N.Y. (1963) and "Laboratory Synthesis of Polyethylene Glycol Derivatives," J. M. Harris, J. Molecular Science--Rev. Macromol. Chem. Phys., C25(3), 325-373 (1985), the disclosures of each of which are totally incorporated herein by reference. The polyalkylene oxide additive is generally present in the ink in an amount of at least about 1 part per million. Typically, the polyalkylene oxide additive is present in amounts of up to 1 percent by weight of the ink, and preferably in amounts of up to 0.5 percent by weight of the ink; larger amounts of the additive may increase the viscosity of the ink beyond the desired level, but larger amounts can be used in applications wherein increased ink viscosity is not a problem. Inks containing these additives are disclosed in U.S. Pat. No. 5,207,825, the disclosure of which is totally incorporated herein by reference.

Optionally, ink compositions of the present invention can also contain a polyethylene oxide-polypropylene oxide block copolymer. Suitable polymers include tetrafunctional block copolymers derived from the sequential addition of propylene oxide and ethylene oxide to ethylenediamine, such as those of the general formula ##STR8## wherein x, x', x", x'", y, y', y", and y'" are each integers representing the number of repeating monomer units and have values such that the molecular weight range of the compound is from about 1,650 to about 27,000, the values of x, x', x", and x'" are each such that the polypropylene oxide segments of the compound have a total molecular weight of at least about 250 and preferably from about 500 to about 7,000, and the values of y, y', y", and y'" are each such that the polyethylene oxide segments constitute from about 5 to about 90 percent by weight of the total molecular weight of the compound, and preferably from about 10 to about 80 percent by weight of the total molecular weight of the compound, with typical values for x, x', x", and x'" being from 1 to about 127 and typical values for y, y', y", and y'" being from 1 to about 110, such as TETRONIC 904, wherein the values of x, x', x", x'", y, y', y", and y'" are each such that the total molecular weight of the polypropylene oxide blocks of the compound is from about 3,900 to about 4,500 and the ethylene oxide segments make up about 40 percent by weight of the compound (average number of propylene oxide groups per molecule from about 68 to about 76 (typically from about 17 to about 19 repeating units per chain, with four chains per molecule), total molecular weight from about 6,500 to about 7,500), TETRONIC 704, wherein the values of x, x', x", x'", y, y', y", and y'" are each such that the total molecular weight of the polypropylene oxide blocks of the compound is from about 2,500 to about 3,600 and the ethylene oxide segments make up about 40 percent by weight of the compound (average number of propylene oxide groups per molecule from about 43 to about 62 (typically from about 13 to about 15 repeating units per chain, with four chains per molecule), total molecular weight from about 4,150 to about 6,000), and TETRONIC 304, wherein the values of x, x', x", x'", y, y', y", and y'" are each such that the total molecular weight of the polypropylene oxide blocks of the compound is from about 500 to about 1,900 and the ethylene oxide segments make up about 40 percent by weight of the compound (average number of propylene oxide groups per molecule from about 8 to about 32 (typically from about 2 to about 8 repeating units per chain, with four chains per molecule), total molecular weight from about 800 to about 3,200), all commercially available from BASF, Parsippany, N.J. Also suitable are polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymers, including those formed by the controlled addition of propylene oxide to the two hydroxyl groups of propylene glycol, followed by addition of ethylene oxide, such as those of the general formula ##STR9## wherein x, x', and y are each integers representing the number of repeating monomer units and have values such that the molecular weight range of the compound is from about 1,000 to about 14,000, the value of y is such that the polypropylene oxide segment of the compound has a molecular weight of at least about 900 and preferably is from about 950 to about 4,000, and the values of x and x' are such that the polyethylene oxide segments constitute from about 5 to about 90 percent by weight of the total molecular weight of the compound, and preferably from about 10 to about 80 percent by weight of the total molecular weight of the compound, such as PLURONIC L35, wherein the values of x, x', and y are each such that the molecular weight of the polypropylene oxide block of the compound is from about 925 to about 1,050 and the ethylene oxide segments make up about 50 percent by weight of the compound (average number of propylene oxide groups per molecule from about 16 to about 18, total molecular weight from about 1,900 to about 2,000), PLURONIC L64, wherein the values of x, x', and y are each such that the molecular weight of the polypropylene oxide block of the compound is from about 1,625 to about 1,875 and the ethylene oxide segments make up about 40 percent by weight of the compound (average number of propylene oxide groups per molecule from about 28 to about 32, total molecular weight from about 2,700 to about 3,150); PLURONIC L62F, which is a mixture containing about 90 percent by weight of a compound wherein the values of x, x', and y are each such that the molecular weight of the polypropylene oxide block of the molecule is from about 1,625 to about 1,875 and the ethylene oxide segments make up about 20 percent by weight of the molecule (average number of propylene oxide groups per molecule from about 28 to about 32, total molecular weight from about 2,000 to about 2,350) and about 10 percent by weight of a compound wherein the values of x, x', and y are each such that the molecular weight of the polypropylene oxide block of the molecule is 1,625 to about 1,875 and the ethylene oxide segments make up about 10 percent by weight of the molecule (average number of propylene oxide groups per molecule from about 28 to about 32, total molecular weight from about 1,800 to about 2,100); and PLURONIC P65, wherein the values of x, x', and y are each such that the molecular weight of the polypropylene oxide block of the molecule is from about 1,625 to about 1,875 and the ethylene oxide segments make up about 50 percent by weight of the molecule (average number of propylene oxide groups per molecule from about 28 to about 32, total molecular weight from about 3,250 to about 3,750), all commercially available from BASF. Also suitable are polypropylene oxide-polyethylene oxide-polypropylene oxide triblock copolymers, including those formed by the addition of ethylene oxide to ethylene glycol, followed by addition of propylene oxide, such as those of the general formula ##STR10## wherein x, x', and y are each integers representing the number of repeating monomer units and have values such that the molecular weight range of the compound is from about 1,000 to about 14,000, the value of x and x' are such that the polypropylene oxide segments of the compound have a molecular weight of at least about 900 and preferably from about 1000 to about 3,100, and the value of y is such that the polyethylene oxide segment constitutes from about 5 to about 90 percent by weight of the total molecular weight of the compound, and preferably from about 10 to about 80 percent by weight of the total molecular weight of the compound, such as PLURONIC 10R-5, wherein the values of x, x', and y are each such that the molecular weight of the polypropylene oxide blocks of the compound is about 1,000 and the ethylene oxide segments make up about 50 percent by weight of the compound, commercially available from BASF. Further information regarding the synthesis and structure of the TETRONICS and PLURONICS materials is disclosed in, for example, U.S. Pat. No. 4,062,907, U.S. Pat. No. 5,114,755, U.S. Pat. No. 5,001,165, U.S. Pat. No. 4,536,254, U.S. Pat. No. 4,670,058, U.S. Pat. No. 4,578,150, U.S. Pat. No. 5,078,781, U.S. Pat. No. 5,634,986, U.S. Pat. No. 5,653,970, U.S. Pat. No. 3,337,463, and U.S. Pat. No. 2,979,528, the disclosures of each of which are totally incorporated herein by reference. Also suitable are ethoxylated 2-naphthol polymers, preferably with a molecular weight of from about 20,000 to about 35,000 and more preferably from about 25,000 to about 30,000, such as SOLSPERSE 27,000, an ethoxylated 2-naphthol polymer with a molecular weight of 27,000, commercially available from ICI, Wilmington, Del. Mixtures of two or more polymers can also be employed. The polymer is present in the ink in any desired or effective amount, typically from about 0.01 to about 3 percent by weight of the ink, preferably from about 0.05 to about 2 percent by weight of the ink, and more preferably from about 0.05 to about 0.5 percent by weight of the ink, although the amount can be outside these ranges.

In embodiments of the present invention wherein the ink contains one of the above polymers, preferably the ink compositions of the present invention also contain an additive selected from the group consisting of (i) diethylene glycol; (ii) glycerol; (iii) trimethylol propane; (iv) urea; (v) n-methyl pyrrolidone; (vi) sulfolane; (vii) 1,4 diazabicyclo(2.2.2)octane; (viii) cyclohexylpyrrolidone; and (ix) mixtures thereof. This additive is present in the ink in any desired or effective amount, typically from about 1 to about 25 percent by weight of the ink, preferably from about 3 to about 20 percent by weight of the ink, and more preferably from about 4 to about 15 percent by weight of the ink, although the amount can be outside these ranges.

While not being limited to any particular theory, it is believed that the polymers in the inks of the present invention inhibit liposomes and emulsified particles formed by the fluorinated material from flocculating, thereby inhibiting coalescence and shelf destabilization. It is further believed that the stabilization mechanism entails an association of the hydrophilic polymer portion with the liposome exterior surface, while the hydrophobic polymer portion points away from the liposome to provide steric hindrance to the approach of another liposome, thus inhibiting flocculation. The particular additive or additives selected, such as diethylene glycol, glycerol, trimethylol propane, urea, n-methyl pyrrolidone, sulfolane, 1,4 diazabicyclo(2.2.2)octane, or cyclohexylpyrrolidone, further enable this stabilization mechanism. Specific additives tend to be preferred for specific polymers. For example, inks containing the TETRONIC 904 polymer preferably contain diethylene glycol, trimethylol propane, urea, or glycerol, and preferably do not contain N-methylpyrrolidinone or sulfolane. Inks containing the TETRONIC 704 polymer preferably contain diethylene glycol, trimethylol propane, N-methylpyrrolidinone, sulfolane, or glycerol, and preferably do not contain urea or 1,4 diazabicyclo(2.2.2)octane. Inks containing the PLURONIC 10R-5 polymer preferably contain diethylene glycol, n-methylpyrrolidone, urea, or glycerol, and preferably do not contain sulfolane or trimethylol propane. Inks containing the PLURONIC L35 polymer preferably contain diethylene glycol, trimethylol propane, N-methylpyrrolidone, urea, or glycerol, and preferably do not contain sulfolane or tripropylene glycol monomethyl ether. Inks containing the PLURONIC L64 polymer preferably contain diethylene glycol, trimethylol propane, N-methylpyrrolidone, urea, or glycerol, and preferably do not contain 1,4 diazabicyclo(2.2.2) octane or tripropylene glycol monomethyl ether. Inks containing the PLURONIC L62F polymer preferably contain diethylene glycol, trimethylol propane, sulfolane, or urea, and preferably do not contain N-methylpyrrolidone or glycerol. Inks containing the TETRONIC 304 polymer preferably contain diethylene glycol, trimethylol propane, N-methylpyrrolidone, urea, or glycerol, and preferably do not contain 1,4 diazabicyclo(2.2.2)octane or tripropylene glycol monomethyl ether. Inks containing the PLURONIC P65 polymer preferably contain diethylene glycol, N-methylpyrrolidone, sulfolane, or glycerol, and preferably do not contain urea or trimethylol propane. Inks containing the SOLSPERSE 27,000 polymer preferably contain 1,4 diazabicyclo(2.2.2)octane or urea.

Other optional additives to the inks include biocides such as Dowicil 150, 200, and 75, benzoate salts, sorbate salts, and the like, present in an amount of from about 0.0001 to about 4 percent by weight, and preferably from about 0.01 to about 2.0 percent by weight, pH controlling agents such as acids or, bases, phosphate salts, carboxylates salts, sulfite salts, amine salts, and the like, present in an amount of from 0 to about 1 percent by weight and preferably from about 0.01 to about 1 percent by weight, or the like.

The ink compositions are generally of a viscosity suitable for use in thermal ink jet printing processes. At room temperature (i.e., about 25.degree. C.), typically, the ink viscosity is no more than about 5 centipoise, and preferably is from about 1 to about 3.5 centipoise, although the viscosity can be outside this range.

Ink compositions of the present invention can be of any suitable or desired pH. For some embodiments, such as thermal ink jet printing processes, typical pH values are from about 8 to about 9.5, preferably from about 8.0 to about 9.0, and more preferably from about 8.5 to about 9.0, although the pH can be outside of these ranges.

Ink compositions suitable for ink jet printing can be prepared by any suitable process. Typically, the inks are prepared by simple mixing of the ingredients. One process entails mixing all of the ink ingredients together and filtering the mixture to obtain an ink. Inks can be prepared by preparing a conventional ink composition according to any desired process, such as by mixing the ingredients and filtering, followed by adding any desired additional additives to the mixture and mixing at room temperature with moderate shaking until a homogeneous mixture is obtained, typically from about 5 to about 10 minutes. Alternatively, the optional ink additives can be mixed with the other ink ingredients during the ink preparation process, which takes place according to any desired procedure, such as by mixing all the ingredients and filtering.

In one specific embodiment, the ink is subjected to ultrasonification to reduce the particle size of the liposomes in the ink formed by the fluorocarbon material. In this embodiment, the ink is subjected to ultrasonication at relatively low intensity, typically for from about 5 to about 90 minutes, preferably from about 10 to about 60 minutes, and in a preferred embodiment for about 20 minutes. In another specific embodiment of the present invention, the fluorocarbon material is subjected to ultrasonification prior to admixing it with the other ink ingredients. In this second embodiment, the fluorocarbon can be ultrasonicated either in the form in which it is received from the supplier (assuming said form is a liquid containing the fluorocarbon) or after admixing it with water, mixtures of water and one or more other desired ink components, or the like. In a particularly preferred embodiment, the ultrasonicated liquid contains the fluorocarbon material in an amount of about 15 percent by weight and water in an amount of about 85 percent by weight. In another particularly preferred embodiment, the ultrasonicated liquid contains the fluorocarbon material in an amount of about 15 percent by weight, 1,4-diazabicyclo(2.2.2)octane in an amount of about 20 percent by weight, and water in an amount of about 65 percent by weight. In another particularly preferred embodiment, the ultrasonicated liquid contains the fluorocarbon material in an amount of from about 9 to about 10 percent by weight, 1,4-diazabicyclo(2.2.2)octane in an amount of from about 6 to about 7 percent by weight, a bisquaternary compound, such as hexamethonium bromide, in an amount of from about 4 to about 5 percent by weight, an acid, such as citric acid, in an amount of from about 2 to about 3 percent by weight, and the balance water.

One specific example of an ultrasonication process is as follows: LODYNE P-502, obtained from Tricon Colors as an aqueous solution containing about 15 percent by weight of the fluorocarbon, is divided into 25 gram portions. In each instance, a 25 gram portion of the LODYNE P-502 is placed in a 30 gram vial. The vial is placed into a 550 SONIC DISMEMBRATOR (obtained from Fisher Scientific Co.) tuned at 20 kiloHertz and the LODYNE P-502 is subjected to ultrasonification for a period of 10 minutes at an amplitude setting of 5, with the power turned on and off every 30 seconds. Thereafter the vial is allowed to stand overnight, after which the top layer in the vial is used to prepare ink compositions.

To avoid excessive heating of the ink during the ultrasonification process, the ink can be jacket cooled during the process, and/or the ultrasonification can be pulsed instead of continuous; for example, for a process entailing application of ultrasonification for 5 minutes, the process can be pulsed at one second on and one second off alternately for a period of 10 minutes. Reduction in liposome size by ultrasonification enables advantages such as enhanced shelf life of the ink and reduced ink viscosity. Ultrasonification also results in a narrower range of liposome particle diameters.

In yet another specific embodiment, neither the fluorocarbon nor the ink is subjected to ultrasonification during the formulation process. Inks suitable for ink jet printing exhibiting a liquid crystalline phase at certain temperatures are known, as disclosed in, for example, U.S. Pat. No. 5,492,559, U.S. Pat. No. 5,551,973, and U.S. Pat. No. 5,643,357, the disclosures of each of which are totally incorporated herein by reference. Fluorocarbon materials such as LODYNE P-502, available from Ciba-Geigy, when received from the manufacturer, contain liquid crystals as observed by microscopic inspection under polarized illumination. Inks containing the fluorocarbon and other ink vehicle ingredients, such as betaine/dipropylene glycol and betaine/imidazole, retain the fluorocarbon liquid crystal structures. When two or more of these inks of different colors are incorporated into a thermal ink jet printer, such as a Hewlett-Packard DeskJet.RTM. 500C, and printed onto a substrate such as plain paper, the resulting multicolored images exhibit improved intercolor bleed repression characteristics compared to inks of identical composition but wherein the fluorocarbon was ultrasonified prior to incorporation into the ink composition and inks of identical composition which were subjected to ultrasonification subsequent to ink preparation.

The present invention is also directed to a process which entails incorporating an ink composition of the present invention into an ink jet printing apparatus and causing droplets of the ink composition to be ejected in an imagewise pattern onto a substrate. In a particularly preferred embodiment, the printing apparatus employs a thermal ink jet process wherein the ink in the nozzles is selectively heated in an imagewise pattern, thereby causing droplets of the ink to be ejected in imagewise pattern. Any suitable substrate can be employed, including plain papers such as Xerox.RTM. 4024 papers, ruled notebook paper, bond paper, silica coated papers such as Sharp Company silica coated paper, JuJo paper, and the like, transparency materials, fabrics, textile products, plastics, polymeric films, inorganic substrates such as metals and wood, and the like. In a preferred embodiment, the process entails printing onto a porous or ink absorbent substrate, such as plain paper.

Specific embodiments of the invention will now be described in detail. These examples are intended to be illustrative, and the invention is not limited to the materials, conditions, or process parameters set forth in these embodiments. All parts and percentages are by weight unless otherwise indicated.

To 59.4 grams of distilled water was added 19.8 grams of 1,4-diazabicyclo(2.2.2)octane (obtained from Aldrich Chemical Co., Milwaukee, Wis., D2,780-2), 7.8 grams of citric acid (obtained from Aldrich Chemical Co., C8,315-5), 13.2 grams of hexamethonium bromide hydrate (obtained from Aldrich Chemical Co., 21,967-3), and 199.8 grams of LODYNE P-502 (containing 14.9 percent by weight of the fluorinated material, obtained from Ciba-Geigy, Ardsley, N.Y. (Greensboro, N.C.)). The mixture was stirred for 15 minutes, after which time it exhibited a viscosity of 6.10 centipoise at 250.degree. C. Thereafter, a 25 gram portion of the mixture was placed in a 30 gram vial. The vial was placed into a 550 SONIC DISMEMBRATOR (obtained from Fisher Scientific Co.) tuned at 20 kiloHertz and the LODYNE P-502 was subjected to ultrasonification for a period of 60 minutes at an amplitude setting of 5, with the power turned on and off every 30 seconds. The resulting colorless mixture had a viscosity of 3.57 centipoise at 25.degree. C., a pH of 9.16 at 25.degree. C., a conductivity of 7.62 millimhos, and a surface tension of 28.9 dynes per centimeter.

An ink composition was prepared as follows. To 46.4 grams of deionized water were added 0.167 gram of DOWICIL 150/200 biocide (obtained from Dow Chemical Co., Midland, Mich.), 0.0833 gram of polyethylene oxide (bisphenol-A derivative, of the formula ##STR11## molecular weight 18,500, obtained from Polysciences Corp.), 20.00 grams of tripropyleneglycol monomethylether (DOWANOL TPM, obtained from Dow Chemical Co.), 41.67 grams of PROJET MAGENTA 1T dye solution (dye solution contained 10 percent by weight dye solids, obtained from Zeneca Colors, Dighton, Mass.), 8.33 grams of Acid Red 52 dye solution (dye solution contained 10 percent by weight dye solids, obtained from Tricon Colors, Elmwood Park, N.J.), and an additional 9.90 grams of deionized water. The mixture thus prepared was then sonified by the process described in Example I. To the mixture were then added 3.30 grams of 1,4-diazabicyclo(2.2.2)octane (obtained from Aldrich Chemical Co., D2,780-2, Milwaukee, Wis.), 1.3 grams of citric acid (obtained from Aldrich Chemical Co.), 2.2 grams of hexamethonium bromide hydrate (obtained from Aldrich Chemical Co., 21,967-3), and 33.3 grams of LODYNE P-502 (solution containing 14.9 percent by weight fluorocarbon material, obtained from Ciba-Geigy, Ardsley, N.Y. (Greensboro, N.C.)). The resulting magenta ink composition was then filtered through a 1.2 micron 47 mm Gelman filter at 10 pounds per square inch over a period of 55 seconds. The ink composition thus prepared exhibited a viscosity of 4.34 centipoise at 25.degree. C., a pH of 8.56 at 25.degree. C., a conductivity of 8.46 millimhos, and a surface tension of 24.6 dynes per centimeter.

The ink composition thus prepared was then incorporated into a Hewlett-Packard 1600C thermal ink jet printer and printed onto Xerox.RTM. 4024 DP paper and Xerox.RTM. Image Series Elite paper. The prints thus formed exhibited low intercolor bleed with a MFLEN value of 5.

An ink composition was prepared as described in Example II except that the initial amount of deionized water was 38.1 grams (and not 46.4 grams) and that 58.33 grams of PROJET CYAN 1 dye solution (dye solution contained 10 percent by weight dye solids, obtained from Zeneca Colors, Dighton, Mass.) was substituted for the PROJET MAGENTA 1T and Acid Red 52 dyes. The resulting cyan ink composition was then filtered through a 1.2 micron 47 mm Gelman filter at 10 pounds per square inch over a period of 65 seconds. The ink composition thus prepared exhibited a viscosity of 3.72 centipoise at 25.degree. C., a pH of 8.79 at 25.degree. C., a conductivity of 7.07 millimhos, and a surface tension of 18.8 dynes per centimeter.

The ink composition thus prepared was then incorporated into a Hewlett-Packard 1600C thermal ink jet printer and printed onto Xerox.RTM. 4024 DP paper and Xerox.RTM. Image Series Elite paper. The prints thus formed exhibited low intercolor bleed with a MFLEN value of 5.

An ink composition was prepared as described in Example II except that the initial amount of deionized water was 38.1 grams (and not 46.4 grams) and that 33.3 grams of PROJET YELLOW 1G dye solution (dye solution contained 7.5 percent by weight dye solids, obtained from Zeneca Colors, Dighton, Mass.) and 25.0 grams of Acid Yellow 17 dye (dye solution contained 10 percent by weight dye solids, obtained from Tricon Colors, Elmwood Park, N.J.) were substituted for the PROJET MAGENTA 1T and Acid Red 52 dyes. The resulting cyan ink composition was then filtered through a 1.2 micron 47 mm Gelman filter at 10 pounds per square inch over a period of 50 seconds. The ink composition thus prepared exhibited a viscosity of 4.46 centipoise at 25.degree. C., a pH of 8.62 at 25.degree. C., a conductivity of 7.81 millimhos, and a surface tension of 20 dynes per centimeter.

The ink composition thus prepared was then incorporated into a Hewlett-Packard 1600C thermal ink jet printer and printed onto Xerox.RTM. 4024 DP paper and Xerox.RTM. Image Series Elite paper. The prints thus formed exhibited low intercolor bleed with a MFLEN value of 5.

An ink composition was prepared by admixing the following ingredients:

The ink composition thus prepared was then incorporated into a Hewlett-Packard 1600C thermal ink jet printer and printed onto Xerox.RTM. 4024 DP paper and Xerox.RTM. Image Series Elite paper. The prints thus formed exhibited low intercolor bleed with a MFLEN value of 5.

An ink composition was prepared by admixing the following ingredients:

The resulting ink composition was then filtered through a 1.2 micron 47 mm Gelman filter at 10 pounds per square inch. The ink composition thus prepared exhibited a viscosity of 2.49 centipoise at 25.degree. C., a pH of 9.02 at 25.degree. C., and a surface tension of 27.1 dynes per centimeter.

The ink composition thus prepared was then incorporated into a Hewlett-Packard 1600C thermal ink jet printer and printed onto Xerox.RTM. 4024 DP paper and Xerox.RTM. Image Series Elite paper. The prints thus formed exhibited low intercolor bleed with a MFLEN value of 5.

An ink composition was prepared by admixing the following ingredients:

The ink composition thus prepared was then incorporated into a Hewlett-Packard 1600C thermal ink jet printer and printed onto Xerox.RTM. 4024 DP paper and Xerox.RTM. Image Series Elite paper. The prints thus formed exhibited low intercolor bleed with a MFLEN value of 5.

Other embodiments and modifications of the present invention may occur to those of ordinary skill in the art subsequent to a review of the information presented herein; these embodiments and modifications, as well as equivalents thereof, are also included within the scope of this invention.