Synergists for dimeric pigments

Abstract

Disclosed herein are compositions comprising a dimeric (diarylate) pigment and a synergist, wherein the synergist has a similar structure to the monomers of the dimeric pigment. Also disclosed are aqueous dispersions and inkjet inks comprising such compositions. In a first preferred composition, the symmetric diarylate pigment has the following structure: (P-1), and the synergist has the following structure: (S-1). In a second preferred composition, the symmetric diarylate pigment has the following structure: (P-2), and the synergist has the following structure: (S-2). # imgabs0 #

Description

Technical Field

[0001] Disclosed herein are synergists for dimeric pigments. Also disclosed are dispersions and inks containing such synergists, which can be used in applications such as inkjet ink applications. Background Art

[0002] Typically, pigments are not easily dispersed in aqueous liquid vehicles, which poses a challenge to the formulation of pigment-based inks. In order 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, the pigment can be modified to include ionic compounds, making the pigment self-dispersible. However, these strategies may not be optimal for certain formulation types. Therefore, there is still a need to develop methods for dispersing pigments in aqueous vehicles. Summary of the Invention

[0003] Disclosed herein are compositions comprising:

[0004] A symmetrical diarylide pigment comprising a monomer; and

[0005] Synergists for monomers structurally similar to diarylide pigments.

[0006] Symmetrical diarylide pigments may have the following structure P-1:

[0007] P-1,

[0008] 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

[0009] The synergist may have the following structure S-1:

[0010] S-1

[0011] 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, wherein 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.

[0012] Symmetrical diarylide pigments may have the following structure P-2:

[0013] ,and

[0014] (b) The synergist has the following structure S-2:

[0015] S-2

[0016] wherein 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 an ionizable group. DETAILED DESCRIPTION

[0017] Stabilizing pigments in aqueous dispersions generally requires providing pigments with charged surfaces. Many techniques and materials have been employed, including reacting the pigments with various electrophilic or free radical reagents bearing charged groups (e.g., diazonium cations, sulfur trioxide, chlorosulfonic acid, 1,3,5-triazinyl groups), or encapsulating the pigment particles in a shell of charged polymers.

[0018] The introduction of a dispersant having at least one functional group can also impart dispersibility to the pigment in an aqueous pigment dispersion or ink (e.g., inkjet ink) composition by adsorption to the pigment. The functional group can be ionic (or ionizable) or can produce steric hindrance. A synergist is a type of dispersant that, due to its structural similarity to the pigment, can be physically adsorbed to the pigment. Synergists typically contain ionic functional groups or ionizable functional groups to provide electrostatic dispersibility in aqueous media to the pigment. Synergist design can also consider one or more factors, including the solubility of the synergist in the dispersion or ink formulation and its affinity for the pigment. In addition, modern inkjet inks with more complex formulations have been developed, which may require consideration of multiple ink parameters, such as particle size distribution and ink viscosity, to achieve stability over an extended period of time. For example, inkjet inks may need to be filterable through a 0.5-2 μm filter, which requires the pigment to substantially maintain its particle size. Due to these multiple factors, designing a synergist for a pigment can be challenging.

[0019] Typically, a chromophore is defined as a molecule or part of a molecule containing 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 connected to an electron-donating group via an azo bond (-N=N-). In this case, the electron-donating group can be a substituted aryl, acetoacetyl arylate, or a heterocyclic group. Common approaches in pigment design involve combining two identical chromophores in a single pigment molecule via a connection through a divalent linker that may or may not be electronically insulating. Examples of linkers can include a bond (e.g., a single C-C bond), an aryl ring system (e.g., a para-substituted benzene ring, a disubstituted fused aryl ring system with 2 (e.g., naphthalene), 3, 4, or more fused aryl rings, etc.), a chromophore with the formula -(CH2) n -alkyl chain, or ether chain such as -O-(CH2) n -O-, wherein n = 1-6. In one embodiment, the linker is a bond, a para-substituted benzene ring, a disubstituted naphthalene ring, a ring having the formula -(CH2) n -alkyl chain, or ether chain such as -O-(CH2) n -O-, where n = 1 to 6. This approach can effectively double the molecular weight of the pigment, which can increase its solvent and heat resistance without affecting color properties.

[0020] 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 monomer of the pigment. Examples of such dimeric pigments include diarylate pigments. Diarylate 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 tetrazotized benzidine or a benzidine derivative. The linker A is a single bond and the monomer B is as shown in the structure of Pigment Yellow 12 below:

[0021]

[0022] To prepare dimeric pigments, a tetrazotized compound (e.g., benzidine or a benzidine derivative) can be coupled with two identical nucleophilic couplers, which can be substituted acetoacetanilide (yellow pigments), pyrazolone (orange pigments), or substituted naphthol (red pigments). Specific examples include Pigment Yellow 12 (coupler: acetoacetanilide), Pigment Orange 13 (coupler: phenylmethylpyrazolone), and Pigment Orange 34 (coupler: tolylmethylpyrazolone). These examples are illustrated in Schemes A and B below, where linker A is a single bond and monomer B contains the corresponding coupler and a 2'-chloroaniline unit derived from (tetrazotized 3,3'-dichlorobenzidine).

[0023]

[0024] Plan A

[0025]

[0026] Plan B

[0027] Synergists can be designed for dimeric pigments such that the synergist is structurally similar to the structure of the parent dimer, i.e., the synergist also has a dimeric structure ("full synergist"). Examples of full synergists are described below:

[0028]

[0029] Unfortunately, these molecules can have high water solubility due to the presence of two or more ionizable groups, such as the two SO3Na groups described above. High solubility in water can reduce the affinity of the complete synergist for the parent pigment. Other symmetrical synergists with similar structures and different configurations of charged groups can be prepared, but the starting materials may not be as readily available.

[0030] It has been found that good performance can be achieved using synergists that are structurally similar to the monomers of the dimeric pigment ("halfsynergists"). The halfsynergists used for Pigment Yellow 12 are described below:

[0031]

[0032] Thus, disclosed herein are dispersions or compositions comprising a pigment and a synergist, wherein the pigment has a dimeric structure (dimeric pigments such as diarylate pigments). The synergist is structurally similar to a monomer of the dimeric structure, for example, a derivative of the monomer. Structural similarity or structural similarity means that the synergist contains the same structural moieties as the monomers of the dimeric pigment and different structural moieties. In one embodiment, the same structural moieties account for at least 50% of the total molecular weight of the monomers of the dimeric or diarylate pigment, for example, at least 60%, at least 70%, at least 80%, or at least 90% of the total molecular weight of the monomers of the pigment, but no more than 99% or no more than 95% of the total molecular weight of the monomers of the pigment. In one embodiment, the synergist is a derivative of the monomers of the pigment. Because the synergist is structurally similar to the monomers of the dimer pigment, as an option, the molecular weight of the synergist is no more than 70% of the molecular weight of the dimer or diarylate pigment, for example no more than 60% of the molecular weight of the dimer pigment, for example, the molecular weight of the synergist ranges from 25-70%, 30-70%, 35-70%, 40-75%, 45-70%, 50-70%, 55-70% or 60-70% of the molecular weight of the dimer pigment. Thus, the synergist is a material separate from the pigment that is capable of providing a stable dispersion of the pigment in the liquid vehicle.

[0033] Without wishing to be bound by any theory, the structural similarity between the monomer of the pigment and the synergist causes the synergist to potentially have a high affinity for the pigment. High affinity can then help the synergist to be adsorbed onto the pigment surface. In one embodiment, this high affinity can take the form of van der Waals interactions (e.g., dipole-dipole interactions). In one embodiment, the synergist further comprises an ionic group or an ionizable group that allows additional 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 have ionic groups or ionizable groups, thereby providing interactions as described herein (e.g., van der Waals interactions, π-π stacking, ionic interactions / bonding, acid / base interactions / bonding, and hydrogen bonding). In addition, the adsorption of synergist molecules on the face of the pigment crystal can produce dislocations, which potentially prevent further crystal growth along the face, thereby providing a handle for controlling and / or maintaining the size and distribution of the pigment particles.

[0034] Without wishing to be bound by any theory, if the pigment comprises two identical chromophores connected by a single bond, symmetry results in a net zero electronic interaction. The chromophores can be considered to be substantially independent. Any absorption characteristics of the monomeric and corresponding dimeric colorant molecules may be similar in hue angle and intensity, so that the synergist added typically will not "dilute" the color of the pigment. As a result, the color of the monomeric synergist may be similar to the color of the dimeric pigment. In addition, compared with a complete synergist, a half synergist will provide a smaller number of water-soluble lower ionizable groups. Therefore, less competition from water interactions can result in a stronger affinity to the pigment surface.

[0035] Finally, because synergists are additives, their use can simplify the ink formulation process by avoiding purification steps that may be required in other dispersion techniques, such as the use of dispersant additives.

[0036] Thus, disclosed herein are compositions comprising a dimeric pigment and a synergist having a structure similar to a monomer of the dimeric pigment. The dimeric pigment may be a diarylate, acetoacetanilide (yellow pigment), arylpyrazolone (orange pigment), substituted naphthol (red pigment), perylene pigments such as Pigment Red 149, Pigment Red 178, and disazocondensation pigments such as Pigment Yellow 93, Pigment Red 144, and Pigment Red 214. The aryl group of the diarylate may be connected by a linker, which may be a single bond to the aryl group of a benzidine or substituted benzidine residue (e.g., a dichlorobenzidine residue, such as a 3,3'-dichlorobenzidine residue).

[0037] In one embodiment, the symmetrical diarylide pigment has the following structure P-1:

[0038] P-1,

[0039] 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 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 can be the primary or secondary pigment in the composition. For example, some commercial grades of Pigment Yellow 126 can contain a small amount of Pigment Yellow 12, and some commercial grades of Pigment Yellow 127 can contain a small amount of Pigment Yellow 13.

[0040] A composition comprising at least one pigment having structure P-1 may have at least one synergist having the following structure S-1:

[0041] S-1

[0042] wherein R1-R3 are as defined for pigment P-1, and 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, wherein L is a divalent linker (e.g. a (single) bond, an aromatic ring system, an ether chain such as -O-(CH2) n -O-, or having the formula -CH n -alkyl chain, wherein n=1-6), 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. "Salts thereof" means that the acid group may be in a partially or fully ionized form with a cationic counterion, for example, M + (e.g. Na + , K + 、Li + or NR'4 +, wherein R' can be the same or different) represents hydrogen or an organic group, such as a substituted or unsubstituted aryl (e.g., phenyl) and / or alkyl (e.g., C1-C6 alkyl). It is also understood that the R1, R2, and R3 substituents of the synergist can be independent of the substituents on the pigment, for example, the same as or different from the substituents on the pigment.

[0043] In another embodiment, the symmetrical diarylide pigment has the following structure P-2:

[0044] P-2

[0045] And the synergist has the following structure:

[0046] S-2

[0047] wherein 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 an ionizable group. Thus, disclosed herein are compositions (e.g., aqueous dispersions, inks, or inkjet compositions) comprising a dimer pigment and a synergist. Examples of such pigments include Pigment Orange 13 and Pigment Orange 34.

[0048] In one embodiment, X=Cl, C1-C2 alkyl or C1-C2 alkoxy, for example, X=Cl or C1-C2 alkoxy (for example, OCH3). In one embodiment, R8=H or C1-C2 alkyl, for example R2=H or CH3. In one embodiment, R9=H, C1-C2 alkyl or CO2CH2CH3, for example R9=H, CH3 or CO2CH2CH3, or R9=H or CH3. The above structure has an azo group, and Z can be located in the ortho position, meta position or para position of the azo group in the structure, for example, Z can be located in the meta position or para position of the azo group in the structure. It should be understood that the R8 and R9 substituents of the synergist can be independent of the substituents on the pigment, for example, the same or different from the substituents of the pigment.

[0049] The synergist may have one or more functional groups that are different from the functional groups of the pigment. In one embodiment, the synergist as described herein has an ionic or ionizable functional group. In one embodiment, the ionic group of the synergist provides a hydrophilic property, which makes the synergist soluble or dispersible in a liquid vehicle (e.g., an aqueous solution or water). When the synergist is adsorbed on the pigment, due to its structure similar to that of the monomer, the adsorption can occur preferentially. The synergist can actually provide a charged group to the pigment surface, thereby also making the pigment dispersible in a liquid vehicle (e.g., an aqueous solution).

[0050] In one embodiment, the synergist comprises an ionic group or an ionizable group. An ionizable group is a group that can form an ionic group in the medium used. An anionic group is a negatively charged ionic group produced by a group having an ionizable substituent (such as an acidic substituent) that can form an anion (anionizable group). A cationic group is a positively charged organic ionic group that can be produced by an ionizable substituent that can form a cation (cationizable group), such as a protonated amine. "Ionic group or ionizable group" should be understood to mean that a mixture can be present in the composition. For example, in the composition, some synergists can have an ionic group (that is, Z is an ionic group), and other synergists can have an ionizable group (that is, Z is an ionizable group). The distribution of ionic groups and ionizable groups in the composition can be selected by means known in the art (such as, controlling pH, counterions, etc.).

[0051] Specific examples of ionic (eg, anionic) groups include -COO - 、-SO3 - 、-OSO3 - 、-HPO3 - 、-OPO3 2- , or -PO3 2- (with cationic counterions, such as M + , as defined herein), and specific examples of ionizable (e.g., anionizable) groups may 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. In addition, specific examples of cationic or cationizable groups include alkyl or aryl amines, which can be protonated in acidic media to form ammonium groups -NR'2H + , wherein R' represents an organic group, such as a substituted or unsubstituted aryl or alkyl group, such as a substituted or unsubstituted C5-C 20 Aryl or C1-C 12 Alkyl groups (eg, C1-C6 alkyl groups). Organic ionic groups include those described in U.S. Patent No. 5,698,016, the disclosure of which is incorporated herein by reference.

[0052] 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 ionizable group is, for example, -COOH, -SO3H, -PO3H2, -R'SH, or -R'OH, such as -COOH, -SO3H, or -PO3H2. In other embodiments, the ionic group or ionizable group is -SO3 - Or -SO3H. In other embodiments, the composition comprises at least a portion of the synergist having an ionic group and at least another portion of the synergist having an ionizable group.

[0053] Without wishing to be bound by any theory, it is believed that due to the relatively low molecular weight of the synergist, providing more than one ionic and / or ionizable group may result in a synergist that is too hydrophilic, potentially making the synergist soluble in water and enabling it to desorb from the pigment surface into the continuous phase.

[0054] Another embodiment provides a composition (e.g., dispersion or ink, such as inkjet ink) comprising at least one synergist as described herein and a dimer pigment. In one embodiment, the at least one synergist is present in the composition in an amount within the range of 3% to 10% by weight relative to the weight of the dimer pigment. For example, the at least one synergist is present in the composition in an amount within the range of 3% to 10% by weight relative to the weight of the dimer pigment.

[0055] In one embodiment, at least one synergist in the composition is a mixture of more than one synergist having a structure described herein, such as a mixture of synergists wherein each synergist has one or more substituents that differ from each other.

[0056] In one embodiment, at least one synergist according to the claimed invention can be prepared by diazotization. For example, a diazotizing agent can be prepared by combining an aminobenzene reactant with an ionic group or an ionizable group at the ortho, meta or para position (for example, meta or para position) of an amine group and a base (for example, NaOH) and sodium nitrite (see the first step of scheme C below, illustrated with the synergist of structure S-2). The aminobenzene reactant can be, for example, sulfanilic acid or aminobenzoic acid. The diazotizing agent of the gained can then be combined with a coupling agent (for example, acetoacetanilide, phenylpyrazolone, naphthol, etc.) to form at least one synergist.

[0057] For example, the phenyl group of phenylpyrazolone can be substituted with an R8 group (e.g., at the ortho, meta, or para position of the pyrazolonyl group, or at the meta or para position of the pyrazolonyl group), and the pyrazolonyl group can contain an R9 group, as shown in Scheme C below, wherein R8 and R9 are as defined above.

[0058]

[0059] Plan C

[0060] Thus, disclosed herein is a method for preparing at least one synergist comprising combining an aminobenzene reactant having an ionic or ionizable group substituted in the aromatic ring with a base to form a diazotizing agent. The method further comprises combining the diazotizing agent with a coupling agent (e.g., acetoacetanilide, phenylpyrazolone, naphthol, etc.) to form at least one synergist. In the case of a synergist having structure S-2, the phenyl group of the phenylpyrazolone has an R8 substituent and the pyrazolone group has an R9 substituent, wherein R8 = H or C1-C6 alkyl, R9 = H, C1-C6 alkyl, or CO2CH2CH3, and Z is an ionic or ionizable group.

[0061] Pigment is a solid material that is usually in the form of a particulate solid. Particulate solids can be powders, dispersions or pressed cakes. Such particle size can be achieved by one or more conventional size reductions, pulverization and / or classification techniques (e.g., ball milling, median milling, jet milling, ultrasonic treatment, fluid impact and centrifugation) to remove undesirable large particles. As an example, median particle size can be measured by the equipment produced by companies such as Microtrac, Inc. and Malvern Panalytical, Ltd. using dynamic light scattering techniques. In one embodiment, pigment has 100nm to 300nm, for example 100nm to 250nm, 100nm to 225nm, 100nm to 200nm, 100nm to 180nm, 120nm to 250nm, 120nm to 225nm, 120nm to 200nm, 120nm to 180nm, 150nm to 250nm, 150nm to 225nm, 150nm to 200nm or 150nm to 180nm median particle size.Particle size can be such mean diameter, and it is based on volume (mean volume, Mv) or number distribution.The dispersion that comprises pigment can be purified by the combination of ultrafiltration, diafiltration, ion exchange, centrifugal or one or more such methods.

[0062] It has been found that the claimed synergists enhance the stability of the pigment in the dispersion or ink. Stability can be measured by, for example, the median particle size of the pigment in the dispersion or ink. In one embodiment, at room temperature or at 60°C, 70°C or 80°C, the median particle size of the pigment dispersion or ink containing the claimed synergist does not increase significantly over a certain period of time (e.g., at least 7 days, or at least two weeks, or at least 6 weeks). In one embodiment, the median particle size increases by no more than 30% relative to its initial median particle size. For example, relative to its initial median particle size, the median particle size increases by no more than 25%, no more than 20%, no more than 15%, no more than 10%, or no more than 10%.

[0063] 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 at room temperature or at 60°C over a period of time (e.g., at least 7 days, or at least two weeks, or at least 6 weeks). In one embodiment, the viscosity increases by no more than 30% relative to its initial viscosity. For example, relative to its initial viscosity, the viscosity increases by no more than 25%, no more than 20%, no more than 15%, no more than 10%, or no more than 10%. When the median particle size or viscosity increases by more than 30% (or other percentages as described herein) relative to its initial median particle size or viscosity, this typically occurs due to agglomeration, which can cause the pigment to undesirably settle and / or gel.

[0064] Additionally, or in alternative embodiments, the ink or dispersion comprising the dimer pigment and the synergist is stable at room temperature or at 60° C. for a certain period of time (e.g., at least 7 days, or at least two weeks, or at least 6 weeks). For example, stability can be measured by the ability of the ink or dispersion to maintain certain physical properties, which may include particle size, pH, surface tension, viscosity, and may remain within 10% of their original values.

[0065] In one embodiment, the composition comprises a liquid carrier. In one embodiment, the liquid carrier is aqueous. For example, the aqueous carrier can 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 (for example, inkjet ink) composition, for example, an aqueous ink (for example, inkjet ink) composition.

[0066] In one embodiment, the composition is an aqueous pigment dispersion comprising the dimer pigment in an amount of 1% to 40% by weight relative to the total weight of the pigment dispersion, for example, 1% to 30% by weight, 1% to 20% by weight, 1% to 10% by weight, 3% to 40% by weight, 3% to 30% by weight, 3% to 20% by weight, 3% to 10% by weight, 5% to 40% by weight, 5% to 30% by weight, 5% to 20% by weight, or 5% to 10% by weight relative to the total weight of the pigment dispersion.

[0067] In one embodiment, the composition is an aqueous ink (e.g., inkjet ink) composition. In one embodiment, the composition comprises a dimerized pigment in an amount of 1% to 15% by weight (e.g., 1% to 10% by weight) relative to the gross weight of the composition, for example, a dimerized pigment in an amount of 2% to 15% by weight, 2% to 10% by weight, 3% to 15% by weight, 3% to 10% by weight, 1% to 7% by weight, 2% to 7% by weight, or 3% to 7% by weight relative to the gross weight of the composition.

[0068] In one embodiment, the composition (e.g., an aqueous pigment dispersion or an aqueous ink (e.g., an inkjet ink) composition) further comprises at least one organic solvent present in an amount of 1% to 50% relative to the total weight of the inkjet ink composition (e.g., the aqueous vehicle is an aqueous solution). For example, the aqueous pigment dispersion or aqueous ink may comprise at least two organic solvents (co-solvents). In addition to at least 40% water (or at least 45% water or at least 50% water), the at least one organic solvent may also be present in the composition. In one embodiment, the organic solvent is soluble in water or miscible in water. In another embodiment, the organic solvent is chemically stable to aqueous hydrolysis conditions (e.g., reacting with water under heat aging conditions, including, for example, the hydrolysis of esters and lactones). In one embodiment, the organic solvent has a dielectric constant lower than the dielectric constant of water, for example, a dielectric constant ranging from about 10 to about 78 at 20°C. Examples of suitable organic solvents include alcohols and polyols (glycols, glycerol, 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.

[0069] Humectants and water-soluble organic compounds other than the at least one organic solvent may also be added to the inkjet ink composition of the present invention, for example, to prevent nozzle clogging and to provide paper penetration (penetrants), improved drying (drying accelerators), and anti-wrinkling 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%.

[0070] In one embodiment, ink composition (such as inkjet ink composition) includes at least one surfactant, for example, when the pigment is not self-dispersible. The at least one surfactant can enhance the colloidal stability of the composition or change the interaction between ink and printing substrate (such as printing paper) or ink print head. Various anionic dispersants, cationic dispersants and nonionic dispersants can be used in combination with the ink composition of the present invention, and these dispersants can be used purely or as aqueous solutions. In one embodiment, the surfactant is present in an amount of 0.05 wt % to 5 wt %, for example, 0.1 wt % to 5 wt %, or 0.5 wt % to 2 wt %, relative to the gross weight of the inkjet ink composition.

[0071] In one embodiment, ink (for example, inkjet ink) composition has the viscosity of 1-25cP.Should be appreciated that viscosity can be regulated by several methods.In one embodiment, polymeric binder can be used in combination with inkjet ink composition disclosed herein, to regulate the viscosity of composition and / or provide other desired properties, for example, durability (for example, at least one durable polymer).Such polymeric binder can be present in composition with the amount of 0.1 % by weight to 20 % by weight relative to the gross weight of composition, for example, with respect to the gross weight of composition with the amount of 0.1 % by weight to 10 % by weight, 0.1 % by weight to 5 % by weight, 0.2 % by weight to 20 % by weight, 0.2 % by weight to 10 % by weight, 0.2 % by weight to 5 % by weight, 0.5 % by weight to 20 % by weight, 0.5 % by weight to 10 % by weight or 0.5 % by weight to 5 % by weight is present in composition.

[0072] In one embodiment, ink (such as inkjet ink) composition may further include one or more suitable additives to impart many desired properties while maintaining the stability of the composition. Other additives are well known in the art and include wetting agents, biocides and fungicides (fungicide), pH control agents, drying accelerators, penetrants, etc. The amount of specific additives will vary according to various factors, but is typically present in an amount in the range of between 0.01% and 40% based on the weight of the ink composition. In one embodiment, the at least one additive is present in an amount of 0.05% to 5% by weight (such as 0.1% to 5% by weight or 0.5% to 2% by weight), relative to the gross weight of the inkjet ink composition.

[0073] Example

[0074] 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 determined using a Nanotrac™ 252 particle size analyzer manufactured by Microtrac, Inc.

[0075] Example 1: Preparation of synergist S-1

[0076] This example describes the preparation of a synergist having structure S- 1. The synthesis is outlined in Scheme D below.

[0077]

[0078] Plan D

[0079] To prepare a diazotized 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 dropwise added to a stirred mixture of 36% hydrochloric acid (18.9 mL) and ice-water (150 g). Excess nitrous acid was neutralized by the addition of 25% sulfamic acid solution (2-4 g).

[0080] A coupler solution was prepared by dissolving acetoacetanilide (AAA, 18.3 g) in a mixture of 40% sodium hydroxide solution (10.4 g), isopropyl alcohol (200 mL), and DI water (200 mL). Azo coupling was performed by adding a diazonium salt solution to the stirred coupler at a pH of 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 prepared in the same manner as shown in Table 1 (using acetoacetyl-2',4'-xylidide (AAX) or acetoacetyl-2'-toluidide (AAOT) instead of AAA), with corresponding yields and purities. For all synergists, R4 and R7 were each H.

[0081] Table 1

[0082]

[0083] *Abbreviations: SA-sulfanilic acid, MA-m-aminobenzenesulfonic acid, AAA-acetoacetanilide, AAOT-acetoacetyl-2'-toluidine, AAX-acetoacetyl-2',4'-xylidine.

[0084] Example 2: Preparation of synergist S-2

[0085] This example describes the preparation of a synergist for Pigment Orange 34 according to the claimed invention, wherein the synergist has structure S-2. The synthesis of synergist S-2 is outlined below in Scheme E. In Scheme E, Z1 or Z2 is an ionic or ionizable group.

[0086]

[0087] Plan E

[0088] The synergists were prepared in a manner similar to Example 1, except that diazotized SA or MA was coupled with PMP or TMP. The results are shown in Table 2.

[0089] Table 2

[0090]

[0091] *Abbreviations: SA-sulfanilic acid, MA-m-aminobenzenesulfonic acid, PMP-phenylmethylpyrazolone, TMP-tolylmethylpyrazolone

[0092] Comparative Example: Preparation of Complete Synergist

[0093] This example describes the preparation of full synergists for yellow and orange pigments as outlined in Schemes F and G, respectively.

[0094]

[0095] Plan F

[0096]

[0097] Plan G

[0098] To prepare the yellow complete synergist, a diazotized 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).

[0099] A coupler solution was prepared by dissolving acetoacetanilide (AAA, 23.1 g) in a mixture of 40% sodium hydroxide solution (13.0 g), isopropyl alcohol (200 mL), and 200 mL of DI water. Azo coupling was performed by adding the diazonium salt solution to the stirred coupler at a pH of 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%; the HPLC purity was 96% (by area).

[0100] Other complete synergists were prepared in a similar manner using acetoacetyl-2',4'-xylidine (AAX) or acetoacetyl-2'-toluidine (AAOT) instead of AAA. The water solubility of the complete synergists based on BDSA 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 isopropyl alcohol-water), but eventually crystallized. Other complete synergists were prepared in the same manner and their yields and purities are given in Table 3.

[0101] Table 3

[0102]

[0103] *Abbreviations: BDSA-benzidine-2,2'-disulfonic acid, AAA-acetoacetanilide, AAX-acetoacetyl-2',4'-xylidine, AAOT-acetoacetyl-2'-toluidine

[0104] Full synergists for orange pigments (Scheme G) were prepared in the same manner, except that tetrasotized BDSA was coupled to PMP or TMP (Table 4).

[0105] Table 4

[0106]

[0107] *Abbreviations: BDSA-benzidine-2,2'-disulfonic acid, PMP-phenylmethylpyrazolone, TMP-tolylmethylpyrazolone

[0108] Pigment dispersion

[0109] Typically, charge-stabilized particles in water have 175-350 μmol of counterions per 1 g of pigment to provide adequate anti-settling properties. In this example, the synergist contains 4.8-6.1% sodium counterions. To achieve a counterion content of ~175 μmol / g, the dispersion contains 6% to 7.5% synergist by weight of the pigment.

[0110] Pigment Yellow 12 (55g Sun Chemical, Sunbrite Yellow 12) was mixed with MA-AAA synergist (3.51g) and deionized water (312mL) in a thick-walled flask. Vacuum was applied to wet the pigment, and the resulting pre-dispersion was homogenized in a rotor-stator mixer at 5,000 rpm for 1 hour and then sonicated for 3 hours using a Misonix sonicator with a horn at 180-200W power. The dispersion was centrifuged at 2,500g for 15 minutes to remove undispersed material and decanted from the centrifuge sludge. The mean volume particle size (Mv) was then measured.

[0111] Other dispersions were prepared in a similar manner. The properties of the dispersions are shown in Table 5 below:

[0112] Table 5

[0113]

[0114] The effect of the synergist was evaluated by heat aging the dispersion at 60°C for 4 weeks. A change of ±10% in the Mv of the dispersion was defined as acceptable. The results are summarized in Table 6:

[0115] Table 6

[0116]

[0117] From the data in Table 6 it can be seen that the dispersions containing the half synergist exhibited good (minimal) Mv growth, whereas all comparative dispersions containing the full synergist exceeded and therefore did not meet the minimum Mv growth requirement.

[0118] Unless otherwise stated herein or clearly contradictory to the context, the use of the terms "a" and "a kind of" and "the (said)" should be interpreted as covering both the singular and the plural. Unless otherwise stated, the terms "comprise", "have", "include" and "contain" should be interpreted as open terms (i.e., meaning "including, but not limited to, "). Unless otherwise stated herein, the description of numerical ranges herein is only intended to be used as a shorthand method for individually referring to each individual value falling within the range, and each individual value is incorporated into this specification as if it were individually narrated herein. Unless otherwise stated herein or clearly contradictory to the context, all methods described herein can be carried out in any suitable order. Unless otherwise stated, the use of any and all examples or exemplary language (e.g., "such as (e.g., as)") provided herein is only intended to better illustrate the present invention, and is not intended to limit the scope of the present invention. Any language in this specification should not be interpreted as indicating that any unclaimed element is essential for the practice of the present invention.

Claims

1. A composition comprising: A symmetrical diarylide pigment comprising a monomer; and Synergists for monomers structurally similar to diarylide pigments.

2. The composition of claim 1 wherein the synergist comprises a moiety identical to and a moiety different from the monomer of the diarylide pigment, wherein the moiety identical to comprises at least 50% of the total molecular weight of the monomer.

3. The composition of claim 1 or 2, wherein the synergist has a molecular weight of no more than 70% of the molecular weight of the pigment.

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

5. The composition according to any one of claims 1 to 4, wherein: Symmetrical diarylide pigments have the following structure P-1: 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: 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, wherein L is a divalent linker and at least one of R4, R5, R6 and R7 is selected from -L-COOH, -L-SO3H, -L-PO3H2.

6. The composition of claim 5, wherein the divalent linker is selected from a bond, an aryl ring system, a ring having the formula -(CH2) n -alkyl chain, or an alkyl chain having the formula -O-(CH2) n -O-ether chain, wherein n=1-6.

7. The composition according to claim 5 or 6, wherein R1 and R2 are independently selected from H, Cl, C1-C6 alkyl and C1-C6 alkoxy, and R3 is selected from H, Cl and C1-C6 alkyl.

8. The composition of claim 5 or 6, wherein R1 is selected from H, methyl and methoxy, R2 is selected from H and methyl, and R3 is H.

9. The composition of any one of claims 5 to 8, wherein at least one of R4, R5, R6 and R7 is selected from -COOH, -SO3H, and -PO3H2, and salts thereof.

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 composition according to any one of claims 1 to 4, wherein: Symmetrical diarylide pigments have the following structure P-2: ,and (b) The synergist has the following structure S-2: S-2 wherein 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 an ionizable group.

12. The composition of claim 11, wherein X = Cl, C1-C2 alkyl or C1-C2 alkoxy.

13. The composition of claim 11, wherein X = Cl or OCH3.

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

15. The composition of any one of claims 11-14, wherein R9 = H, C1-C2 alkyl, or CO2CH2CH3.

16. The composition according to any one of claims 11 to 15, wherein R9 = H, CH3 or CO2CH2CH3.

17. The composition according to any one of claims 11 to 16, wherein R8 = H or C1-C2 alkyl.

18. The composition of any one of claims 11-17, wherein R8 = H or CH3, and R9 = H or CH3.

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

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

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

22. The composition according to any one of claims 11 to 21, wherein the ionic group is -COO - 、-SO3 - 、-OSO3 - 、-HPO3 - 、-OPO3 2- or-PO3 2- .

23. The composition according to any one of claims 11 to 22, wherein the ionic group is -COO - 、-SO3 - or-PO3 2- .

24. The composition of any one of claims 11-23, wherein the ionizable group is an anionizable group.

25. The composition of any one of claims 11-24, wherein the ionizable group is -COOH, -SO3H, -PO3H2, -R'SH, or -R'OH, and R' is H or a substituted or unsubstituted C5-C 20 Aryl or C1-C 12 alkyl.

26. The composition of any one of claims 11-25, wherein the ionizable group is -COOH, -SO3H, or -PO3H2.

27. The composition of any one of claims 1 to 26, 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 1-27, 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 1-27, 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 1-29, wherein the composition further comprises a liquid carrier.

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

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

33. The composition of any one of claims 1-32, wherein the composition is an aqueous pigment dispersion.

34. The composition of any one of claims 1-32, wherein the composition is an aqueous ink composition.

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