Improved ink compositions for thermal ink jet printing

Abstract: Disclosed is an ink composition which comprises water, a colorant, betaine, a tertiary amine, and a material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ], 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 2 CH 2 ) 2 NH 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 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] is subjected to centrifugation. Also disclosed are ink jet printing processes employing the aforementioned ink.

Description: 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. 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°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. Patent 4,601,777, U.S. Patent 4,251,824, U.S. Patent 4,410,899, U.S. Patent 4,412,224, and U.S. Patent 4,532,530. U.S. Patent 5,019,166 (Schwarz), 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. Patent 5,401,303 (Stoffel et al.), 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. 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 improved viscosity stability over time, particularly when exposed to elevated temperatures. Further, a need remains for ink compositions for which reduced heater deposits are observed when the inks are used in thermal ink jet printers. Additionally, a need remains for ink compositions which exhibit improved waterfastness. There is also a need for ink compositions which enable excellent color gamut In addition, there is a need for ink compositions which enable production of images with high optical densities. Further, there is a need for ink compositions which enable excellent color gamut and high optical density in combination with reduced dye concentration in the ink. Additionally, there is a need for ink compositions with desirable surface tension characteristics. A need also remains for ink compositions which exhibit desirable values for characteristics such as latency, jitter, drop size, and transit time. In addition, a need remains for ink compositions which exhibit improved filterability through 0.2 micron filters and reduced large particulates or flocculated particles. Further, a need remains for ink compositions which exhibit improved homogeneity. Additionally, a need remains for ink compositions with improved thermal stability. There is also a need for ink compositions which enable printing of images with sharp edges. In addition, there is a need for ink compositions which enable printing of images with high solid area density. Further, there is a need for ink compositions which enable printing of images on paper with reduced showthrough and thus with the possibility of printing on both surfaces of the paper sheet. Additionally, there is a need for ink compositions which enable thermal ink jet printing of images onto a substrate wherein the substrate exhibits reduced or no curling subsequent to printing. A need further remains for ink compositions suitable for use in thermal ink jet printing processes wherein the generated images exhibit reduced or no cockle. In addition, a need remains for ink compositions which enable printing of two or more adjacent color areas with reduced or no intercolor bleed. It is an object of the present invention to provide ink compositions with the above noted advantages. These and other objects of the present invention (or specific embodiments thereof) can be achieved by providing an ink composition which comprises water, a colorant, betaine, a tertiary amine, and a material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ], wherein n is an integer of from 8 to 20 and B is a cation. In one specific embodiment, n is 10 and B is (HO-CH 2 CH 2 ) 2 NH 2 + . In another specific embodiment, the tertiary amine is 1-methylimidazole. Another embodiment of the present invention is directed to an ink composition which comprises water, a colorant, betaine, a tertiary amine, a material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ], wherein n is an integer of from 8 to 20 and B is a cation, and an anionic dye with carboxylate groups, sulfonate groups, or both carboxylate and sulfonate groups. Yet another embodiment of the present invention is directed to a process for preparing an ink composition which comprises (a) providing a liquid composition containing a material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ], wherein n is an integer of from 8 to 20 and B is a cation; (b) subjecting the liquid composition to centrifugation, thereby causing the composition to separate into a supernatant top layer and a flocculated bottom layer; (c) separating the supernatant top layer from the flocculated bottom layer; and (d) admixing the supernatant top layer with an aqueous liquid vehicle and a colorant, thereby forming an ink composition. Inks of the present invention contain an aqueous liquid vehicle. 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 100:0 to 30:70, and preferably from 97:3 to 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°C). In the ink compositions of the present invention, the liquid vehicle is typically present in an amount of from 60 to 95 percent by weight of the ink, and preferably from 70 to 90 percent by weight of the ink, although the amount can be outside these ranges. Also contained in the ink composition of the present invention is a colorant. Any suitable colorant can be employed, including dyes, pigments, mixtures thereof, and the like. Suitable dye or mixture of dyes compatible with the ink liquid vehicle include acid dyes, direct dyes, reactive dyes, and the like, with water soluble anionic dyes being preferred. The dye is present in the ink composition in any effective amount, typically from 0.5 to 15 percent by weight of the ink, and preferably from 1 to 10 percent by weight of the ink, although the amount can be outside of these ranges. In one specific embodiment of the present invention, the dye is an anionic dye having carboxylate groups, sulfonate groups, or both carboxylate and sulfonate groups. Examples of these dyes which are commercially available include the PROJET FAST 2 Series of dyes, available from Zeneca Colours, Dighton, Massachusetts, such as PROJET FAST CYAN 2, PROJET FAST YELLOW 2, PROJET FAST MAGENTA 2, PROJET FAST BLACK 2, and the like. Other examples of suitable anionic dyes include those disclosed in, for example, U.S. Patent 4,963,189 and U.S. Patent 5,062,893. Use of these dyes enables ink advantages such as improved thermal stability with respect to viscosity increase, reduced or no heater deposits after 1 million pulses, improved waterfastness, excellent color gamut, high optical density, and the ability to reduce the concentration of dye in the ink. Examples of suitable pigments for the inks of the present invention include various carbon blacks such as channel black, furnace black, lamp black, and the like. Colored pigments include red, green, blue, brown, magenta, cyan, and yellow particles, as well as mixtures thereof. Typically, the pigment is present in an amount of from 0.1 to 8 percent by weight of the ink, and preferably from 2 to 7 percent by weight of the ink, although the amount can be outside these ranges. Also contained in the ink is a material of the formula wherein n is an integer of from 8 to 20 and B is a cation. In one specific embodiment, n is 10 and B is (HO-CH 2 CH 2 ) 2 NH 2 + . Other examples of suitable cations include ammonium, (HO-CH 2 CH 2 ) 3 NH + , (HO-CH 2 CH 2 )NH 3 + , an imidazolium cation such as imidazolium, 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, NC) as LODYNE P-201. The fluorinated material of the above formula is present in the ink in any effective or desired amount; typically, the amount ranges from 0.1 to 10 percent by weight of the ink, and preferably from 0.5 to 5 percent by weight of the ink, although the amount can be outside these ranges. Also present in the inks of the present invention is betaine. 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 5 to 25 percent by weight of the ink, and preferably from 10 to 20 percent by weight of the ink, although the amount can be outside these ranges. Also present in the inks of the present invention is a tertiary amine. Suitable tertiary amines include those of the formula wherein R 1 , R 2 , and R 3 each, independently of the others, is an alkyl group (including saturated, unsaturated, and cyclic alkyl groups), preferably with from 1 to about 10 carbon atoms, more preferably with from 1 to about 4 carbon atoms, a substituted alkyl group, preferably with from 1 to about 4 carbon atoms, more preferably with from 1 to about 2 carbon atoms, wherein the substituents can be hydroxy groups, alkoxy groups, preferably wherein the alkyl portion of the alkoxy group contains from 1 to about 4 carbon atoms and more preferably from 1 to about 2 carbon atoms, or the like, and wherein two or more of R 1 , R 2 , and R 3 can be joined together to form a ring. Examples of suitable tertiary amines for the inks of the present invention include triethanolamine, triethylamine, tris[2-(2-methoxyethoxy)ethyl]amine, imidazole, N-butyl imidazole, diethanolamine, and the like. In a specific embodiment of the present invention, the tertiary amine is 1-methylimidazole, of the formula In general, it is believed that lower basicity of the tertiary amine leads to lower pH values at which ink stability and viscosity stability can be achieved; for example, the presence of an amine such as N(OCH 2 CH 3 ) 3 enables ink viscosity stability at pH values of about 9.5 or greater, whereas the presence of an amine such as 1-methylimidazole enables ink viscosity stability at pH values of about 8.5 or greater. The tertiary amine is present in the ink in any effective or desired amount; typically, the amount ranges from 1 to 25 percent by weight of the ink, and preferably from 3 to 20 percent by weight of the ink, although the amount can be outside these ranges. The presence of the tertiary amine in the ink in combination with betaine and the material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] enables advantages such as improved homogeneity, improved 1.2 micron filterability, and thermal stability with respect to viscosity increase. In addition, the basicity of the tertiary amine is reduced when electron withdrawing groups are present, shifting the pH at which amine protonation occurs toward neutrality. For example, thermal stability of inks containing triethanol amine in an amount of from about one to about three times the amount of the material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] in the ink was observed at a pH of over about 8.5. Thermal stability of inks containing the more basic tris[2-(2-methoxyethoxy)ethyl]amine in an amount of from about one to about three times the amount of the material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] in the ink was observed at a pH of over about 9.0. Thermal stability of inks containing the highly basic triethyl amine in an amount of from about one to about three times the amount of the material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] in the ink was observed at a pH of about 10.5 or more. Thermal stability of inks containing 1-methylimidazole (which is less basic than triethanolamine as a result of lone electron pair conjugation with the aromatic ring) in an amount of from about one to about three times the amount of the material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] in the ink was observed at a pH of about 8.0 or more, and in some instances at a pH of about 7.6 or more. Inks containing 1-methylimidazole also exhibited advantages such as reduced or no ink deposits on the printhead heaters after 1×10 7 pulses and kogation-free performance in thermal ink jet printers. These inks also exhibited microscopic phase separation (i.e., formation of liposomes) under jetting conditions, which, it is believed, resulted in a significantly reduced surface area to mass ratio that reduced contact with the printer heater surface and thus reduced kogation. The inks also exhibited no macroscopic phase separation (which is undesirable) when maintained at pH conditions of about 7.6 or higher and heated to about 60°C. Any suitable or desired acid can be employed to adjust the pH of the ink to the desired level, such as hydrochloric acid, formic acid, phosphorous acid, or the like, with monomeric compound having at least two carboxylic acid functional groups, such as 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, being preferred. The ink compositions are generally of a viscosity suitable for use in thermal ink jet printing processes. At room temperature (i.e., about 25°C), typically, the ink viscosity is no more than about 5 centipoise, and preferably is from 1 to 2.5 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 8 to 9.5, and preferably from 8.0 to 9.0, although the pH can be outside of these ranges. In one specific embodiment of the present invention, the material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] is purified prior to admixing it with the other ink ingredients. This material is frequently supplied in liquid form from the commercial supplier as a colloidal suspension. Purification is accomplished by centrifugation of the liquid containing the material. The liquid can contain the material in any suitable or desired amount. Typically, the material of the formula ((F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] is present in the liquid in an amount of from 20 to 50 percent by weight, and preferably from 25 to 35 percent by weight, although the amount can be outside these ranges. To obtain these concentrations, typically a commercially supplied colloidal suspension is diluted by admixing one part by weight of the suspension with about 5 parts by weight of water. Subsequent to centrifugation, the clear supemate contains the purified material and the milky, flocculated bottom layer contains impurities. Typical centrifugation speeds are from 1,000 to 20,000 revolutions per minute, and preferably from 5,000 to 15,000 revolutions per minute, although the speed can be outside these ranges. Typical centrifugation times are from 10 to 60 minutes, and preferably from 15 to 30 minutes, although the time can be outside these ranges. In one specific example of this process, LODYNE P-201, which is sold as a solution of the material in water at a concentration of about 30 percent by weight solids, is further diluted by admixing one part by weight of the LODYNE P-201 solution and five parts by weight water. This mixture is then centrifuged at about 10,000 rpm for about 1 hour, thereby generating a supernate containing about 4.25 percent by weight of the solid material. Advantages of inks containing the purified material over inks containing the unpurified material include increased surface tension, improved 1.2 micron filterability, and improved thermal stability with respect to viscosity increase. The inks containing the purified material also exhibit good latency, jitter characteristics, drop size, and transit time. 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® 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. All parts and percentages in the examples are by weight unless otherwise indicated. EXAMPLE I A solution was prepared as follows. Deionized water (64.99 grams) was admixed with 15.01 grams of betaine (obtained from Finnsugar Biomedical, Helsinki, Finland) and 6.01 grams of triethanolamine (obtained from Aldrich Chemical Co., Milwaukee, WI). These materials were stirred for 5 minutes at 23.8°C, after which the pH of the solution was 10.64. Thereafter, dilute phosphorous acid (7 percent by weight of the acid in water) (obtained from Rhone Poulenc, Cranbury, New Jersey) was added in an amount of 0.81 grams, bringing the pH of the solution to 9.52 at 23.8°C. Subsequently, 0.101 gram of DOWICIL 150 biocide (obtained from Dow Chemical Co., Midland, MI), 3 grams of LODYNE P-201 (obtained from Ciba-Geigy, Ardsley, New York), and 7.08 grams of deionized water were added to the solution, which was then stirred for 30 minutes, after which the solution was homogeneous, very slightly milky, and colorless. The solution was then filtered through a 1.2 micron/#1 Whatman/Celite filter at 137,9 kPa 20 pounds per square inch over a period of 2 minutes and 20 seconds, yielding 86 grams of filtrate. The freshly filtered solution exhibited a viscosity of 2.09 centipoise and a pH of 9.48 at 23.8°C. After sitting for one day under ambient conditions, the solution exhibited a viscosity of 2.05 centipoise. Colored inks were then prepared as follows: To 19.30 grams of the solution thus prepared was added Acid Yellow 23 dye (added as a solution containing 3 percent by weight dye solids, obtained from Tricon, Elmwood Park, New Jersey, so that a total of 0.7013 gram of dye solids was added), after which the yellow solution was stirred for 10 minutes at room temperature, resulting in a yellow ink. To 19.31 grams of the solution thus prepared were added Acid Blue 9 dye (added as a solution containing 3 percent by weight dye solids, obtained from Tricon, Elmwood Park, New Jersey, so that a total of 0.6009 gram of dye solids was added) and 0.11 gram of deionized water, after which the cyan solution was stirred for 10 minutes at room temperature, resulting in a cyan ink. To 19.34 grams of the solution thus prepared was added Reactive Red 180 dye (added as a solution containing 3 percent by weight dye solids, obtained from Hoechst, Coventry, Rhode Island, so that a total of 0.7000 gram of dye solids was added), after which the magenta solution was stirred for 10 minutes at room temperature, resulting in a magenta ink. The inks thus prepared were incorporated into a Hewlett-Packard DJ-500C thermal ink jet printer and used to generate prints at 300 dots per inch on a variety of plain papers, recycled office papers, and paper towels. A five second delay was employed between printing of colors, during which the printed colors were subjected to heat with a heat gun. The resulting prints exhibited no intercolor bleed. It is believed that no heat and delay process will be needed to reduce intercolor bleed when the inks are employed to generate images at 600 dots per inch. EXAMPLE II A solution was prepared as follows. Deionized water (129.42 grams) was admixed with 30 grams of betaine (obtained from Finnsugar Biomedical, Helsinki, Finland) and 12 grams of 1-methylimidazole (obtained from Aldrich Chemical Co., Milwaukee, WI). These materials were stirred to homogeneity at 25.0°C, after which the pH of the solution was 10.73. Thereafter, phosphorous acid (70 percent by weight of the acid in water) (obtained from Rhone Poulenc, Cranbury, New Jersey) was added in an amount of 0.82 grams, bringing the pH of the solution to 8.12 at 26.1°C. Subsequently, 0.2003 gram of DOWICIL 150 biocide (obtained from Dow Chemical Co., Midland, MI), 5.99 grams of LODYNE P-201 (obtained from Ciba-Geigy, Ardsley, New York), and 14.58 grams of deionized water were added to the solution, which was then stirred for 30 minutes, after which the solution was homogeneous, very slightly milky, and colorless. The solution was then filtered through a 1.2 micron nylon filter and a 5 micron nylon/Celite filter at 20 pounds per square inch 137,9 kPa over a period of 1 minutes and 40 seconds. The freshly filtered solution exhibited a viscosity of 1.97 centipoise, a pH of 8.22 at 26.1°C, and a surface tension of 31.2 dynes per centimeter 3,12×10 -4 N/cm. The solution was then placed in an oven and maintained at 60°C for 20 hours, after which the solution exhibited a viscosity of 2.40 centipoise and exhibited no phase separation. To 48.25 grams of the solution thus prepared were added 1.74 grams of Acid Yellow 23 dye (DUASYN Acid Yellow XX-SF LP-413, obtained from Hoechst, Coventry, Rhode Island). The yellow solution was stirred for 10 minutes at room temperature, resulting in formation of a yellow ink with a viscosity of 2.19 centipoise and a pH of 8.27 at 26.1°C. The yellow ink was then placed in an oven and maintained at 60°C for 20 hours, after which the yellow ink exhibited a viscosity of 2.86 centipoise and exhibited no phase separation. The ink thus prepared was incorporated into a thermal ink jet test fixture and used to generate images. No traces of ink deposits on the printhead heater were observed after 8×10 6 pulses at 31.0 volts. To 48.25 grams of the solution thus prepared were added 1.76 grams of Reactive Red 180 dye (DUASYN Brilliant Red F3B-SF VP218, obtained from Hoechst, Coventry, Rhode Island). The magenta solution was stirred for 10 minutes at room temperature, resulting in formation of a yellow ink with a viscosity of 2.15 centipoise and a pH of 8.22 at 26.1°C. The magenta ink was then placed in an oven and maintained at 60°C for 20 hours, after which the magenta ink exhibited a viscosity of 2.09 centipoise and exhibited no phase separation. The magenta ink was maintained for another day under ambient conditions, after which the magenta ink exhibited a viscosity of 2.15 centipoise. The ink thus prepared was incorporated into a thermal ink jet test fixture and used to generate images. No traces of ink deposits on the printhead heater were observed after 4×10 6 pulses at 31.0 volts. To 48.75 grams of the solution thus prepared were added 1.49 grams of Acid Blue 9 dye (DUASYN Acid Blue AE-SF VP344, obtained from Hoechst, Coventry, Rhode Island) and 0.25 gram of deionized water. The cyan solution was stirred for 10 minutes at room temperature, resulting in formation of a cyan ink with a viscosity of 1.99 centipoise and a pH of 8.21 at 26.1°C. The cyan ink was then placed in an oven and maintained at 60°C for 20 hours, after which the cyan ink exhibited a viscosity of 7.78 centipoise and exhibited no phase separation. The cyan ink was maintained for another day under ambient conditions, after which the cyan ink exhibited a viscosity of 1.99 centipoise. The inks thus prepared were incorporated into a Hewlett-Packard DJ-500C thermal ink jet printer and used to generate prints at 300 dots per inch on a variety of plain papers, recycled office papers, and paper towels. A five second delay was employed between printing of colors, during which the printed colors were subjected to heat with a heat gun. The resulting prints exhibited no intercolor bleed. It is believed that no heat and delay process will be needed to reduce intercolor bleed when the inks are employed to generate images at 600 dots per inch. EXAMPLE III A yellow ink composition was prepared as follows. To 66.65 grams of PROJET FAST YELLOW 2 dye (containing 4.5 percent by weight dye solids, obtained from Zeneca, Dighton, Massachusetts) was added 15.02 grams of betaine (obtained from Finnsugar Biomedical, Helsinki, Finland) and 6.01 grams of 1-methylimidazole (obtained from Aldrich Chemical Co., Milwaukee, WI). These materials were stirred to homogeneity at 25.4°C, after which the pH of the solution was 9.09. Thereafter, phosphorous acid (70 percent by weight of the acid in water) (obtained from Rhone Poulenc, Cranbury, New Jersey) was added in an amount of 0.37 gram, bringing the pH of the solution to 8.47 at 26.1°C. Subsequently, 0.1001 gram of DOWICIL 150 biocide (obtained from Dow Chemical Co., Midland, MI), 3.01 grams of LODYNE P-201 (obtained from Ciba-Geigy, Ardsley, New York), and 8.96 grams of deionized water were added to the solution, which was then stirred for 30 minutes, after which the solution was homogeneous. The solution was then filtered through a 1.2 micron nylon filter and a 5 micron nylon/Celite filter at 20 pounds per square inch 137,9 kPa over a period of 45 seconds. The freshly filtered yellow ink exhibited a viscosity of 2.17 centipoise and a pH of 8.52 at 26.1°C. The yellow ink was then placed in an oven and maintained at 60°C for 3 days, after which the yellow ink exhibited a viscosity of 2.35 centipoise and exhibited no phase separation. The yellow ink was maintained for another 3 days at 60°C, after which the yellow ink exhibited a viscosity of 2.64 centipoise. The yellow ink was subsequently maintained for 6 more days under ambient conditions, after which the yellow ink exhibited a viscosity of 2.09 centipoise. The yellow ink was applied to COURTLAND 4024 DP paper with a #3 wire wound rod to form an image, which image was then allowed to remain under ambient conditions for 1 day. Thereafter, the image was soaked in deionized water for 5 minutes. The optical density of the image prior to soaking was 0.78 and subsequent to soaking was 0.70, indicating a waterfastness of 90 percent. A cyan ink composition was prepared as follows. To 66.68 grams of PROJET FAST CYAN 2 dye (containing 4.5 percent by weight dye solids, obtained from Zeneca, Dighton, Massachusetts) was added 15.01 grams of betaine (obtained from Finnsugar Biomedical, Helsinki, Finland) and 6 grams of 1-methylimidazole (obtained from Aldrich Chemical Co., Milwaukee, WI). These materials were stirred to homogeneity at 25.6°C, after which the pH of the solution was 8.83. Thereafter, phosphorous acid (70 percent by weight of the acid in water) (obtained from Rhone Poulenc, Cranbury, New Jersey) was added in an amount of 0.22 gram, bringing the pH of the solution to 8.49 at 26.1°C. Subsequently, 0.1004 gram of DOWICIL 150 biocide (obtained from Dow Chemical Co., Midland, MI), 3.01 grams of LODYNE P-201 (obtained from Ciba-Geigy, Ardsley, New York), and 9.12 grams of deionized water were added to the solution, which was then stirred for 30 minutes, after which the solution was homogeneous. The solution was then filtered through a 1.2 micron nylon filter and a 5 micron nylon/Celite filter at 20 pounds per square inch 137,9 kPa over a period of 2 minutes. The freshly filtered cyan ink exhibited a viscosity of 2.15 centipoise and a pH of 8.64 at 26.1°C. The cyan ink was then placed in an oven and maintained at 60°C for 3 days, after which the cyan ink exhibited a viscosity of 2.20 centipoise and exhibited no phase separation. The cyan ink was maintained for another 3 days at 60°C, after which the cyan ink exhibited a viscosity of 2.27 centipoise. The cyan ink was subsequently maintained for 6 more days under ambient conditions, after which the cyan ink exhibited a viscosity of 2.12 centipoise. The cyan ink was applied to COURTLAND 4024 DP paper with a #3 wire wound rod to form an image, which image was then allowed to remain under ambient conditions for 1 day. Thereafter, the image was soaked in deionized water for 5 minutes. The optical density of the image prior to soaking was 1.25 and subsequent to soaking was 1.17, indicating a waterfastness of 94 percent. A magenta ink composition was prepared as follows. To 60.03 grams of PROJET FAST MAGENTA 2 dye (containing 5 percent by weight dye solids, obtained from Zeneca, Dighton, Massachusetts) was added 5.07 grams of deionized water, 15.01 grams of betaine (obtained from Finnsugar Biomedical, Helsinki, Finland) and 6.01 grams of 1-methylimidazole (obtained from Aldrich Chemical Co., Milwaukee, WI). These materials were stirred to homogeneity at 25.6°C, after which the pH of the solution was 8.83. Thereafter, phosphorous acid (70 percent by weight of the acid in water) (obtained from Rhone Poulenc, Cranbury, New Jersey) was added in an amount of 0.18 gram, bringing the pH of the solution to 8.49 at 26.1°C. Subsequently, 0.1003 gram of DOWICIL 150 biocide (obtained from Dow Chemical Co., Midland, MI), 3 grams of LODYNE P-201 (obtained from Ciba-Geigy, Ardsley, New York), and 10.73 grams of deionized water were added to the solution, which was then stirred for 30 minutes, after which the solution was homogeneous. The solution was then filtered through a 1.2 micron nylon filter and a 5 micron nylon/Celite filter at 20 pounds per square inch 137,9 kPa over a period of 43 seconds. The freshly filtered magenta ink exhibited a viscosity of 2.27 centipoise and a pH of 8.56 at 26.1°C. The magenta ink was then placed in an oven and maintained at 60°C for 3 days, after which the magenta ink exhibited a viscosity of 2.27 centipoise and exhibited no phase separation. The magenta ink was maintained for another 3 days at 60°C, after which the magenta ink exhibited a viscosity of 2.35 centipoise. The magenta ink was subsequently maintained for 6 more days under ambient conditions, after which the magenta ink exhibited a viscosity of 2.35 centipoise. When subjected to shear at 60 rpm over 15 minutes, the ink viscosity rose to 2.61 centipoise. The magenta ink was applied to COURTLAND 4024 DP paper with a #3 wire wound rod to form an image, which image was then allowed to remain under ambient conditions for 1 day. Thereafter, the image was soaked in deionized water for 5 minutes. The optical density of the image prior to soaking was 1.28 and subsequent to soaking was 1.06, indicating a waterfastness of 83 percent. A black ink composition was prepared as follows. To 70.01 grams of PROJET FAST BLACK 2 dye (containing 5 percent by weight dye solids, obtained from Zeneca, Dlghton, Massachusetts) was added 15.01 grams of betaine (obtained from Finnsugar Biomedical, Helsinki, Finland) and 6 grams of 1-methylimidazole (obtained from Aldrich Chemical Co., Milwaukee, WI). These materials were stirred to homogeneity at 25.1°C, after which the pH of the solution was 8.91. Thereafter, phosphorous acid (70 percent by weight of the acid in water) (obtained from Rhone Poulenc, Cranbury, New Jersey) was added in an amount of 0.31 gram, bringing the pH of the solution to 8.43 at 25.9°C. Subsequently, 0.0997 gram of DOWICIL 150 biocide (obtained from Dow Chemical Co., Midland, Ml), 3.01 grams of LODYNE P-201 (obtained from Ciba-Geigy, Ardsley, New York), and 5.86 grams of deionized water were added to the solution, which was then stirred for 30 minutes, after which the solution was homogeneous. The solution was then filtered through a 1.2 micron nylon filter and a 5 micron nylon/Celite filter at 20 pounds per square inch 137,9 kPa over a period of 40 seconds. The freshly filtered black ink exhibited a viscosity of 2.09 centipoise and a pH of 8.62 at 25.9°C. The black ink was then placed in an oven and maintained at 60°C for 3 days, after which the black ink exhibited a viscosity of 2.02 centipoise and exhibited no phase separation. The black ink was maintained for another 3 days at 60°C, after which the black ink exhibited a viscosity of 2.19 centipoise. The black ink was subsequently maintained for 6 more days under ambient conditions, after which the black ink exhibited a viscosity of 1.99 centipoise. The black ink was applied to COURTLAND 4024 DP paper with a #3 wire wound rod to form an image, which image was then allowed to remain under ambient conditions for 1 day. Thereafter, the image was soaked in deionized water for 5 minutes. The optical density of the image prior to soaking was 1.31 and subsequent to soaking was 1.28, indicating a waterfastness of 98 percent. EXAMPLE IV To 800 grams of deionized water was added 200 grams of LODYNE P-201 (obtained from Ciba-Geigy, Ardsley, New York), resulting in formation of a light green, milky colloidal solution. The solution thus prepared was centrifuged for 1 hour at 10,000 rpm in 40 gram portions after which the supernatant liquid was removed with a pipet from the flocculated bottom layer. Deionized water (115.44 grams) was admixed with 45 grams of betaine (obtained from Finnsugar Biomedical, Helsinki, Finland) and 18 grams of 1-methylimidazole (obtained from Aldrich Chemical Co., Milwaukee, WI). These materials were stirred to homogeneity at 25.0°C, after which the pH of the solution was 10.73. Thereafter, phosphorous acid (70 percent by weight of the acid in water) (obtained from Rhone Poulenc, Cranbury, New Jersey) was added in an amount of 0.34 grams, bringing the pH of the solution to 8.70 at 26.3°C. Subsequently, 0.2999 gram of DOWICIL 150 biocide (obtained from Dow Chemical Co., Midland, MI), 99.99 grams of the purified LODYNE P-201 prepared by centrifugation hereinabove, and 12.19 grams of deionized water were added to the solution, which was then stirred for 30 minutes, after which the solution was homogeneous. The solution was then filtered through a 1.2 micron nylon filter and a 5 micron nylon/Celite filter at 5 pounds per square inch 34,5 kPa over a period of 40 seconds. To 87.3 grams of the solution thus prepared were added 2.71 grams of Acid Yellow 23 dye (DUASYN Acid Yellow XX-SF LP-413, obtained from Hoechst, Ardsley, New York). The yellow solution was stirred for 30 minutes at room temperature, resulting in formation of a yellow ink with a viscosity of 2.29 centipoise, a surface tension of 36.3 3,63 x 10 -4 N/cm dynes per centimeter, a conductivity of 6.58 millimhos, and a pH of 8.87 at 25.0°C. The yellow ink was then placed in an oven and maintained at 60°C for 3 days, after which the yellow ink exhibited a viscosity of 2.70 centipoise. To 87.29 grams of the solution thus prepared were added 2.47 grams of Acid Blue 9 dye (DUASYN Acid Blue AE-SF VP344, obtained from Hoechst, Ardsley, New York) and 0.21 gram of deionized water. The cyan solution was stirred for 30 minutes at room temperature, resulting in formation of a cyan ink with a viscosity of 2.07 centipoise, a surface tension of 37.3 dynes per centimeter 3,73 x 10 -4 N/cm a conductivity of 3.80 millimhos, and a pH of 8.83 at 24.4°C. The cyan ink was then placed in an oven and maintained at 60°C for 3 days, after which the cyan ink exhibited a viscosity of 2.05 centipoise. To 87.3 grams of the solution thus prepared were added 2.7 grams of Reactive Red 180 dye (DUASYN Brilliant Red F3B-SF VP218, obtained from Hoechst, Ardsley, New York). The magenta solution was stirred for 30 minutes at room temperature, resulting in formation of a magenta ink with a viscosity of 2.24 centipoise, a surface tension of 36.7 dynes per centimeter 3.67 x 10 -4 N/cm, a conductivity of 5.85 millimhos, and a pH of 8.74 at 24.4°C. The magenta ink was then placed in an oven and maintained at 60°C for 3 days, after which the magenta ink exhibited a viscosity of 2.20 centipoise. The inks thus prepared were incorporated into a Hewlett-Packard DJ-500C thermal ink jet printer and used to generate prints at 300 dots per inch on a variety of plain papers, recycled office papers, and paper towels. A five second delay was employed between printing of colors, during which the printed colors were subjected to heat with a heat gun.

Claims: An ink composition which comprises water, a colorant, betaine, a tertiary amine, and a material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ], wherein n is an integer of from 8 to 20 and B is a cation. The ink composition according to claim 1 wherein n is 10. The ink composition according to claim 1 wherein B is (HO-CH 2 CH 2 ) 2 NH 2 + . The ink composition according to claim 1 wherein the tertiary amine is 1-methylimidazole. The ink composition according to claim 1 wherein the tertiary amine is triethanolamine, triethylamine, tris[2-(2-methoxyethoxy)ethyl]amine, imidazole, N-butyl imidazole, or diethanolamine. The ink composition according to claim 1 wherein the colorant is selected from anionic dyes having carboxylate groups, anionic dyes having sulfonate groups, anionic dyes having both carboxylate and sulfonate groups, and mixtures thereof. A process for preparing an ink composition which comprises (a) providing a liquid composition containing a material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ], wherein n is an integer of from 8 to 20 and B is a cation; (b) subjecting the liquid composition to centrifugation, thereby causing the composition to separate into a supernatant top layer and a flocculated bottom layer; (c) separating the supernatant top layer from the flocculated bottom layer; and (d) admixing the supernatant top layer with an aqueous liquid vehicle and a colorant, thereby forming an ink composition. The process according to claim 7 wherein the material of the formula [(F 2n+1 C n CH 2 S) 2 (CH 3 )C-CH 2 CH 2 COO - ][B + ] is present in the liquid in an amount of from 20 to 50 percent by weight. A process which entails incorporating an ink according to claim 1 into an ink jet printing apparatus and causing droplets of the ink composition to be ejected in an imagewise pattern onto a substrate. The process according to claim 9 wherein 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.

Inventors: COLT RICHARD L, GUNDLACH KURT B, RADIGAN EDWARD J JR, COLT, RICHARD L., GUNDLACH, KURT B., RADIGAN, EDWARD J., JR.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1998
Main classification: C09D11
IPC codes: B41J2, C09D11, B41M5