Aqueous inkjet ink compositions

Abstract

To provide aqueous inkjet ink compositions which exhibit excellent colloidal stability and jetting performance, extended latency time and decap time, and high opacity.SOLUTION: In an embodiment, such an aqueous inkjet ink composition comprises: a solvent system comprising water, a first organic solvent and a second organic solvent, where the second organic solvent is an alkanediol having 2 to 8 carbon atoms and is present in an amount from more than 0 wt.% to about 8 wt.%; a white pigment; and resin particles. Methods of making and using the aqueous inkjet ink compositions are also provided.SELECTED DRAWING: None

Description

[Background technology]

[0001] White ink is added to standard CMYK color sets to improve image quality. White ink also helps correct perceived colors when printing on transparent or off-white substrates. Despite the benefits of including white ink in inkjet color sets, the complexity and challenges of formulating the inks prevent them from reaching their full potential. One obstacle is the premature precipitation and lack of long-term colloidal stability of white pigments (generally titanium dioxide nanoparticles). Titanium dioxide nanoparticles (rutile, anatase, or both) have very high densities. In low-viscosity mixtures (generally <10 cP), such as aqueous inkjet ink compositions, they precipitate rapidly. When precipitation occurs, gravity forms a compact, cement-like residue at the bottom of the container, which is generally not dispersible. Precipitation clogs ink supply tubes, print heads, and nozzles. Precipitation also results in a short shelf life, as well as short latency and decapping times. Finally, precipitation reduces the optical density of the printed ink and impairs print opacity. [Overview of the project]

[0002] This disclosure provides white and gray aqueous inkjet ink compositions. Embodiments of the aqueous inkjet ink compositions exhibit excellent colloidal stability and spray performance, extended latency and decapping times, and high opacity. They also exhibit excellent coating properties, including uniform film formation, wetting and spreading, and durability and water resistance on various substrates. Methods for forming and using the aqueous inkjet ink compositions are also provided. An aqueous inkjet ink composition is provided. In one embodiment, such an aqueous inkjet ink composition comprises a solvent system comprising water, a first organic solvent, and a second organic solvent, wherein the second organic solvent is an alkanediol having 2 to 8 carbon atoms, and the second organic solvent is present in an amount of more than 0% to about 8% by weight, a white pigment, and resin particles.

[0003] Methods for preparing aqueous inkjet ink compositions and methods for using aqueous inkjet ink compositions are also provided.

[0004] Other key features and advantages of this disclosure will become apparent to those skilled in the art upon consideration of the following drawings, modes for carrying out the invention, and the appended claims. [Modes for carrying out the invention]

[0005] A water-based inkjet ink composition comprises a solvent system containing water, a white pigment, and resin particles. Other components, such as colorants, waxes, and other additives, may be included. These components are described in detail below.

[0006] Solvent system

[0007] As described above, the aqueous inkjet ink composition contains water. In the embodiment, the amount of water used is in the range of 40% to 70% by weight compared to the total weight of the aqueous inkjet ink composition. This includes 50% to 70% by weight, 40% to 60% by weight, 40% to 50% by weight, and 50% to 60% by weight.

[0008] Water is one component of a solvent system that also includes water-soluble or water-particle organic solvents. In embodiments, a first such organic solvent is used. The first organic solvent may be a diol. The diol may be an alkanediol having 2, 3, or 4 carbon atoms. The alkanediol may be a branched alkanediol. An exemplary branched alkanediol is propylene glycol. A single type or a combination of different types of the first organic solvent may be used. The total amount of the first organic solvent may be present in the aqueous inkjet ink composition in an amount of 10% to 40% by weight compared to the total weight of the aqueous inkjet ink composition. This includes 15% to 40% by weight and 20% to 40% by weight.

[0009] In the embodiments, the first organic solvent is not pyrrolidone, for example, 2-pyrrolidone, dipropylene glycol monomethyl ether, tetrahydrofurfuryl alcohol, or propylene glycol monopropyl ether. In such embodiments, the aqueous inkjet ink composition does not contain any of these compounds.

[0010] In embodiments, a second organic solvent is used in the solvent system. The second organic solvent may also be a diol, but is different from the first organic solvent. As shown in the following examples, the colloidal stability of the aqueous inkjet ink composition was determined to be highly sensitive to the presence of the second organic solvent. In embodiments, the second organic solvent is an alkanediol. The alkanediol may have 2 to 8 carbon atoms, i.e., 2, 3, 4, 6, 7, or 8 carbon atoms. In embodiments, the alkanediol may have more than 4 carbon atoms, e.g., 5, 6, 7, or 8. The alkanediol may be linear or branched. The two hydroxyl groups may be at any position on the alkanediol. Examples of linear alkanediols include the following: ethylene glycol, triethylene glycol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,4-pentanediol, 1,5-pentanediol, 2,4-pentanediol, 1,2-hexanediol, 1, Examples include 3-hexanediol, 1,6-hexanediol, 2,5-hexanediol, 1,2-heptanediol, 1,3-heptanediol, 1,7-heptanediol, 1,2-octanediol, 1,3-octanediol, 1,5-octanediol, 1,6-octanediol, 1,7-octanediol, 1,8-octanediol, 2,4-octanediol, I, and 3,6-octanediol. Other exemplary alkanediols include 2-methyl-2,4-pentanediol, 3-methyl-1,5-pentanediol, 2-ethyl-1,3-hexanediol, diethylene glycol, 3-methyl-1,3-butanediol, 2-ethyl-1,3-hexanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,5-dimethyl-hexanediol, and 2,2,4-trimethyl-1,3-pentanediol.

[0011] In embodiments, the second organic solvent is a hexanediol containing any of the hexanediols described above. In embodiments, the second organic solvent is 1,2-hexanediol. In embodiments, the second organic solvent is not 1,6-hexanediol. In such embodiments, the aqueous inkjet ink composition does not contain (i.e., does not have) 1,6-hexanediol.

[0012] A single type or combination of different types of second organic solvents may be used. The total amount of the second organic solvent may be present in the aqueous inkjet ink composition in an amount greater than 0% to 8% by weight, relative to the total weight of the aqueous inkjet ink composition. This includes amounts greater than 0% to 6% by weight, greater than 0% to 5% by weight, 2% to 6% by weight, 3% to 6% by weight, and 3% to 5% by weight.

[0013] In embodiments, the solvent system consists of water, a first organic solvent, and a second organic solvent. In such embodiments, any of the first and second organic solvents described above may be used. Any of the amounts of water and the first and second organic solvents described above may be used.

[0014] White pigment

[0015] Water-based inkjet ink compositions contain a white pigment. The white pigment is generally titanium dioxide (TiO2). The crystalline structure of TiO2 can be anatase, rutile, or a combination of different crystalline structures may be used. Other examples include zinc oxide (ZnO), zinc sulfide (ZnS), lithopone (BaSO4 and ZnS), alumina hydrate, calcium carbonate (CaCO3), barium sulfate (BaSO4), and talc (Mg3Si4O). 10 Other white pigments such as (OH)2, silica (SiO2), and china clay (Al2O3.2SiO2.2H2O) may be used. Combinations of different types of white pigments may be used. However, in this embodiment, only TiO2 is used as the white colorant.

[0016] White pigments are generally in the form of particles. The particle size is D 50 This may be reported as particle size, meaning that 50% (by volume) of the sample consists of particles with a diameter less than the given diameter value. In embodiments, white pigment particles are D in the range of 20 nm to 500 nm. 50 It has a particle size. However, in the embodiment, D includes 20nm to 80nm, or 30nm to 70nm, less than 150nm, less than 125nm, and less than 100nm. 50 Relatively small white pigment particles with a specific particle size are used. 50 Particle size can be measured using a Malvern Zetasizer Nano ZS. For verification of light scattering techniques and methods, NIST polystyrene nanosphere control samples with diameters in the range of 20 nm to 200 nm, available from Microspheres-Nanospheres (Corpuscular company of Microtrac) or third-party vendors (such as ThermoFisher Scientific), may be used.

[0017] Various amounts of white pigment can be used. In embodiments, the white pigment is present in an amount ranging from 0.1% to 15% by weight relative to the total weight of the aqueous inkjet ink composition. This includes 1% to 10% by weight and 1% to 5% by weight. If two or more types of white pigment are used, these amounts refer to the total amount of white pigment. These amounts refer to the solids content, as opposed to the amount of dispersion containing the white pigment.

[0018] resin particles

[0019] Water-based inkjet ink compositions also include resin particles. The resin particles are synthesized from various monomers to form polymer materials, and these polymer materials constitute the resin particles. The types of monomers, and therefore the polymer materials, are not particularly limited. However, exemplary examples include the following monomers and combinations thereof (the use of "(meth)" as in "(meth)acrylate" refers to both acrylate and methacrylate): styrene; alkyl (meth)acrylates such as methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate, methyl methacrylate, ethyl methacrylate, and butyl methacrylate; β-carboxyethyl acrylate (β-CEA), phenyl acrylate, methyl alpha chloroacrylate; butadiene; isoprene; methacrylonitrile; acrylonitrile; vinyl Vinyl ethers such as methyl ether, vinyl isobutyl ether, and vinyl ethyl ether; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl butyrate; vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone; vinylidenes such as vinylidene chloride and vinylidene chlorofluoride; N-vinylindole; N-vinylpyrrolidone; methacrylate; acrylamide; methacrylamide; vinylpyridine; vinylpyrrolidone; vinyl-N-methylpyridinium chloride; vinylnaphthalene; p-chlorostyrene; vinyl chloride; vinyl bromide; vinyl fluoride; ethylene; propylene; butylene; and isobutylene. In embodiments, monomers used to form resin particles include styrene and alkyl acrylates.

[0020] Acidic monomers can be used to form resin particles, including (meth)acrylic acid monomers, sulfonic acid monomers, sulfonate monomers, and combinations thereof. Exemplary acidic monomers include acrylic acid, methacrylic acid, ethacrylic acid, dimethylacrylic acid, maleic anhydride, maleic acid, styrenesulfonic acid, vinyl sulfonate, cyanoacrylic acid, vinyl acetic acid, allyl acetic acid, ethylidine acetic acid, propylidine acetic acid, crotonic acid, fumaric acid, itaconic acid, sorbic acid, angelic acid, cinnamic acid, styrylacrylic acid, citraconic acid, glutaconic acid, aconitic acid, phenylacrylic acid, acryloxypropionic acid, aconitic acid, phenylacrylic acid, acryloxypropionic acid, vinyl benzoic acid, N-vinyl succinamic acid, mesaconic acid, methacryloylalanine, acryloylhydroxyglycine, sulfoethyl methacrylate, sulfopropyl acrylate, styrenesulfonic acid, sulfoethyl acrylate, 2-methacryloyloxymethane-1-sulfonic acid, 3-methacryloyloxypropane-1-sulfonic acid, 3-(vinyloxy)propane-1-sulfonic acid, ethylenesulfonic acid, vinyl sulfuric acid, 4-vinylphenyl sulfuric acid, ethylenephosphonic acid, vinyl phosphoric acid, vinyl benzoic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, and combinations thereof. These acidic monomers also include their salts, such as salts of sulfonic acid.

[0021] Two different acidic monomers can be used to form resin particles each having a different pK a value. This is useful for improving colloidal stability over a wide range of pH and a wide range of pigment grades. The pK a values of the two different acidic monomers may differ from each other by at least 2 units, at least 3 units, at least 4 units, or at least 5 units. In embodiments, the two different acidic monomers are present in the monomer emulsion used to form resin particles at a weight ratio in the range of 0.1 to 10. This includes the ranges of 0.5 to 8 and 1 to 6. In embodiments, the two different types of acidic monomers used to form resin particles include methacrylic acid and sulfonic acid.

[0022] Hydrophilic monomers can be used to form resin particles. The term “hydrophilic monomer” is distinguished from the “acidic monomer” described above. That is, selected acidic monomers may also be hydrophilic, but these terms refer to different, chemically distinct species of monomers. Hydrophilic monomers are generally monofunctional, i.e., they contain a single polymerizable group. Suitable hydrophilic monomers are those that can absorb a relatively substantial amount of water through hydrogen bonds formed between the water-bonding and hydrogen-bonding portions of the hydrophilic monomer. Hydroxyl and glycol portions are exemplary hydrogen-bonding portions. For example, poly(ethylene glycol)- and poly(propylene glycol) hydrophilic monomers are particularly useful because the glycol-containing chain can absorb a substantial amount of water. Suitable hydrophilic monomers also polymerize near the surface of the resin particle such that the hydrogen-bonding portions extend from the surface of the resin particle into the surrounding aqueous medium.

[0023] As described above, exemplary hydrophilic monomers include those containing a hydroxyl moiety such as hydroxyethyl (meth)acrylate, n-hydroxyethyl (meth)acrylamide, hydroxypropyl (meth)acrylate, and hydroxypropyl (meth)acrylamide. Other exemplary hydrophilic monomers include those containing a glycol moiety such as ethylene glycol (meth)acrylate and propylene glycol (meth)acrylate. Poly(ethylene glycol) (meth)acrylate and poly(propylene glycol) (meth)acrylate are other examples. In an embodiment, the hydrophilic monomer is poly(ethylene glycol) (meth)acrylate having a molecular weight in the range of 185 g / mol to 1500 g / mol. This includes the ranges of 360 g / mol to 1500 g / mol, and 500 g / mol to 1000 g / mol. In an embodiment, the hydrophilic monomer is poly(propylene glycol) (meth)acrylate having a molecular weight in the range of 260 g / mol to 1000 g / mol. This includes the ranges of 360 g / mol to 1000 g / mol, and 500 g / mol to 1000 g / mol. Gel permeation chromatography can be used to determine these molecular weights.

[0024] Polyfunctional monomers can be used to form resin particles, i.e., those containing two or more polymerizable groups (e.g., two, three, or four). These are useful for promoting crosslinking within the resin particles. Exemplary polyfunctional monomers include difunctional monomers such as poly(ethylene glycol) diacrylate, for example, poly(ethylene glycol) diacrylate with a molecular weight of 250 g / mol. Other poly(ethylene glycol) di(meth)acrylates may be used, including those with molecular weights in the ranges of 214 g / mol to 1000 g / mol, 214 g / mol to 500 g / mol, and 214 g / mol to 300 g / mol. These difunctional monomers may also be considered hydrophilic as described above. Furthermore, gel permeation chromatography may be used to determine these molecular weights. Other hydrophilic bifunctional monomers include diacrylate compounds bonded to alkyl chains containing ether bonds, such as diethylene glycol diacrylate, triethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol #400 diacrylate, polyethylene glycol #600 diacrylate, and dipropylene glycol diacrylate; compounds obtained by substituting the acrylate of these compounds with methacrylate; diacrylate compounds bonded to chains containing aromatic groups and ether bonds, such as polyoxyethylene (2)-2,2-bis(4-hydroxyphenyl)propane diacrylate and polyoxyethylene (4)-2,2-bis(4-hydroxyphenyl)propane diacrylate; and compounds obtained by substituting the acrylate of these compounds with methacrylate.Other bifunctional monomers include diene compounds such as isoprene and butadiene, aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene, diacrylate compounds bonded to alkyl chains such as ethylene glycol diacrylate, 1,3-butylene glycol diacrylate, 1,4-butanediol diacrylate, 1,5-pentanediol diacrylate, 1,6-hexanediol diacrylate, 1,10-dodecanediol diacrylate, and neopentyl glycol diacrylate, as well as compounds obtained by substituting the acrylate of these compounds with methacrylate. Polyfunctional monomers include pentaerythritol triacrylate, trimethylolmethane triacrylate, trimethylolpropane triacrylate, tetramethylolmethane tetraacrylate, oligoester acrylates, and compounds obtained by substituting the acrylate of these compounds with methacrylate.

[0025] Reactive surfactants can be used to form resin particles. Suitable reactive surfactants contain polymerizable (and therefore reactive) groups that can be incorporated into the resin particles. Exemplary reactive surfactants include anionic ether sulfate reactive surfactants such as those in the commercially available Hitenol BC series, such as Hitenol BC10-25. Other suitable reactive surfactants include polyoxyethylene alkylphenyl ether ammonium sulfate, Hitenol BC-10, BC-20, BC-2020, BC-30; polyoxyethylene styrene-phenyl ether ammonium sulfate containing Hitenol AR-10, AR-20, AR10-25, AR-2020; nonionic polyoxyethylene alkylphenyl ethers containing Noigen RN-10, RN-20, RN-30, RN-40, RN-5065; and reactive surfactants available from Ethox containing E-sperse RX-201, RX-202, RX-203, RS-1596, RS-1616, RS-1617, RS-1618, RS-1684.

[0026] Chain transfer agents can be used to form resin particles. The chain transfer agent can be a mercaptan or thiol. Suitable chain transfer agents include n-dodecylmercaptan (NDM), n-dodecanethiol (DDT), tert-dodecylmercaptan, 1-butanethiol, 2-butanethiol, octanethiol, and combinations thereof. Carbon tetrabromide, carbon tetrachloride, and halogenated carbons such as combinations thereof can be used as chain transfer agents.

[0027] When forming the resin particles, any of the monomers described above can be used in a monomer emulsion containing a solvent. Water is commonly used as the solvent, but water-soluble or water-miscible organic solvents (e.g., ethanol) can also be included. The types of monomers and their relative amounts can be selected to adjust the properties of the resin particles.

[0028] The acidic monomer can be used in the monomer emulsion in an amount ranging from 1.5 wt% to 15 wt%. (Here, wt% refers to (total weight of acidic monomer) / (total weight of monomers in the monomer emulsion excluding the reactive surfactant) * × 100). This range includes 5 wt% to 10 wt%. As described above, different pK aTwo different types of acidic monomers having values ​​may be used in the weight ratios described above. Hydrophilic monomers may be used in the monomer emulsion in amounts ranging from 1% to 15% by weight. (Weight percent has a similar meaning to that described for acidic monomers.) This range includes 2% to 15% by weight and 5% to 15% by weight. Polyfunctional monomers, including difunctional monomers, may be used in the monomer emulsion in similar amounts. In embodiments, the amounts are in the range of 0.01% to 0.8% by weight, 0.03% to 0.3% by weight, or 0.4% to 0.6% by weight. Other monomers (e.g., styrene, alkyl (meth)acrylates) may be present in amounts ranging from 70% to 97% by weight. (Weight percent has a similar meaning to that described for acidic monomers.) This range includes 75% to 90% by weight.

[0029] In addition, the amounts of acidic monomers, hydrophilic monomers, and polyfunctional monomers (e.g., hydrophilic polyfunctional monomers) may be present in the monomer emulsion in the range of 10% to 30% by weight. (Here, weight % is (total weight of acidic monomers, hydrophilic monomers, and polyfunctional monomers) / (total weight of monomers in the monomer emulsion excluding reactive surfactants) * (Refers to 100). This range includes 15% by weight to 30% by weight, and 15% by weight to 25% by weight.

[0030] Reactive surfactants can be used in monomer emulsions in amounts ranging from 1.5% to 6.5% by weight. (where weight % is (total weight of reactive surfactant) / (total weight of monomers in the monomer emulsion containing the reactive surfactant monomer) * (Refers to 100). This range includes 1.5% by weight to 5% by weight.

[0031] The chain transfer agent may be present in the monomer emulsion and may be used in various suitable amounts, for example, 0.25% to 2.5% by weight. (where wt% is (total weight of chain transfer agent) / (total weight of monomers in the monomer emulsion excluding reactive surfactants) *(It refers to 100.)

[0032] In embodiments, the monomer emulsion comprises (or consists of) a solvent (e.g., water), styrene, alkyl acrylate (e.g., butyl acrylate), acidic monomer, hydrophilic monomer, polyfunctional monomer (e.g., difunctional monomer), a reactive surfactant, and a chain transfer agent. In such embodiments, one or different types of monomers may be used. Similarly, one or different types of solvents and / or one or different types of chain transfer agents may be used. In embodiments, the monomer emulsion comprises (or consists of) a solvent (e.g., water), styrene, alkyl acrylate (e.g., butyl acrylate), two different types of acidic monomers (e.g., methacrylic acid and sulfonic acid), hydrophilic monomer (e.g., hydroxyethyl acrylate), difunctional monomer (e.g., poly(ethylene glycol) diacrylate), a reactive surfactant, and a chain transfer agent. In any of these embodiments, amounts of various monomers and chain transfer agents may be used as described above. The remainder may consist of a solvent.

[0033] In at least one embodiment, the monomer emulsion is surfactant-free (i.e., does not contain) surfactants. Here, “surfactant” refers to non-reactive, non-polymerizable anionic surfactants such as sodium dodecylsulfate (SDS), sodium dodecylbenzenesulfonate, sodium dodecylnaphthalene sulfate; dialkylbenzenealkyl sulfates; palmitic acid; alkyldiphenyl oxide disulfonates; and branched sodium dodecylbenzenesulfonate. “Surfactant” also refers to non-reactive, non-polymerizable cationic surfactants such as alkylbenzyldimethylammonium chloride, dialkylbenzenealkylammonium chloride, lauryltrimethylammonium chloride, alkylbenzylmethylammonium chloride, alkylbenzyldimethylammonium bromide, benzalkonium chloride, cetylpyridinium bromide, trimethylbromide, quaternary polyoxyethylalkylamine halide salts, and dodecylbenzyltriethylammonium chloride. "Surfactants" also refer to non-reactive, non-polymerizable nonionic surfactants such as polyoxyethylene cetyl ether, polyoxyethylene lauryl ether, polyoxyethylene octyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene oleyl ether, polyoxyethylene sorbitan monolaurate, polyoxyethylene stearyl ether, polyoxyethylene nonylphenyl ether, dialkylphenoxypoly(ethyleneoxy)ethanol, and block copolymers of polyethylene oxide and polypropylene oxide. Therefore, monomer emulsions may not contain any of these surfactants (i.e., they do not contain any).

[0034] The process steps for forming resin particles may include adding one of the monomer emulsions described above to a reactive surfactant solution at a certain supply rate over a certain period of time. The reactive surfactant solution comprises a solvent and a reactive surfactant. One of the solvents and one of the reactive surfactants described above may be used. One or different types of solvents and / or reactive surfactants may be used. The reactive surfactant in the reactive surfactant solution may be the same or different type compared to the reactive surfactant that may be present in the monomer emulsion. The reactive surfactant solution may further contain a buffer. Various buffers such as sodium bicarbonate, sodium carbonate, and ammonium hydroxide may be used. The reactive surfactant may be used in an amount ranging from 1% to 10% by weight. (where wt% is (total weight of reactive surfactant) / (total weight of reactive surfactant solution)) * (Refers to 100.) This range includes 2% by weight to 5% by weight. The buffer can be used in amounts ranging from 0.25% by weight to 2.5% by weight. (Weight % has the same meaning as described above.)

[0035] The reactive surfactant solution may contain an initiator. Alternatively, a separate initiator solution containing the initiator and one of the solvents described above may be formed and added to the reactive surfactant solution. The separate initiator solution may be added before the monomer emulsion is added. Additional amounts of the separate initiator solution may be added after the monomer emulsion is added. One or different types of solvents and / or initiators may be used. Examples of suitable initiators include water-soluble initiators such as ammonium persulfate (APS), sodium persulfate, and potassium persulfate, as well as organic soluble initiators containing organic peroxides and azo compounds including Vazo peroxides such as VAZO 64™, 2-methyl 2-2'-azobispropanenitrile, VAZO 88™, and 2-2'-azobisisobutylamide anhydride, and combinations thereof.Other water-soluble initiators that can be used include azoamidine compounds, such as 2,2'-azobis(2-methyl-N-phenylpropionamidine)dihydrochloride, 2,2'-azobis[N-(4-chlorophenyl)-2-methylpropionamidine]dihydrochloride, 2,2'-azobis[N-(4-hydroxyphenyl)-2-methylpropionamidine]dihydrochloride, 2,2'-azobis[N-(4-aminophenyl)-2-methylpropionamidine]tetrahydrochloride, 2,2'-azobis[2-methyl-N(phenylmethyl)propionamidine]dihydrochloride, 2,2'-azobis[2-methyl-N-2-propenylpropionamidine]dihydrochloride, and 2,2'-azobis[N-(2-hydroxy-ethyl)2-methylpropion Amidine dihydrochloride, 2,2'-azobis[2(5-methyl-2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride, 2,2'-azobis[2-(4,5,6,7-tetrahydro-1H-1,3-diazepine-2-yl)propane]dihydrochloride, 2,2'-azobis[2-( Examples include 3,4,5,6-tetrahydropyrimidine-2-yl)propane]dihydrochloride, 2,2'-azobis[2-(5-hydroxy-3,4,5,6-tetrahydropyrimidine-2-yl)propane]dihydrochloride, 2,2'-azobis{2-[1-(2-hydroxyethyl)-2-imidazolin-2-yl]propane}dihydrochloride, and combinations thereof. The initiator may be used in an amount ranging from 0.1% to 2.5% by weight (where wt% is (total weight of initiator) / (total weight of reactive surfactant solution)). * (It refers to 100.)

[0036] Silica nanoparticles may be present in the reactive surfactant solution. The silica nanoparticles may bind to the hydrogen bonding portions of hydrophilic monomers and / or to water molecules bonded to these hydrogen bonding portions. The use of silica nanoparticles is beneficial, at least in part, because small amounts of non-silica white pigments (e.g., titanium dioxide) can be used in aqueous inkjet ink compositions. Rather than including silica nanoparticles during the polymerization process, silica nanoparticles may be included as additives when preparing aqueous inkjet ink compositions, as described below.

[0037] The size of the silica nanoparticles used is generally very small, for example, less than 100 nm, less than 50 nm, or in the range of 5 nm to 50 nm. 50 Silica nanoparticles with a specific particle size may be used. The silica nanoparticles may be included in the reactive surfactant solution in an amount ranging from 0.5% to 5% by weight. (where weight % is (total weight of silica nanoparticles) / (total weight of reactive surfactant solution)) * It refers to 100. The total weight of silica nanoparticles refers to the weight of the solids, not the weight of the silica nanoparticle dispersion / solution. Commercially available silica nanoparticles that may be used include: various grades of LUDOX Colloidal Silica such as FM, SM, HS-30, HS-40, LS, TM-40, TM-50, SM-AS, AS-30, AS-40, AM, HSA, TMA, P X-30, P t-40, P W-50, CL, and CL-P, as well as various grades of Nissan Chemical Silica such as SNOWTEX ST-20L, ST-30, ST-40, ST-50, ST-OS, ST-O, ST-O-40, ST-OL, ST-C, ST-C-30, ST-CM, ST-N, STN30G, ST-N40, ST-NS, ST-XS, ST-S, ST-UP, ST-O-UP, MA-ST-UP, ST-PS-S, AMT-330S, HX-305M1, and HX-305M5.

[0038] In some embodiments, the reactive surfactant solution comprises (or consists of) a solvent (e.g., water), a reactive surfactant, and optionally one or more of an initiator, a buffer, and silica nanoparticles. In such embodiments, one or different types of these components may be used. In any of these embodiments, the amounts of reactive surfactant, initiator, buffer, and silica nanoparticles may be as described above. The remainder may consist of a solvent. In at least some embodiments, the reactive surfactant solution does not contain (i.e., does not include) any of the surfactants described above. In at least some embodiments, the reactive surfactant solution does not contain (i.e., does not include) any monomers other than the reactive surfactant monomer present in the solution.

[0039] The addition of monomer emulsions to reactive surfactant solutions can be carried out under the influence of an inert gas (e.g., nitrogen) and at high temperatures (e.g., temperatures higher than room temperature, such as in the range of 50°C to 90°C). This can be achieved by purging with an inert gas and heating the reactive surfactant solution before adding the monomer emulsion, and continuing this heating during the addition of the monomer emulsion.

[0040] As described above, the monomer emulsion can be added at a certain rate over a set period of time. In the presence of an initiator, the monomers of the monomer emulsion undergo polymerization to form latex resin particles. The rate of addition is generally slow enough so that polymerization is carried out under "monomer-deficient" conditions. This means that the rate of addition is less than or equal to the rate of polymerization, for example, the rate between styrene and acrylate monomers. Exemplary rates of addition range from 1 mL / min to 10 mL / min based on a total reaction volume of 1 L. Exemplary periods include those ranging from 60 minutes to 600 minutes. After the addition of the monomer emulsion, polymerization can be continued for a further period with or without the addition of further initiators. Exemplary additional periods range from 1 hour to 18 hours. Both the addition of the monomer emulsion and the polymerization after addition can be carried out under an inert gas and at high temperatures. The result of the process steps described above is latex containing resin particles. The latex can be used as is or processed by standard techniques such as coagulation, dissolution, and precipitation, filtration, washing, or drying.

[0041] In some embodiments, the method for forming resin particles does not involve the use of resin seeds in forming the resin particles. In such embodiments, neither the monomer emulsion nor the reactive surfactant solution contains such resin seeds. The polymerization reaction that forms the resin particles also does not involve such resin seeds. Similarly, in at least some embodiments, the method does not involve the use of any of the surfactants described above (other than reactive surfactant monomers). In other embodiments, the method for forming resin particles may use resin seeds, for example, to initiate and stabilize polymerization.

[0042] This method may further include forming a monomer emulsion, forming a reactive surfactant solution, and / or forming an initiator solution. Each of these may be formed by combining and mixing desired components in desired amounts.

[0043] The composition of the resin particles depends on the selection of monomers, their relative amounts, and the polymerization reactions between the selected monomers that produce polymerization products as described above. Therefore, a variety of compositions are encompassed, including those based on various polymerization products of reactants containing various combinations of monomers. As stated above, the selection of monomers is not particularly limited. However, in embodiments, the resin particles include (or consist of) polymerization products (e.g., copolymers) of reactants containing styrene, alkyl acrylates (e.g., butyl acrylate), acidic monomers, hydrophilic monomers, polyfunctional monomers (e.g., difunctional monomers), and reactive surfactants. In such embodiments, one or a variety of different types of monomers may be present. In embodiments, the resin particles include (or consist of) polymerization products of reactants containing styrene, alkyl acrylates (e.g., butyl acrylate), two different types of acidic monomers (e.g., methacrylic acid and sulfonic acid), hydrophilic monomers (e.g., hydroxyethyl acrylate), difunctional monomers (e.g., poly(ethylene glycol) diacrylate), and reactive surfactants. In each of these embodiments, initiators may be incorporated into the start and end of each polymer chain in the resin particles. In each of these embodiments, the resin may be crosslinked due to polyfunctional / bifunctional monomers. In each of these embodiments, monomers may be present in the resin particles in the amounts described above. For example, the amounts of acidic monomers, hydrophilic monomers, and polyfunctional monomers together may be in the range of 10% to 30% by weight in the resin particles. As described above, this weight percentage is (total weight of acidic monomers, hydrophilic monomers, and polyfunctional monomers) / (total weight of monomers in the resin particles excluding reactive surfactants). * It refers to 100.

[0044] Resin particles can be characterized by their size and size distribution. Resin particles may have relatively small sizes and a narrow size distribution. The size of resin particles is measured using a nanoparticle analyzer such as a Malvern Nano Zetasizer. (z、ave) It can be reported as a value. In the embodiment, D- (z、ave)The size distribution is in the range of 200 nm or less, 190 nm or less, 180 nm or less, 170 nm or less, or 80 nm to 200 nm. The size distribution can be reported as the polydispersity index (PDI) measured using a nanoparticle analyzer such as Malvern Nano-ZS. In embodiments, the PDI is in the range of 0.1 or less, 0.050 or less, 0.040 or less, 0.035 or less, 0.030 or less, or 0.001 to 0.1.

[0045] Due to their small size and narrow size distribution, the resin particles may be further characterized by the absence (i.e., not containing) large particles. This is because the particles are less than 200 nm, less than 175 nm, or less than 150 nm. (v、90) It can be proven by the value.

[0046] The small size and narrow size distribution of the resin particles can be further demonstrated by their ability to form three-dimensional (3D) photonic crystals when the solvent is removed (i.e., dried) from the latex containing the resin particles. Such crystal formation is possible due to the uniform size distribution of the resin particles. The ability of local crystallization and 3D photonic crystal formation can be confirmed using scanning tunneling electron microscopy (STEM). 3D photonic crystals can be achieved using controlled heating.

[0047] Resin particles may be present in the aqueous inkjet ink composition in various amounts ranging from 1% to 10% by weight. (where weight % is (total weight of resin particles) / (total weight of aqueous inkjet ink composition)) * (Refers to 100.) This range includes 1% by weight to 6% by weight. Although combinations of different types of resin particles may be used, in this embodiment, the aqueous inkjet ink composition contains a single type of resin particle.

[0048] Coloring agents

[0049] In addition to white pigment, aqueous inkjet ink compositions may contain colorants. Colorants include pigments, dyes, and combinations thereof. Examples of suitable dyes include anionic dyes, cationic dyes, nonionic dyes, and zwitterionic dyes. Specific examples of suitable dyes include food colorants such as black No. 1, black No. 2, red No. 40, blue No. 1, and yellow No. 7, FD&C dyes, acid black dyes (No. 1, 7, 9, 24, 26, 48, 52, 58, 60, 61, 63, 92, 107, 109, 118, 119, 131, 140, 155, 156, 172, 194), acid red dyes (No. 1, 8, 32, 35, 37, 52, 57, 92, 115, 119, 154, 249, 254, 256), Acid Blue Dye (No. 1, 7, 9, 25, 40, 45, 62, 78, 80, 92, 102, 104, 113, 117, 127, 158, 175, 183, 193, 209), Acid Yellow Dye (No. 3, 7, 17, 19, 23, 25, 29, 38, 42, 49, 59, 61, 72, 73, 114, 128, 151), Direct Black Dye (No. 4 , 14, 17, 22, 27, 38, 51, 112, 117, 154, 168), Direct Blue Dye (No. 1, 6, 8, 14, 15, 25, 71, 76, 78, 80, 86, 90, 106, 108, 123, 163, 165, 199, 226), Direct Red Dye (No. 1, 2, 16, 23, 24, 28, 39, 62, 72, 236), Direct Yellow Dye (No. 4, 11, 12, 27, 28, 33, 34, 39, 50, 58, 86, 1 Examples include reactive dyes such as 00, 106, 107, 118, 127, 132, 142, 157), reactive red dyes (No. 4, 31, 56, 180), reactive black dye (No. 31), and reactive yellow dye (No. 37), as well as anthraquinone dyes, monoazo dyes, disazo dyes, phthalocyanine derivatives including various phthalocyanine sulfonates, aza(18)annulene, formazan copper complexes, and triphenodioxazine.

[0050] Examples of suitable pigments include black pigment, cyan pigment, magenta pigment, and yellow pigment. The pigment may be organic or inorganic particles. A suitable inorganic pigment is carbon black. However, other inorganic pigments such as cobalt blue (CoO-Al2O3), chromium yellow (PbCrO4), and iron oxide may be suitable. Suitable organic pigments include, for example, azo pigments such as diazo pigments and monoazo pigments, polycyclic pigments (e.g., phthalocyanine pigments such as phthalocyanine blue and phthalocyanine green), perylene pigments, perinone pigments, anthraquinone pigments, quinacridone pigments, dioxazine pigments, thioindigo pigments, isoindolinone pigments, pyrantron pigments, and quinophthalone pigments), insoluble dye chelates (e.g., basic dye type chelates and acid dye type chelates), nitro pigments, nitroso pigments, and anthanthrone pigments such as PR168. Representative examples of phthalocyanine blue and green include copper phthalocyanine blue, copper phthalocyanine green, and their derivatives (pigment blue 15, pigment green 7, and pigment green 36). Representative examples of quinacridone include pigment orange 48, pigment orange 49, pigment red 122, pigment red 192, pigment red 202, pigment red 206, pigment red 207, pigment red 209, pigment violet 19, and pigment violet 42. Representative examples of anthraquinone include pigment red 43, pigment red 194, pigment red 177, pigment red 216, and pigment red 226. Representative examples of perylene include Pigment Red 123, Pigment Red 149, Pigment Red 179, Pigment Red 190, Pigment Red 189, and Pigment Red 224. Representative examples of thioindigoids include Pigment Red 86, Pigment Red 87, Pigment Red 88, Pigment Red 181, Pigment Red 198, Pigment Violet 36, and Pigment Violet 38.Representative examples of heterocyclic yellows include Pigment Yellow 1, Pigment Yellow 3, Pigment Yellow 12, Pigment Yellow 13, Pigment Yellow 14, Pigment Yellow 17, Pigment Yellow 65, Pigment Yellow 73, Pigment Yellow 74, Pigment Yellow 90, Pigment Yellow 110, Pigment Yellow 117, Pigment Yellow 120, Pigment Yellow 128, Pigment Yellow 138, Pigment Yellow 150, Pigment Yellow 151, Pigment Yellow 155, and Pigment Yellow 213. Such pigments are commercially available in powder or press cake form from many suppliers, including BASF Corporation, Engelhard Corporation, and Sun Chemical Corporation. Examples of usable black pigments include carbon pigments. Carbon pigments can be any commercially available carbon pigment that provides acceptable optical density and printing properties. Suitable carbon pigments for use in this system and method include, but are not limited to, carbon black, graphite, glassy carbon, charcoal, and combinations thereof. Such carbon pigments can be manufactured by various known methods, such as the channel process, contact process, furnace process, acetylene process, or thermal process, and are commercially available from such suppliers such as Cabot Corporation, Columbian Chemicals Company, Evonik, and EIDuPont de Nemours and Company.Suitable carbon black pigments include MONARCH® 1400, MONARCH® 1300, MONARCH® 1100, MONARCH® 1000, MONARCH® 900, MONARCH® 880, MONARCH® 800, MONARCH® 700, CAB-O-JET® 200, CAB-O-JET® 300, CAB-O-JET® 450, REGAL®, and BLACK. Examples of pigments include, but are not limited to, those manufactured by Cabot, such as PEARLS®, ELFTEX®, MOGUL®, and VULCAN® pigments; pigments manufactured by Columbia, such as RAVEN® 5000 and RAVEN® 3500; and pigments manufactured by Evonik, such as Color Black FW200, FW2, FW2V, FW1, FW18, FW5160, FW5170, Special Black 6, Special Black 5, Special Black 4A, Special Black 4, PRINTEX® U, PRINTEX® 140U, PRINTEX® V, and PRINTEX® 140V. Other pigments include CAB-O-JET 352K, CAB-O-JET 250C, CAB-O-JET 260M, CAB-O-JET 270Y, CAB-O-JET 465M, CAB-O-JET 470Y, and CAB-O-JET 480V (available from Cabot Corporation).

[0051] When used, colorants may be present in varying amounts in the aqueous inkjet ink composition. In embodiments, the colorants are present in amounts ranging from 0.01% to 5% by weight relative to the total weight of the aqueous inkjet ink composition. This includes amounts ranging from 0.01% to 2% by weight and 0.01% to 1% by weight. If two or more colorants are used, these amounts refer to the total amount of colorants. These amounts refer to the solids content, as opposed to the amount of dispersion containing the colorants.

[0052] In embodiments, in addition to the white pigment, the aqueous inkjet ink composition includes a black colorant, a cyan colorant, or a combination thereof. Including such colorants in the white pigment-containing aqueous inkjet ink composition is useful for providing a gray aqueous inkjet ink composition. In embodiments, the colorants in the aqueous inkjet ink composition consist of the white pigment and, optionally, one or more of the black colorant and the cyan colorant. In such embodiments, any of the white pigment, black colorant, and cyan colorant described above may be used. Any of the amounts of the white pigment, black colorant, and cyan colorant described above may be used.

[0053] wax

[0054] Aqueous inkjet ink compositions may contain waxes. Examples of waxes include paraffin wax, polyethylene wax, polypropylene wax, microcrystalline wax, polyolefin wax, montan ester wax, and carnauba wax. Waxes with melting points in the range of 50°C to 150°C may be used. Nanoscale wax emulsions (e.g., with diameters of 1000 nm or less, 500 nm or less, or 100 nm or less) based on carnauba wax and paraffin wax may be used. Waxes from Michelman and others may be used (e.g., Michem Lube 103DI, 124, 124P135, 156, 180, 182, 190, 270R, 368, 511, 693, 723, 743, 743P, and 985; as well as Michem Emulsion 24414, 34935, 36840, 41740, 43040, 43240, 44730, 47950, 48040M2, 61355, 62330, 66035, 67235, 70750, 71150, 71152, 91735, 93235, 93335, 93935, and 94340). Waxes from Byk may also be used, including Aquacer 2500, Aquacer 507, Aquacer 513, Aquacer 530, Aquacer 531, Aquacer 532, Aquacer 535, Aquacer 537, Aquacer 539, and Aquacer 593.

[0055] Nanoscale wax emulsions based on charged waxes (e.g., anionic waxes) have been found to be particularly useful. An exemplary such wax is Michem Lube 190.

[0056] When used, wax may be present in the aqueous inkjet ink composition in varying amounts. In embodiments, the amount ranges from 0.1% to 5% by weight relative to the total weight of the aqueous inkjet ink composition. If two or more types of wax are used, these amounts refer to the total amount of wax. These amounts refer to the solids content, as opposed to the amount of dispersion containing wax.

[0057] surfactants

[0058] Water-based inkjet ink compositions may contain surfactants. Examples of suitable surfactants include anionic surfactants (such as sodium lauryl sulfate (SLS), Dextrol OC-40, Strodex PK 90, ammonium lauryl sulfate, potassium lauryl sulfate, mireth sulfate, and sodium dioctyl sulfosuccinate series), nonionic surfactants (such as Surfynol® 104 series, Surfynol® 400 series, Dynol® 604, Dynol® 607, Dynol® 810, EnviroGem® 360, Tergitol® 15-s-7, Tergitol® 15-s-9, TMN-6, TMN-100x, and secondary alcohol ethoxylate series such as Tergitol® NP-9 and Triton® X-100), and cationic surfactants (such as Chemguard S-106A, Chemguard Examples include S-208M and Chemguard S-216M. Several fluorinated or silicone surfactants may be used, such as PolyFox™ TMPF-136A, 156A, 151N, Chemguard S-761p, S-764p, Silsurf™ A008, Siltec™ C-408, BYK 345, 346, 347, 348, and 349, 3410, 333, 3455, 342, 333, 302, polyethersiloxane copolymer TEGO™ Wet-260, 270, 500, and TEGO™ Tween 4000. Several amphoteric fluorinated surfactants may also be used, such as alkylbetaine fluorosurfactants or alkylamine oxide fluorosurfactants, such as Chemguard S-500 and Chemguard S-111.

[0059] When used, surfactants may be present in the aqueous inkjet ink composition in varying amounts. In embodiments, surfactants are present in amounts ranging from 0.01% to 2% by weight relative to the total weight of the aqueous inkjet ink composition. If two or more surfactants are used, these amounts refer to the total amount of surfactants.

[0060] Other resins, emulsions, binders, dispersants

[0061] While not essential, aqueous inkjet ink compositions may include water-soluble resins or emulsions, aqueous binders, polymer dispersants, or combinations thereof. Various water-soluble resins, such as polyethylene glycol and polyvinylpyrrolidone, may be used. Polyethylene glycols with molecular weights in the range of 3000 g / mol to 9000 g / mol, 3000 g / mol to 7000 g / mol, 3000 g / mol to 5000 g / mol, or 4000 g / mol may be used. These molecular weights can be measured using gel permeation chromatography.

[0062] Examples of aqueous binders include Rhoplex I-1955, Rhoplex I-2426D, Rhoplex I-62, Rhoplex I-98, and Rhoplex E-1691, available from Rhohm & Haas. Others include Lucidene 190, Lucidene 400, and Lucidene 243, available from DSM Corporation; NeoCryl A-1110, NeoCryl A-2092, NeoCryl A-639, NeoRad R-440, NeoRad R-441, NeoRez N-55, 972, PVP K-15, PVP K-30, PVP K-60, and PVP K-85, available from ISP; and Ganex P-904LC and PVP / VA W-63. Other exemplary aqueous binders include those available from Johnson Polymers (BASF), such as Joncryl 537, Joncryl H538, and Joncryl H538.

[0063] Examples of polymer dispersants that may be used include acrylic polymers such as styrene-acrylic copolymers, vinylpyrrolidone copolymers, urethane or polyurethane dispersions, and acrylic-urethane hybrid dispersions. More specific examples of polymer dispersants include those available from Johnson Polymers (BASF), such as Joncryl® 671, Joncryl® 683, Joncryl® 296, Joncryl® 690, Joncryl HPD 296, Joncryl HPD96-E, Joncryl LMV 7085, and Joncryl 8082. Other dispersants that may be used include those described in EP Patent No. 2097265 incorporated by reference for dispersant purposes, and those described in U.S. Patent Application No. 2019 / 284414 incorporated by reference for dispersant purposes.

[0064] If present, various amounts of the above components may be used in the aqueous inkjet ink composition. In embodiments, the resin / emulsion / binder / dispersant is present in an amount ranging from 0.01% to 5% by weight relative to the total weight of the aqueous inkjet ink composition. If a combination is used, or if two or more types are used, these amounts refer to the total amount of the resin / emulsion / binder / dispersant.

[0065] However, in at least one embodiment, the aqueous inkjet ink composition does not contain (i.e., does not include) a water-soluble resin or emulsion. Similarly, in one embodiment, the aqueous inkjet ink composition does not contain (i.e., does not include) an aqueous binder. Similarly, in one embodiment, the aqueous inkjet ink composition does not contain (i.e., does not include) a polymer dispersant. This means that it does not contain (i.e., does not include) any of the water-soluble resin or emulsion, aqueous binder, and polymer dispersant described above. The terms water-soluble resin, water-soluble emulsion, aqueous binder, and polymer dispersant do not include resin particles in the aqueous inkjet ink composition.

[0066] additives

[0067] Various additives can be used in aqueous inkjet ink compositions to adjust their properties. Suitable additives include biocides; fungicides; stabilizers; pH adjusters such as acids or bases, phosphates, carboxylates, sulfites, amine salts, and buffers; metal ion sequestering agents such as EDTA (ethylenediamine tetraacetic acid); humectants; defoamers; wetting agents; and one or more of the silica nanoparticles listed above (for example, if not already included in the monomer polymerization).

[0068] Various amounts of additives can be used in aqueous inkjet ink compositions. In embodiments, the additives are present in amounts ranging from 0.01% to 5% by weight relative to the total weight of the aqueous inkjet ink composition. If two or more additives are used, these amounts refer to the total amount of additives.

[0069] In at least one embodiment, the aqueous inkjet ink composition is free of coagulants, flocculants, and plasticizers. In the embodiment, the ink composition is free of any pyrrolidone-based solvent such as N-methylpyrrolidone, and is free of Texanol and Texanol isobutyrate.

[0070] In the embodiments, the aqueous inkjet ink composition comprises (or consists of) a solvent system, a white pigment, resin particles, and optionally one or more of a colorant, a wax, and an additive. In the embodiments, the aqueous inkjet ink composition comprises (or consists of) a solvent system, a white pigment, resin particles, wax, and optionally one or more of a colorant and an additive. In the embodiments, the solvent system comprises water, a first organic solvent, and a second organic solvent. In the embodiments, a colorant may be present and may be selected from a black colorant, a cyan colorant, and combinations thereof. In the embodiments, the additive may be selected from stabilizers, surfactants, defoamers, wetting agents, humectants, and biocides. In any of these embodiments, the components may be selected from any of the solvent systems, organic solvents, resin particles, white pigments, colorants, waxes, and additives disclosed herein. In any of these embodiments, amounts of the components as described above may be used.

[0071] Aqueous inkjet ink compositions can be formed by combining and mixing desired components in desired amounts. An exemplary method includes adding a white pigment (which may be provided as a dispersion) to water, adding resin particles (which may be provided as latex) to water, adding an organic solvent to water, and adding any additives to water. The organic solvent and any additives may be combined as separate mixtures before being added to water. If a wax (which may be provided as a dispersion) is included, it may be added separately. The wax may be added after the addition of the organic solvent and additives. If a colorant is included, the colloidal stability of the aqueous inkjet ink composition has been determined to be highly sensitive to the order in which the colorant is added. These results are demonstrated in the following examples. Specifically, any colorant (which may be added as a separate or combined dispersion) is preferably added before the white pigment. Mixing and / or heating may be used in the method. The aqueous inkjet ink composition may be filtered before use.

[0072] characteristics

[0073] Aqueous inkjet ink compositions may be characterized by their viscosity. Viscosity may be the average shear viscosity, measured at a temperature of 37°C over a range of 4 to 400 Hz. The average shear viscosity may be measured using an ARES-G2 rheometer by TA Instruments. The number of measurements to provide an average value may be 10. The average shear viscosity value may refer to an aqueous inkjet ink composition having a white pigment solids content in the range of 4% to 15% by weight, relative to the total weight of the aqueous inkjet ink composition. In embodiments, the average shear viscosity is in the range of 1 mPa·s to 8 mPa·s, 2 mPa·s to 7 mPa·s, or 3 mPa·s to 6 mPa·s. These viscosities are all initial viscosities measured within one day after the formation of the aqueous inkjet ink composition.

[0074] As described above, embodiments of the aqueous inkjet ink composition exhibit high long-term colloidal stability. As described in the following examples, average shear viscosity provides a measure of the colloidal stability of the aqueous inkjet ink composition. Embodiments of the aqueous inkjet ink composition exhibit very stable average shear viscosity over long periods and at high temperatures. Specifically, embodiments of the aqueous inkjet ink composition exhibit an average shear viscosity after 3 days at 60°C that is within 5% of their respective initial average shear viscosity. Embodiments of the aqueous inkjet ink composition exhibit an average shear viscosity after 6 days at 60°C that is within 5% of their respective initial average shear viscosity. As demonstrated in the following examples, the stability of the average shear viscosity, and therefore the stability of the colloidal dispersion, was found to be highly sensitive to a second organic solvent in the aqueous inkjet ink composition. For aqueous inkjet ink compositions containing one or more colorants in addition to a white pigment (e.g., a gray aqueous inkjet ink composition), the stability is also highly sensitive to the order of addition of the colorants / white pigment.

[0075] Aqueous inkjet ink compositions may be used to form printed images. In embodiments, such a method includes ejecting droplets of any of the disclosed aqueous inkjet ink compositions onto a substrate to form an image thereon. Such a method may further include incorporating the ink composition into an inkjet printing apparatus. The printing apparatus may use a thermal inkjet process, in which the ink composition in the nozzle is selectively heated in an image pattern, thereby ejecting droplets of the ink composition in an image pattern. Alternatively, the printing apparatus may use an acoustic inkjet process, in which droplets of the ink composition are ejected in an image pattern by an acoustic beam. In yet another embodiment, the printing apparatus may use a piezoelectric inkjet process, in which droplets of the ink composition are ejected in an image pattern by vibration of a piezoelectric vibrating element. Any suitable substrate may be used.

[0076] The method may include: injecting ink droplets in an image pattern onto an intermediate transfer member; heating the image to partially or completely remove the solvent; and transferring the ink composition in an image pattern from the intermediate transfer member to a final recording substrate. The intermediate transfer member may be heated to a temperature higher than the temperature of the final recording sheet but lower than the temperature of the ink composition in the printing apparatus. Offset or indirect printing processes are also disclosed, for example, in U.S. Patent No. 5,389,958, the disclosure of which is fully incorporated herein by reference.

[0077] Any suitable substrate or recording sheet can be used as the final recording sheet. Examples of substrates include McCoy® Gloss #100 coated substrate, Xerox® Bold uncoated substrate, Kodak photographic paper, Sterling® Ultra Web Matte (offset coating), TrueJet® Gloss Text (inkjet coated), and McCoy® Silk (offset coating). Other substrates are provided in the following examples. [Examples]

[0078] The following examples are provided to further define the various types of this disclosure. These examples are for illustrative purposes only and are not intended to limit the scope of this disclosure. Unless otherwise stated, proportions and percentages are given by weight. As used herein, “room temperature” refers to a temperature of about 20°C to about 25°C.

[0079] Example 1: Latex

[0080] A solution was prepared by mixing 1.4 grams of reactive surfactant solution (Hitenol BC 1025 from Montello), 36 grams of deionized water, and 0.7 g of silica nanoparticle solution (34% Ludox TMA) in a glass reactor. The reaction mixture was then purged with nitrogen for 30 minutes. The reactor was then continuously purged with nitrogen while stirring at 250 rpm. The reactor was then heated to approximately 75°C and maintained there. Separately, 0.3 grams of ammonium persulfate (APS) initiator was dissolved in 5 grams of deionized water and added to the reactor.

[0081] Separately, a monomer emulsion was prepared in the following manner: 28 g of styrene, 6 g of butyl acrylate, 3 g of methacrylic acid, 1 g of sodium 4-styrenesulfonate (styrenesulfonic acid), 1 g of hydroxyethyl acrylate (HEA), 0.6 g of 1-dodecanethiol (DDT), 0.2 g of PEGDA 250, 0.8 g of Hitenol BC 1025, and 16 g of deionized water were mixed to form an emulsion. The emulsified mixture was slowly supplied to the reactor for about 2 hours, and the reaction continued for about 1.5 hours. A further 0.1 g of APS initiator was dissolved in deionized water and added to the reactor over about 10 minutes, and the reaction continued for another 1.5 hours. The resulting latex was cooled to room temperature and neutralized to pH 8.0 with 0.5 M KOH solution.

[0082] Monomer conversion was measured and showed a conversion rate exceeding 99.9%. Therefore, the weight of monomers in the monomer emulsion is, from calculations, the same as that of resin particles, excluding the polymerizable surfactant.

[0083] Example 2: White aqueous inkjet ink composition

[0084] A white aqueous inkjet ink composition was formed using the latex from Example 1. The aqueous inkjet ink composition was formed using the following steps, and the formulation is shown in Table 1.

[0085] 1. The titanium dioxide dispersion was added to deionized water and mixed using a cowl blade impeller at a speed of approximately 650 RPM for about 15 minutes.

[0086] 2. The latex resin particles (Example 1) were slowly added to the titanium dioxide dispersion and mixed for about 20 minutes (Mixture A).

[0087] 3. In a separate beaker, the solvent, humectant, stabilizer, defoamer, surfactant, and wetting agent were mixed to form a homogeneous mixture (mixture B).

[0088] 4. Mixture B was slowly added to mixture A. Once the addition was complete, the components were mixed for approximately 20 minutes.

[0089] 5. Add the wax and continue mixing for approximately 15 minutes.

[0090] 6. After mixing, the aqueous inkjet ink composition was left at room temperature for approximately 60 minutes, and then its pH, conductivity, and surface tension were checked.

[0091] [Table 1]

[0092] Example 4: Gray aqueous inkjet ink composition

[0093] A gray aqueous inkjet ink composition was formed using the first process (Process I). The process was as follows:

[0094] Process I

[0095] 1. Add titanium dioxide to water and mix at approximately 650 rpm.

[0096] 2. Addition of the Black dispersion to the mixture in step 1.

[0097] 3. Addition of the cyanide dispersion to the mixture in step 2.

[0098] 3. Addition of latex having resin particles (Example 1) to the mixture in step 3.

[0099] 4. Stir the mixture for approximately 25-30 minutes.

[0100] 5. Prepare a mixture of the solvent and the additive (mixture B from Example 1).

[0101] 6. After adding mixtures B and A at approximately 650 rpm, the mixing speed was reduced to approximately 500 rpm, and the mixture was stirred for approximately 50-55 minutes.

[0102] 7. Add the wax dispersion to the solution in step 7 at approximately 400 rpm and mix for approximately 20 minutes.

[0103] The gray aqueous inkjet ink composition prepared via Process I has a drawback: stability issues, as evidenced by visible particle formation. The degree of particle formation was so large that the composition could not be passed through a 1-micron filter.

[0104] To mitigate stability issues associated with Process I, a change process was developed.

[0105] Process II

[0106] 1. Add the Black dispersion to water.

[0107] 2. Addition of the cyanide dispersion to the mixture in step 1.

[0108] 3. Addition of titanium dioxide dispersion to the mixture in step 2.

[0109] 4. Addition of latex having resin particles (Example 1) to the mixture in step 3.

[0110] 5. Follow steps 4-7 of Process I.

[0111] The gray aqueous inkjet ink compositions prepared via Process II easily pass through a 1-micron filter and are ejected without clogging or latency issues. Typical formulations are shown in Table 2.

[0112] [Table 2]

[0113] Colloidal Stability

[0114] To test the colloidal stability of aqueous inkjet ink compositions, white aqueous inkjet ink compositions were aged for either 3 days (±12 hours) or 6 days (±12 hours) in an oven at approximately 60°C (e.g., ±5°C) for accelerated aging. Rheology and particle size were measured before and after aging. Average shear viscosity was measured at 37°C over a range of 4–400 Hz using a TA Instruments ARES-G2 rheometer. The reported value was the average of 10 measurements. Rheology measurements were deemed a more accurate indicator of colloidal stability compared to particle size measurements because they are sensitive to structure formation, gelation, solidification, or precipitation during ink aging. Table 3 below shows the results for white inks A–G in Table 1. In Table 3, the first measurement for each ink A–G is the initial average shear viscosity of the ink, measured within 1 day of ink preparation. The percentage change in viscosity is calculated as (the magnitude of the difference between the initial average shear viscosity and the average shear viscosity after aging) / (initial average shear viscosity). * The result is given as 100. The results are significant for white inks C to G, showing that the average shear viscosity after aging at 60°C for 6 days is the same as the initial average shear viscosity (within 4%). These white inks contain 5% by weight or less of 1,2-hexanediol. White inks A and B contain 7% by weight of 1,2-hexanediol.

[0115] [Table 3]

[0116] Printing performance

[0117] Aqueous inkjet ink compositions were sprayed onto different paper substrates using a Dimatix DMP2800 printer. The first set of key test parameters used was as follows: droplet mass = 4.5–4.8 ng (i.e., approximately 4.5 ng), droplet velocity = 6–7 m / sec, frequency = 5 kHz, voltage = 16–20 V, and printing temperature = 37°C. The second set of key test parameters used was as follows: droplet mass = 8.5–9 ng (i.e., approximately 9 ng), droplet velocity = 9–11 m / sec, frequency = 5 kHz, voltage = 24–27 V, and printing temperature = 37°C. The printing parameter was 600 × 600 dpi printing. Measurements were performed using a PIAS II instrument, a personal image analysis system with a digital magnifying glass. A high-resolution optical module with a field of view of approximately 3.2 mm × 2.4 mm and approximately 5 μm / pixel was used to measure dot size and diameter. The results are shown in Table 4 (for white inks C and G) and Table 5 (for gray ink).

[0118] [Table 4]

[0119] White aqueous inkjet ink compositions C and G also exhibited exceptional water resistance. White ink C withstood more than 20 wet rubs, and white ink G withstood more than 25 wet rubs. Wet rub resistance was measured using two rubs with a wet Q-tip. A thin layer of each ink was coated onto McCoy Gloss #100 paper and then dried in a convection oven at 130°C for 2 minutes.

[0120] Microscopic images were obtained of images printed using white aqueous inkjet ink compositions C and G. The images showed excellent dot circularity and homogeneity in line width. The solid content printed blocks of both white inks C and G exhibited very smooth sides and edges, which is usually difficult to obtain with aqueous inkjet inks.

[0121] [Table 5]

[0122] As described above, the results from the characterization of the gray aqueous inkjet ink composition are summarized in Table 5. This table also includes reference measurements from Pantone samples of cool gray and warm gray. The results of 4.5 ng and 9 ng prints of the gray ink were consistent with the reference Pantone cool gray and warm gray. Furthermore, mottling, roundness, and granularity were within specifications.

[0123] The term “exemplary” is used herein to mean an example, case, or representation. Any embodiment or design described herein as “exemplary” is not necessarily construed as being preferable or advantageous to other embodiments or designs. Furthermore, for the purposes of this disclosure, unless otherwise specified, “a” or “an” means “one or more.”

[0124] Where not already included, all numerical values ​​of parameters in this disclosure are referred to by the term “approximately,” meaning approximate. This includes variations inherent in the measurement of the relevant parameters as understood by those skilled in the art. This also includes the exact values ​​of the disclosed numerical values ​​and the rounded values ​​of the disclosed numerical values.

[0125] The foregoing description of exemplary embodiments of the Disclosure is provided for illustrative and explanatory purposes only. It is not intended to be exhaustive or to limit the Disclosure to the exact form disclosed, and modifications and variations are possible in light of the above teachings or may be obtained from practices of the Disclosure. Embodiments are selected and described in order to illustrate the principles of the Disclosure and to enable those skilled in the art to utilize the Disclosure in various embodiments as a practical application of the Disclosure, and with various modifications suitable for the particular intended use. The scope of the Disclosure is intended to be defined by the claims and equivalents thereof appended herein.

Claims

1. 1. An aqueous inkjet ink composition comprising: a solvent system comprising water, a first organic solvent, and a second organic solvent, wherein the first organic solvent is an alkanediol having 2 or 3 carbon atoms and the first organic solvent is present in an amount of from about 28.5% to about 40% by weight, and further wherein the second organic solvent is an alkanediol having 2 to 8 carbon atoms and the second organic solvent is present in an amount of from greater than 0% to about 8% by weight; White pigment, resin particles comprising a polymerization product of reactants comprising a monomer, an acidic monomer, a hydrophilic monomer, a multifunctional monomer, and a reactive surfactant; 1. An aqueous ink-jet ink composition comprising:

2. 2. The aqueous ink-jet ink composition of claim 1, wherein the amount of the second organic solvent is from about 2% to about 6% by weight.

3. The aqueous ink-jet ink composition of claim 1 , wherein the second organic solvent is a linear alkanediol.

4. The aqueous ink-jet ink composition of claim 3 , wherein the second organic solvent is hexanediol.

5. The aqueous ink-jet ink composition of claim 4, wherein the hexanediol is 1,2-hexanediol.

6. The aqueous inkjet ink composition of claim 1, which does not contain any of pyrrolidone, dipropylene glycol monomethyl ether, tetrahydrofurfuryl alcohol, propylene glycol monopropyl ether, or combinations thereof.

7. The aqueous ink-jet ink composition of claim 1 , wherein the first organic solvent is propylene glycol.

8. The aqueous ink-jet ink composition of claim 1 , wherein the white pigment is titanium dioxide.

9. The titanium dioxide has a D of less than about 150 nm. 50 9. The aqueous ink-jet ink composition of claim 8, wherein the titanium dioxide is in the form of particles having a particle size and is present in an amount ranging from about 0.1% to about 15% by weight.

10. The aqueous ink-jet ink composition of claim 1 , wherein the resin particles further comprise silica nanoparticles.

11. The aqueous inkjet ink composition of claim 1, further comprising a colorant selected from the group consisting of black pigments, cyan pigments, and combinations thereof.

12. 2. The aqueous ink-jet ink composition of claim 1, wherein the aqueous ink-jet ink composition exhibits an average shear viscosity after about 3 days at about 60° C. that is within about 5% of the initial average shear viscosity of the aqueous ink-jet ink composition, an average shear viscosity after about 6 days at about 60° C. that is within about 5% of the initial average shear viscosity of the aqueous ink-jet ink composition, or both.

13. 10. The aqueous ink-jet ink composition of claim 1, wherein the aqueous ink-jet ink composition is free of water-soluble resins, water-soluble emulsions, aqueous binders, and polymeric dispersants.

14. The aqueous ink-jet ink composition of claim 1, wherein the second organic solvent is present in an amount of about 3% to about 5% by weight.

15. The aqueous ink-jet ink composition of claim 14, wherein the second organic solvent is 1,2-hexanediol.

16. The aqueous ink-jet ink composition of claim 15, wherein the first organic solvent is propylene glycol.

17. The aqueous ink-jet ink composition of claim 16, wherein the white pigment is titanium dioxide.