Synergist for dimeric pigments

Abstract

Disclosed herein are compositions comprising a dimeric (diarylide) pigment and a synergist having a structure similar to the monomer of the dimeric pigment. The synergist is also disclosed. Aqueous dispersions and ink-jet inks comprising such compositions are also disclosed.

Description

[Technical Field]

[0001] Disclosed herein are synergists for dimeric pigments. Dispersions and inks containing such synergists are also disclosed, which can be useful in applications such as ink-jet ink applications. [Background technology]

[0002] Generally, pigments are not easily dispersible in aqueous liquid vehicles, which poses challenges in formulating pigment-based inks. To improve dispersibility, various developments have been made, including the use of dispersing aids or dispersants, which are typically surfactants and water-soluble polymers. Alternatively, pigments can be modified to include ionic compounds to make them self-dispersible. However, these strategies may not be optimal for certain formulation types. Therefore, there remains a need to develop methods for dispersing pigments in aqueous vehicles. Summary of the Invention

[0003] a symmetric diarylide pigment comprising a monomer; A synergist structurally similar to the diarylide pigment monomer Disclosed herein is a composition comprising:

[0004] The symmetric diarylide pigment has the following structure P-1: [ka] , P-1 wherein R1, R2, and R3 are independently selected from H, Cl, C1-C6 alkyl, and C1-C6 alkoxy; X is selected from Cl and C1-C6 alkyl; and Y is selected from H and Cl. and The synergist has the following structure S-1: [ka] S-1 wherein R4, R5, R6, and R7 are independently selected from H, Cl, C1-C6 alkyl, C1-C6 alkoxy, -L-OH, -L-COOH, -L-SO3H, and -L-PO3H2, and salts thereof; L is a divalent linker; and at least one of R4, R5, R6, and R7 is selected from -L-COOH, -L-SO3H, -L-PO3H2, and salts thereof. may have

[0005] The symmetric diarylide pigment has the following structure P-2: [ka] and (b) The synergist has the following structure S-2: [ka] S-2 where X=Cl, C1-C6 alkyl, or C1-C6 alkoxy; R8=H, or C1-C6 alkyl; R9=H, C1-C6 alkyl, or CO2CH2CH3; and Z is an ionic group or ionizable group. DETAILED DESCRIPTION OF THE INVENTION

[0006] Stabilization of pigments in aqueous dispersions generally requires providing the pigment with a charged surface. Many techniques and materials have been employed, including reacting the pigment with various electrophiles or radical agents bearing charged groups (e.g., diazonium cations, sulfur trioxide, chlorosulfonic acid, 1,3,5-triazinyl radicals), or encapsulating the pigment particles within a charged polymer shell.

[0007] Incorporating a dispersant with at least one functional group can also impart dispersibility to a pigment in an aqueous pigment dispersion or ink (e.g., inkjet ink) composition by adsorbing to the pigment. The functional group may be either an ionic group (or ionizable group) or a steric hindrance group. A synergist is a type of dispersant that can physically adsorb to a pigment due to its structural similarity to the pigment. Synergists often contain ionic or ionizable functional groups to impart electrostatic dispersibility to the pigment in aqueous media. The design of a synergist can also depend on one or more factors, including its affinity for the pigment as well as the solubility of the synergist in the dispersion or ink formulation. Furthermore, modern inkjet inks are developed with more complex formulations, which may require consideration of multiple ink parameters, such as particle size distribution and ink viscosity, to achieve long-term stability. For example, inkjet inks may be required to be filterable through 0.5-2 μm filters, which requires that the pigments substantially maintain their particle size. Due to these multiple factors, designing a synergist for a pigment can generally be difficult.

[0008] Generally, a chromophore is defined as a molecule or portion of a molecule that contains a sufficient number of conjugated double bonds to absorb visible light (360-750 nm). For example, an azo chromophore has an electron-withdrawing aryl group linked to an electron-donating group via an azo bond (-N=N-). The electron-donating group in this case may be a substituted aryl group, an acetoacetarylide, or a heterocyclic group. A common approach in pigment design involves linking two identical chromophores in a single pigment molecule via a bivalent linker that may or may not be electronically insulating. Examples of linkers include bonds (such as a single C-C bond), aryl ring systems (e.g., para-substituted phenyl rings, disubstituted fused aryl ring systems with two fused aryl rings (e.g., naphthalene), or disubstituted fused aryl ring systems with three, four, or more rings), and groups of the formula -(CH2) n Alkyl chain with -, or -O-(CH2) nIn one embodiment, the linker can be a bond, a para-substituted phenyl ring, a di-substituted naphthalene ring, or a group of the formula -(CH2) n Alkyl chain with -, or -O-(CH2) n -O- (where n = 1 to 6) is an ether chain. This approach can effectively double the molecular weight of the pigment, thereby improving its solvent and heat resistance without affecting its color properties.

[0009] Typically, these dimeric pigments are symmetrical and can be represented as AB2, where A represents a linker connecting two chromophore residues B. The chromophore residue B can also be referred to as a pigment monomer. Examples of such dimeric pigments include diarylide pigments. Diarylide pigments can be prepared by tetrazotization of benzidine or substituted benzidine. In a more specific example, the linker A in Pigment Yellow 12 is a single bond between the aryl residues of the tetrazotized benzidine or benzidine derivative. The linker A is a single bond, and the monomer B is as shown in the structure of Pigment Yellow 12 below: [ka] Pigment Yellow 12

[0010] To prepare dimeric pigments, a tetrazotized compound (e.g., benzidine or a benzidine derivative) can be linked to two identical nucleophilic couplers, which can be substituted acetoacetanilides (yellow pigments), pyrazolones (orange pigments), or substituted naphthols (red pigments). Specific examples include Pigment Yellow 12 (the coupler is acetoacetanilide), Pigment Orange 13 (the coupler is phenylmethylpyrazolone), and Pigment Orange 34 (the coupler is tolylmethylpyrazolone). These examples are illustrated in Schemes A and B below, where the linker A is a single bond and the monomer B contains the respective coupler and a 2'-chloroaniline unit resulting from (tetrazotized 3,3'-dichlorobenzidine). [ka] [ka]

[0011] Synergists can be designed for dimeric pigments so that they are structurally similar to the parent dimer, i.e., so that the synergist also has a dimeric structure (a "full synergist"). An example of a full synergist is illustrated below: [ka]

[0012] Unfortunately, these molecules can have high water solubility due to the presence of two or more ionic groups, such as the two SO3Na groups shown above. High water solubility can reduce the affinity of the full synergist to the parent pigment. Other symmetric synergists with similar structures and different configurations of charged groups can be prepared, but the starting materials may not be readily available.

[0013] It has been found that good performance can be achieved with a synergist that is structurally similar to the monomer of the dimeric pigment (a "half synergist"). A half synergist for Pigment Yellow 12 is illustrated below: [ka]

[0014] Thus, a dispersion or composition comprising a pigment having a dimeric structure (a dimeric pigment, such as a diarylide pigment) and a synergist is disclosed herein. The synergist is structurally similar to the monomer of the dimeric structure, e.g., a derivative of the monomer. By structural similarity or structurally similar, it is meant that the synergist contains structural moieties that are identical to and different from the monomer of the dimeric pigment. In one embodiment, the identical structural moieties constitute at least 50% of the total molecular weight of the monomer of the dimeric pigment or diarylide pigment, e.g., at least 60%, at least 70%, at least 80%, or at least 90% of the total molecular weight of the monomer of the pigment, but not more than 99% or not more than 95% of the total molecular weight of the monomer of the pigment. In one embodiment, the synergist is a derivative of the monomer of the pigment. Because the synergist is structurally similar to the monomer of the dimeric pigment, optionally the molecular weight of the synergist is 70% or less of the molecular weight of the dimeric pigment or diarylide pigment, e.g., 60% or less of the molecular weight of the dimeric pigment, e.g., the molecular weight of the synergist is in the range of 25-70%, 30-70%, 35-70%, 40-75%, 45-70%, 50-70%, 55-70%, or 60-70% of the molecular weight of the dimeric pigment. Thus, the synergist is a separate substance from the pigment that is capable of providing a stable dispersion of the pigment in a liquid vehicle.

[0015] Without wishing to be bound by any theory, the structural similarity between the pigment monomer and the synergist potentially results in the synergist having a high affinity for the pigment. This high affinity, in turn, may aid in the adsorption of the synergist to the pigment surface. In one embodiment, this high affinity may take the form of van der Waals interactions (e.g., dipole-dipole interactions). In one embodiment, the synergist further comprises ionic or ionizable groups that enable further interactions between the pigment and the synergist, including one or more of π-π stacking, ionic interactions / bonding, hydrogen bonding, and acid / base interactions / reactions. In one embodiment, both the pigment and the synergist possess ionic or ionizable groups, thereby providing the interactions described herein (e.g., van der Waals interactions, π-π stacking, ionic interactions / bonding, acid / base interactions / bonding, and hydrogen bonding). Furthermore, adsorption of synergist molecules onto the faces of pigment crystals may create dislocations, which may hinder further crystal growth along these faces, thereby providing a means for controlling and / or maintaining the size and distribution of pigment particles.

[0016] Without wishing to be bound by any theory, when a pigment contains two identical chromophores connected by a single bond, symmetry results in essentially zero electronic interaction. The chromophores can be considered essentially independent. Because the absorption characteristics of the monomeric and corresponding dimeric colorant molecules tend to be similar in terms of hue angle and intensity, the added synergist typically does not "dilute" the pigment color. As a result, the color of the monomeric synergist tends to be similar to that of the dimeric pigment. Furthermore, half-synergists offer fewer ionic groups, which are less water-soluble than full-synergists. Less competitive water interactions may result in a stronger affinity for the pigment surface.

[0017] Finally, because synergists are additives, their use can simplify the ink formulation process by avoiding purification steps that may be required with other dispersion techniques, such as with dispersing additives. Thus, disclosed herein are compositions comprising a dimeric pigment and a synergist structurally similar to the monomer of the dimeric pigment. The dimeric pigment may be a diarylide, acetoacetanilide (yellow pigment), arylpyrazolone (orange pigment), substituted naphthol (red pigment), perylene pigment such as Pigment Red 149, Pigment Red 178, and diazo condensation pigment such as Pigment Yellow 93, Pigment Red 144, and Pigment Red 214. The aryl groups of the diarylide may be connected by a linker, which may be a single bond connecting the aryl groups of a benzidine or substituted benzidine residue (e.g., a dichlorobenzidine residue, such as 3,3'-dichlorobenzidine residue).

[0018] In one embodiment, the symmetric diarylide pigment has the following structure P-1: [ka] , P-1 wherein R1, R2, and R3 are independently selected from H, Cl, C1-C6 alkyl (e.g., methyl or ethyl), and C1-C6 alkoxy (e.g., methoxy or alkoxy); X is selected from Cl and C1-C6 alkyl (e.g., methyl or ethyl); and Y is selected from H and Cl. For example, R1 and R2 are independently selected from H, Cl, C1-C6 alkyl (e.g., methyl or ethyl), and C1-C6 alkoxy (e.g., methoxy or alkoxy), and R3 is selected from H, Cl, and C1-C6 alkyl (e.g., methyl or ethyl). In another example, R1 and R2 are independently selected from H, Cl, methyl, and methoxy, R3 is selected from H and methoxy (e.g., R3 is H), X is selected from Cl and methyl, and Y is selected from H and Cl. In yet another example, R1 is selected from H, methyl, and methoxy (e.g., R1 is selected from H and methyl), R2 is selected from H and methyl, and R3 is H. Exemplary pigments include yellow pigments such as Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 16, Pigment Yellow 17, Pigment Yellow 81, and Pigment Yellow 83. The diarylide pigment may be the predominant or minor pigment in the composition. For example, some commercial grades of Pigment Yellow 126 may contain minor amounts of Pigment Yellow 12, and some commercial grades of Pigment Yellow 127 may contain minor amounts of Pigment Yellow 13.

[0019] The composition containing at least one pigment having the structure P-1 comprises the following structure S-1: [ka] S-1 wherein R1-R3 are as defined for pigment P-1, R4, R5, R6, and R7 are independently selected from H, Cl, C1-C6 alkyl (e.g., methyl or ethyl), and C1-C6 alkoxy (e.g., methoxy or alkoxy), -L-OH, -L-COOH, -L-SO3H, -L-PO3H2, and salts thereof, and L is a divalent linker (a (single) bond, an aryl ring system, -O-(CH2) n Ether chains such as -O- or of the formula -CH n- (where n=1 to 6), and at least one of R4, R5, R6, and R7 is selected from -L-COOH, -L-SO3H, -L-PO3H2, and salts thereof, for example, at least one of R4, R5, R6, and R7 is selected from -COOH, -SO3H, and -PO3H2, and salts thereof. The term "salts thereof" refers to salts of the acid group of the synergist, e.g., Na + , K. + , Li + , or NR'4 + wherein R' may be the same or different and represent hydrogen or an organic group, such as a substituted or unsubstituted aryl (e.g., phenyl) and / or alkyl group (e.g., C1-C6 alkyl), etc.; + It is also understood that the R, R, and R substitutions on the synergist may be independent of the substitutions on the pigment, e.g., may be the same as or different from the substitutions on the pigment.

[0020] In another embodiment, the symmetric diarylide pigment has the following structure P-2: [ka] P-2 and the synergist has the following structure: [ka] S-2 where X=Cl, C1-C6 alkyl, or C1-C6 alkoxy; R8=H or C1-C6 alkyl; R9=H, C1-C6 alkyl, or CO2CH2CH3; and Z is an ionic or ionizable group. Thus, disclosed herein are compositions (e.g., aqueous dispersions, inks, or inkjet compositions) comprising the dimeric pigment and a synergist. Examples of such pigments include Pigment Orange 13 and Pigment Orange 34.

[0021] In one embodiment, X=Cl, C1-C2 alkyl, or C1-C2 alkoxy, e.g., X=Cl or C1-C2 alkoxy (e.g., OCH3). In one embodiment, R8=H or C1-C2 alkyl, e.g., R2=H or CH3. In one embodiment, R9=H, C1-C2 alkyl, or CO2CH2CH3, e.g., R9=H, CH3, or CO2CH2CH3, or R9=H or CH3. The above structure has an azo group, and Z can be ortho, meta, or para to the azo group in the structure, e.g., Z can be meta or para to the azo group in the structure. It is understood that the substitutions of R8 and R9 on the synergist can be independent of the substitutions on the pigment, e.g., can be the same as or different from the substitutions on the pigment.

[0022] The synergist may have one or more functional groups that are different from the functional groups of the pigment. In one embodiment, the synergist described herein has one functional group that is an ionic or ionizable group. In one embodiment, the ionic group of the synergist confers hydrophilicity, making the synergist soluble or dispersible in a liquid vehicle, such as an aqueous solution or water. When the synergist is adsorbed onto the pigment, this adsorption can occur selectively due to its similar structure to the monomer. The synergist may actually provide charged groups on the pigment surface, making the pigment dispersible in a liquid vehicle (e.g., an aqueous solution).

[0023] In one embodiment, the synergist contains an ionic group or an ionizable group. An ionic group is a group capable of forming an ionic group in the medium of use. An anionic group is a negatively charged ionic group that can result from a group having an ionic substituent (anionic group) capable of forming an anion, such as an acidic substituent. A cationic group is a positively charged organic ionic group that can result from an ionic substituent (cationic group) capable of forming a cation, such as a protonated amine. By "ionic group or ionizable group," it is understood that a mixture may exist in the composition. For example, in the composition, some of the synergists may have an ionic group (i.e., Z is an ionic group) and other synergists may have an ionic group (i.e., Z is an ionizable group). The ionic group and the distribution of the ionic group in the composition can be selected by means known in the art, such as by controlling pH, counterions, etc.

[0024] Specific examples of ionic groups (for example, anionic groups) include -COO - , -SO3 - , -OSO3 - , -HPO3 - ;-OPO3 2- , or -PO3 2- (including cation counterions as defined herein, e.g., M + Specific examples of ionic groups (e.g., anionic groups) include -COOH, -SO3H, -PO3H2, -R'SH, or -R'OH, where R' represents H or an organic group, such as a substituted or unsubstituted aryl or alkyl group. Specific examples of cationic groups include alkylamines or arylamines, which can be protonated in an acidic medium to form an ammonium group, -NR'2H + wherein R' is an organic group, such as a substituted or unsubstituted aryl or alkyl group, for example, a substituted or unsubstituted C5-C 20 Aryl or C1-C 12represents an alkyl (e.g., C1-C6 alkyl) group. Organic ionic groups include those described in U.S. Pat. No. 5,698,016, the disclosure of which is incorporated herein by reference.

[0025] In certain embodiments, the ionic group is, for example, —COO - , -SO3 - , -OSO3 - , -HPO3 - , -OPO3 2- , or -PO3 2- For example, -COO - , -SO3 - , or -PO3 2- In other embodiments, the ionic group or ionizable group is, for example, —COOH, —SO3H, —PO3H2, —R'SH, or —R'OH, such as, for example, —COOH, —SO3H, or —PO3H2. In other embodiments, the ionic group or ionizable group is, for example, —SO3 - or -SO3H. In another embodiment, the composition comprises at least one synergist with an ionic group and at least another synergist with an ionizable group. Without wishing to be bound by any theory, it is believed that due to the relatively low molecular weight of the synergist, having more than one ionic and / or ionizable group may result in a synergist that is too hydrophilic, which may make the synergist soluble in water and allow desorption of the synergist from the pigment surface into the continuous phase.

[0026] Another embodiment provides a composition (e.g., a dispersion or ink, such as an ink-jet ink) comprising a dimeric pigment and at least one synergist described herein. In one embodiment, the at least one synergist is present in the composition in an amount ranging from 3% to 10% by weight, relative to the weight of the dimeric pigment. For example, the at least one synergist is present in the composition in an amount ranging from 3% to 9%, 3% to 8%, 4% to 10%, 4% to 9%, 4% to 8%, 5% to 10%, 5% to 9%, or 5% to 8% by weight, relative to the weight of the dimeric pigment. In one embodiment, the at least one synergist in the composition is a mixture of more than one synergist having a structure described herein, e.g., a mixture of synergists each having one or more substituents that are different from each other.

[0027] In one embodiment, at least one synergist according to the claimed invention can be prepared by a diazonium reaction. For example, a diazonium reagent can be prepared from an aminobenzene reactant having an ionic or ionizable group ortho, meta, or para (e.g., meta or para) relative to the amine group by combining it with a base (e.g., NaOH) and sodium nitrite (see the first step of Scheme C below, which illustrates a synergist of structure S-2). The aminobenzene reactant can be, for example, a sulfanilic acid or an aminobenzoic acid. The resulting diazonium reagent can then be combined with a coupler (e.g., acetoacetanilide, phenylpyrazolone, naphthol, etc.) to form at least one synergist.

[0028] For example, the phenyl group of the phenylpyrazolone may be substituted with an R8 group (e.g., ortho, meta, or para to the pyrazolonyl, or meta or para to the pyrazolonyl), and the pyrazolonyl may contain an R9 group, as shown in Scheme C below, where R8 and R9 are as defined above. [ka] Scheme C

[0029] Thus, disclosed herein is a method for preparing at least one synergist, comprising combining an aminobenzene reactant substituted on the aryl ring with an ionic or ionizable group with a base to form a diazonium reagent. The method further comprises combining the diazonium reagent with a coupler (e.g., acetoacetanilide, phenylpyrazolone, naphthol, etc.) to form at least one synergist. For synergists having structure S-2, the phenyl group of the phenylpyrazolone has an R8 substituent, and the pyrazolonyl has an R9 substituent, where R8 = H or C1-C6 alkyl, R9 = H, C1-C6 alkyl, or CO2CH2CH3, and Z is an ionic or ionizable group.

[0030] Pigments are generally solid materials in the form of particulate solids. The particulate solids may be powders, dispersions, or pressed cakes. The size of such particles can be achieved by one or more conventional size reduction, grinding, and / or classification techniques, such as ball milling, media milling, jet milling, ultrasonic treatment, fluid impingement, and centrifugation to remove undesirable large particles. Median particle size can be determined by dynamic light scattering using equipment manufactured by companies such as Microtrac, Inc. and Malvern Panalytical, Ltd. In one embodiment, the pigment has a median particle size in the range of 100 nm to 300 nm, e.g., 100 nm to 250 nm, 100 nm to 225 nm, 100 nm to 200 nm, 100 nm to 180 nm, 120 nm to 250 nm, 120 nm to 225 nm, 120 nm to 200 nm, 120 nm to 180 nm, 150 nm to 250 nm, 150 nm to 225 nm, 150 nm to 200 nm, or 150 nm to 180 nm. Particle size may be based on volume (mean volume, Mv) or on a number distribution. Pigment-containing dispersions can be purified by ultrafiltration, diafiltration, ion exchange, centrifugation, or a combination of one or more such methods.

[0031] The claimed synergists have been found to improve the stability of pigments in dispersions or inks. Stability can be measured, for example, by the median particle size of the pigment in the dispersion or ink. In one embodiment, the median particle size of a pigment dispersion or ink containing the claimed synergists does not increase significantly in size over a specified period of time, such as at least 7 days, or at least 2 weeks, or at least 6 weeks, at room temperature or at 60°C, 70°C, or 80°C. In one embodiment, the median particle size does not increase by more than 30% relative to its initial median particle size. For example, the median particle size does not increase by more than 25%, 20%, 15%, 10%, or 10% relative to its initial median particle size.

[0032] Alternatively, or in addition, stability can be measured by the viscosity of the pigment dispersion or ink. In one embodiment, the viscosity (cP) of the pigment dispersion or ink does not increase significantly over a certain period of time, such as at least 7 days, or at least 2 weeks, or at least 6 weeks, at either room temperature or 60°C. In one embodiment, the viscosity does not increase by more than 30% relative to its initial viscosity. For example, the viscosity does not increase by more than 25%, or more than 20%, or more than 15%, or more than 10%, or more than 10% relative to its initial viscosity. If the median particle size or viscosity increases by more than 30% relative to its initial median particle size or viscosity (or other percentages described herein), this typically occurs as a result of aggregation, which can cause the pigment to experience undesirable settling and / or gelation. In further or alternative embodiments, the ink or dispersion comprising the dimeric pigment and synergist is stable for a certain period of time, such as at least 7 days, or at least 2 weeks, or at least 6 weeks, at either room temperature or 60° C. For example, stability can be determined by the ability of the ink or dispersion to maintain certain physical properties, which can include particle size, pH, surface tension, viscosity, within 10% of their original values.

[0033] In one embodiment, the composition comprises a liquid vehicle. In one embodiment, the liquid vehicle is aqueous. For example, the aqueous vehicle may be an aqueous solution, for example, comprising at least 40% water, for example, at least 45% water, or at least 50% water. In one embodiment, the composition is a pigment dispersion, for example, an aqueous pigment dispersion. In another embodiment, the composition is an ink (e.g., inkjet ink) composition, for example, an aqueous ink (e.g., inkjet ink) composition. In one embodiment, the composition is an aqueous pigment dispersion comprising the dimeric pigment in an amount ranging from 1% to 40% by weight, based on the total weight of the pigment dispersion, for example, from 1% to 30%, 1% to 20%, 1% to 10%, 3% to 40%, 3% to 30%, 3% to 20%, 3% to 10%, 5% to 40%, 5% to 30%, 5% to 20%, or 5% to 10% by weight, based on the total weight of the pigment dispersion.

[0034] In one embodiment, the composition is an aqueous ink (e.g., ink-jet ink) composition. In one embodiment, the composition comprises the dimeric pigment in an amount ranging from 1% to 15% by weight, for example, from 1% to 10% by weight, relative to the total weight of the composition, for example, in an amount ranging from 2% to 15%, 2% to 10%, 3% to 15%, 3% to 10%, 1% to 7%, 2% to 7%, or 3% to 7% by weight, relative to the total weight of the composition.

[0035] In one embodiment, the composition, such as an aqueous pigment dispersion or aqueous ink (e.g., inkjet ink) composition, further comprises at least one organic solvent present in an amount ranging from 1% to 50% based on the total weight of the inkjet ink composition (e.g., the aqueous vehicle is an aqueous solution). For example, the aqueous pigment dispersion or ink may comprise at least two organic solvents (co-solvents). The at least one organic solvent may be present in the composition in addition to at least 40% water (or at least 45% water, or at least 50% water). In one embodiment, the organic solvent is soluble or miscible in water. In another embodiment, the organic solvent is chemically stable to aqueous hydrolysis conditions (e.g., reaction with water under heat aging conditions, including hydrolysis of esters and lactones). In one embodiment, the organic solvent has a dielectric constant lower than that of water, such as a dielectric constant ranging from about 10 to about 78 at 20°C. Examples of suitable organic solvents include alcohols and polyols (glycols, glycerin, etc.), amides, ketones or ketoalcohols, ethers, urea or urea derivatives, hydroxyamide derivatives, sugars, sulfoxide derivatives, and sulfone derivatives. The at least one organic solvent may comprise a mixture of organic solvents.

[0036] A humectant and a water-soluble organic compound other than the at least one organic solvent may also be added to the ink-jet ink composition of the present invention, for example, to prevent nozzle clogging, to achieve paper penetration (penetrant), to achieve improved drying (drying accelerator), and to achieve anti-cockling properties. In one embodiment, the humectant and / or water-soluble compound is present in an amount ranging from 0.1% to 50%, for example, from 1% to 50%, from 0.1% to 30%, from 1% to 30%, from 0.1% to 10%, or from 1% to 10%. In one embodiment, the ink composition (e.g., inkjet ink composition) includes at least one surfactant, for example, if the pigment is not self-dispersible. The at least one surfactant can improve the colloidal stability of the composition or can modify the interaction of the ink with either the printing substrate, such as the printing paper, or the ink printhead. Various anionic, cationic, and nonionic dispersants can be used in conjunction with the ink composition of the present invention, and may be used neat or as an aqueous solution. In one embodiment, the surfactant is present in an amount ranging from 0.05% to 5% by weight, for example, from 0.1% to 5%, or from 0.5% to 2%, based on the total weight of the inkjet ink composition.

[0037] In one embodiment, the ink (e.g., ink-jet ink) composition has a viscosity in the range of 1 to 25 cP. It is understood that viscosity can be adjusted by various methods. In one embodiment, a polymeric binder can be used in conjunction with the ink-jet ink compositions disclosed herein to adjust the viscosity of the composition and / or achieve other desirable properties, such as durability (e.g., at least one durable polymer). Such polymeric binders may be present in the composition in an amount ranging from 0.1% to 20% by weight, based on the total weight of the composition, such as 0.1% to 10%, 0.1% to 5%, 0.2% to 20%, 0.2% to 10%, 0.2% to 5%, 0.5% to 20%, 0.5% to 10%, or 0.5% to 5% by weight, based on the total weight of the composition.

[0038] In one embodiment, the ink (e.g., ink-jet ink) composition may further include one or more suitable additives to impart certain desired properties while maintaining the stability of the composition. Other additives are well known in the art and include humectants, biocides and mildewcides, pH adjusters, drying accelerators, penetrants, and the like. The amount of a particular additive will vary depending on various factors, but is generally present in an amount ranging from 0.01% to 40% by weight of the ink composition. In one embodiment, at least one additive is present in an amount ranging from 0.05% to 5%, e.g., from 0.1% to 5%, or from 0.5% to 2%, by weight, based on the total weight of the ink-jet ink composition. [Example]

[0039] The reaction products were identified by HPLC-MS (Agilent 1100 connected to a Thermo LTQ XL with electrospray ionization; column: Zorbax Extend C18, 4.6 × 150 mm, 5 μm) from Agilent Technologies, Inc. The particle size (Mv) was measured by using a Nanotrac™ 252 particle size analyzer from Microtrac, Inc.

[0040] Example 1 Preparation of synergist S-1 This example illustrates the preparation of a synergist having the structure S-1, the synthesis of which is outlined in Scheme D below. [ka] Scheme D

[0041] To prepare the diazonium solution, sulfanilic acid (17.7 g) was dissolved in a mixture of 100 mL of deionized water and 40% sodium hydroxide solution (10.2 g), followed by the addition of sodium nitrite (7.0 g). The resulting solution was added dropwise to a stirred mixture of 36% hydrochloric acid (18.9 mL) and ice water (150 g). Excess nitrite was neutralized by the addition of a 25% solution of sulfamic acid (2-4 g).

[0042] A coupler solution was prepared by dissolving acetoacetanilide (AAA, 18.3 g) in a mixture of 40% sodium hydroxide solution (10.4 g), isopropanol (200 mL), and DI water (200 mL). Azo coupling was performed by adding the diazonium salt solution to the stirred coupler at pH 4-6; the pH was maintained by adding 1 M sodium hydroxide as needed. The precipitated dye was filtered and washed with a small amount of ice water. The yield was 85%; the HPLC purity was 96% by area. Other yellow synergists were similarly prepared (using acetoaceto-2',4'-xylidide (AAX) or acetoaceto-2'-toluidide (AAOT) instead of AAA) with corresponding yields and purities, as shown in Table 1. For all synergists, R4 and R7 are H. [Table 1]

[0043] Example 2 Preparation of synergist S-2 This example illustrates the preparation of a synergist for Pigment Orange 34 in accordance with the claimed invention, the synergist having the structure S-2. The synthesis of synergist S-2 is outlined below in Scheme E. In Scheme E, either Z1 or Z2 is an ionic or ionizable group. [ka] Scheme E

[0044] Synergists were prepared in a similar manner to Example 1, except that diazotized SA or MA was coupled with either PMP or TMP. The results are shown in Table 2. [Table 2]

[0045] Comparative Example Preparation of full synergist This example illustrates the preparation of a full synergist for both yellow and orange pigments, as outlined in Schemes F and G, respectively. [ka] Scheme F [ka] Scheme G

[0046] To prepare the yellow full synergist, a diazonium solution of benzidine-2,2'-disulfonic acid ("BDSA") (TCI Chemical; 26.2 g of an 82% solution) was dissolved in a mixture of 150 ml of deionized water and 40% sodium hydroxide solution (12.8 g), followed by the addition of sodium nitrite (8.6 g). The resulting solution was added dropwise to a stirred mixture of 36% hydrochloric acid (23.6 mL) and ice water (250 g). Excess nitrous acid was neutralized by the addition of 25% sulfamic acid solution (2-4 g).

[0047] A coupler solution was prepared by dissolving acetoacetanilide (AAA, 23.1 g) in a mixture of 40% sodium hydroxide solution (13.0 g), isopropanol (200 mL), and 200 mL of DI water. Azo coupling was achieved by adding the diazonium salt solution to the stirred coupler at pH 4-6; the pH was maintained by adding 1 M sodium hydroxide as needed. The precipitated dye was filtered and washed with a small amount of ice water. The yield was 70%; HPLC purity was 96% by area.

[0048] Other full synergists were similarly prepared using acetoaceto-2',4'-xylidide (AAX) or acetoaceto-2'-toluidide (AAOT) instead of AAA. The water solubility of the BDSA-based full synergists was much higher than that of the corresponding half synergists of Example 1. The dye sometimes precipitated as a reddish-yellow oil (saturated solution in isopropanol-water), but eventually the dye crystallized. Other full synergists were similarly prepared, and their yields and purities are shown in Table 3. [Table 3]

[0049] Full synergists for orange pigments (Scheme G) were prepared similarly, except that tetrazotized BDSA was coupled with either PMP or TMP (Table 4). [Table 4]

[0050] pigment dispersion Typically, charge-stabilized particles in water have 175-350 μmol counterion per gram of pigment to achieve adequate settling resistance. In this example, the synergist contained 4.8-6.1% sodium counterion. To achieve a counterion content of approximately 175 μmol / g, the dispersion contained 6%-7.5% synergist by pigment mass.

[0051] Pigment Yellow 12 (55 g Sun Chemical, Sunbrite Yellow 12) was mixed with MA-AAA synergist (3.51 g) and deionized water (312 mL) in a heavy-walled flask. Vacuum was applied to wet the pigment, and the resulting predispersion was homogenized in a rotor / stator mixer at 5,000 rpm for 1 hour and then sonicated for 3 hours at 180-200 W using a Misonix sonicator equipped with a horn. The dispersion was centrifuged at 2,500 g for 15 minutes to remove undispersed material, which was then decanted from the centrifuge sludge. The volume-average particle size (Mv) was then measured.

[0052] Other dispersions were prepared similarly and the dispersion properties are shown in Table 5 below: [Table 5]

[0053] The effect of the synergists was evaluated by heat aging the dispersions at 60°C for 4 weeks. A ±10% change in the Mv of the dispersion was defined as acceptable. The results are summarized in Table 6: [Table 6]

[0054] The data in Table 6 show that the dispersions containing half synergists showed good (smallest) Mv increase, while all comparative dispersions containing full synergists exceeded the minimum Mv increase requirement and therefore failed.

[0055] The use of the terms "a," "an," and "the" should be construed to include both the singular and the plural unless otherwise specified herein or clearly contradicted by context. The terms "comprising," "having," "including," and "containing" should be construed as open ended (i.e., meaning "including, but not limited to") unless otherwise noted. The recitation of ranges of values ​​herein, unless otherwise specified herein, is intended to serve merely as a shorthand method of referring individually to each separate value falling within the range, and each separate value is incorporated herein as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise specified herein or clearly contradicted by context. The use of any and all examples, or exemplary language presented herein (e.g., "such as"), is intended merely to facilitate understanding of the invention and does not pose a limitation on the scope of the invention unless otherwise asserted. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Claims

1. a symmetric diarylide pigment comprising a monomer; A synergist structurally similar to the diarylide pigment monomer A composition comprising:

2. 10. The composition of claim 1, wherein the synergist contains structural moieties identical to and different from the monomers of the diarylide pigment, the identical structural moieties comprising at least 50% of the total molecular weight of the monomers.

3. 3. The composition of claim 1, wherein the synergist has a molecular weight that is no greater than 70% of the molecular weight of the pigment.

4. The composition of any one of claims 1 to 3, wherein the monomer comprises (a) an acetoacetanilide, pyrazolone, or naphthol-containing residue, and (b) a benzidine-containing residue.

5. The symmetric diarylide pigment has the following structure P-1: 【Chemistry 1】 , P-1 (In the formula, R 1 , R 2 , and R 3 are independently H, Cl, C 1 -C 6 Alkyl, and C 1 -C 6 alkoxy, X is selected from Cl and C 1 -C 6 alkyl, and Y is selected from H and Cl. and The synergist has the following structure S-1: 【Chemistry 2】 S-1 (In the formula, R 4 , R 5 , R 6 , and R 7 are independently H, Cl, C 1 -C 6 Alkyl, C 1 -C 6 Alkoxy, -L-OH, -L-COOH, -L-SO 3 H, and -L-PO 3 H 2 and salts thereof, L is a divalent linker, and R 4 , R 5 , R 6 , and R 7 At least one of the groups is -L-COOH, -L-SO 3 H, -L-PO 3 H 2 (selected from having The composition according to any one of claims 1 to 4.

6. The divalent linker may be a bond, an aryl ring system, a group of the formula -(CH 2 ) n or an alkyl chain having the formula —O—(CH 2 ) n 6. The composition of claim 5, wherein the ether chain is selected from an ether chain having -O-, where n=1 to 6.

7. R 1 and R 2 are independently H, Cl, C 1 -C 6 Alkyl, and C 1 -C 6 alkoxy; R 3 is H, Cl, and C 1 -C 6 7. The composition of claim 5 or 6, wherein the alkyl is selected from the group consisting of aryl, arylsulfonyl ...

8. R 1 is selected from H, methyl, and methoxy; R 2 is selected from H and methyl, and R 3 7. The composition of claim 5 or 6, wherein is H.

9. R 4 , R 5 , R 6 , and R 7 At least one of the groups is —COOH, —SO 3 H, and -PO 3 H 2 The composition according to any one of claims 5 to 8, wherein the compound is selected from the group consisting of:

10. The composition according to any one of claims 1 to 6, wherein the pigment is selected from Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 16, Pigment Yellow 17, Pigment Yellow 81, and Pigment Yellow 83.

11. The symmetric diarylide pigment has the following structure P-2: 【Transformation 3】 and (b) The synergist has the following structure S-2: 【Chemistry 4】 S-2 and In the formula, X=Cl, C 1 -C 6 Alkyl, or C 1 -C 6 is alkoxy, and R 8 = H, or C 1 -C 6 alkyl, and R 9 = H, C 1 -C 6 Alkyl or CO 2 CH 2 CH 3 and Z is an ionic or ionizable group. The composition according to any one of claims 1 to 4.

12. X = Cl, C 1 -C 2 Alkyl, or C 1 -C 2 The composition of claim 11 which is an alkoxy.

13. X = Cl or OCH 3 The composition of claim 11, wherein

14. 12. The composition of claim 11, wherein X = Cl.

15. R 9 = H, C 1 -C 2 Alkyl or CO 2 CH 2 CH 3 The composition according to any one of claims 11 to 14, wherein

16. R 9 = H, CH 3 , or CO 2 CH 2 CH 3 The composition according to any one of claims 11 to 15,

17. R 8 = H or C 1 -C 2 The composition of any one of claims 11 to 16, wherein the alkyl is alkyl.

18. R 8 = H or CH 3 and R 9 = H or CH 3 The composition according to any one of claims 11 to 17, wherein

19. The composition of any one of claims 11 to 18, wherein Z is meta or para to the azo group in the structure.

20. The composition of any one of claims 11 to 19, wherein Z is an ionic group.

21. The composition of any one of claims 11 to 20, wherein the ionic group is an anionic group.

22. The ionic group is —COO - , -SO 3 - , -OSO 3 - , -HPO 3 - ;-OPO 3 2- , or -PO 3 2- The composition according to any one of claims 11 to 21, wherein

23. The ionic group is —COO - , -SO 3 - , or -PO 3 2- The composition according to any one of claims 11 to 22, wherein

24. The composition according to any one of claims 11 to 23, wherein the ionic group is an anionic group.

25. The ionic group is —COOH, —SO 3 H, -PO 3 H 2 , —R′SH, or —R′OH, where R′ is H or substituted or unsubstituted C 5 -C 20 Aryl or C 1 -C 12 The composition according to any one of claims 11 to 24, wherein the group is an alkyl group.

26. The ionic group is —COOH, —SO 3 H, or -PO 3 H 2 The composition according to any one of claims 11 to 25,

27. A composition according to any preceding claim, wherein the synergist is present in the composition in an amount ranging from 3% to 10% by weight relative to the weight of the pigment.

28. The composition of any one of claims 1 to 27, wherein the pigment has a median particle size in the range of 100 nm to 300 nm.

29. The composition of any one of claims 1 to 27, wherein the pigment has a median particle size in the range of 100 nm to 250 nm.

30. The composition of any one of claims 1 to 29, further comprising a liquid vehicle.

31. 31. The composition of claim 30, wherein the liquid vehicle comprises water.

32. 32. The composition of claim 31, wherein the liquid vehicle further comprises at least one solvent.

33. The composition of any one of claims 1 to 32, which is an aqueous pigment dispersion.

34. The composition according to any one of claims 1 to 32, which is an aqueous ink composition.

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