HK1118852B - Process for preparing modified pigments - Google Patents

Description

Process for preparing modified pigments

Background

Technical Field

The present invention relates to a process for preparing a modified pigment comprising a pigment having attached at least one organic group, and the resulting modified pigment. Inkjet ink compositions are also disclosed.

Background

The surface of the pigment contains a variety of different functional groups, the type of functional group present depending on the particular type of pigment. Several methods have been developed for grafting materials to the surface of these pigments. For example, it has been shown that polymers can be attached to carbon blacks containing surface groups such as phenols and carboxyl groups. However, methods relying on the inherent functionality of the pigment surface cannot be widely used, since not all pigments have the same specific functional group.

Methods of preparing modified pigment products have also been developed that can provide pigments having a variety of different attached functional groups. For example, U.S. Pat. No.5,851,280 discloses methods of attaching organic groups to pigments, including, for example, attachment via a diazotization reaction, where the organic groups are part of a diazonium salt. The resulting surface-modified pigments can be used in a variety of applications, such as inks, inkjet inks, coatings, toners, plastics, rubbers, and the like. Also, U.S. patent nos. 6,328,894, 6,398,858, 6,214,100 and 6,221,142 describe modified pigments having attached organic groups that include groups containing at least two carboxylate groups.

Other methods of preparing the modified pigments are also described. For example, PCT publication No. wo 01/51566 discloses a method of preparing a modified pigment by reacting a first chemical group with a second chemical group to form a pigment having attached a third chemical group. Ink compositions comprising these pigments are also described.

Although these methods provide modified pigments having attached groups, there remains a need for improved methods of attaching groups, particularly organic groups comprising at least two carboxylic acid groups or salts thereof, to pigments. These additional methods may provide advantageous alternatives for forming improved pigments and for providing improved pigments with good overall properties in applications such as inkjet inks.

Disclosure of Invention

The present invention relates to a process for preparing modified pigments. In one embodiment, the method comprises the steps of: a) combining, in any order, a pigment, an aromatic amine, a base, and an aqueous medium to form a mixture, and b) combining the mixture with a diazotizing agent to form a modified pigment. In a second embodiment, the method comprises the steps of: a) combining, in any order, a pigment, a diazotizing agent, a base, and an aqueous medium to form a mixture, and b) combining the mixture with an aromatic amine to form a modified pigment. For both embodiments, the aromatic amine comprises at least two carboxylic acid groups, preferably at least one ortho-dicarboxylic acid group.

The present invention further relates to a modified pigment made by the process described herein, and an inkjet ink composition comprising a liquid vehicle and the modified pigment. It has been found that images formed on substrates using the inkjet ink compositions of the present invention have improved overall performance.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are intended to provide further explanation of the invention as claimed.

Detailed Description

The present invention relates to a method of preparing a modified pigment having attached at least one organic group, and an inkjet ink composition.

In one embodiment, the method of the present invention includes the step of combining a pigment, an aromatic amine, a base, and an aqueous medium to form a mixture. These substances may be combined in any order. The resulting mixture is then combined with a diazotizing agent to form a modified pigment. The components will be described in more detail below.

The pigment used in the method of the present invention may be any kind of pigment conventionally used by those skilled in the art, such as black pigments and other colored pigments. Preferably, when the pigment is a black pigment, the pigment is carbon black. Mixtures of different pigments may also be used. These pigments can also be used in combination with a variety of different types of dispersants to form stable dispersions and inks.

Substitutes for black pigmentsIllustrative examples include various carbon blacks (Pigment Black 7) such as channel blacks, furnace blacks and lamp blacks, and include those available from Cabot Corporation, for exampleAndcarbon blacks sold under the trademark Perkins (e.g. Perkins TM))。

The pigments may also be selected from a wide range of conventional colored pigments. The colored pigment can be blue, black, brown, cyan, green, white, violet, magenta, red, orange, yellow, and mixtures thereof. Suitable classes of colored pigments include, for example, anthraquinones, phthalocyanine blues, phthalocyanine greens, diazos, monoazos, pyranthrones, perylenes, heterocyclic yellows, quinacridones and (thio) indigoids. Such pigments are commercially available in powder or presscake form from a number of sources, including BASF Corporation, Engelhardcorporation, and Sun Chemical Corporation. Examples of other suitable colored pigments are described in The Colour Index, 3 rd edition (The Society of Dyers and Colourists, 1982).

Depending on the desired pigment properties, the pigment may have a wide range of BET surface areas, as measured by nitrogen adsorption. As is well known to those skilled in the art, a higher surface area corresponds to a smaller particle size. If a higher surface area is not readily available for the desired application, one skilled in the art will also fully appreciate that the pigment may be subjected to conventional crushing or pulverizing techniques such as ball or jet milling to reduce the pigment to a smaller particle size if desired.

The aromatic amine used in the process of the present invention may be any aromatic or heteroaromatic compound substituted with an amine group, including, for example, aniline derivatives (i.e., substituted anilines). The aromatic amine further comprises at least two carboxylic acid groups. Preferably, the carboxylic acid groups are adjacent, i.e. they are contiguous to each other. Thus, the aromatic amine used in the process of the present invention is substituted with at least one group comprising two adjacent carboxylic acid groups (i.e., carboxylic acid groups bound to adjacent or neighboring carbon atoms) having the general structure (HOOC) -C-C- (COOH), which are sometimes also referred to as ortho-dicarboxylic acids or 1, 2-dicarboxylic acids. The group comprising two carboxylic acid groups may be an aromatic group or an alkyl group, whereby the ortho-dicarboxylic acid group may be an ortho-alkyl dicarboxylic acid or an ortho-aryl dicarboxylic acid group. Preferably, the group containing an o-dicarboxylic acid group is an aromatic group. Thus, the aromatic amine preferably comprises-C₆H₃-(COOH)₂Wherein the carboxylic acid groups are located adjacent to each other. More preferably, the aromatic amine is a group comprising the two carboxylic acid groups. Thus, for example, aromatic amines are more preferably anilines substituted with at least two carboxylic acid groups in positions adjacent to one another, such as 4-aminobenzene-1, 2-dicarboxylic acid (also referred to as 4-aminophthalic acid). Other substitutions are also possible and known to those skilled in the art. In addition, other substituents besides the carboxylic acid groups may also be present in the aromatic amine, as long as these substituents do not interfere with the formation of the modified pigment.

The aromatic amine may comprise more than two carboxylic acid groups. Thus, the aromatic amine may comprise a group having three or more carboxylic acid groups, wherein at least two of the carboxylic acid groups are adjacent to form an ortho-dicarboxylic acid group. For example, the aromatic amine may comprise a 1,2, 3-or 1,2, 4-tricarboxylic acid group, such as-C₆H₂-(COOH)₃Or may comprise 1,2, 3, 4-or 1,2, 4, 5-tetracarboxylic acid groups, e.g. -C₆H-(COOH)₄And (4) a base. Other substitutions are also possible and known to those skilled in the art. More preferably, the aromatic amine is 5-aminobenzene-1, 2, 3-tricarboxylic acid or 5-aminobenzene-1, 2, 4-tricarboxylic acid.

The base used in the process of the invention may be any water-soluble base reagent which generates OH "ions in the aqueous medium, thereby raising the pH of the medium. Examples include carbonates such as sodium carbonate, bicarbonates such as sodium bicarbonate, and alkoxides such as sodium methoxide and sodium ethoxide. Preferably, the base is an hydroxide reagent, which is any reagent comprising an OH "ion, such as a salt with a hydroxide counterion. Examples include sodium hydroxide, potassium hydroxide, lithium hydroxide and ammonium hydroxide. Other hydroxide salts and mixtures of hydroxide reagents may also be used.

The aqueous medium used in the process of the invention may be any medium comprising more than 50% water. Thus, the aqueous medium may be, for example, water or a mixture of water and a water-soluble solvent such as an alcohol. Preferably, the aqueous carrier is water.

For this embodiment of the inventive process, the pigment, aromatic amine, base, and aqueous medium may be combined to form a mixture. Depending on the amount of aqueous medium used, the mixture may be in the form of a wet paste or may be a dispersion. Preferably, the mixture is a dispersion, and more preferably, the resulting modified pigment is also in the form of a dispersion. In addition, additional components such as dispersants or surfactants may also be included in any step of the process of the present invention, although such additives are not particularly necessary to make the disclosed modified pigments. Such additional components may provide additional advantages such as improved stability of the mixture or modified pigment when in dispersion form.

The amount of base used in the process of the present invention can be any amount as long as the level does not adversely affect the preparation of the modified pigment. Preferably, the amount of base used is chosen with respect to the type of aromatic amine used, and more preferably on the basis of the molar amount of carboxylic acid groups present. For example, it is preferred that the molar ratio of base to carboxylic acid groups in the aromatic amine is less than 1: 1. Preferably, the molar ratio of base to carboxylic acid groups in the aromatic amine is from 0.33 to 0.67: 1, more preferably from 0.37 to 0.6: 1, and most preferably from 0.4 to 0.5: 1. For example, if the aromatic amine includes a tricarboxylic acid group, the molar ratio of base to carboxylic acid is preferably 1-2: 1, more preferably 1.1-1.8: 1, and most preferably 1.2-1.5: 1.

The pigment, aromatic amine, base, and aqueous medium may be combined in any order to form a mixture for preparing the modified pigment. For example, the aromatic amine and base are optionally mixed in an aqueous medium. Since, as discussed in more detail above, the amount of base is preferably less than the total amount of carboxylic acid groups present (i.e., the molar ratio of base to carboxylic acid groups is less than 1: 1), the combination of aromatic amine and base typically forms an aromatic amine mixture. The mixture includes an aromatic amine having at least one carboxylic acid group and at least one carboxylic acid salt group. In general, the combination of the aromatic amine comprising at least two carboxylic acid groups and a base forms an aromatic amine product mixture comprising an aromatic amine in which one carboxylic acid group has been deprotonated. The resulting aromatic amine mixture may then be combined with a pigment, optionally further in an aqueous medium, to form a mixture for preparing the desired modified pigment.

As another example, the pigment can be combined with an aromatic amine, optionally with an aqueous medium, to form a pigment mixture. The base is then combined with the mixture, optionally further in an aqueous medium, to form a mixture for preparing the desired modified pigment.

For this first embodiment of the inventive process, the process further comprises the step of combining a diazotizing agent with the mixture obtained by combining the pigment, the aromatic amine, the base, and the aqueous medium in any order described above to form the modified pigment. The diazotising agent used in the process of the present invention may be any agent which reacts with an amino group to form a diazonium salt. Examples include nitrous acid and nitrite salts. Preferably, the diazotizing agent is a salt with a nitrite counterion, such as sodium nitrite, potassium nitrite or calcium nitrite.

In a second embodiment of the process of the present invention, the process comprises the step of combining a pigment, a diazotizing agent, a base, and an aqueous medium to form a mixture. These may be combined in any order. The resulting mixture is then combined with an aromatic amine to form a modified pigment. These components may be any of those described in detail above.

For both embodiments of the method of the present invention, the components may be combined using any method known in the art. For example, the components may be combined under high shear conditions. For the purposes of the present invention, "high shear" refers to energy sufficient to generate and/or maintain a pigment particle size distribution throughout the mixing step, which continuously exposes new surfaces of the pigment to the added components, thereby improving the distribution and level of attachment, as well as overall product yield. The mixing can be carried out under high shear conditions in any suitable vessel and utilizing a device capable of providing continuous particle comminution. Examples include, but are not limited to, devices capable of providing grinding, impact, or similar impact action, such as horizontal media mills, vertical media mills such as attritors, ball mills, hammer mills, pin mills with rotating discs, fluid energy mills, jet mills, impact jet mills, rotor stators, pelletizers, homogenizers, sonicators, cavitators (cavitators), and the like.

Furthermore, the vessel is preferably equipped with suitable heating means, such as heating jackets, thermocouples, etc. The mixing can be carried out at a variety of temperatures and for any suitable time to form the desired modified pigment. For example, the components may be combined at a temperature of from about-10 to about 50 ℃, such as from about 0 to about 25 ℃ or from about 0 to about 10 ℃. It has been found that combining the components in these temperature ranges effectively and with minimal by-products forms an aqueous colored pigment dispersion. Furthermore, the mixing can preferably also be carried out under high solids conditions, i.e. the pigment is present in the mixture at a level of preferably more than 10% by weight.

Surprisingly, it has been found that modified pigments can be prepared by combining a pigment, an aromatic amine comprising more than one carboxylic acid group, an aqueous medium, and a diazotizing agent in the order described above, and further comprising a base. Although processes for forming modified pigments having attached organic groups are known in which a diazotizing agent is combined with an aromatic amine to form a diazonium salt, which is then combined with a pigment to form a modified pigment, these processes typically do not include a base. An acid is required to aid the diazonium salt formation and ligation process. If a base is used in these processes, it is generally added after the modified pigment has been prepared. However, it has now been found that the base can be added at the beginning of the process prior to the addition of the diazotizing agent without adversely affecting the preparation of the modified pigment having attached carboxylate groups. It has also been found that when the above preferred base levels are used, the modified pigments prepared have improved properties, particularly in inkjet ink compositions, compared to those prepared by similar processes in which no base is included.

The present invention also relates to a modified pigment comprising a pigment having attached at least one organic group, wherein the organic group comprises at least one carboxylate group. The pigment may be any of those described in more detail above. Preferably, the organic group comprises at least two carboxylate groups, and more preferably at least three carboxylate groups. The modified pigments can be made by any method known in the art, but are preferably made using the method of the present invention.

The amount of attached organic group can vary depending on the desired use of the modified pigment and the type of linking group. Preferably, the total amount of organic groups is from about 0.01 to about 10.0 micromoles of groups per m2 of pigment surface area, as measured by nitrogen adsorption (BET method). For example, the amount of electrophilic groups can be about 0.5 to about 4.0 micromoles/m²Comprising about 1 to about 3 micromoles/m²Or from about 2 to about 2.5 micromoles/m². Additional attached organic groups not including carboxylate groups may also be present.

The modified pigment may be in a solid form such as a powder or paste, or may be in the form of a dispersion. For example, the modified pigment may be produced in dispersion form and isolated from the dispersion in solid form. Alternatively, the solid form of the modified pigment can be produced directly. Preferably, the modified pigment is in the form of a dispersion. The modified pigment dispersion can be purified by washing, such as filtration, centrifugation, or a combination of the two, to remove unreacted starting materials, byproduct salts, and other reaction impurities. The product may also be isolated, for example, by evaporation, or may be recovered by filtration and drying using techniques known to those skilled in the art.

The modified pigment dispersion can be purified by washing, such as filtration, centrifugation, or a combination of the two, to remove unreacted starting materials, byproduct salts, and other reaction impurities. The modified pigment may also be isolated, for example, by evaporation, or may be recovered by filtration and drying using techniques known to those skilled in the art. The modified pigment may also be dispersed in a liquid medium and the resulting dispersion purified or sorted to remove impurities and other undesirable free species that may co-exist in the dispersion due to the manufacturing process. For example, the dispersion may be purified using well-known techniques such as ultrafiltration/diafiltration, reverse osmosis or ion exchange to remove any undesirable free impurities such as unreacted treating agent.

The modified pigments of the present invention can also be used in a variety of applications. In particular, the colored pigment dispersion has surprisingly been found to be an effective inkjet ink composition. Accordingly, the present invention further relates to an inkjet ink composition comprising a liquid vehicle and the modified pigment of the present invention. The carrier may be an aqueous or non-aqueous liquid carrier, but is preferably an aqueous carrier. Thus, the carrier is preferably an aqueous carrier, which is a carrier comprising more than 50% water, and the carrier may for example be water or a mixture of water and a water-soluble solvent such as an alcohol. Preferably, the aqueous carrier is water and the inkjet ink composition is an aqueous inkjet ink composition.

The modified pigment can be present in the inkjet ink composition in an amount effective to provide a desired image quality (e.g., optical density) without adversely affecting the performance of the inkjet ink. For example, typically, the modified pigment may be present in an amount of about 0.1% to about 30% based on the weight of the ink. Depending on the amount of attached organic groups or the amount of carboxylate groups present, more or less modified pigment may be used. It is also within the scope of the invention to use a mixture of the modified pigments described herein with unmodified pigments, other modified pigments, or both.

The ink jet ink composition of the present invention can be formed with a minimum of additional components (additives and/or cosolvents) and processing steps. However, suitable additives may be incorporated to impart a number of desired properties while maintaining the stability of the composition. For example, surfactants and/or dispersants, wetting agents, drying promoters, penetrants, biocides, binders, and pH control agents, as well as other additives known in the art, may be added. The amount of a particular additive will vary depending on a number of factors, but is typically between 0% and 40%.

Dispersants (surfactants or dispersants) may be added to further enhance the colloidal stability of the composition, or to modify the interaction between the ink and a printing substrate such as printing paper or with an ink print head. Various anionic, cationic and nonionic dispersants can be used with the ink compositions of the present invention, and these materials can be in solid form or as aqueous solutions.

Representative examples of anionic dispersants or surfactants include, but are not limited to, higher fatty acid salts, higher alkyl dicarboxylic acid salts, sulfuric acid ester salts of higher alcohols, higher alkyl-sulfonic acid salts, alkylbenzene sulfonic acid salts, alkylnaphthalene sulfonic acid salts, naphthalene sulfonic acid salts (Na, K, Li, Ca, etc.), formalin polycondensates, condensates of higher fatty acids with amino acids, dialkyl sulfosuccinic acid ester salts, alkyl sulfosuccinic acid salts, naphthenic acid salts, alkyl ether saltsCarboxylate, acylated peptide, olefin sulfonate, N-acryloylmethyl aminoethanesulfonic acid, alkyl ether sulfonate, secondary higher alcohol ethoxy sulfate, polyoxyethylene alkylphenyl ether sulfate, monoglycosyl sulfate, alkyl ether phosphate, and alkyl phosphate. For example, styrene sulfonate, substituted and unsubstituted naphthalene sulfonates (e.g., alkyl or alkoxy substituted naphthalene derivatives), aldehyde derivatives (e.g., unsubstituted alkyl aldehyde derivatives including formaldehyde, acetaldehyde, propionaldehyde, and the like), polymers and copolymers of maleic acid salts, and mixtures thereof may be used as the anionic dispersing aid. Salts include, for example, Na⁺、Li⁺、K⁺、Cs⁺、Rb⁺And substituted and unsubstituted ammonium cations. Specific examples include, but are not limited to, commercial products such asAnd(National Starch and Chemical Co.)；(Diamond Shamrock Chemicals Co.)；and(w.r.grace Co.); and(Rohm&haas). Representative examples of cationic surfactants include fatty amines, quaternary ammonium salts, sulfonium salts, phosphonium salts, and the like.

Representative examples of nonionic dispersants or surfactants useful in the ink-jet ink of the present invention include fluorine derivatives, silicone derivatives, acrylic copolymers, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene secondary alcohol ethers, polyoxyethylene styrene ethers, polyoxyethylene lanolin derivatives, alkylphenol ethoxylatesAn ethylene oxide derivative of an elmalin condensate, a polyoxyethylene polyoxypropylene block polymer, a fatty acid ester of a polyoxyethylene polyoxypropylene alkyl ether polyoxyethylene compound, a glycol fatty acid ester of a polyoxyethylene condensation type, a fatty acid monoglyceride, a fatty acid ester of polyglycerol, a fatty acid ester of propylene glycol, a sucrose fatty acid ester, a fatty acid alkanolamide, a polyoxyethylene fatty acid amide, and a polyoxyethylene alkylamine oxide. For example, ethoxylated monoalkyl or dialkyl phenols may be used, such asCA and CO series of materials (Rhone-Poulenc Co.),Series of materials (ICI Americas, Inc.) andseries of materials (Union Carbide Company). These nonionic surfactants or dispersants may be used alone or in combination with the above-mentioned anionic and cationic dispersants.

The dispersant may also be a natural polymer or synthetic polymer dispersant. Specific examples of the natural polymer dispersant include proteins such as animal glue, gelatin, casein and albumin; natural rubbers such as gum arabic and tragacanth; glucosides such as saponin; alginic acid, and alginic acid derivatives such as propylene glycol alginate, triethanolamine alginate, and ammonium alginate; and cellulose derivatives such as methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose and hydroxyethyl (ethylhydroxy) cellulose. Specific examples of polymeric dispersants including synthetic polymeric dispersants include polyvinyl alcohol; polyvinylpyrrolidone; acrylic or methacrylic resins (commonly written as "(meth) acrylic") such as poly (meth) acrylic acid, acrylic acid- (meth) acrylonitrile copolymers, (meth) acrylic acid potassium- (meth) acrylonitrile copolymers, vinyl acetate- (meth) acrylate copolymers, and (meth) acrylic acid- (meth) acrylate copolymers; styrene-acrylic or methacrylic resins such as styrene- (meth) acrylic acid copolymer, styrene- (meth) acrylic acid- (meth) acrylate ester copolymer, styrene-methylstyrene- (meth) acrylic acid- (meth) acrylate ester copolymer; styrene-maleic acid copolymers; styrene-maleic anhydride copolymers, vinylnaphthalene-acrylic acid or methacrylic acid copolymers; vinyl naphthalene-maleic acid copolymers; and vinyl acetate copolymers such as vinyl acetate-ethylene copolymer, vinyl acetate-fatty acid vinyl ethylene copolymer, vinyl acetate-maleic acid ester copolymer, vinyl acetate-crotonic acid copolymer and vinyl acetate-acrylic acid copolymer; and salts thereof.

Humectants and water-soluble organic compounds may also be added to the ink jet ink compositions of the present invention, particularly to prevent nozzle clogging and to provide paper penetration (penetrants), improved drying (drying accelerators), and wrinkle resistance. Specific examples of other water-soluble compounds and wetting agents that can be used include low molecular weight glycols such as ethylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and dipropylene glycol; diols containing from about 2 to about 40 carbon atoms such as 1, 3-pentanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 4-pentanediol, 1, 6-hexanediol, 1, 5-hexanediol, 2, 6-hexanediol, neopentyl glycol (2, 2-dimethyl-1, 3-propanediol), 1, 3-propanediol, 1, 4-butanediol, 1, 5-pentanediol, 1, 6-hexanediol, 1,2, 6-hexanetriol, poly (ethylene-co-propylene) glycol, and the like, and reaction products thereof with alkylene oxides, including ethylene oxide and propylene oxide; triol derivatives containing from about 3 to about 40 carbon atoms including glycerol, trimethylpropane, 1, 3, 5-pentanetriol, 1,2, 6-hexanetriol, and the like, and reaction products thereof with alkylene oxides including ethylene oxide, propylene oxide, and mixtures thereof; neopentyl glycol, (2, 2-dimethyl-1, 3-propanediol), and the like, as well as reaction products thereof with alkylene oxides, including ethylene oxide and propylene oxide, in any desired molar ratio to form materials having a wide range of molecular weights; thiodiglycol; pentaerythritol and lower alcohols such as ethanol, propanol, isopropanol, n-butanol, sec-butanol and tert-butanol, 2-propyn-1-ol (propargyl alcohol), 2-buten-1-ol, 3-buten-2-ol, 3-butyn-2-ol and cyclopropanol; amides such as dimethylformamide and dimethylacetamide; ketones or ketoalcohols such as acetone and diacetone alcohol; ethers such as tetrahydrofuran and dioxane; cellosolves such as ethylene glycol monomethyl ether and ethylene glycol monoethyl ether, triethylene glycol monomethyl (or monoethyl) ether; carbitols such as diethylene glycol monomethyl ether, diethylene glycol monoethyl ether and diethylene glycol monobutyl ether; lactams such as 2-pyrrolidone, N-methyl-2-pyrrolidone and caprolactam; urea and urea derivatives; internal salts such as betaine, etc.; thio (thio) derivatives of the above materials including 1-butanethiol; tert-butylmercaptan 1-methyl-1-propanethiol, 2-methyl-1-propanethiol; 2-methyl-2-propanethiol; thiocyclopropanol, thioethylene glycol, thiodiethylene glycol, trithio or dithiodiethylene glycol, and the like; hydroxyamide derivatives including acetylethanolamine, acetylpropanolamine, propylcarboxyethanolamine, propylcarboxypropanolamine, and the like; the reaction product of the above materials with an alkylene oxide; and mixtures thereof. Other examples include sugars such as maltitol, sorbitol, gluconolactone and maltose; polyhydric alcohols such as trimethylolpropane and trimethylolethane; n-methyl-2-pyrrolidine; 1, 3-dimethyl-2-imidazolidinone; sulfoxide derivatives containing from about 2 to about 40 carbon atoms, including dialkyl sulfoxides (symmetric and asymmetric sulfoxides) such as dimethyl sulfoxide, methyl ethyl sulfoxide, alkyl phenyl sulfoxides and the like; and sulfone derivatives (symmetric and asymmetric sulfones) containing from about 2 to about 40 carbon atoms, such as dimethyl sulfone, methyl ethyl sulfone, sulfolane (tetramethylene sulfone, cyclic sulfones), dialkyl sulfones, alkyl phenyl sulfones, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone, ethyl propyl sulfone, methyl phenyl sulfone, methyl sulfolane, dimethyl sulfolane, and the like. These materials may be used alone or in combination.

Biocides and/or fungicides may also be added to the inkjet ink compositions of the present invention. Biocides are important to prevent bacterial growth as bacteria are often larger than ink nozzles and can cause clogging and other printing problems. Examples of useful biocides include, but are not limited to, benzoic acid or sorbate salts and isothiazolinones.

Various polymeric binders can also be tested with the ink jet ink compositions of the present invention to adjust the viscosity of the composition and to provide other desired properties. Suitable polymeric binders include, but are not limited to, water soluble polymers and copolymers such as acacia, polyacrylate, polymethacrylate, polyvinyl alcohol, hydroxypropyl cellulose, hydroxyethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, starch, polysaccharides, with or without polyethylene imine derived from ethylene oxide and propylene oxide includingSeries (DKS International);series (Texaco) and the like. Other examples of the water-soluble polymer compound include the above-mentioned various dispersants or surfactants, including, for example, styrene-acrylic acid copolymer, styrene-acrylic acid-alkyl acrylate terpolymer, styrene-methacrylic acid copolymer, styrene-maleic acid-alkyl acrylate terpolymer, styrene-methacrylic acid-alkyl acrylate terpolymer, styrene-maleic acid half ester copolymer, vinyl naphthalene-acrylic acid copolymer, alginic acid, polyacrylic acid or its salt, and its derivatives. Furthermore, the binder may be added or present in the form of a dispersion or latex. For example, the polymeric binder may be a latex of an acrylate or methacrylate copolymer, or a water-dispersible polyurethane.

Various additives may also be used to control or adjust the pH of the inkjet ink composition of the present invention. Examples of suitable pH adjusters include various amines such as diethanolamine and triethanolamine as well as various hydroxide reagents. The hydroxide reagent can be any of those described above, including sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, and tetramethylammonium hydroxide. Other hydroxide salts and mixtures of hydroxide reagents may also be used. In addition, other alkaline agents which generate OH-ions in aqueous media can also be used. Examples include carbonates such as sodium carbonate, bicarbonates such as sodium bicarbonate, and alkoxides such as sodium methoxide and sodium ethoxide. Buffers may also be added.

In addition, the inkjet ink composition of the present invention may further incorporate a dye to improve color balance and adjust optical density. Such dyes include food dyes, FD & C dyes, acid dyes, direct dyes, reactive dyes, phthalocyanine sulfonic acid derivatives including copper phthalocyanine derivatives, sodium salts, ammonium salts, potassium salts, lithium salts, and the like.

The inkjet ink composition may be purified and/or sorted using methods such as those described above for the modified pigments of the present invention. An optional counter ion exchange step may also be used. In this way, unwanted impurities or undesirable large particles can be removed to produce an ink with good overall properties.

The present invention further relates to an inkjet ink set comprising a plurality of inkjet ink compositions and including the inkjet ink composition of the present invention. The ink-jet ink compositions of the set can differ in any manner known in the art. For example, the inkjet ink set can include inkjet ink compositions including different types and/or colors of pigments, including, for example, an inkjet ink composition including a cyan pigment, an inkjet ink composition including a magenta pigment, and/or an inkjet ink composition including a black pigment. Other types of inkjet ink compositions can also be used, including, for example, compositions that include agents designed to fix the inkjet ink composition to a substrate. Other combinations are known in the art.

The invention will be further clarified by the following examples, which are intended to be only exemplary in nature.

Examples

Examples 1 to 21

The following general procedure, which is an embodiment of the process of the present invention, is used to prepare the modified pigments of the present invention.

Will be provided withCarbon black (obtained from Cabot Corporation), 5-aminobenzene-1, 2, 3-tricarboxylic acid (ABTA) and water were combined in a ProcessAll 4HV Mixer (4 liters) which was then closed and mixing was started. A 10% NaOH solution was prepared and added to the reactor over 1-2 minutes. The total amount of water used was 850 mL. The resulting mixture was mixed in ProcessAll at the set temperature for 1 hour. Then, a 20% aqueous solution of sodium nitrite (1 equivalent relative to the amount of aromatic amine used) was added to the mixture over about 15 minutes, and mixing was continued for an additional 2 hours. The modified pigment was formed and then removed from the reactor as a thick paste (about 35% solids). To this ProcessAll was added 1 volume of dilution water (approximately 850mL) and two volumes of rinse water to rinse off any residue and combined with the paste to form a dispersion of modified pigment. The pH of the dispersion was then adjusted to 8.5 using 2M NaOH solution and the sample was further diluted with water to 10% solids. It was then centrifuged using CarrPowerfuge at 300 mL/min and 15 KG. The centrifugation is continuous and the sample is centrifuged into a clean bucket and then recirculated for about 5 minutes. The centrifuged dispersion was diafiltered with a Spectrum Diafiltration membrane supplemented with deionized water. 5 volumes of make-up water were used and the final conductivity of the permeate was below 250 μ S. At the end of the diafiltration process, the sample was concentrated so that the final solid was about 15%. Proxel biocide (0.2 wt%) was then added and the sample was then filtered using a Pall apparatus with a 0.5 μm filter to form a dispersion containing the modified pigment with attached carboxylate groups.

The amounts and conditions of the components employed in these examples are shown in table 1 below. The amount of base is expressed as the molar ratio of base to carboxylic acid groups in the ABTA.

TABLE 1

Examples	Molar ratio of NaOH	ABTA (mmol/g pigment)	Temperature (. degree.C.)
				1	1.00	0.40	65
2	1.20	0.37	56
				3	1.20	0.37	74
4	1.20	0.43	56
				5	1.20	0.43	73
6	1.20	0.43	74
				7	1.20	0.47	73
8	1.20	0.52	73
				9	1.20	0.60	73
10	1.50	0.35	65
				11	1.50	0.40	50
12	1.50	0.40	65
				13	1.50	0.40	65
14	1.50	0.40	65
				15	1.50	0.40	80
16	1.50	0.45	65
				17	1.80	0.37	56
18	1.80	0.37	74
				19	1.80	0.43	56
20	1.80	0.43	74
				21	2.00	0.40	65

The properties of the resulting modified pigment dispersion are shown in table 2 below. The modified pigment of example 21 was not prepared in a stable dispersion form and thus is not included in table 2. For each of these examples, the following appliesThe particle size was determined and the value reported was the volume average particle size (mV). Na (Na)⁺The concentration was measured using an ion selective electrode (Thermo Orion Sure-flow Ross sodium detector, calibrated for solutions containing 20ppm to 6000ppm sodium ions). Or alternatively, Na⁺Concentrations can also be determined by combustion analysis with comparable results. Titratable levels in millimoles of titratable groups per gram of pigment were measured by titration using a Titrino 736 auto-titrator over a pH range of 4-10. Viscosity was measured using a Brookfield IV II + programmable viscometer.

TABLE 2

Examples	Final pH	% solids	mv(m)	Viscosity (cp)	Na+Horizontal (ppm)	Titratable (mmol/g)
							1	8.46	14.96	0.129	2.01	9227	0.38
2	9.05	14.68	0.132	2.02	8896	0.34
							3	8.70	15.09	0.129	2.09	8820	0.35
4	8.48	15.06	0.122	1.86	9977	0.39
							5	8.86	15.45	0.133	1.84	11607	0.33
6	9.03	14.58	0.122	1.95	11390	0.44
							7	8.72	14.52	0.128	1.83	12112.5	0.46
8	8.67	15.11	0.130	1.86	12177.5	0.45
							9	8.96	14.87	0.126	1.78	14260.5	0.50
10	9.05	14.89	0.131	2.14	8773	0.32
							11	8.80	14.55	0.131	2.20	8026	0.34
12	8.90	14.54	0.161	2.27	5605	0.26
							13	9.02	14.05	0.130	1.95	9641	0.37
14	8.58	15.32	0.129	2.17	8101	0.33
							15	9.48	14.94	0.134	1.98	9856	0.35
16	9.05	14.70	0.131	2.04	9526	0.37
							17	8.61	14.98	0.153	2.39	5929	0.25
18	10.1	14.71	0.149	2.23	7683	0.28
							19	8.77	14.07	0.164	2.42	7095	0.30
20	10.31	15.32	0.149	2.15	8789	0.29

As shown by the data in Table 2, the process of the present invention provides modified pigments having attached carboxylate groups, such as by purified Na⁺Level and confirmed by titration results. In addition, these modified pigments produced dispersions with small particle size and low viscosity, indicating that they can be used in inkjet ink compositions.

Examples 22 to 24

Modified pigments having attached carboxylate groups were prepared using a procedure similar to that described above, except that Pigment Blue 15: 4 (example 22), Pigment Red 122 (example 23), and Pigment Yellow74 (example 24) (presscake, available from Sun Chemical) were used in place of Pigment Blue 15: 4 (example 22), Pigment Red 122 (example 23), and Pigment Yellow74 (example 24)Carbon black. The temperature of the method is 50-55 ℃. The molar ratio of base to carboxylic acid groups in the ABTA was 1.2, and the amount of ABTA was 1.0mmol/g pigment.

The properties of the resulting modified pigment dispersion are shown in table 3 below.

TABLE 3

Examples	Final pH	% solids	Mv(m)	Viscosity (cp)	Na+Horizontal (ppm)	Titratable (mmol/g)
							22	8.59	9.84	0.0924	1.74	3021	0.12
23	8.55	10.65	0.1037	2.06	2924	0.09
							24	9.06	9.57	0.1128	1.50	3863	0.13

As shown by the data in Table 3, the method of the present invention provides modified pigments having attached carboxylate groups, such as by purified Na⁺Level and confirmed by titration results. In addition, these modified pigments produced dispersions with small particle size and low viscosity, indicating that they can be used in inkjet ink compositions.

Example 25

An ink jet ink composition was prepared which included the modified pigment of this invention prepared in accordance with the method of examples 1-21 above, using a NaOH molar ratio of 1.50 and an ABTA level of 0.40mmol/g pigment similar to those in examples 11-15 above. The formulations used are shown in table 5 below.

TABLE 5

Components	Measurement of
		2-pyrrolidone	7.0％
1, 5-pentanediol	7.0％
		Trimethylolpropane	5.0％
Surfynol 465	0.20％

The pH of the modified pigment dispersion was adjusted to 8.5 prior to preparing the inkjet ink composition. The target pigment level was 4.0% considering the weight of attached groups. The balance of the formulation is water.

Print performance testing was performed by printing test images on three plain papers using an HP Photosmart P1000 printer: great White Ink Jet (GWIJ), Hammermill Copy Plus (HCP) and Hewlett Packard Bright White (HPBW). The optical density (OD or visual density) of the test images was measured using a MacBeth densitometer and averaged over the sheet set. The resulting average OD was found to be 1.23.

This indicates that the modified pigments of the present invention can be used to prepare inkjet ink compositions that produce images with good properties. It is expected that one skilled in the art can modify the formulation to produce images with improved or adjusted performance properties including bleeding, water resistance, stain resistance, and the like.

Examples 26 to 28

An ink jet ink composition was prepared as described in example 25, except that the modified pigments of examples 22-24 were used. For example 26, the modified cyan pigment of example 22 was used; for example 27, the modified magenta pigment of example 23 was used; and for example 28, the modified yellow pigment of example 24 was used. Print performance testing was performed by printing test images on three plain papers using an HP Photosmart P1000 printer: hammermill Copy Plus (HCP), Hewlett packard White (HPBW), and Xerox 4024 (X4024). L, a and b for the test images were measured using Image X-Pert. The results are shown in table 6 below.

TABLE 6

This indicates that the modified colored pigments of the present invention can be used to prepare inkjet ink compositions that produce images with good properties. It is expected that one skilled in the art can modify the formulation to produce images with improved or adjusted performance properties including bleeding, water resistance, stain resistance, and the like.

Comparative example 1

Modified pigments having attached carboxylate groups are prepared by procedures similar to those described above, except that no base is used. For this example, the amount of ABTA was 0.4mmole/g pigment. The properties of the resulting modified pigment dispersant are shown in table 4 below.

TABLE 4

Examples of the present invention	Final pH	% solids	mv(m)	Viscosity (cp)	Na+Horizontal (ppm)	Titratable (mmol/g)
							Comparative example 1	8.38	15.8	0.1208	2.10	11139	0.36

As the data show, the modified pigment dispersions prepared without the addition of base have overall properties similar to those prepared using the method of the present invention.

Ink jet ink compositions were prepared using the same formulations as shown in examples 25-28, except that the pigment was the modified pigment of comparative example 1. The average optical density was measured as described above and found to be 1.17.

Thus, the inkjet ink composition of comparative example 1, which included a modified pigment not prepared by the method of the present invention, exhibited a lower average optical density than the image formed using the inkjet ink composition of example 25, which was the inkjet ink composition of the present invention. In addition, the images produced with the ink jet ink compositions of the present invention were visually observed to have better hue unevenness (gray scale variation) and edge sharpness than the images formed with the comparative ink jet ink compositions. Thus, although the modified pigments of example 25 and comparative example 1 were prepared using a similar process, the introduction of a base into the process prior to attachment resulted in a modified pigment that was different from the modified pigment prepared without a base in the same inkjet ink formulation, and the inkjet ink composition containing the modified pigment of the present invention was found to have improved properties. Further, it is contemplated that the formulations may be further optimized by those skilled in the art to produce images having improved or customized performance properties, including bleeding, water resistance, stain resistance, and the like.

The foregoing description of the preferred embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications or variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principles of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. The scope of the invention should be defined by the appended claims and equivalents thereof.

Claims (35)

1. A method of preparing a modified pigment comprising the steps of:

a) combining, in any order, a pigment, an aromatic amine, a base, and an aqueous medium to form a mixture, and

b) combining the mixture with a diazotizing agent to form the modified pigment,

wherein the aromatic amine comprises at least two carboxylic acid groups, the base and carboxylic acid groups being present in the mixture in a molar ratio of 0.33-0.67: 1.

2. The process of claim 1, wherein the at least two carboxylic acid groups are vicinal.

3. The method of claim 1, wherein the aromatic amine comprises at least three carboxylic acid groups.

4. The process of claim 1, wherein the base and carboxylic acid groups are present in the mixture in a molar ratio of 0.37 to 0.60: 1.

5. The process of claim 1, wherein the base and carboxylic acid groups are present in the mixture in a molar ratio of 0.4 to 0.6: 1.

6. The process of claim 1, wherein an aqueous dispersion of the modified pigment is formed in step b).

7. The method of claim 1, wherein the pigment comprises a blue pigment, a black pigment, a brown pigment, a cyan pigment, a green pigment, a white pigment, a violet pigment, a magenta pigment, a red pigment, an orange pigment, a yellow pigment, or mixtures thereof.

8. The method of claim 1, wherein the pigment is carbon black.

9. The method of claim 1, wherein the aromatic amine comprises at least one-C₆H₃-(COOH)₂or-C₆H₂-(COOH)₃A group.

10. The process of claim 1, wherein the aromatic amine is 5-aminobenzene-1, 2, 3-tricarboxylic acid, 5-aminobenzene-1, 2, 4-tricarboxylic acid, or 4-aminobenzene-1, 2-dicarboxylic acid.

11. The method of claim 1, wherein the base is an hydroxide reagent.

12. The method of claim 11, wherein the hydroxide reagent is sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, or a mixture thereof.

13. The method of claim 1, wherein the aqueous medium is water.

14. The method of claim 1, wherein the diazotizing agent is a nitrite.

15. The process of claim 1, wherein in step a), the aromatic amine and base are combined, optionally in an aqueous medium, to form an aromatic amine mixture.

16. The method of claim 15, wherein the aromatic amine mixture comprises at least one aromatic amine comprising at least one carboxylic acid group and at least one carboxylic acid salt group.

17. The method of claim 1, wherein in step a), the pigment and aromatic amine are combined, optionally in an aqueous medium, to form a pigment mixture.

18. The method of claim 1, wherein the modified pigment comprises a pigment having attached at least one organic group, wherein the organic group comprises at least one carboxylic acid salt group.

19. The method of claim 18, wherein the organic group comprises at least two carboxylate groups.

20. The method of claim 18, wherein the organic group comprises at least three carboxylate groups.

21. A method of preparing a modified pigment comprising the steps of:

a) combining, in any order, a pigment, a diazotizing agent, a base, and an aqueous medium to form a mixture, and

b) combining the mixture with an aromatic amine to form the modified pigment,

wherein the aromatic amine comprises at least two carboxylic acid groups, the base and carboxylic acid groups being present in the mixture in a molar ratio of 0.33-0.67: 1.

22. A modified pigment comprising a pigment having attached at least one organic group, wherein the modified pigment is prepared by a process comprising the steps of:

a) combining, in any order, a pigment, an aromatic amine, a base, and an aqueous medium to form a mixture, and

b) combining the mixture with a diazotizing agent to form the modified pigment,

wherein the aromatic amine comprises at least two carboxylic acid groups, wherein the organic group comprises at least one carboxylic acid salt group, the base and carboxylic acid groups being present in the mixture in a molar ratio of 0.33-0.67: 1.

23. The modified pigment of claim 22, wherein the at least two carboxylic acid groups are vicinal.

24. The modified pigment of claim 22, wherein the aromatic amine comprises at least three carboxylic acid groups.

25. The modified pigment of claim 22, wherein the organic group comprises at least two carboxylate groups.

26. The modified pigment of claim 22, wherein the organic group comprises at least three carboxylate groups.

27. A modified pigment comprising a pigment having attached at least one organic group, wherein the modified pigment is prepared by a process comprising the steps of:

a) combining, in any order, a pigment, a diazotizing agent, a base, and an aqueous medium to form a mixture, and

b) combining the mixture with an aromatic amine to form the modified pigment,

wherein the aromatic amine comprises at least two carboxylic acid groups, the organic group comprises at least one carboxylic acid salt group, and the base and carboxylic acid groups are present in the mixture in a molar ratio of 0.33-0.67: 1.

28. An inkjet ink composition comprising a liquid vehicle and a modified pigment comprising a pigment having attached at least one organic group, wherein the modified pigment is prepared by a process comprising the steps of:

a) combining, in any order, a pigment, an aromatic amine, a base, and an aqueous medium to form a mixture, and

b) combining the mixture with a diazotizing agent to form the modified pigment,

wherein the aromatic amine comprises at least two carboxylic acid groups, wherein the organic group comprises at least one carboxylic acid salt group, the base and carboxylic acid groups being present in the mixture in a molar ratio of 0.33-0.67: 1.

29. The inkjet ink composition of claim 28, wherein the at least two carboxylic acid groups are vicinal.

30. The inkjet ink composition of claim 28, wherein the aromatic amine comprises at least three carboxylic acid groups.

31. The inkjet ink composition of claim 28, wherein the organic group comprises at least two carboxylate groups.

32. The inkjet ink composition of claim 28, wherein the organic group comprises at least three carboxylate groups.

33. The inkjet ink composition of claim 28, wherein the liquid carrier is an aqueous carrier.

34. The inkjet ink composition of claim 28, wherein an image produced on a substrate using the inkjet ink composition has an optical density greater than or equal to 1.5.

35. An inkjet ink composition comprising a liquid vehicle and a modified pigment comprising a pigment having attached at least one organic group, wherein the modified pigment is prepared by a process comprising the steps of:

a) combining, in any order, a pigment, a diazotizing agent, a base, and an aqueous medium to form a mixture, and

b) combining the mixture with an aromatic amine to form the modified pigment,

wherein the aromatic amine comprises at least two carboxylic acid groups, the organic group comprises at least one carboxylic acid salt group, and the base and carboxylic acid groups are present in the mixture in a molar ratio of 0.33-0.67: 1.