WO1998044058A1

WO1998044058A1 - High intensity ultrasonic milling in the preparation of ink jet inks

Info

Publication number: WO1998044058A1
Application number: PCT/US1998/005878
Authority: WO
Inventors: Bonnie Dornblaser Piro; Howard Zakheim
Original assignee: E.I. Du Pont De Nemours And Company
Priority date: 1997-03-27
Filing date: 1998-03-26
Publication date: 1998-10-08

Abstract

A process for preparing ink jet comprises mixing together a pigment, a polymeric dispersant and an aqueous vehicle and subjecting the mixture to ultrasonic milling to reduce the percentage of particles with a size greater than about 200 nm.

Description

HIGH INTENSITY ULTRASONIC MILLING IN THE PREPARATION OF INK JET INKS

Background Of The Invention

This invention relates to a process for preparing ink jet inks and more specifically a high intensity ultrasonic milling process for preparing ink jet inks.

Inkjet printing is a non-impact method that produces droplets of ink which are deposited on a substrate such as paper or transparent film in response to a digital signal. Inkjet printers, especially thermal or bubble-jet drop-on-demand printers, have found broad application as output for personal computers in the office and the home.

Thermal ink jet print heads use multiple nozzles, each in line with a resistor element in a firing chamber, to fire ink droplets towards the print media. During proper operation of the printer, the resistor provides enough energy to clear the ink mass from the firing chamber upon firing. Mass left behind in the chamber after firing could subsequently impair the resistor's ability to fire. For ink jet inks containing particles such as pigment, particles above 200 nanometers may settle from the bulk ink into the firing chamber. This creates an increased number of solid particles in the firing chamber which increases the amount of energy needed to clear the chamber above that which the resistor is able to provide. On this condition, the resistor will no longer fire, resulting in decreased print quality from the ink jet print head. Pigment particles start in an agglomerated or flocculated state. Thus, it is necessary to disperse and stabilize the pigment so as to prevent flocculation and settling. The quality of the pigment dispersivity may also affect some ink jet printing characteristics such as ejectability, print quality, optical density, etc.

Inkjet inks have been made using a variety of different processes. U.S. Patent No. 5,026,427 teaches the use of a liquid jet interaction chamber in the preparation of pigmented ink jet inks. U.S. Patent No. 5,310,778 teaches the use of a two-roll mill in the preparation of ink jet inks. U.S. Patent No. 5,085,598 teaches the preparation of aqueous pigmented inks for ink jet printers using a media mill, a ball mill, an attritor or a liquid interaction chamber. U.S. Patent No. 4,597,794 teaches the preparation of pigmented ink jet inks by ball mill, roll-mill, speed line mill, homomixer, sand grinder and the like.

T. C. Patton, "Paint Flow and Pigment Dispersion", John Wiley & Sons, N.Y., N.Y., p. 386 (1979) discloses that a variety of different processes can be used to disperse pigments. These include ball and pebble mills, high speed disk impellers, high speed impingement mills, three-roll mills, high speed stone and colloid mills, sand mills and batch attritors.

However, there is a need in the art for an improved process of making pigmented ink jet inks having a decrease in the number of particles above 200 nanometers.

Summary Of The Invention

The present invention provides a process for making aqueous pigmented ink jet inks wherein a pigment and a polymeric dispersant are dispersed in an aqueous vehicle, the improvement wherein comprising subjecting the mixture of pigment, polymeric dispersant and aqueous medium to ultrasonic energy whereby the percentage of particles above 200 nanometers in the ink is decreased. Preferably, the step of subjecting the mixture to ultrasonic energy is used in combination with a dispersion step selected from the group consisting of media milling, two-roll milling and microfluidizing.

Detailed Description Of The Invention

Aqueous pigmented ink jet inks comprise an aqueous carrier medium and a pigment dispersion. The term "pigment dispersion as used herein means a pigment and a polymeric dispersant. The term "pigment" means an insoluble colorant which is in particulate form. Disperse dyes are included within the "pigment".

Inks made according to the process of the invention have been found to have remarkably improved stability and few nozzle clogs. This is a result of very tight particle size control and distribution achieved using the process of the invention. The present process has also been found to permit the preparation of inks having a wider range of pigment to polymer (P/B) ratios, which provides greater flexibility in the manufacture and formulation of ink jet inks.

Pigments

A wide variety of organic and inorganic pigments, alone or in combination are known in the art as suitable for the preparation of ink jet inks and these may be used in the present process as well. Small pigment particles also have an influence on stability of the pigment dispersion, which is critical throughout the life of the ink. Brownian motion of minute particles will help prevent the particles from settling. It is also desirable to use small particles for maximum color strength. The range of useful particle size is approximately 0.005 micron to 15 microns. Preferably, the pigment particle size should range from 0.005 to 5 micron, more preferably from 0.005 to 1 micron, and most preferably, from 0.01 to 0.5 micron.

The selected pigment may be used in dry or wet form. For example, pigments are usually manufactured in aqueous media and the resulting pigment is obtained as water wet presscake. Representative commercial dry and presscake pigments that may be used in practicing the invention are disclosed in the aforementioned US Patent 5,085,698, the disclosure of which is incorporated by reference. Fine particles of metal or metal oxides also may be used to practice the invention. For example, metal and metal oxides are suitable for the preparation of magnetic ink jet inks. Fine particle size oxides, such as silica, alumina, titania, and the like, also may be selected. Furthermore, finely divided metal particles, such as copper, iron, steel, aluminum and alloys, may be selected for appropriate applications.

In the case of organic pigments, the ink may contain up to approximately 30% pigment by weight, but will generally be in the range of approximately 0.1 to 15%, preferably approximately 0.1 to 8%, by weight of the total ink composition for most thermal ink jet printing applications. If an inorganic pigment is selected, the ink will tend to contain higher weight percentages of pigment than with comparable inks employing organic pigment, and may be as high as approximately 75% in some cases, because inorganic pigments generally have higher specific gravities than organic pigments.

Dispersants

Polymeric dispersants are the preferred dispersants for pigments. Polymeric dispersants suitable for practicing the invention include random, block, branched or graft polymers or copolymers. Most preferred are polymeric dispersants made by the group transfer polymerization process because these are free from higher molecular weight species that tend to plug pen nozzles. In AB or BAB block copolymers, the A segment is a hydrophobic homopolymer or copolymer which serves to link with the pigment and the B block is a hydrophilic homopolymer or copolymer, or salts thereof, and serves to disperse the pigment in the aqueous medium. Such polymeric dispersants and the synthesis thereof are disclosed in Ma et al.. US Patent 5,085,698. ABC triblocks are also useful as pigment dispersants. In the ABC triblock, the A block is a polymer compatible with water, the B block is a polymer capable of binding to the pigment and the C block is compatible with the organic solvent. The A and C blocks are end blocks. ABC triblocks and their synthesis are disclosed European Patent Application 0 556 649 Al published August 28, 1993. Some suitable graft polymers are disclosed in U.S. Patent 5,231,131.

The polymeric dispersant is generally present in the range of approximately 0.1 to 30% by weight of the total ink composition, preferably in the range of approximately 0.1% to 8% by weight of the total ink composition. Dispersion stability of the pigment particles is adversely affected if insufficient polymeric dispersant is present.

In addition to, or in place of the preferred polymeric dispersant compounds, surfactant compounds may be used as dispersants. These may be anionic, cationic, nonionic, or amphoteric surfactants. A detailed list of non- polymeric as well as some polymeric dispersants is provided in the section on dispersants, pages 110-129, 1990 McCutcheon's Functional Materials, North American Edition, Manufacturing Confection Publishing Co., Glen Rock, NJ, 07452, the disclosure of which is incorporated herein by reference.

Aqueous Carrier Medium

The aqueous carrier medium is water or a mixture of water and at least one water soluble organic solvent. Deionized water is commonly used. Water-soluble organic solvents are well known, representative examples of which are disclosed in US Patent 5,085,698. Selection of a suitable mixture of water and water soluble organic solvent depends upon requirements of the specific application, such as desired surface tension and viscosity, the selected colorant, drying time of the ink, and the media substrate onto which the ink will be printed. A mixture of a water soluble organic solvent having at least two hydroxyl groups (e.g, diethylene glycol) and deionized water is preferred as the aqueous carrier medium.

In the event that a mixture of water and organic solvent is used as the aqueous carrier medium, water would comprise between 30% and 95%, preferably 60% to 95%, by weight of the aqueous medium, based on the total weight of the aqueous carrier medium.

The amount of aqueous carrier medium is in the range of approximately 70 to 99.8%, preferably approximately 84 to 99.8%, based on total weight of the ink when an organic pigment is selected, approximately 25 to 99.8%, preferably approximately 70 to 99.8% when an inorganic pigment is selected and 80 to 99.8% when a dve is selected. Other Ingredients

The ink may contain other ingredients well known to those skilled in the art. For example surfactants may be used to alter surface tension as well as to maximize penetration. However, because surfactants may destabilize pigment dispersions, care should be taken to insure compatibility of the surfactant with the other ink components. In aqueous inks, the surfactants may be present in the amount of 0.01-5% and preferably 0.2-3%, based on the total weight of the ink.

Biocides may be used in the ink compositions to inhibit growth of microorganisms. Sequestering agents such as EDTA may also be included to eliminate deleterious effects of heavy metal impurities. Other known additives, such as viscosity modifiers and other acrylic or non-acrylic polymers may also be added to improve various properties of the ink compositions.

Dispersion Process The process for making aqueous pigmented ink jet inks according to the present invention comprises dispersing a pigment and a polymeric dispersant in an aqueous carrier medium, the improvement wherein the mixture of pigment, polymeric dispersant and aqueous medium is subjected to ultrasonic energy whereby a narrower particle size distribution is obtained in the ink. Preferably, the step of subjecting the mixture to ultrasonic energy is used in combination with a dispersion step selected from the group consisting of media milling, two-roll milling and microfluidizing.

The ultrasonic energy imparted to the mixture of pigment, polymeric dispersant and aqueous medium may be delivered by any system capable of applying ultrasonic longitudinal pressure oscillations sufficient to achieve performance results of the invention. The amount of cavitation energy input to the mixture being treated depends on the frequency of the ultrasonic vibrator and can be from about 10 to 85 KHz, preferably 15 to 60 KHz. Choice of the particular system to deliver the required energy can vary, the most energy efficient being preferred. Ultrasonic energy sources such as Telsonic Ultrasonics DG- 100, manufactured by Telsonic Ultrasonics (Bridgeport. NJ) and the Reverbatory Ultrasonic Mixer (RUM) commercially available from Lewis Corporation (Oxford, CT) may be successfully used in this invention. The Reverbatory Ultrasonic Mixer (RUM) is described in U.S. Patent 4,071,225, Col 3, line 64 et seq, the disclosure of which is incorporated herein by reference. Preferably, the ultrasonic milling of the mixture being processed is done in a recirculation process. The ultrasonic treating device is available from Branson Ultrasonics (Danbury, CT): Telsonic Ultrasonics (Bridgeport, NJ): Sonics and Materials Inc. (Danbury, CT) and Heat Systems/Misonix (Farmington, NY). A constant amplitude control over the entire load range is essential to achieve comparable and reproducible results. The ultrasonic probe itself has a flat face with which the ultrasonic waves are emitted to the fluid. A flow through reactor, such as that available from Quark Enterprises (Vineland, NJ) can be useful. The flow through reactor allows the fluid to remain in contact with the ultrasonic probe for a predetermined residence time.

Briefly, in one embodiment, the dispersion being processed is recirculated at various flow rates through the flow through reactor. The flow is from the bottom, and once this flow is established the ultrasonic probe is turned on. The ultrasonic waves are concentrated and emitted from the flat surface into the liquid mixture or dispersion. The system desirably provides very high ultrasonic intensities per unit volume without increasing input intensity per unit area, thus making treatment economical with dispersions of relatively high pigment concentrations or viscosities.

The concentration of the pigment particles in the mixture to be treated is tailored to the specific treatment system chosen and will also vary with the various components present in the mixture. Generally, the mixture should not be so viscous as to be difficult to handle, for example, by resisting flow in the treating device or so dilute as to prolong exposure time unnecessarily. Preferably the pigment concentration ranges from 2 to 40% based on the weight of pigment and dispersant.

The ultrasonic energy required for this process varies with the particle size of the pigments, efficiency of the treatment system and the solids content of the mixture. At the solids concentration noted above, the energy input of the dispersion is at least 10 watt-hr per cubic centimeter of the mixture at 7-30 KHz frequency.

In the preferred embodiment, before or after ultrasonic treatment, (preferably before) the mixture of the pigment and the polymeric dispersant in the aqueous vehicle is subjected to a dispersion step selected from the group consisting of media milling, two-roll milling and microfluidizing, etc. The two- roll milling process is described in U.S. Patent 5,310,778, the disclosure of which is incorporated herein by reference. The microfluidizing process is described in detail in U.S. Patent 5.026.427, the disclosure of which is incorporated herein by reference. In the media milling process, the mixture of ingredients is passed through a horizontal media mill containing grinding media until the desired particle size is obtained. The grinding media may be selected from the group consisting of glass, ceramic, plastic, steel, etc. It is generally desirable to make the ink jet inks in concentrated form, which is subsequently diluted with a suitable liquid to the appropriate concentration for use in the ink jet printing system. By dilution, the ink is adjusted to the desired viscosity, color, hue, saturation density, and print area coverage for the particular application.

Ink Properties

Jet velocity, separation length of the droplets, drop size, and stream stability are greatly affected by the surface tension and the viscosity of the ink. Ink jet inks suitable for use with ink jet printing systems should have a surface tension in the range of about 18 dyne/cm to about 70 dyne/cm and, more preferably, in the range 20 dyne/cm to about 50 dyne/cm at 20°C. Acceptable viscosities are no greater than 20 cP, and preferably in the range of about 1.0 cP to about 10.0 cP at 20°C with appropriate rheology for both image setting and thermal ink jet firing refill frequencies.

The ink has physical properties compatible with a wide range of ejecting conditions, i.e., driving voltage and pulse width for thermal ink jet printing devices, driving frequency of the piezo element for either a drop-on-demand device or a continuous device, and the shape and size of the nozzle. They may be used with a variety of ink jet or air brush printers such as continuous, piezoelectric drop-on-demand, thermal or bubble jet drop-on-demand and valve jet, and are particularly adapted for use in thermal ink jet printers. The inks have excellent storage stability for a long period and do not clog in an ink jet apparatus. Although particularly advantageous for use in printing plain-paper elements, the inks of this invention are also suitable for use with a variety of print media, such as fabrics, transparencies, etc. The printed ink images have clear color tones and high density. The inks are compatible with the component parts of ink jet printing devices and they are essentially odorless.

Examples

The invention will now be further illustrated by the following examples, in which parts and percentages are by weight unless otherwise noted. All ingredients used in the ink formulations were obtained from Aldrich Chemical (Milwaukee, WI) unless otherwise indicated. Preparation for Macromonomer used in Polymers 2 and 4

The macromonomer ethoxytriethyleneglycol methacrylate-co-methacrylic acid, 12.5/87.5 by weight was prepared using the following procedure:

Ingredients Weight (gram)

Portion 1 isopropanol 453.5 acetone 152.0 Portion 2 methacrylic acid monomer 360.5 ethoxytriethyleneglycol methacrylate monomer 52.2

Portion 3 Diaquabis(borondifluorodiphenyl glyoximato) 0.31 cobaltate (II), Co(DPG-BF2) 2,2'-azobis(2,2-dimethylvaleronitrile), 11.86

(Vazo® 52, by Du Pont Co., Wilmington, DE) acetone 150.0

The Portion 1 mixture was charged into a 3 liter flask equipped with a thermometer, stirrer, additional funnels, reflux condenser and a means of maintaining a nitrogen blanket over the reactants. The mixture was heated to reflux temperature and refluxed for about 20 minutes. Portions 2 and 3 were simultaneously added while the reaction mixture was held at the reflux temperature of about 70-71 °C. The addition of Portion 2 was completed in 4 hours and the addition of Portion 3 was completed in 4 1/2 hours. Reflux was continued for another 2 1/2 hours and the solution was cooled to room temperature. The resulting macromonomer solution was a clear thin polymer solution and had a solids content of about 32.2%. The macromonomer contained 12.5% of ethoxytriethyleneglycol methacrylate and 87.5% of methacrylic acid and had a weight average molecular weight of 3,350 and a number average molecular weight of 2,570 as measured by Gel Permeation Chromatography (GPC) on a methylated macromonomer sample using polymethyl methacrylate as the standard.

Preparation for Polymer 2

This shows the preparation of poly(methacrylic acid [48 mol%]-6-benzyl methacrylate [37 mol%]-6-ethoxy-triethylene glycol methacrylate [15 mol%]); MAA//BzMA//ETEGMA ( 13//10//4).

To a solution of 9.05 g ( 10.5 mL. 51.9 mmol) of 1 -methoxy- 1 - trimethylsiloxy-2-methyl-l-propene and 2 mL of tetrabutvlammonium biacetate (0.1 M in propylene carbonate) in 150 L of THF was added dropwise 107 g (121 mL, 0.677 mole) of trimethylsilyl methacrylate. During the course of the addition, the temperature of the reaction mixture rose slowly and an additional 2 mL portion of tetrabutylammonium biacetate (0.1 M in propylene carbonate) was added. The temperature continued to rise to 57°C after all of the monomer had been added. When the temperature fell to 33 °C, the addition of a mixture of 91.6 g (88.6 mL, 0.52 mole) of benzyl methacrylate (purified by passage over a column of basic alumina under argon) was begun. An additional 1 mL of tetrabutylammonium biacetate (0.1 M in propylene carbonate) was added when the temperature leveled off at 39°C. As the addition of monomer was complete, the temperature rose to 57°C. When the temperature had decreased to 35°C, 51.2 g (51.2 mL, 0.205 mole) of ethoxytriethylene glycol methacrylate (purified by passage over a column of basic alumina under argon) was added dropwise from an addition funnel, and the mixture was stirred overnight. Analysis of an aliquot of the solution by * H NMR showed that there was no residual monomer present. The solution of poly(trimethylsilyl methacrylate [48 mol%]-6-benzyl methacrylate [37 mol%]-ό-ethoxy-triethylene glycol methacrylate [15 mol%]) was refluxed for 12 hr with 150 mL of 0.03 M methanolic tetrabutyl-ammonium fluoride and an additional 100 mL of THF. After evaporation in a rotary evaporator under reduced pressure, the residual polymer was dried for 48 hr in a vacuum oven at 50°C to give 186.3 g of the polymer. ^H NMR analysis of the product showed that no trimethylsilyl ester groups remained.

The block polymer was neutralized with potassium hydroxide by mixing 20 g of the block polymer with 7 g of potassium hydroxide (45.6% solution in deionized water) and 173 g of deionized water until a homogeneous 10% polymer solution was obtained.

Preparation for Polymer 2

This shows the preparation of a graft copolymer, 2-phenoxyethyl acrylate- co-methyl methacrylate-g-ethoxytriethyleneglycol methacrylate-co-methacrylic acid, 56.9/19.8//2.9/20.4% by weight, from a macromonomer. Ingredients Weight (gram)

Portion 1

Macromonomer of Example 2 85.7 2-Pyrrolidone 30.0

Portion 2 t-butyl peroxypivalate (Lupersol® 1 1 , Elf 0.75 Atochem, North America, Inc.. Philadelphia, PA)

Acetone 5.0

Portion 3

2-Phenoxyethyl acrylate 73.2 Methyl methacrylate 25.5

Portion 4

Lupersol® 11 3.0

Acetone 20.0 Portion 5

Lupersol® 11 0.75

Acetone 5.0

The Portion 1 mixture was charged into a 500 mL flask equipped with a thermometer, stirrer, additional funnels, reflux condenser and a means of maintaining a nitrogen blanket over the reaction mixture. The mixture was heated to reflux temperature and refluxed for about 10 minutes. The Portion 2 solution was added. Subsequently, Portions 3 and 4 were simultaneously added while the reaction mixture was held at reflux temperature. The addition of Portions 3 and 4 was completed in 3 hours. The reaction mixture was refluxed for 1 hour. The Portion 5 solution was added. The reaction mixture was refluxed at about 66°C for an additional 2 hours. The mixture was distilled until about 74.5 g of volatiles were collected and 111.6 g of 2-pyrrolidone were added to yield 286.0 g of a 43.7% polymer solution. This graft copolymer contained a random copolymer of 56.9% by weight of 2-phenoxyethyl acrylate and 19.8% by weight of methyl methacrylate in the backbone and a random copolymer of 2.9% by weight of ethoxytriethyleneglycol methacrylate and 20.4% by weight of methacrylic acid in the arms. The graft copolymer had a weight average molecular weight of 60,460 and a number average molecular weight of 11 ,990 as measured by Gel Permeation Chromatography (GPC) using polystyrene as the standard.

Preparation for Polymer 3

Step 1: Preparation of macromonomer ethoxytriethyleneglycol methacrylate-co-methacrylic acid, 12.5/87.5 by weight ΛVO 98/44058

PCT/US98/05878

Ingredients Weight (gram)

Portion 1 isopropanol 453.5 acetone 152.0

Portion 2 methacrylic acid monomer 360.5 ethoxytriethyleneglycol methacrylate monomer 52.2

10

Portion 3

Diaquabis(borondifluorodiphenyl glyoximato) 0.31 cobaltate (II), Co(DPG-BF2)

2,2'-azobis(2,2-dimethylvaleronitrile), (Vazo® 52 11.86

15 by Du Pont Co., Wilmington, DE) acetone 150.0

The Portion 1 mixture was charged into a 3 liter flask equipped with a thermometer, stirrer, additional funnels, reflux condenser and a means of

20 maintaining a nitrogen blanket over the reactants. The mixture was heated to reflux temperature and refluxed for about 20 minutes. Portions 2 and 3 were simultaneously added while the reaction mixture was held at a reflux temperature of about 70-71 °C. The addition of Portion 2 was completed in 4 hours and the addition of Portion 3 was completed in 4 1/2 hours. Reflux was continued for

25 another 2 1/2 hours and the solution was cooled to room temperature.

The resulting macromonomer solution was a clear thin polymer solution and had a solid content of about 32.2%. The macromonomer contained 12.5% of ethoxytriethyleneglycol methacrylate and 87.5% of methacrylic acid and had a weight averge molecular weight of 3,350 and a number average molecular weight 0 of 2,570 as measured by Gel Permeation Chromatography (GPC) on a methylated macromonomer sample using polymethyl methacrylate as the standard.

Step 2: This shows the preparation of a graft copolymer, 2-phenoxyethyl acrylate-co-ethoxytriethyleneglycol methacrylate-g-ethoxytriethyleneglycol 5 methacrylate-co-methacrylic acid, 50.0/19.2//3.8/26.9% by weight, from macromonomer of Step 1. Ingredients Weight (gram)

Portion 1

Macromonomer 3605.6

2-Pyrrolidone (94.5% in deionized water) 584.8

Portion 2

Lupersol® 1 1 19.5

Isopropanol 146.2 Portion 3

2-Phenoxyethyl acrylate 1902.6

Ethoxytriethyleneglycol methacrylate 731.0

Portion 4 Lupersol® 11 78.0

Isopropanol 584.8

Portion 5

Lupersol® 11 19.5 Isopropanol 146.2

The Portion 1 mixture was charged into a 12L flask equipped with a thermometer, stirrer, additional funnels, reflux condenser and a means of maintaining a nitrogen blanket over the reaction mixture. The mixture was heated to reflux temperature and refluxed for about 10 minutes. The Portion 2 solution was added. Subsequently, Portion 3 and 4 were simultaneously added while the reaction mixture was held at the reflux temperature. The addition of Portions 3 and 4 was completed in 3 hours. The reaction mixture was refluxed for 1 hour. The Portion 5 solution was added. The reaction mixture was refluxed at about 71 °C for additional 2 hours. The mixture was distilled until about 3100 g of volatiles were collected and 4043.5 g of 2-pyrrolidone (94.5% in deionized water) were added to yield 8948.5 g of a 42.5% polymer solution.

Preparation for Polymer 4 This shows the preparation of a graft copolymer, butyl acrylate-co-methyl acrylate-g-ethoxytriethyleneglycol methacrylate-co-methacrylic acid, 66.2//4.2/29.6% by weight, from a macromonomer. Ingredients Weight (gram)

Portion 1

Macromonomer of Example 2 107.2

2-Pyrrolidone 30.0

Portion 2

Lupersol® 11 0.5

Isopropanol 5.0 Portion 3

Butyl acrylate 73.4

Portion 4

Lupersol® 11 3.0 Isopropanol 20.0

Portion 5

Lupersol® 11 0.5

Isopropanol 5.0

The Portion 1 mixture was charged into a 500 mL flask equipped with a thermometer, stirrer, additional funnels, reflux condenser and a means for maintaining a nitrogen blanket over the reaction mixture. The mixture was heated to the reflux temperature and refluxed for about 10 minutes. The Portion 2 solution was added. Subsequently, Portions 3 and 4 were simultaneously added while the reaction mixture was held at reflux temperature. The addition of Portions 3 and 4 was completed in 3 hours. The reaction mixture was refluxed for 1 hour. The Portion 5 solution was added. The reaction mixture was refluxed for another hour. The mixture was distilled until about 98.6 g of volatiles were collected and 92.0 g of 2-pyrrolidone were added to yield 238 g of a 45.4% polymer solution. This graft copolymer contained a homopolymer of 66.2% by weight of butyl acrylate in the backbone and a random copolymer of 4.2% by weight of ethoxytriethyleneglycol methacrylate and 29.6% by weight of methacrylic acid in the arms. The graft copolymer had a weight average molecular weight of 33,500 and a number average molecular weight of 18,600 as measured by Gel Permeation Chromatography (GPC) on a methylated sample using polymethyl methacrylate as the standard.

Preparation for Polymer 5 This shows the prepatation of BMA/MMA//MAA (10/5//10) block copolymer.

A 12-liter flask was equipped with a mechanical stirrer, thermometer, N2 inlet, drying tube outlet, and addition funnels. Tetrahydrofuran THF, 3027 gm, and p-xylene, 6.2 gm, were charged to the flask. The catalyst tetrabutyl ammonium m-chlorobenzoate. 2.5 ml of a 1.0 M solution in acetonitrile, was then added. Initiator, 1,1 -bis(trimethylsiloxy)-2-methyl propene, 234.4 gm (1.01 M) was injected. Feed I [tetrabutyl ammonium m-chlorobenzoate, 2.5 ml of a 1.0 M solution in acetonitrile] was started and added over 150 minutes. Feed II [trimethylsilyl methacrylate, 1580 gm (10.0 M)] was started at 0.0 minutes and added over 30 minutes. One hundred and twenty minutes after Feed II was completed (over 99 % of the monomers had reacted), Feed III [butyl methacrylate, 1425 gm (10.0 M), and methyl methacrylate, 503 gm (5.0 M)] was started and added over 30 minutes. At 320 minutes, 650 gm of dry methanol were added to the above solution and distillation was begun. During the first stage of distillation, 1250.0 gm of material were removed from the flask. I-propanol, 1182 gm total, was added. Distillation continued and a total of 2792 gm of solvent were removed. This made a butyl methacry late/methyl methacrylate//methacrylic acid (10/5// 10) AB block polymer of 2900 Mn and 50.5 % solids.

Preparation for Polymer 6

This shows the preparation of BZMA//MAA 13// 10 block copolymer. A 12-liter flask was equipped with a mechanical stirrer, thermometer, N2 inlet, drying tube outlet, and addition funnels. Tetrahydrofiiran THF, 3750 gm, and p-xylene, 7.4 gm, were charged to the flask. The catalyst tetrabutyl ammonium m-chlorobenzoate, 3.0 ml of a 1.0 M solution in acetonitrile, was then added. Initiator, l,l-bis(trimethylsiloxy)-2 -methyl propene, 291.1 gm (1.25 M) was injected. Feed I [tetrabutyl ammonium m-chlorobenzoate, 3.0 ml of a 1.0 M solution in acetonitrile] was started and added over 180 minutes. Feed II

[trimethylsilyl methacrylate, 1975 gm (12.5 M)] was started at 0.0 minutes and added over 35 minutes. One hundred minutes after Feed II was completed (over 99 % of the monomers had reacted) Feed III [benzyl methacrylate, 2860 gm (16.3 M)] was started and added over 30 minutes. At 400 minutes, 720 gm of methanol were added to the above solution and distillation begun. During the first stage of distillation, 1764.0 gm of material were removed. Then more methanol 304.0 gm was added and an additional 2255.0 gm of material were distilled out.

The polymer has a composition of BZMA//MAA 13//10. It has a molecular weight of Mn = 3.200 and 49.7% solids. Example 1

A black pigment dispersion was prepared by premixing 731.7 grams of Polymer 1; 600 grams of FW-18 black pigment (Degussa Corp., Allendale, NJ); 2548.3 grams of deionized water and 120 grams of 45% potassium hydroxide. The premix was charged to a microfluidizer (Microfluidics Corporation, Newton, MA) under a liquid pressure of 9000 to 10,000 psi, 5 times, to give a 15% concentrate with a pigment to dispersant ratio (P/D) of 2.0 and a mean particle size of about lOOnm as measured by a Microtrac® UPA 150 Particle Size Analyzer (Honeywell, Clearwater, FL). The dispersion was divided into two portions. One portion was reserved as the control sample. The other portion of the dispersion was then recirculated at a set flowrate in a flow through glass reactor supplied by Quark Enterprise, Vineland, NJ. The recirculating dispersion was subjected to ultrasonic energy via a cell disruptor (Telsonic Ultrasonics DG-10, Bridgeport, NJ) for a period of time, shown in Table 1 below, to form a dispersion having a more uniform particle size distribution. The particle size of the was measured using the Microtrac® UPA 150 Particle Size Analyzer. Results are shown in Table 1 below.

Example la Example 1 was repeated with the following exception: the premix was subjected to only 4 passes through the microfluidizer. Results are shown in Table 1.

Example lb Example 1 was repeated with the following exception: the premix was subjected to only 3 passes through the microfluidizer. Results are shown in Table 1.

Example lc Example 1 was repeated with the following exception: the premix was subjected to only 2 passes through the microfluidizer. Results are shown in Table

1.

Example Id Example 1 was repeated with the following exception: the premix was subjected to only 1 pass through the microfluidizer. Results are shown in Table 1. Example 2

Example 1 was repeated with the following exception: the premix was prepared and subjected to 2 hours in a high speed dispersing apparatus manufactured by Hockmeyer, (Harrison, NJ) at 3000 rpm. Results are shown in Table 1.

Example 3

Example 1 was repeated with the following exception: the amounts of Polymer 1, deionized water and potassium hydroxide were 609.7 grams, 2690.3 grams and 100 grams, respectively. The P/D ratio was 2.4.

Example 4

Example 1 was repeated with the following exceptions: Polymer 2 was used instead of Polymer 1. The amounts of Polymer 2, deionized water and potassium hydroxide were 522.6 grams, 2794.4 grams and 85 grams, respectively. The P/D ratio was 2.8.

Example 5

Example 4 was repeated with the following exceptions: the premix was processed in a horizontal media mill (Dynomill manufactured by C. B. Mills, Illinois), 8 times using 0.8 mm zirconia media at an 85% media load. Polymer 3 was used instead of Polymer 2.

Example 6 Example 4 was repeated with the following exceptions: the P/D ratio was

3.8.

TABLE 1

Example Time (minutes) Flow rate (L/min) Median Particle Size (nm Particles of size <204 nm (%) Controi Example Control Example Portion Portion Portion Portion

1 360 0.5 102.7 93.1 97.46 98.41 la 240 0.5 92.1 92.7 97.91 97.98 lb 240 0.5 106.0 96.9 87.97 98.13 lc 240 0.5 102.2 95.1 97.81 97.63 id 240 0.5 105.7 100.9 96.47 97.49

2 240 0.5 128.4 104.2 90.61 98.79

3 360 0.5 109.9 100.3 97.03 97.82

4 180 0.11 109.5 108.9 95.70 96.56

7 pass 1 - - 153.7 74.63 - pass 4 - - 135.0 81.05 - pass 8 240 0.5 121.1 96.6 89.18 96.83

8 pass 1 - - 163.7 65.34 - pass 4 - - 137.7 82.70 - pass 8 240 0.5 124.5 95.2 88.73 97.79

Example 7 A black pigment dispersion was prepared by mixing together 100 grams of

Polymer 5; 200 grams of FW-18 pigment and 200 grams of diethylene glycol. The premixture was then charged to a two roll mill (Model XJF-S2637 Adalet Manufacturing Co., Cleveland OH) and processed for 45 minutes. The temperature of one roll was held at 150°C and the other roll was approximately 10°C cooler. This made a pigment dispersion that contained 50% pigment, 25% polymer (P/D ratio =2/1) and 25% diethylene glycol.

An aqueous pigment concentrate using potassium hydroxide as the neutralizing agent was then prepared by mixing 1193 grams of pigment dispersion prepared above with 109.8 grams of 45% KOH and 2697.2 grams of deionized water with stirring. The resulting pigment concentrate contained 15% pigment. The pigment concentrate was divided into two portions. One portion was reserved as the control sample. The second portion was subjected to ultrasonic milling as in Example 1. The particle size distribution of the concentrate was then measured by Microtrac UPA 150. Results are shown in Table 2 below. Example 8

A yellow pigment dispersion was prepared by mixing together 305.4 grams of Polymer 6; 183.3 grams of Y- 128 pigment (Diazo Yellow 8GN from Ciba) and 64 grams of diethylene glycol. The premixture was then charged to a two roll mill and processed for 45 minutes as in Example 7. This made a pigment dispersion that contained 45.82% pigment, 38.18% polymer (P/D ratio =1.2/1) and 16% diethylene glycol.

An aqueous pigment concentrate using potassium hydroxide as the neutralizing agent was then prepared by mixing 1309.4 grams of pigment dispersion prepared above with 136 grams of 45% KOH and 2554.6 grams of deionized water with stirring. The resulting pigment concentrate contained 15% pigment.

The pigment concentrate was divided into two portions, with one portion being reserved as the control and the other subjected to ultrasonic milling and measured as in Examples 1 and 2. Results are shown in Table 2 below.

Example 9

A magenta pigment dispersion was prepared by mixing together 272 grams of Polymer 6; 204 grams of PR-122 pigment (Quindo Magenta 122, BASF) and 66 grams of diethylene glycol. The premixture was then charged to a two roll mill and processed as in Example 7. This made a pigment dispersion that contained 51% pigment, 34% polymer (P/D ratio =1.5/1) and 15% diethylene glycol. An aqueous pigment concentrate using potassium hydroxide as the neutralizing agent was then prepared by mixing 1176.4 grams of pigment dispersion prepared above with 140 grams of 45% KOH and 2683.6 grams of deionized water with stirring. The resulting pigment concentrate contained 15% pigment. The pigment concentrate was divided, subjected to ultrasonic milling and sized as in the previous examples. Results are reported in Table 2.

Example 10

A cyan pigment dispersion was prepared by mixing together 144 grams of Polymer 6; 216 grams of PB 15:3 pigment (Endurophthal Blue GF BT-617-D) and 40 grams of diethylene glycol. The premixture was then charged to a two roll mill and processed as in previous examples. This made a pigment dispersion that 44058

PCT/US98/05878

contained 54% pigment, 36% polymer (P/D ratio =1.5/1) and 10% diethylene glycol.

An aqueous pigment concentrate using potassium hydroxide as the neutralizing agent was then prepared by mixing 1111.2 grams of pigment dispersion prepared above with 136 grams of 45% KOH and 2752.8 grams of deionized water with stirring. The resulting pigment concentrate contained 15% pigment. The pigment concentrate was divided, milled and sized as above. Results are shown in Table 2.

10 TABLE 2

Example Time (minutes) Flow rate (IJiriin) Median Particle Size (nm) Particles of size <204 nm Control Example Control Example Portion Portion Portion Portion

7 240 0.5 129.1 90.53 97.6 97.33

8 240 0.5 99.2 71.7 89.9 95.67

9 240 0.5 105.4 100 60.3 100.0

10 240 0.5 93.4 95.53 85.9 98.44

Claims

WHAT IS CLAIMED IS:

1. In a process for making aqueous pigmented ink jet inks wherein a pigment and a polymeric dispersant are dispersed in an aqueous vehicle, the improvement wherein comprises subjecting the mixture of pigment, polymeric dispersant and aqueous medium to ultrasonic energy to reduce the percentage of particles having a size greater than about 200 nm.

2. The improved process of claim 1 , wherein the ultrasonic energy is provided by an ultrasonic vibrator at a frequency of 10 to 85 KHz.

3. The improved process of claim 2, wherein the frequency of the ultrasonic vibrator is 15 to 60 KHz.

4. The improved process of claim 1 , further comprising the step of subjecting the mixture to a dispersion step selected from the group consisting of media milling, two-roll milling and microfluidizing.

5. The improved process of claim 1, wherein the polymeric dispersant is selected from the group consisting of random, block, graft and branched polymers and copolymers.

6. The improved process of claim 5, wherein the polymeric dispersant is selected from the group consisting of AB diblock co-polymers, ABC triblock copolymers and branched co-polymers.

7. The improved process of claim 5, wherein the polymeric dispersant is present in the amount of 0.1 to 30% by weight based on the weight of the total ink composition.

8. The improved process of claim 1 , wherein the pigment is present in the amount of 2 to 40% based on the weight of the pigment and dispersant.

9. The improved process of claim 1, wherein the aqueous carrier medium comprises a mixture of water and a water soluble organic solvent.

10. A process for making an aqueous pigmented ink jet ink comprising the steps of:

(a) mixing a pigment and a polymeric dispersant together in an aqueous vehicle; and (b) subjecting the mixture to ultrasonic energy to reduce the percentage of particles having a size greater than about 200 nm.

11. The process of claim 10, wherein the ultrasonic energy is provided by an ultrasonic vibrator at a frequency of 10 to 85 KHz.

12. The improved process of claim 11, wherein the frequency of the ultrasonic vibrator is 15 to 60 KHz.

13. The process of claim 10, further comprising the step of subjecting the mixture to a dispersion step selected from the group consisting of two-roll milling, media milling and microfluidizing.

14. The process of claim 10, wherein the polymeric dispersant is selected from the group consisting of random, block, graft and branched polymers and copolymers.

15. The process of claim 14, wherein the polymeric dispersant is selected from the group consisting of AB diblock co-polymers, ABC triblock co-polymers and branched co-polymers.

16. The process of claim 14, wherein the polymeric dispersant is present in the amount of 0.1 to 30% by weight based on the weight of the total ink composition.

17. The process of claim 10, wherein the pigment is present in the amount of 2 to 40% based on the weight of the pigment and dispersant.

18. The process of claim 10, wherein the aqueous carrier medium comprises a mixture of water and a water soluble organic solvent.