WO2021262162A1

WO2021262162A1 - Fluid set for textile printing

Info

Publication number: WO2021262162A1
Application number: PCT/US2020/039372
Authority: WO
Inventors: Zhang-Lin Zhou; Or Brandstein; Qianhan YANG
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2020-06-24
Filing date: 2020-06-24
Publication date: 2021-12-30

Abstract

A fluid set includes a fixer fluid and an inkjet ink. The fixer fluid includes a cationic polyurethane including a phosphonium salt and an aqueous fixer vehicle. The inkjet ink includes a colorant, an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group, a polymeric UV absorber, and an aqueous ink vehicle.

Description

FLUID SET FOR TEXTILE PRINTING

BACKGROUND

[0001] Textile printing methods often include rotary and/or flat-screen printing. Traditional analog printing typically involves the creation of a plate or a screen, i.e., an actual physical image from which ink is transferred to the textile. Both rotary and flat screen printing have great volume throughput capacity, but also have limitations on the maximum image size that can be printed. For large images, pattern repeats are used. Conversely, digital inkjet printing enables greater flexibility in the printing process, where images of any desirable size can be printed immediately from an electronic image without pattern repeats. Inkjet printers are gaining acceptance for digital textile printing. Inkjet printing is a non-impact printing method that utilizes electronic signals to control and direct droplets or a stream of ink to be deposited on media.

BRIEF DESCRIPTION OF THE DRAWINGS [0002] Features of examples of the present disclosure will become apparent by reference to the following detailed description and drawings, in which like reference numerals correspond to similar, though perhaps not identical, components. For the sake of brevity, reference numerals or features having a previously described function may or may not be described in connection with other drawings in which they appear. [0003] Fig. 1 schematically illustrates an example fluid set and an example textile printing kit, each of which includes an example of a fixer fluid and an example of an inkjet ink; [0004] Figs. 2 through 5 schematically depict different examples of the cationic polyurethane that is present in examples of the fixer fluid disclosed herein;

[0005] Fig. 6 schematically depicts an example of the UV light curable polyurethane binder in examples of the inkjet ink disclosed herein;

[0006] Fig. 7 schematically depicts an example of a reactive polyol that may be used in the synthesis of an example of the UV light curable polyurethane binder;

[0007] Fig. 8 is a flow diagram illustrating an example printing method; and [0008] Figs. 9A and 9B are schematic diagrams of different examples of a printing system disclosed herein.

DETAILED DESCRIPTION

[0009] The textile market is a major industry, and printing on textiles, such as cotton, polyester, etc., has been evolving to include digital printing methods. Some inks that are digitally printed on textiles are exposed to heating in order to dry the ink and fix the ink colorant to the fabric. Some heating techniques involve relatively long exposure times (e.g., several minutes) at lower temperatures in order to avoid burning or other deleterious effects. This can prolong the overall printing process. Other heating techniques utilize ultraviolet (UV) curing, which involves exposure to ultraviolet light to initiate a photochemical reaction that generates a cross-linked network. In some examples when UV curing is used, the ink or other liquid used in printing includes a photoinitiator to initiate the photochemical reaction. This adds an additional component to the ink. In other examples when UV curing is used, an additional thermal curing is performed to enhance the durability. This thermal curing process involves an additional cross-linking agent and heating to high temperatures for an extended time period (e.g., 3 minutes or longer). This adds additional components and prolongs the overall printing process.

[0010] Disclosed herein is a fluid set that is particularly suitable for textile printing using UV curing. The fluid set includes a fixer composition and an inkjet ink. The fixer composition includes a cationic polyurethane having a phosphonium salt, and the inkjet ink includes a UV light curable polyurethane binder having a UV reactive group and an ionic stabilization group. When printed and exposed to UV curing, the cationic polyurethane and UV light curable polyurethane binder have a synergistic effect that improves both the optical density and the durability of the resulting print. These characteristics are significantly improved when compared to a variety of prints, such as those prepared with a similar ink, a traditional fixer fluid containing an inorganic salt, such as calcium salt, and either thermal or UV curing. Moreover, the UV light curable polyurethane binder in the ink is reactive in the absence of a photoinitiator, and can be cured in 30 seconds or less.

[0011] Throughout this disclosure, a weight percentage that is referred to as “wt% active" refers to the loading of an active component of a dispersion or other formulation that is present in the fixer fluid or the inkjet ink. For example, a pigment may be incorporated into the inkjet ink as a stock solution or dispersion, which includes water and potentially other components in addition to the pigment. In this example, the wt% active of the pigment accounts for the loading (as a weight percent) of the pigment that is present in the inkjet ink, and does not account for the weight of the other components (e.g., water, etc.) that may be present in with the pigment. The term “wt%,” without the term actives, refers to the loading (in the fixer fluid or inkjet ink) of a 100% active component that does not include other non-active components therein.

[0012] The terms “acid value” and “acid number" are used herein in conjunction with the cationic polyurethane and the UV light curable polyurethane binder. These terms refer to the mass of potassium hydroxide (KOH) in milligrams that can be used to neutralize one gram of substance, such as the cationic polyurethane polymer or the UV light curable polyurethane binder disclosed herein. The test for determining the acid number of a particular substance may vary, depending on the substance. As one example, the acid value can be determined by dissolving or dispersing a known quantity of a material in an organic solvent and then titrating with a solution of potassium hydroxide (KOH) of known concentration for measurement. As another example, the acid number of a polyurethane may be determined by dispersing a known amount of the polyurethane sample in water and the aqueous dispersion may be titrated with a polyelectrolyte titrant of a known concentration. In this example, a current detector for colloidal charge measurement may be used. An example of a current detector is the Miitek PCD-05 Smart Particle Charge Detector (available from BTG). The current detector measures colloidal substances in an aqueous sample by detecting the streaming potential as the sample is titrated with the polyelectrolyte titrant to the point of zero charge. An example of a suitable polyelectrolyte titrant is poly(diallyldimethylammonium chloride) (i.e., PolyDADMAC). It is to be understood that any suitable test for a particular component may be used.

[0013] Multi-fluid and Textile Printing Kits

[0014] The fixer fluid and inkjet ink disclosed herein may be part of a fluid kit and/or of a textile printing kit, both of which are shown schematically in Fig. 1.

[0015] The fluid kit 10 includes i) a fixer fluid 12 including a cationic polyurethane including a phosphonium salt, and an aqueous fixer vehicle; and ii) an inkjet ink 14 including a colorant, an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group, a polymeric UV absorber, and an aqueous ink vehicle. It is to be understood that any example of the fixer fluid 12 and the inkjet ink 14 disclosed herein may be used in the examples of the fluid kit 10.

[0016] In one example, the fixer fluid 12 and the inkjet ink 14 are formulated for thermal inkjet printing.

[0017] In any example of the fluid kit 10, the fixer fluid 12 and the inkjet ink 14 may be maintained in separate containers (e.g., respective reservoirs/fluid supplies of respective inkjet cartridges) or separate compartments (e.g., respective reservoirs/fluid supplies) in a single container (e.g., inkjet cartridge).

[0018] The textile printing kit 18 includes i) a textile fabric 16; ii) a fixer fluid 12 including a cationic polyurethane including a phosphonium salt, and an aqueous fixer vehicle; and iii) an inkjet ink 14 including a colorant, an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group, a polymeric UV absorber, and an aqueous ink vehicle. It is to be understood that any example of the fixer fluid 12 and the inkjet ink 14 disclosed herein may be used in the examples of the textile printing kit 18. It is also to be understood that any example of the textile fabric 16 may be used in the examples of the textile printing kit 18. [0019] Fixer Fluid

[0020] Examples of the fixer fluid 12 disclosed herein include a cationic polyurethane including a phosphonium salt and an aqueous fixer vehicle.

[0021] The cationic polyurethane may be present in the form of particles. These particles may have a D50 particle size ranging from about 20 nm to about 500 nm. The “D50” particle size is defined as the particle size at which about half of the particles are larger than the D50 particle size and about half of the other particles are smaller than the D50 particle size in other examples, the cationic polyurethane particles have a D50 particle size ranging from about 20 nm to about 200 nm, from about 40 nm to about 400 nm, from about 60 nm to about 300 nm, or from about 100 nm to about 500 nm. As used herein, particle size with respect to the cationic polyurethane particles can be calculated using volume of the particle size normalized to a spherical shape for diameter measurement. Particle size information can also be determined and/or verified using a scanning electron microscope (SEM)

[0022] The cationic polyurethane polymer structure includes a polyurethane backbone, pendant side chain groups along the polyurethane backbone, and end cap groups terminating the polyurethane backbone. The pendant side chain groups and the end cap groups collectively include aliphatic phosphonium salts and polyalkylene oxides. As discussed in more detail below, the aliphatic phosphonium salts may be pendant side chain groups and/or end cap groups, and the polyalkylene oxides may be pendant side chain groups and/or end cap groups.

[0023] Several examples of the cationic polyurethane polymer structure 20A, 20B, 20C, 20D are respectively shown in Fig. 2 through Fig. 5.

[0024] In each of the schematic structures 20A, 20B, 20C, 20D respectively shown in Fig. 2 through Fig. 5, “m” can be from 1 to 18, each “R” is independently selected from a straight-chain or branched C1 to C5 alkyl, and “X” can be any counterion suitable for the positively charged phosphorus atom of the aliphatic phosphonium salt. As other examples, m can range from 1 to 14, from 1 to 10, from 2 to 18, from 2 to 10, from 1 to 5, or from 2 to 5; each “R” is independently selected from a straight-chain or branched C2 to C5 alkyl; and “X” is Cl, Br, I, sulfonate, toluenesulfonate, trifluoromethanesulfonate, etc. [0025] Each of the cationic polyurethane polymer structures in Fig. 2 through Fig. 5 includes several chemical moieties, such as urethane linkage groups 22 (formed by the reaction of isocyanate groups 24 with any of a number of polyols 26 that may be present). A carbon atom of an isocyanate group 24 reacts with an oxygen atom of a hydroxyl of the polyol 26 to form the urethane linkage group 22. The polyols 26 and the isocyanate groups 24 are shown schematically after polymerization. The isocyanate groups 24 are shown along the cationic polyurethane backbone, and are schematically represented by a circle with isocyanate groups on either side thereof. Other chemical moieties represented in each of Fig. 2 through Fig. 5 include the polyalkylene oxides 28 and the aliphatic phosphonium salts 30. The polyalkylene oxides 28 are shown as PEO/PPO, indicating that the polyalkylene oxide 28 can be polyethylene oxide (PEO), polypropylene oxide (PPO), or include both types of monomeric units as a hybrid polyalkylene.

[0026] The cationic polyurethane polymer structure 20A shown in Fig. 2 includes two aliphatic phosphonium salts 30 as the end cap groups EG. In this example, the polyalkylene oxides 28 are included as a pendant side chain group PG.

[0027] The cationic polyurethane polymer structure 20B shown in Fig. 3 includes two aliphatic phosphonium salts 30 as the end cap groups EG. In this example, both polyalkylene oxides 28 and additional aliphatic phosphonium salts 30 are included as pendant side chain groups PG.

[0028] The cationic polyurethane polymer structure 20C shown in Fig. 4 includes two polyalkylene oxides 28 as the end cap groups EG. In this example, aliphatic phosphonium salts 30 are included as pendant side chain groups PG.

[0029] The cationic polyurethane polymer structure 20D shown in Fig. 5 includes two polyalkylene oxides 28 as the end cap groups EG. In this example, both aliphatic phosphonium salts 30 and additional polyalkylene oxides 28 are included as pendant side chain groups PG.

[0030] The cationic polyurethane polymer structures 20A, 20B, 20C, and 20D shown in Fig. 2 through Fig. 5 are not intended to depict specific polymers, but rather show examples of the types of pendent groups PG that may be present along the polyurethane backbone and/or end cap groups EG of the polyurethane backbone. It is contemplated that the cationic polyurethane polymer structures 20A, 20B, 20C, and 20D may include additional polymerized polymeric diols, polymerized isocyanates, urethane linkage groups, polyalkylene oxides, or even other moieties not shown in these examples, such as epoxides, organic acids, etc. provided by other diols. As used herein, the terms “polymerized polyols/diols” and “polymerized isocyanates" refer to the respective monomers in their polymerized states (e.g., after the monomers have bonded together to form a polyurethane chain). It is to be understood that the monomers change in certain ways during polymerizing, and do not exist as separate molecules in the polymer.

[0031] Examples of other types of compounds that can be used in the formation of the cationic polyurethane polymer structures 20A, 20B, 20C, and 20D include various organic acid diols, C2-C20 aliphatic diols, glycidyl-containing diols to generate epoxy functional groups, functional amine groups derived from isocyanate groups that do not form a urethane linkage group, acid groups introduced from sulfonic acid or carboxylic acid diamines, or the like. These and other types of moieties can be included.

[0032] As mentioned, the cationic polyurethane may be prepared by the reaction of the isocyanate 24 and the polyol 26. As described hereinbelow, mono-alcohols may also be included in the reaction mixture, for example, to incorporate end cap groups EC. The reaction between the isocyanate 24 and the polyol 26 can also occur in the presence of a catalyst in acetone under reflux.

[0033] The isocyanate 24 may be a diisocyanate. Example diisocyanates include 2,2,4 (or 2, 4, 4)-trimethylhexane-1 ,6-diisocyanate (TMDI), hexamethylene diisocyanate (HDI), methylene diphenyl diisocyanate (MDI), isophorone diisocyanate (IPDI), and/or 1-lsocyanato-4-[(4-isocyanatocyclohexyl)methyl]cyclohexane (H12MDI), etc., or combinations thereof. Others can likewise be used alone, or in combination with these diisocyanates, or in combination with other diisocyanates.

[0034] Some examples of the polyol 26 are diols that include the aliphatic phosphonium salts. Aliphatic phosphonium salt-based diols may be desirable to incorporate the aliphatic phosphonium salts as pendant side chain groups PG in the cationic polymeric polymer. Aliphatic phosphonium salt-based diols may be prepared following the reaction scheme in equation 1. In this example, an alkyl phosphine (I) is reacted with a halogenated primary alcohol (II) at a high temperature, e.g., 100°C, to give a trialkylphosphonium salt-based alcohol (III).

Equation 1 where R is independently selected from a straight-chain or branched C1 to C5 alkyl; m can be from 1 to 18; and X can be any suitable counterion for the positively charged phosphorus atom, such as bromide, chloride, or iodide, sulfonate, p-toluenesulfonate, trifluoromethanesulfonate, for example.

[0035] In accordance with Equation 1 , several example trialkylphosphonium salt- based diols can be formed, as shown below:

[0036] Other polymeric diols may be used, for example, if it is not desirable to incorporate the aliphatic phosphonium salts 30 as pendent side chain groups PG. Example polymeric diols that can be used include polyether diols (or polyalkylene diols), such as polyethylene oxide diols, polypropoylene oxide diols (or a hybrid diol of polyethylene oxide and polypropylene oxide), or polytetrahydrofuran. Still other polymeric diois that can be used include polyester diols, such as polyadipic ester diol, polyisophthalic acid ester diol, polyphthalic acid ester diol; or polycarbonate diols, such as hexanediol based polycarbonate diol, pentanediol based polycarbonate diol, hybrid hexanediol and pentanediol based polycarbonate diol, etc. Combinations of polymeric diols can also be used.

[0037] In some examples, it may be desirable to incorporate the aliphatic phosphonium salts 39 as end cap groups EG in the cationic polymeric polymer. In these examples, mono-alcohols may be prepared following the reaction scheme in equation 2.

Equation 2 where R is independently selected from a straight-chain or branched C1 to C5 alkyl; m can be from 1 to 18; and X can be any suitable counterion for the positively charged phosphorus atom, such as bromide, chloride, or iodide, sulfonate, p-toluenesulfonate, trifluoromethanesulfonate, for example.

[0038] In accordance with Equation 2, several example aliphatic phosphonium salt- based mono-alcohols can be formed, as shown below:

[0039] As mentioned, the polyalkylene oxides 28 can be included, for example, as pendant side chain groups PG and/or as end cap groups EG. The polyalkylene oxides 28 can include polyethylene oxide (PEO), polypropylene oxide (PPO), or a hybrid of both PEO and PPO, which includes both types of monomeric units as a hybrid polyalkylene. In one example, the polyalkylene oxides 28 can be grafted or copolymerized during the formation of the cationic polyurethane. This provides polyalkylene oxide 28 moieties as pendent side chain groups PG along the polyurethane backbone. In another example, the polyalkylene oxides 28 can be added after the cationic polyurethane is synthesized. In this example, the polyalkylene oxides 28 are reacted with the end isocyanate groups of the cationic polyurethane. Either way, the polyalkylene oxide 28 moieties can have a number average molecular weight (Mn, g/mol or Daltons) from about 200 Mn to about 15,000 Mn, from about 500 Mn to about 15,000 Mn, from about 1,000 Mn to about 12,000 Mn, from about 2,000 Mn to about 10,000 Mn, or from about 3,000 Mn to about 8,000 Mn, which can be measured by gel permeation chromatography.

[0040] The cationic polyurethane polymer that is formed has an acid number ranging from 0 mg KOH/g to 10 mg KOH/g, or from 0 mg KOH/g to 5mg KOH/g. In one specific example, the acid number of the cationic polyurethane polymer is 0 mg KOH/g.

[0041] The cationic polyurethane polymer that is formed has an NCO/OH ratio ranging from 1.2 to 2.2. In another example, the cationic polyurethane polymer can be prepared with an NCO/OH ratio ranging from 1.4 to 2.0. In yet another example, the cationic polyurethane polymer can be prepared with an NCO/OH ratio from 1.6 to 1.8. As used herein, "NCO/OH ratio" refers to the mole ratio of NCO groups to OH groups in the monomers that react to form the polymer backbone.

[0042] The weight average molecular weight (Mw, g/mol or Daltons) of the cationic polyurethane polymer (which makes up the cationic polyurethane particles) can range from about 5,000 Mw to about 500,000 Mw, from about 10,000 Mw to about 400,000 Mw, from about 20,000 Mw to about 250,000 Mw, from about 10,000 Mw to about 200,000 Mw, or from about 50,000 Mw to about 500,000 Mw, as measured by gel permeation chromatography, for example.

[0043] As mentioned the cationic polyurethane polymer can be in form of particles. Reaction(s) may be performed to generate the cationic polyurethane polymer, and then additional processing may be performed in order to obtain cationic polyurethane particles. In one example method, a diisocyanate is reacted with a polyalkylene oxide diol in the presence of a catalyst in acetone (or another organic solvent) under reflux to generate a pre-polymer including isocyanate end groups with polyalkylene oxideside chains positioned along a polyurethane backbone. After the pre-polymer is formed, an alkyl phosphonium salt with a single hydroxyl group, such as a triphenylphosphonium- based alcohol, is reacted with the isocyanate end groups to form alkyl phosphonium salt end cap groups. In another example method, a diisocyanate is reacted with an aliphatic phosphonium salt in the form of a diol to a the pre-polymer including aliphatic phosphonium salt pendant side chain groups, and then the pre-polymer can be reacted with polyalkylene oxides associated with a single hydroxyl group to form the end cap groups. In either example, more water can be added, and the organic solvent can be removed by vacuum distillation, for example, to provide cationic polyurethane particles that are stable in water. As such, the cationic polyurethane, and particles thereof, are water dispersible.

[0044] The cationic polyurethane including the phosphonium salt is present in the fixer fluid 12 in an amount ranging from about 1 wt% to about 15 wt%, based on a total weight of the fixer fluid 12. In another example, the cationic polyurethane is present in the fixer fluid 12 in an amount ranging from about 2 wt% to about 10 wt%, based on a total weight of the fixer fluid 12. If the cationic polyurethane is incorporated into the aqueous fixer vehicle in the form of a water-based dispersion, it is to be understood that these weight percentages reflect the active weight percent of the cationic polyurethane.

[0045] In addition to the cationic polyurethane, the fixer fluid 12 includes an aqueous fixer vehicle. The aqueous fixer vehicle includes water and any of a cosolvent, a surfactant, an acid, or combinations thereof.

[0046] The aqueous fixer vehicle includes water. The water may be purified water or deionized water. The amount of water will depend on the other components in the fixer fluid 12. In some instances, the aqueous fixer vehicle includes water, without any other components. In other instances, the aqueous fixer vehicle includes water and one or more additives. Some suitable additives may include a co-solvent, a surfactant, an acid, or combinations thereof.

[0047] The aqueous fixer vehicle may include co-solvent(s). In an example, the cosolvent is a water soluble or water miscible organic co-solvent. Examples of cosolvents include alcohols, amides, esters, ketones, lactones, and ethers. In additional detail, the co-solvents may include aliphatic alcohols, aromatic alcohols, diols, glycol ethers, polyglycol ethers, lactams, formamides, acetamides, glycols, and long chain alcohols. Examples of such compounds include primary aliphatic alcohols, secondary aliphatic alcohols, 1,2-alcohols, 1 ,3-alcohols, 1 ,5-alcohols, ethylene glycol alkyl ethers, propylene glycol alkyl ethers (e.g., DOWANOL™ TPM or DOWANOL™ TPnB (from Dow Chemical), higher homologs (C₆-C₁₂) of polyethylene glycol alkyl ethers, N-alkyl caprolactams, unsubstituted caprolactams, both substituted and unsubstituted formamides, both substituted and unsubstituted acetamides, and the like. Some specific examples include dimethyl sulfoxide, sulfolane, propylene carbonate, ethylene carbonate, 2-pyrrolidone, 1-(2-hydroxyethyl)-2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexylpyrrolidone, and triethanolamine. Specific examples of alcohols may include ethanol, isopropyl alcohol, butyl alcohol, and benzyl alcohol. Other alcohols, such as polyhydric alcohols or derivatives thereof, may also be used. Examples of polyhydric alcohols may include ethylene glycol, diethylene glycol, propylene glycol, 2,2-dimethyl-1 ,3-propanediol, 2-ethyl-2-(hydroxymethyl)-1 ,3-propanediol, butylene glycol, triethylene glycol, 1 ,5-pentanediol, 1 ,2-hexanediol, 1 ,2-butanediol, 1,2,6- hexanetriol, glycerin, trimethylolpropane, and xylitol. Examples of polyhydric alcohol derivatives may include an ethylene oxide adduct of diglycerin. Some examples of the co-solvent also function as a humectant.

[0048] The co-solvent(s) may be present in the fixer fluid 12 in an amount ranging from about 4 wt% to about 30 wt% (based on the total weight of the fixer fluid 12). In an example, the total amount of co-solvent(s) present in the fixer fluid 12 is about 10 wt% (based on the total weight of the fixer fluid 12).

[0049] When included, the surfactant in the aqueous fixer vehicle may be any nonionic or cationic surfactant.

[0050] Examples of the non-ionic surfactant may include polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene glycerin fatty acid ester, polyglycerin fatty acid ester, polyoxyethylene alkylamine, polyoxyethylene fatty acid amide, alkylalkanolamide, polyethylene glycol polypropylene glycol block copolymer, acetylene glycol, and a polyoxyethylene adduct of acetylene glycol. Specific examples of the non-ionic surfactant may include polyoxyethylenenonyl phenylether, polyoxyethyleneoctyl phenylether, and polyoxyethylenedodecyl. Further examples of the non-ionic surfactant may include silicon surfactants such as a polysiloxane oxyethylene adduct; fluorine surfactants such as perfluoroalkylcarboxylate, perfluoroalkyl sulfonate, and oxyethyleneperfluoro alkylether; and biosurfactants such as spiculisporic acid, rhamnolipid, and lysolecithin.

[0051] In some examples, the aqueous fixer vehicle may include a silicone-free alkoxylated alcohol surfactant such as, for example, TEGO® Wet 510 (Evonik Degussa) and/or a self-emulsifiable wetting agent based on acetylenic diol chemistry, such as, for example, SURFYNOL® SE-F (Evonik Degussa). Other suitable commercially available surfactants include SURFYNOL® 465 (ethoxylatedacetylenic diol), SURFYNOL® 440 (an ethoxylated low-foam wetting agent) SURFYNOL® CT- 211 (now CARBOWET® GA-211 , non-ionic, alkylphenylethoxylate and solvent free), and SURFYNOL® 104 (non-ionic wetting agent based on acetylenic diol chemistry), (all of which are from Evonik Degussa); ZONYL® FSO (a.k.a. CAPSTONE®, which is a water-soluble, ethoxylated non-ionic fluorosurfactant from DuPont); TERGITOL® TMN-3 and TERGITOL® TMN-6 (both of which are branched secondary alcohol ethoxylate, non-ionic surfactants), and TERGITOL® 15-S-3, TERGITOL® 15-S-5, and TERGITOL® 15-S-7 (each of which is a secondary alcohol ethoxylate, non-ionic surfactant) (all of the TERGITOL® surfactants are available from The Dow Chemical Company); and BYK® 345, BYK® 346, BYK® 347, BYK® 348, BYK® 349 (each of which is a silicone surfactant) (all of which are available from BYK Chemie).

[0052] Examples of the cationic surfactant include quaternary ammonium salts, such as benzalkonium chloride, benzethonium chloride, methylbenzethonium chloride, cetalkonium chloride, cetylpyridinium chloride, cetrimonium, cetrimide, dofanium chloride, tetraethylammonium bromide, didecyldimethylammonium chloride, domiphen bromide, alkylbenzyldimethylammonium chlorides, distearyldimethylammonium chloride, diethyl ester dimethyl ammonium chloride, dipalmitoylethyl hydroxyethylmonium methosulfate, and ACCOSOFT® 808 (methyl (1) tallow amidoethyl (2) tallow imidazolinium methyl sulfate available from Stepan Company). Other examples of the cationic surfactant include amine oxides, such as lauryldimethylamine oxide, myristamine oxide, cocamine oxide, stearamine oxide, and cetamine oxide.

[0053] When included in the aqueous fixer vehicle, the surfactant may be present in an amount ranging from about 0.01 wt% active to about 5 wt% active, based on the total weight of the fixer fluid 12. In an example, the surfactant is present in an amount ranging from about 0.05 wt% active to about 3 wt% active, based on the total weight of the fixer fluid 12. In another example, the surfactant is present in an amount of about 0.3 wt% active, based on the total weight of the fixer fluid 12.

[0054] The fixer fluid 12 may also include an acid. The acid may be used, in part, to control the pH of the fixer fluid 12. The acid may be included in the fixer fluid 12 to achieve a desired pH (e.g., ranging from about 4 to less than 7) and/or to counteract any slight pH increase that may occur over time. In an example, the total amount of acid(s) in the fixer fluid 12 ranges from greater than 0 wt% to about 3 wt% (based on the total weight of the fixer fluid 12). Examples of suitable acids that may be used in the fixer fluid 12 includes diluted hydrochloric acid (10%) or succinic acid.

[0055] The fixer fluid 12 is also devoid of colorant. This means that a pigment and/or dye is not included in the fixer fluid 12.

[0056] Inkjet Ink

[0057] Examples of the inkjet ink 14 disclosed herein include a colorant, an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group, a polymeric UV absorber, and an aqueous ink vehicle. In some examples, the inkjet ink 14 consists of a colorant, an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group, a polymeric UV absorber, and an aqueous ink vehicle; and thus does not include any other components. The aqueous ink vehicle may include water, water and a co-solvent, or water, a co-solvent and one or more additives. Example additives include a humectant, a non-ionic or an anionic surfactant, an anti-kogation agent, an anti-microbial agent, a viscosity modifier, a pH adjuster, a sequestering agent, or combinations thereof. [0058] The colorant in the inkjet ink 14 is pigment, a dye, or combinations thereof. As used herein, the term “pigment” generally includes organic or inorganic pigment colorants, magnetic particles, aluminas, silicas, and/or other ceramics, or organo- metallics or other opaque particles. The present description primarily illustrates the use of pigment colorants, but it is to be understood that other pigments, such as organometallics, ferrites, ceramics, etc., may also be used.

[0059] In some examples, the colorant in the inkjet ink 14 is a black pigment, a cyan pigment, a yellow pigment, or a magenta pigment. In other examples, the colorant may be a white pigment, an orange pigment, a green pigment, or any other desirable color.

[0060] Specific examples of black pigment include carbon black pigments. An example of an organic black pigment includes aniline black, such as C.l. Pigment Black 1.

[0061] Specific examples of a cyan pigment may include C.l. Pigment Blue -1 , -2, - 3, -15, -15:1 , -15:2, -15:3, -15:4, -16, -22, and -60.

[0062] Specific examples of a yellow pigment may include C.l. Pigment Yellow -1 , - 2, -3, -12, -13, -14, -16, -17, -73, -74, -75, -83, -93, -95, -97, -98, -114, -128, -129, - 138, -151 , -154, and -180.

[0063] Specific examples of a magenta pigment may include C.l. Pigment Red -5, - 7, -12, -48, -48:1, -57, -112, -122, -123, -146, -168, -177, -184, -202, and C.l. Pigment Violet-19.

[0064] The colorant may be a white pigment, such as titanium dioxide, or other colored inorganic pigments such as zinc oxide and iron oxide.

[0065] Suitable pigments include the following, which are available from BASF Corp.: PALIOGEN® Orange, HELIOGEN® Blue L 6901 F, HELIOGEN® Blue NBD 7010, HELIOGEN® Blue K 7090, HELIOGEN® Blue L 7101F, PALIOGEN® Blue L 6470, HELIOGEN® Green K 8683, HELIOGEN® Green L 9140, CHROMOPHTAL® Yellow 3G, CHROMOPHTAL® Yellow GR, CHROMOPHTAL® Yellow 8G, IGRAZIN® Yellow 5GT, and IGRALITE® Rubine 4BL. The following pigments are available from Degussa Corp.: Color Black FWI, Color Black FW2, Color Black FW2V, Color Black 18, Color Black, FW200, Color Black 5150, Color Black S160, and Color Black 5170. The following black pigments are available from Cabot Corp.: REGAL® 400R, REGAL® 330R, REGAL® 660R, MOGUL® L, BLACK PEARLS® L, MONARCH® 1400, MONARCH® 1300, MONARCH® 1100, MONARCH® 1000, MONARCH® 900, MONARCH® 880, MONARCH® 800, and MONARCH® 700. The following pigments are available from Orion Engineered Carbons GMBH: PRINTEX® U, PRINTEX® V, PRINTEX® 140U, PRINTEX® 140V, PRINTEX® 35, Color Black FW 200, Color Black FW 2, Color Black FW 2V, Color Black FW 1, Color Black FW 18, Color Black S 160, Color Black S 170, Special Black 6, Special Black 5, Special Black 4A, and Special Black 4. The following pigment is available from DuPont: TI-PURE® R-101. The following pigments are available from Heubach: MONASTRAL® Magenta, MONASTRAL® Scarlet, MONASTRAL® Violet R, MONASTRAL® Red B, and MONASTRAL® Violet Maroon B. The following pigments are available from Clariant: DALAMAR® Yellow YT-858-D, Permanent Yellow GR, Permanent Yellow G, Permanent Yellow DHG, Permanent Yellow NCG-71 , Permanent Yellow GG, Hansa Yellow RA, Hansa Brilliant Yellow 5GX-02, Hansa Yellow-X, NOVOPERM® Yellow HR, NOVOPERM® Yellow FGL, Hansa Brilliant Yellow 10GX, Permanent Yellow G3R-01 , HOSTAPERM® Yellow H4G, HOSTAPERM® Yellow H3G, HOSTAPERM® Orange GR, HOSTAPERM® Scarlet GO, and Permanent Rubine F6B. The following pigments are available from Sun Chemical: QUINDO® Magenta, INDOFAST® Brilliant Scarlet, QUINDO® Red R6700, QUINDO® Red R6713, INDOFAST® Violet, L74-1357 Yellow, L75-1331 Yellow, L75-2577 Yellow, and LHD9303 Black. The following pigments are available from Birla Carbon: RAVEN® 7000, RAVEN® 5750, RAVEN® 5250, RAVEN® 5000 Ultra® II, RAVEN® 2000, RAVEN® 1500, RAVEN® 1250, RAVEN® 1200, RAVEN® 1190 Ultra®. RAVEN® 1170, RAVEN® 1255, RAVEN® 1080, and RAVEN® 1060. The following pigments are available from Mitsubishi Chemical Corp.: No. 25, No. 33, No. 40, No. 47, No. 52, No. 900, No. 2300, MCF-88, MA600, MA7, MA8, and MA100.

[0066] While several examples have been given herein, it is to be understood that any other pigment can be used that is useful in modifying the color of the inkjet ink 14. [0067] The pigment can be present in the inkjet ink 14 in an amount from about 0.5 wt% to about 15 wt% based on a total weight of the inkjet ink 14. In one example, the pigment can be present in an amount from about 1 wt% to about 12 wt%. In another example, the pigment can be present in an amount from about 5 wt% to about 10 wt%. [0068] In some examples, the colorant may be a dye. The dye (prior to being incorporated into the ink formulation), may be dispersed in water alone or in combination with an additional water soluble or water miscible co-solvent. It is to be understood however, that the liquid components of the dye dispersion become part of the ink vehicle in the inkjet ink 14.

[0069] The dye can be nonionic, anionic, or a mixture of nonionic and anionic dyes. The dye can be a hydrophilic anionic dye, a direct dye, a reactive dye, a polymer dye or an oil soluble dye. Specific examples of dyes that may be used include Sulforhodamine B, Acid Blue 113, Acid Blue 29, Acid Red 4, Rose Bengal, Acid Yellow 17, Acid Yellow 29, Acid Yellow 42, Acridine Yellow G, Acid Yellow 23, Acid Blue 9, Nitro Blue Tetrazolium Chloride Monohydrate or Nitro BT, Rhodamine 6G, Rhodamine 123, Rhodamine B, Rhodamine B Isocyanate, Safranine O, Azure B, and Azure B Eosinate, which are available from Sigma-Aldrich Chemical Company (St. Louis, Mo.). Examples of anionic, water-soluble dyes include Direct Yellow 132, Direct Blue 199, Magenta 377 (available from Ilford AG, Switzerland), alone or together with Acid Red 52. Examples of water-insoluble dyes include azo, xanthene, methine, polymethine, and anthraquinone dyes. Specific examples of water-insoluble dyes include ORASOL® Blue GN, ORASOL® Pink, and ORASOL® Yellow dyes available from BASF Corp. Black dyes may include Direct Black 154, Direct Black 168, Fast Black 2, Direct Black 171, Direct Black 19, Acid Black 1, Acid Black 191 , Mobay Black SP, and Acid Black 2.

[0070] In some examples, the dye may be present in an amount ranging from about 0.5 wt% active to about 15 wt% active based on a total weight of the inkjet ink 14. In one example, the dye may be present in an amount ranging from about 1 wt% active to about 10 wt% active. In another example, the dye may be present in an amount ranging from about 5 wt% active to about 10 wt% active.

[0071] The inkjet ink 14 also includes the UV light curable polyurethane binder, which includes a UV reactive group and an ionic stabilization group. [0072] The UV light curable polyurethane binder may be in the form of binder particles, which may have a D50 particle size ranging from about 20 nm to about 200 nm. It is to be understood that the UV light curable polyurethane binder and the corresponding binder particles are not the same as the cationic polyurethane and the corresponding cationic polyurethane particles present in the fixer fluid 12.

[0073] An example of the UV light curable polyurethane binder structure 32 is shown in Fig. 6. The UV light curable polyurethane binder structure 32 includes several chemical moieties, such as urethane linkage groups 22 (formed by the reaction of isocyanate groups 24 with any of a number of reactive polyols 26’ that may be present). Similar to Fig. 2 through Fig. 5, the polyol 26’ and the isocyanate groups 24 in Fig. 6 are shown schematically after polymerization. The UV light curable polyurethane binder structure 32 also includes a UV reactive group 34 and an ionic stabilization group 36. In the example shown Fig. 6, one UV reactive group 34, shown at R-i, and the ionic stabilization group 36, shown at R₄, are positioned at terminal ends of the UV light curable polyurethane binder 32, and the UV light curable polyurethane binder 32 further includes a second UV reactive group 34, shown at R₃, attached along a backbone of the UV light curable polyurethane binder 32. In this example, the polymer backbone is devoid of ionic stabilizing groups 36.

[0074] In the schematic structure 32, n can be any integer, for example, those ranging from 1 to 1,000. R_1, i.e., the UV reactive group 34 that is suitable as the end cap group EG, can be an organic group that includes an acrylate, a methacrylate, an acrylamide, a methacrylamide, a styrene, an allyl, or an amine. R₂ is an organic group that is part of the isocyanate 24. R₃, i.e., the UV reactive group 34 that is integrated along the polymer backbone, can be an organic group containing an acrylate, a methacrylate, an acrylamide, or a methacrylamide. R₄, i.e., the ionic stabilizing group 36, is an organic group that includes an acidic functional group or other ionic functional group that can stabilize the dispersion of the polyurethane binder 32 in water. R₅ can be hydrogen or an additional organic group. The term “organic group” refers to carbon-containing groups with from 1 to 20 carbon atoms, and can be straight chained, branched, alicyclic, aromatic, etc. Organic groups can be substituted with O, S, P, N, B, etc. [0075] In some examples, the UV light curable polyurethane binder structure 32 includes different end capping groups EG at each end of the polymer strand.

However, in other examples, the polymer strand can have two identical end cap groups EGs. As is described in more detail below, each of the end cap groups EG is added through a reaction with a terminal isocyanate during the formation of the polymer strands. As such, some of the stands may be represented by Fig. 6, with one UV reactive end group 34, EG (shown as R₁ and one ionic stabilizing end group 36, EG (shown as R₄); but other strands may have two UV reactive end groups 34, EG (e.g., R₁ at both ends) or two ionic stabilizing end groups 36, EG (e.g., R₄ at both ends). Generally, more than 50% of the UV light curable polyurethane binder strands that are generated have the UV reactive group 34, EG, R₃ at one end and the ionic stabilization group 36, EG, R₄ at the other end. Moreover, because these different stands are incorporated together as the binder particles, the pH stability of the binder particles is not deleteriously affected.

[0076] In an example, the polymer backbone of the UV light curable polyurethane binder structure 32 may be formed by polymerizing a diisocyanate and a reactive diol. The polymer backbone shown in Fig. 6 can be formed by reacting a diisocyanate having Formula 1 with a reactive diol having Formula 2:

Formula 1

Formula 2

[0077] Any one or more of the diisocyanates set forth herein for the cationic polyurethane 20A, 20B, 20C, 20D may be used to form the UV light curable polyurethane binder structure 32.

[0078] The reactive diol may have the general formula shown in Formula 2. This reactive diol includes R₃, which is the UV reactive group 34 that is ultimately integrated along the polymer backbone. This UV reactive group 34, R₃ is selected from the group consisting of an acrylate-containing diol, a methacrylate-containing diol, an acrylamide-containing diol, a methacrylamide-containing diol, or combination thereof. As used herein, “acrylate-containing diol” refers to a chemical compound that has two hydroxyl groups and an acrylate functional group. Similarly, “methacrylate-containing diols,” “acrylamide-containing diols,” and “methacrylamide-containing diols” refer to diol compounds that include methacrylate, acrylamide, and methacrylamide functional groups, respectively. These reactive functional groups can participate in UV curing through their double bonds. Thus, when the UV light curable polyurethane binder is cured, the double bonds in the acrylate, methacrylate, acrylamide, and/or methacrylamide groups can link together to form cross-linking between polymer strands.

[0079] Some examples of the reactive diol monomer with Formula 2 include:

[0080] Other examples of the reactive diol monomer are shown in Fig. 7. This reactive diol monomer includes R₆-R₁₅, which are independently selected from H and an alkyl group; UV reactive groups 34 selected from acrylate and methacrylate groups; and unit 38, which is a saturated hydrocarbyl moiety. In these reactive diol monomers, a, b, c, and d are each independently selected from an integer in the range of 1 to 6. [0081] Some examples of the reactive diol monomer of Fig. 7 include:

[0082] The end cap groups EG can be added to the polymer backbone by polymerizing a monofunctional monomer with a respective isocyanate group at each terminal ends of the polymer backbone. In some examples, two distinct end cap groups EG can be included in the polyurethane binder strands.

[0083] The first end cap group EG in the UV light curable polyurethane binder structure 32 can be the UV reactive group 34, R₃. As mentioned R₃ may be an acrylate, a methacrylate, an acrylamide, a methacrylamide, a styrene, an allyl, or an amine. Any of these may be monoalcohols, which include one hydroxyl group for reaction with a terminal isocyanate group. Some specific examples of the UV reactive group 34, R₃ include N-hydroxylethyl acrylate (HEA) (an acrylate), pentaerythritol triacrylate (PETA) (an acrylate), N-hydroxylethyl methacrylate (HEMA) (a methacrylate), glycerol 1,3-dimethylacrylate (HPBMA) (a methacrylate), N- hydroxylethyl acrylamide (HEAA) (an acrylamide), N-hydroxylethyl methacrylamide (HEAMA) (a methacrylamide), glycerol alpha, alpha-diallyl ether (GDAE) (an allyl), 4- diethanolaminomethyl styrene (a styrene), 4-(hydroxymethyl)styrene (a styrene), and 4-(2-Hydroxyethyl)styrene (a styrene).

[0084] The second end cap group EG in the UV light curable polyurethane binder structure 32 can be the ionic stabilizing group 36, R₄. The ionic stabilizing group 36 can be an acidic stabilizing group, such as a carboxylic acid group or a sulfonic acid group. It is to be understood that in the inkjet ink 14, the ionic stabilizing group 36 may be in acidic form or salt form, depending upon the pH.

[0085] Monomers used to introduce the ionic stabilizing group 36, R₄ include amino carboxylic acids or amino sulfonic acids. Some specific examples of amino sulfonic acids include taurine, 3-(cyclohexylamino)-1-propanesulfonic acid (CAPS), and 2- (cyclohexylamino)ethanesulfonic acid (CHES).

[0086] The UV light curable polyurethane binder that is formed has an acid number ranging from 20 mg KOH/g to 100 mg KOH/g, from 25 mg KOH/g to 80 mg KOH/g, or from 30 mg KOH/g to 60 mg KOH/g.

[0087] The UV light curable polyurethane binder that is formed has an NCO/OH ratio ranging from 1.2 to 10. In another example, the cationic polyurethane polymer can be prepared with an NCO/OH ratio ranging from 2 to 3 or from 4 to 6.

[0088] The UV light curable polyurethane binder that is formed has a double bond density ranging from 1.5 meq/g to 10 meq/g. In other examples, the UV light curable polyurethane binder can have a double bond density of 2 meq/g to 10 meq/g, 3 meq/g to 10 meq/g, or 4 meq/g to 10 meq/g. As used herein, "double bond density” refers to the number of millimoles of double bonds in 1 g of the polyurethane polymer by dry weight. [0089] The UV light curable polyurethane binder may have a minimum film forming temperature ranging from about -50°C to about 80°C, e.g., from about -30°C to about 60°C or from about -25°C to about 50°C.

[0090] The weight average molecular weight (Mw, g/mol or Daltons) of the cationic polyurethane polymer (which makes up the cationic polyurethane particles) can range from about 1 ,000 Mw to about 50,000 Mw, e.g., from about 2,000 Mw to about 25,000 Mw or from about 3,000 Mw to about 10,000 Mw, as measured by gel permeation chromatography, for example.

[0091] As mentioned, the UV light curable polyurethane binder can be in form of binder particles. Reaction(s) may be performed to generate the UV light curable polyurethane binder, and then additional processing may be performed in order to obtain binder particles. In one example method, a diisocyanate is reacted with a reactive diol in the presence of a catalyst in acetone (or another organic solvent) under reflux to generate a pre-polymer including isocyanate end groups with UV reactive group(s) positioned along a polyurethane backbone.

[0092] After the pre-polymer is formed, another UV reactive group, with a single hydroxyl group, is reacted with the isocyanate end groups to form UV reactive end cap groups 34, EG, R₃. This reaction is carried out such at least some of the pre-polymer strands are capped. For example, at least 10% of unreacted -N=C=O (isocyanate) groups are capped by this reaction. In some instances, 50% to 99%, for instance,

60% to 95% or 65% to 90% of unreacted -N=C=O groups are capped by this reaction. [0093] Once the first capping reaction is complete, a monomer with an ionic stabilization group, is reacted with any remaining isocyanate end groups to form the ionic stabilization end cap groups 36, EG, R₄. This reaction is carried out until completion.

[0094] More water can be added, and the organic solvent can be removed by vacuum distillation, for example, to provide binder particles that are stable in water. As such, the binder polyurethane, and particles thereof, are water dispersible.

[0095] The UV light curable polyurethane binder is present in the inkjet ink 14 in an amount ranging from about 0.1 wt% to about 30 wt%, based on a total weight of the inkjet ink 14. In another example, the UV light curable polyurethane binder is present in the inkjet ink 14 in an amount ranging from about 0.1 wt% to about 20 wt%, e.g., from about 0.1 wt% to about 10 wt%, from about 0.5 wt% to about 7 wt%, or from about 0.6 wt% to about 5 wt%, each of which is based on a total weight of the inkjet ink 14. If the light curable polyurethane polymer is incorporated into the aqueous ink vehicle in the form of a water-based dispersion, it is to be understood that these weight percentages reflect the active weight percent of the light curable polyurethane polymer.

[0096] Because the UV light curable polyurethane binder is reactive when exposed to UV light, the inkjet ink 14 is devoid of a photoinitiator.

[0097] The inkjet ink 14 also includes the UV absorber. The UV absorber may be any water soluble polymeric UV synergist.

[0098] In one example, the UV absorber includes a functionalized anthrone moiety (e.g., thioxanthrenone), a polyether chain, and an amide linkage or an ether linkage attaching one end of the polyether chain to the functionalized anthrone moiety.

[0099] An example of this UV absorber with an ether linkage is:

where Z is O, S, or NH; the polyether chain has n number of repeating monomer units, where n ranges from 1 to 200; and R₁₆, R₁₇ R₁₈, R₁₉, and R₂₀ are each independently selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted allyl group, a substituted or unsubstituted alkene or alkenyl group, a substituted or unsubstituted aryl group, a substituted or unsubstituted aralkyl group, a halogen atom, -NO₂, -O-Rd, -CO-Rd, -CO-O-Rd, -O-CO- Rd, -CO-NRdRe, -NRdRe, -NRd-CO-Re, -NRd-CO-O-Re, -NRd-CO-NReRf, -SRd, - SO-Rd, -SO2-Rd, -SO2-O-Rd, -SO₂NRdRe, and a perfluoroalkyl group. Rd, Re, and Rf are each independently selected from the group consisting of a hydrogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted allyl group, a substituted or unsubstituted alkene or alkenyl group, a substituted or unsubstituted aryl group, and a substituted or unsubstituted aralkyl group. Some examples of suitable alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, hexyl, etc. One example of a suitable alkene group is an ethylene group. Some examples of suitable aryl groups include phenyl, phenylmethyl, etc.

[0100] The UV absorber is present in the inkjet ink 14 in an amount ranging from about 0.1 wt% to about 10 wt%, based on a total weight of the inkjet ink 14. In another example, the UV absorber is present in the inkjet ink 14 in an amount ranging from about 0.5 wt% to about 8 wt%, e.g., from about 1 wt% to about 7 wt%, or from about 2 wt% to about 5 wt%, each of which is based on a total weight of the inkjet ink 14.

[0101] In addition to the UV light absorbing polyurethane and the UV absorber, the inkjet ink 14 includes an aqueous ink vehicle. The aqueous ink vehicle includes water and any of a co-solvent, a humectant, a non-ionic or an anionic surfactant, an anti- kogation agent, an anti-microbial agent, a viscosity modifier, a pH adjuster, a sequestering agent, and combinations thereof.

[0102] The aqueous ink vehicle includes water. The water may be purified water or deionized water. The amount of water will depend on the other components in the inkjet ink 14. In some instances, the aqueous ink vehicle includes water, without any other components. In other instances, the aqueous ink vehicle includes water and one or more of the additives set forth herein.

[0103] The aqueous ink vehicle may include co-solvent(s). Any of the co-solvents set forth herein for the fixer fluid 12 may be used in the inkjet ink 14. The amount of the co-solvent in the inkjet ink 14 may be up to 50 wt%, depending on the jetting architecture. As other example, the co-solvent(s) may range from about 1 wt% to about 30 wt%, or from about 5 wt% to about 20 wt% of the total weight of the inkjet ink 14.

[0104] The aqueous ink vehicle may include a humectant. An example of a suitable humectant is ethoxylated glycerin having the following formula:

in which the total of a+b+c ranges from about 5 to about 60, or in other examples, from about 20 to about 30. An example of the ethoxylated glycerin is LIPONIC® EG-1 (LEG-1 , glycereth-26, a+b+c=26, available from Lipo Chemicals). Other examples of suitable humectants include alcohols, for example, glycols such as 2,2’-thiodiethanol, glycerol, 1,3-propanediol, 1 ,5-pentanediol, polyethylene glycol, ethylene glycol, diethylene glycol, propylene glycol and/or tetraethylene glycol; pyrrolidones, such as 2- pyrrolidone, N-methyl-2-pyrrolidone, and/or N-methyl-2-oxazolidinone; and/or monoalcohols, such as n-propanol and/or iso-propanol. In an example, the humectant includes a mixture of alcohols. In another example, the humectant includes a mixture of 2,2'-thiodiethanol and a glycol, such as a polyalkylene glycol.

[0105] The humectant(s) may be present in an amount ranging from about 0.2 wt% to about 5 wt% (based on the total weight of the inkjet ink 14). In an example, the humectant is present in the inkjet ink 14 in an amount of about 1 wt%, based on the total weight of the inkjet ink 14.

[0106] The surfactant in the aqueous ink vehicle may be any example of the nonionic surfactant set forth herein for the fixer fluid 12. The surfactant in the aqueous ink vehicle may also or alternatively be an anionic surfactant. Examples of the anionic surfactant may include alkylbenzene sulfonate, alkylphenyl sulfonate, alkylnaphthalene sulfonate, higher fatty acid salt, sulfate ester salt of higher fatty acid ester, sulfonate of higher fatty acid ester, sulfate ester salt and sulfonate of higher alcohol ether, higher alkyl sulfosuccinate, polyoxyethylene alkylether carboxylate, polyoxyethylene alkylether sulfate, alkyl phosphate, and polyoxyethylene alkyl ether phosphate.

Specific examples of the anionic surfactant may include dodecylbenzenesulfonate, isopropylnaphthalenesulfonate, monobutylphenylphenol monosulfonate, monobutylbiphenyl sulfonate, monobutylbiphenylsul fonate, and dibutylphenylphenol disulfonate.

[0107] The amount of the non-ionic and/or anionic surfactant present in the inkjet ink 14 may be any amount set forth herein for the surfactant(s) in the fixer fluid 12 (except that the amount(s) are based on the total weight of the inkjet ink 14 instead of the fixer fluid 12).

[0108] An anti-kogation agent may also be included in the vehicle of the inkjet ink 14, for example, when the inkjet ink 14 is to be applied via a thermal inkjet printhead. Anti-kogation agent(s) is/are included to assist in preventing the buildup of kogation.

In some examples, the anti-kogation agent may improve the jettability of the inkjet ink 14.

[0109] Examples of suitable anti-kogation agents include oleth-3-phosphate (commercially available as CRODAFOS™ 03A or CRODAFOS™ N-3A) or dextran 500k. Other suitable examples of the anti-kogation agents include CRODAFOS™ HCE (phosphate-ester from Croda Int.), CRODAFOS® 010A (oleth-10-phosphate from Croda Int.), or DISPERSOGEN® LFH (polymeric dispersing agent with aromatic anchoring groups, acid form, anionic, from Clariant), etc. It is to be understood that any combination of the anti-kogation agents listed may be used.

[0110] The anti-kogation agent may be present in the inkjet ink 14 in an amount ranging from about 0.1 wt% active to about 1.5 wt% active, based on the total weight of inkjet ink 14. In an example, the anti-kogation agent is present in an amount of about 0.5 wt% active, based on the total weight of the inkjet ink 14.

[0111] The aqueous ink vehicle may also include anti-microbial agent(s). Antimicrobial agents are also known as biocides and/or fungicides. Examples of suitable anti-microbial agents include the NUOSEPT® (Ashland Inc.), UCARCIDE™ or KORDEK™ or ROCIMA™ (The Dow Chemical Company), PROXEL® (Arch Chemicals) series, ACTICIDE® B20 and ACTICIDE® M20 and ACTICIDE® MBL (blends of 2-methyl-4-isothiazolin-3-one (MIT), 1 ,2-benzisothiazolin-3-one (BIT) and Bronopol) (Thor Chemicals), AXIDE™ (Planet Chemical), NIPACIDE™ (Clariant), blends of 5-chloro-2-methyl-4-isothiazolin-3-one (CIT or CMIT) and MIT under the tradename KATHON™ (The Dow Chemical Company), and combinations thereof. [0112] In an example, the total amount of anti-microbial agent(s) in the inkjet ink 14 ranges from about 0.001 wt% active to about 0.05 wt% active (based on the total weight of the inkjet ink 14). In another example, the total amount of anti-microbial agent(s) in the inkjet ink 14 is about 0.04 wt% active (based on the total weight of the inkjet ink 14).

[0113] Any suitable viscosity modifier may also be added to the aqueous ink vehicle. In an example, the viscosity modifier is added in an amount up to 5 wt% active based on the total weight of the ink. The viscosity modifier may be used to achieve suitable jetting viscosity. Some examples viscosity modifiers include LUCANT™ Hydrocarbon Synthetic Fluid (commercially available from Lubrizol), maleic anhydride styrene copolymer (MSC), olefin copolymer (OCP), polyisobutylene (PIB), polymethacrylate (PMA), pour point depressants (PPD), styrene butadiene (SBR), and combinations thereof.

[0114] The aqueous ink vehicle may also include chelating agent/sequestering agent. In an example, the chelating agent is selected from the group consisting of methylglycinediacetic acid, trisodium salt; 4,5-dihydroxy-1 ,3-benzenedisulfonic acid disodium salt monohydrate; ethylenediaminetetraacetic acid (EDTA); hexamethylenediamine tetra(methylene phosphonic acid), potassium salt; and combinations thereof. Methylglycinediacetic acid, trisodium salt (Na3MGDA) is commercially available as TRILON® M from BASF Corp. 4,5-dihydroxy-1,3- benzenedisulfonic acid disodium salt monohydrate is commercially available as TIRON™ monohydrate. Hexamethylenediamine tetra(methylene phosphonic acid), potassium salt is commercially available as DEQUEST® 2054 from Italmatch Chemicals.

[0115] When included in the inkjet ink 14, the chelating agent is present in an amount greater than 0 wt% active and less than or equal to 0.5 wt% active based on the total weight of the inkjet ink 14. In an example, the chelating agent is present in an amount ranging from about 0.05 wt% active to about 0.2 wt% active based on the total weight of the inkjet ink 14.

[0116] The aqueous ink vehicle may also include a pH control agent. A pH control agent (or pH adjuster) may be included in the inkjet ink 14 to achieve a desired pH (e.g., 8.5) and/or to counteract any slight pH drop that may occur over time. In an example, the total amount of pH adjuster(s) in the inkjet ink 14 ranges from greater than 0 wt% to about 0.1 wt% (based on the total weight of the inkjet ink 14). In another example, the total amount of pH adjuster(s) in the inkjet ink 14 is about 0.03 wt% (based on the total weight of the inkjet ink 14).

[0117] Examples of suitable pH adjusters include metal hydroxide bases, such as potassium hydroxide (KOH), sodium hydroxide (NaOH), etc. In an example, the metal hydroxide base may be added to the inkjet ink 14 in an aqueous solution. In another example, the metal hydroxide base may be added to the inkjet ink 14 in an aqueous solution including 5 wt% of the metal hydroxide base (e.g., a 5 wt% potassium hydroxide aqueous solution).

[0118] Suitable pH ranges for examples of the inkjet ink 14 can be from pH 7 to pH 11 , from pH 7 to pH 10, from pH 7.2 to pH 10, from pH 7.5 to pH 10, from pH 8 to pH 10, 7 to pH 9, from pH 7.2 to pH 9, from pH 7.5 to pH 9, from pH 8 to pH 9, from 7 to pH 8.5, from pH 7.2 to pH 8.5, from pH 7.5 to pH 8.5, from pH 8 to pH 8.5, from 7 to pH 8, from pH 7.2 to pH 8, or from pH 7.5 to pH 8.

[0119] The UV light curable polyurethane binder and the binder particles thereof are pH stable in the inkjet ink 14. While the UV reactive groups 34 may be susceptible to hydrolysis in the basic ink conditions (resulting in a pH drop over time), the ionic stabilization group 36 can help to stabilize the UV light curable polyurethane binder and the particles thereof and reduce or prevent hydrolysis. CAPS and CHES may be particularly suitable for obtaining binder particles that are pH stable. The PU stability renders the ink stable, where the ink experiences a change of less than 1 pH unit after two weeks in accelerated shelf-life (ASL) conditions ASL refers to an experimental test designed to test the shelf-life of a composition in an accelerated time frame. In an example, ASL tests may be performed by placing a composition in a container open to air at a temperature of 50°C. It is assumed that each week under these conditions simulates six months of shelf-life time under normal storage conditions. [0120] Textile Fabric

[0121] The textile fabric 16 may be selected from the group consisting of polyester fabrics, polyester blend fabrics, cotton fabrics, cotton blend fabrics, nylon fabrics, nylon blend fabrics, silk fabrics, silk blend fabrics, wool fabrics, wool blend fabrics, and combinations thereof. In a further example, the textile fabric 16 is selected from the group consisting of cotton fabrics and cotton blend fabrics.

[0122] It is to be understood that organic textile fabrics and/or inorganic textile fabrics may be used for the textile fabric 16. Some types of fabrics that can be used include various fabrics of natural and/or synthetic fibers. It is to be understood that the polyester fabrics may be a polyester coated surface. The polyester blend fabrics may be blends of polyester and other materials (e.g., cotton, linen, etc.). In another example, the textile fabric 16 may be selected from nylons (polyamides) or other synthetic fabrics.

[0123] Example natural fiber fabrics that can be used include treated or untreated natural fabric textile substrates, e.g., wool, cotton, silk, linen, jute, flax, hemp, rayon fibers, thermoplastic aliphatic polymeric fibers derived from renewable resources (e.g. cornstarch, tapioca products, sugarcanes), etc. Example synthetic fibers used in the textile fabric/substrate 16 can include polymeric fibers such as nylon fibers, polyvinyl chloride (PVC) fibers, PVC-free fibers made of polyester, polyamide, polyimide, polyacrylic, polypropylene, polyethylene, polyurethane, polystyrene, polyaramid (e.g., KEVLAR®) polytetrafluoroethylene (PTFE) (TEFLON®) (both trademarks of Chemours), fiberglass, polytrimethylene, polycarbonate, polyethylene terephthalate, polyester terephthalate, polybutylene terephthalate, or a combination thereof. In an example, natural and synthetic fibers may be combined at ratios of 1:1, 1:2, 1:3, 1:4, 1 :5, 1:6, 1:7, 1:8, 1:9, 1:10, 1 :11, 1:12, 1:13, 1:14, 1:15, 1:16, 1 :17, 1:18, 1 :19, 1:20, or vice versa. In some examples, the fiber can be a modified fiber from the above-listed polymers. The term “modified fiber” refers to one or both of the polymeric fiber and the fabric as a whole having undergone a chemical or physical process such as, but not limited to, copolymerization with monomers of other polymers, a chemical grafting reaction to contact a chemical functional group with one or both the polymeric fiber and a surface of the fabric, a plasma treatment, a solvent treatment, acid etching, or a biological treatment, an enzyme treatment, or antimicrobial treatment to prevent biological degradation.

[0124] In addition, the textile fabric 16 can contain additives, such as a colorant (e.g., pigments, dyes, and tints), an antistatic agent, a brightening agent, a nucleating agent, an antioxidant, a UV stabilizer, a filler, and/or a lubricant, for example.

[0125] It is to be understood that the terms “textile fabric” or “fabric substrate” do not include materials commonly known as any kind of paper (even though paper can include multiple types of natural and synthetic fibers or mixtures of both types of fibers). Fabric substrates can include textiles in filament form, textiles in the form of fabric material, or textiles in the form of fabric that has been crafted into finished articles (e.g., clothing, blankets, tablecloths, napkins, towels, bedding material, curtains, carpet, handbags, shoes, banners, signs, flags, etc.). In some examples, the fabric substrate can have a woven, knitted, non-woven, or tufted fabric structure. In one example, the fabric substrate can be a woven fabric where warp yarns and weft yarns can be mutually positioned at an angle of about 90°. This woven fabric can include fabric with a plain weave structure, fabric with twill weave structure where the twill weave produces diagonal lines on a face of the fabric, or a satin weave. In another example, the fabric substrate can be a knitted fabric with a loop structure. The loop structure can be a warp-knit fabric, a weft-knit fabric, or a combination thereof. A warp-knit fabric refers to every loop in a fabric structure that can be formed from a separate yarn mainly introduced in a longitudinal fabric direction. A weft-knit fabric refers to loops of one row of fabric that can be formed from the same yarn. In a further example, the fabric substrate can be a non-woven fabric. For example, the non-woven fabric can be a flexible fabric that can include a plurality of fibers or filaments that are one or both bonded together and interlocked together by a chemical treatment process (e.g., a solvent treatment), a mechanical treatment process (e.g., embossing), a thermal treatment process, or a combination of multiple processes.

[0126] In one example, the textile fabric 16 can have a basis weight ranging from 10 gsm to 500 gsm. In another example, the textile fabric 16 can have a basis weight ranging from 50 gsm to 400 gsm. In other examples, the textile fabric 16 can have a basis weight ranging from 100 gsm to 300 gsm, from 75 gsm to 250 gsm, from 125 gsm to 300 gsm, or from 150 gsm to 350 gsm.

[0127] Printing Method and System

[0128] Fig. 8 depicts an example of the printing method 100. The method 100 includes applying a fixer fluid to a textile fabric, the fixer fluid including a cationic polyurethane including a phosphonium salt and an aqueous fixer vehicle (reference numeral 102); applying an inkjet ink to the textile fabric, the inkjet ink including a colorant, an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group, a polymeric UV absorber; and an aqueous ink vehicle (reference numeral 104); and exposing the textile fabric, having the fixer fluid and the inkjet ink thereon, to UV light from a UV light source for a total exposure time of 30 seconds or less (reference numeral 106).

[0129] As used herein, the phrase “total exposure time" refers to the total time that the textile fabric 16 having the fixer fluid 12 and the inkjet ink 14 printed thereon is exposed to the emission wavelength. In some examples, the total exposure time may take place during a single event where the light source is turned on (i.e., light source on event). In other examples, the total exposure time may take place over a series of light source on events that are shorter in duration than the total exposure time and whose sum equals the total exposure time. As such, the exposing of the textile fabric 16 to the UV light may involve intermittent light source on events and light source off events, wherein each light source on event is a fraction of the total exposure time. In some examples, light source on events may be separated by light source off events, during which the light source is turned off and the fabric is not exposed to the emission wavelength. In these examples, the total time to achieve pigment fixation is longer than the total exposure time due to the time periods when the light source is off. However, in these examples, the total exposure time is still 30 seconds or less because the textile fabric 16 is not exposure to the light emission during the off events. [0130] It is to be understood that any example of the fixer fluid 12 may be used in the examples of the method 100. In some examples, the fixer fluid 12 may be applied digitally using inkjet technology. Any suitable inkjet applicator, such as a thermal inkjet cartridge/printhead, a piezoelectric cartridge/printhead, or a continuous inkjet cartridge/printhead, may eject the fixer fluid 12 in a single pass or in multiple passes. As an example of single pass printing, the cartridge(s) of an inkjet printer deposit the desired amount of the fixer fluid 12 during the same pass of the cartridge(s) across the textile fabric 16. In other examples, the cartridge(s) of an inkjet printer deposit the desired amount of the fixer fluid 12 over several passes of the cartridge(s) across the textile fabric 16.

[0131] It is also to be understood that any example of the inkjet ink 14 may be used in the examples of the method 100. The inkjet ink 14 may be ejected onto the textile fabric 16 using inkjet technology. Any of the inkjet applicators may eject the inkjet ink 14 in a single pass or in multiple passes (as described herein).

[0132] The UV light source used in the method 100 may be selected from the group consisting of a UV light emitting diode (LED), a UV lamp, and a UV laser. In one example, the UV light source is a light emitting diode that emits emission wavelengths ranging from about 1365 nm to about 400 nm. In another example, the UV light source is a narrow wavelength light emitting diode having an emission wavelength ranging from about 365 nm to about 395 nm. In still another example, the UV light source is a 395 nm light emitting diode.

[0133] The method 100 may also include setting the UV light source so that the energy density applied during the exposing ranges from about 2 J/cm² to about 28 J/cm².

[0134] When exposed to the UV radiation, the double bonds of the UV reactive groups 34 of the UV light curable polyurethane binder can link together to form cross- linking between polymer strands. These cross-linked polyurethane stands form a durable polyurethane structure. These cross-linked polyurethane strands can also trap the pigments from the inkjet ink 14. The cationic polyurethane in the fixer fluid 12 can also interact with the pigment and/or the UV light curable polyurethane binder in the inkjet ink 14 to fix the components to the textile fabric 16. The interactions of the polyurethanes and the pigment helps fix the pigment and improve the optical density, and also improve the durability of the resulting print. [0135] In examples of the method 100, the desired amount of the fixer fluid 12 and of the inkjet ink 14 are deposited in a single pass or in multiple passes, and then UV curing occurs. In these examples, the application of the fixer fluid 12 occurs prior to the application of the inkjet ink 14, the application of the inkjet ink 14 occurs prior to the UV curing, and the UV curing involves intermittent light source on events and light source off events. During light source on events, the UV light source is turned on, and during light source off events, the UV light source is turned off. The intermittent on and off events can effectively cure the UV light curable polyurethane binder in the printed ink without overheating the textile fabric 16. The light source on events may range from about 0.1 second to about 5 seconds. Since the total exposure time is 30 seconds or less, the number of light source on events will depend upon the duration of each on event and the desired total exposure time. For example, when each light source on event is 1 second long, a total of thirty light source on events may take place so that the total exposure time is 30 seconds. For another example, a single on event may be 2.5 seconds or 5 seconds. The light source off events may be long enough to allow the textile fabric 16 to cool.

[0136] In the example method 100, the inkjet ink 14 is printed onto the printed fixer fluid 12 while the fixer fluid 12 is wet. Wet on wet printing may be desirable because less fixer fluid 12 may be applied during this process, because it is desirable for the cationic polyurethane to interact with the curing UV light curable polyurethane binder strands, and because the printing workflow may be simplified without the additional drying. In an example of wet on wet printing, the inkjet ink 14 is printed onto the printed fixer fluid 12 within a period of time ranging from about 0.01 second to about 30 seconds after the fixer fluid 12 is printed. In further examples, the inkjet ink 14 is printed onto the previously applied fixer fluid 12 within a period of time ranging from about 0.1 second to about 20 seconds; or from about 0.2 second to about 10 seconds; or from about 0.2 second to about 5 seconds after the fixer fluid 12 is printed. Wet on wet printing may be accomplished in a single pass or each fluid 12/ink 14 may be deposited in multiple passes. [0137] Referring now to Figs. 9A and 9B, schematic diagrams of two different printing systems 40, 40’ including inkjet applicators 42, 44 or 42’, 44’ and a UV light source 46.

[0138] The example system 40 shown in Fig. 9A illustrates a system for single pass printing and selective UV curing, and the example system 40’ shown in Fig. 9B illustrates a system for multiple pass printing and single or multiple pass selective UV curing.

[0139] In the example system 40 shown in Fig. 8A, the textile fabric/ fabric substrate 16 be transported through the printing system 40 along the path shown by the arrow 48. In this example, pagewide applicators 42, 44 (i.e., each including a series of printheads extending the width of the textile fabric 16) is in a fixed position relative to the textile fabric 16. When the textile fabric 16 is moved relative to the pagewide applicator 42, the fixer fluid 12 is inkjet printed directly onto the textile fabric 16. When the textile fabric 16 is moved relative to the pagewide applicator 42, a single color or multiple colors of the inkjet ink 14 is/are inkjet printed directly onto the textile fabric 16. The color(s), amount(s), and/or arrangement of the fixer fluid 12 and the inkjet ink 14 that are applied depend upon the digital image from which the print 50 is being generated. In this example, after the fixer fluid 12 and the inkjet ink 14 are dispensed, the UV light source 46 is operated to expose the textile fabric 16 to UV radiation for a total exposure time of 30 seconds or less. UV radiation exposure may take place in one light source on event or in intermittent light source on events (where the UV light source 46 is turned on an off while the textile fabric 16 is positioned relative to the light source 46. In this single pass printing system 40, printing and selective UV curing are each performed as the textile fabric 16 is within proximity of the respective printer component.

[0140] The single pass printing and selective UV curing performed using the printing system 40 results in the printed article 50 on the textile fabric 16.

[0141] In the example system 40’ shown in Fig. 9B, the textile fabric/ fabric substrate 16 may be transported through the printing system 40’ along the path shown by the arrow 48’. In this example, the inkjet applicators 42’, 44’ are attached to a carriage (not shown) or other mechanism that moves the inkjet applicators 42’, 44’ relative to the textile fabric 16 in the path shown by the arrow 52. When the inkjet applicator 42’ is activated and moved relative to the textile fabric 16, the fixer fluid 12 is inkjet printed directly onto textile fabric 16. When the inkjet applicator 44’ is activated and moved relative to the textile fabric 16, a single color or multiple colors of the inkjet ink 14 is/are inkjet printed directly onto textile fabric 16. The color(s), amount(s), and/or arrangement of the fixer fluid 12 and the inkjet ink 14 that are applied depend upon the digital image from which the print 50 is being generated. In this example, the total desired amount of fixer fluid 12 and inkjet ink 14 that is dispensed takes place over multiple passes of each of the inkjet applicators 42’, 44’.

[0142] Exposure to the UV radiation occurs after the multiple printing passes. In this example, the UV light source 46’ is attached to a carriage (not shown) or other mechanism that moves the UV light source 46’ relative to the textile fabric 16 in the path shown by the arrow 52. As discussed in reference to the method 100, the total exposure time is 30 seconds or less, whether exposure takes place in a single pass or multiple passes.

[0143] The multiple pass printing and single or multiple pass selective UV curing performed using the printing system 40’ results in the printed article 50 on the textile fabric 16.

[0144] To further illustrate the present disclosure, examples are given herein. It is to be understood that these examples are provided for illustrative purposes and are not to be construed as limiting the scope of the present disclosure.

EXAMPLES

[0145] An example fixer fluid (Ex. FF 1), a comparative fixer fluid (Comp. Ex. FF 2), an example magenta ink (Ex. Ink M), two different comparative example magenta inks (Comp. Ex. Ink M1 and Comp. Ex. Ink M2), an example black ink (Ex. Ink K), two different comparative example black inks (Comp. Ex. Ink K1 and Comp. Ex. Ink K2) were prepared.

[0146] Preparation of Cationic Polyurethane

[0147] Ex. FF 1 was prepared with an example of the cationic polyurethane disclosed herein. The cationic polyurethane was prepared as follows. [0148] First, 2-hydroxyethyltributylphosphonium chloride was prepared (as the phosphonium salt). A 500 ml 4-necked flask equipped with a mechanical stirrer, a thermometer, a dropping funnel, and a condenser was sufficiently purged with nitrogen, and about 150.0 g of tri-n-butylphosphine was added. At 80°C, about 62.7 g of 2-chloroethanol was added dropwise over 30 minutes, and the solution turned into white and cloudy. Then, the solution was continued to heat to 100°C for 2 days under nitrogen and stirring. The reaction solution was an extremely viscous colorless and transparent liquid. The presence of unreacted trialklphopshine was tested using carbon disulphide, but trialkylphosphine was not detected. The solution was concentrated using an evaporator and then dried with a vacuum pump to give about

206.4 g of a colorless and transparent viscous liquid.

[0149] The 2-hydroxyethyltributylphosphonium chloride was then used in the preparation of the cationic polyurethane. About 24.9 g of YMER™ N-120 (from Perstorp, molecular weight 1000), about 25.2 g of isophorone disisocyanate (IPDI), and about 64 g of acetone were mixed in a 500 ml of 4-neck round bottom flask. A mechanical stirrer with glass rod and a polytetrafluoroethylene (PTFE) blade was attached. A condenser was attached. The flask was immersed in a constant temperature bath at 75°C. The system was kept under a drying tube. Three drops of bismuth catalyst (REAXIS™ C3203) was added to initiate the polymerization. Polymerization was continued for 3 hours at 75°C. About 0.5 g of pre-polymer was withdrawn for final % NCO titration. The measured NCO value was 14.75%. The theoretical % NCO should be 14.81%.

[0150] About 49.9 g of the 2-hydroxylethyltributylphosphonium chloride (3, TBPHECI) in 20 ml of acetone was added to the pre-polymer over 10 minutes. After 60 minutes, the polymerization temperature was reduced to 50°C and then about

259.4 g of deionized (Dl) water was added over 20 minutes. The solution became milky and white color and the milky dispersion was continued to stir for overnight at room temperature. The cationic polyurethane dispersion was filtered through 400 mesh stainless sieve. Acetone was removed with rotorvap at 50°C (added 2 drops (20 mg) BYK-011 de-foaming agent to control foaming). The final cationic polyurethane dispersion was filtered through fiber glass filter paper. The D50 particle size measured by Malvern Zetasizer was 307.1 nm. The pH was 8.0. The solid content was 33.47%. [0151] Preparation of UV Light Curable Polyurethane Binder [0152] Ex. Ink M and Ex. Ink K were prepared with an example of the UV light curable polyurethane binder disclosed herein. The UV light curable polyurethane binder was prepared as follows.

[0153] About 22.5 g of bisphenol A glycerolate (1 glycerol/phenol) diacrylate (BGDA), about 0.2 g of 4-methoxyphenol (MEHQ), about 36.5 g of 4,4’-methylene dicyclohexyl diisocyanate (H12MDI) and about 30 g of acetone were mixed in a 500 ml 4-neck round bottom flask. A mechanical stirrer with glass rod and Teflon blade was attached. A condenser was attached. The flask was immersed in a constant temperature bath at 60°C. The system was kept under a drying tube. 3 drops of dibutyltin dilaurate (DBTDL) was added to initiate the polymerization. Polymerization was continued for 3 hours at 60°C. About 0.5 g samples of the pre-polymer were withdrawn for % NCO titration to confirm the reaction.

[0154] About 26.5 g of glycerol 1 ,3-dimethylacrylate (HPBMA), about 0.3 g of MEHQ, and about 19 g of acetone were mixed in a beaker and added to the reactor over 30 seconds. About 9 g of acetone was used to rinse off the residual monomers on the beaker and was added to the reactor. The polymerization was continued 3 hours at 60°C. The polymerization temperature was reduced to 40°C. About 14.4 g of 2-(cyclohexylamino)ethansesullfonic acid (CHES), about 5.9 g of 50% NaOH, and about 38.1 g of deionized water were mixed in a beaker until CHES was completely dissolved. The CHES solution was added to the pre-polymer solution at 40°C with vigorous stirring over 1-3 minutes. The solution became viscous and slight hazy. Stirring was continued for 30 minutes at 40°C. The mixture became clear and viscous after 15 to 20 minutes at 40°C. About 187.6 g of cold Dl water was added to the polymer mixture over 1 to 3 minutes with good agitation to form the UV light curable polyurethane binder dispersion. The agitation was continued for 60 minutes at 40°C. The UV light curable polyurethane binder dispersion was filtered through 400 mesh stainless sieve. Acetone was removed with rotorvap at 50°C (added 2 drops (20mg) BYK-011 de-foaming agent to control foaming). The final UV light curable polyurethane binder dispersion was filtered through fiber glass filter paper. The D50 particle size measured by Malvern Zetasizer was 21.93 nm. The pH was 87.0. The solid content was 27.22%.

[0155] Preparation of UV Absorber

[0156] All of the example inks were prepared with an example of the UV absorber. The UV absorber was prepared as follows.

[0157] First, chloro mono-methyl polyethylene glycol ether 550 was prepared. A mixture of mono-methyl polyethylene glycol ether 550 (about 100 grams), thionyl chloride (about 60 grams), and about 0.1 grams of N-dimetthylformamide (DMF) was heated and refluxed for 5 hours. After cooling down to room temperature, 20 ml of methanol was added slowly to the solution and stirred for 1 hour. Then, the methanol and unreacted thionyl chloride were removed by vacuum to give the desired chloro mono-methyl polyethylene glycohol ether 550 (100 grams, 97%).

[0158] A mixture of 2-hydroxythioxanthone (about 28.5 g), chloro mono-methyl polyethylene glycol ether 550 (about 71.1 g) and cesium carbonate (about 40.7 g) in 100 ml of dimethylformamide (DMF) was heated and refluxed for 2 hours. Then, DMF was removed by distillation to give a residue, which was further purified by flash chromatography, giving rise to the desired mono-(2-oxythioxanthone) derivative of polyethylene glycol (76 g, 80% of the yield).

[0159] Preparation of Non-UV-Reactive Polyurethane Binder

[0160] Comp. Ex. Inks M1 and M2 and Comp. Ex. Inks K1 and K2 were prepared with non-UV-reactive polyurethane binders. The non-UV-reactive polyurethane binders were prepared as follows.

[0161] Non-UV-reactive polyurethane binder A

[0162] About 72.6 g of polyester polyol (Stephanol PC-1015-55), and about 20.6 g of isophorone diisocyanate (IPDI) in about 80 g of acetone were mixed in a 500 ml 4- neck round bottom flask. A mechanical stirrer with glass rod and PTFE blade was attached. A condenser was attached. The flask was immersed in a constant temperature bath at 75°C. The system was kept under a drying tube. 3 drops of dibutyltin dilaurate (DBTDL) was added to initiate the polymerization. Polymerization was continued for 6 hours at 75°C. About 0.5 g samples were withdrawn for % NCO titration to confirm the reaction. The measured NCO value was 5.10 %. Theoretical % NCO should be 5.13%.

[0163] The polymerization temperature was reduced to 50°C. About 3.8 g of 2,2,4 (or 2, 4, 4)-trimethylhexane-1 ,6-diamine (TMD), about 5.9 g of sodium aminoalklysulphonate (A-95, 50% in water) and about 14.8 g of deionized water were mixed in a beaker until TMD and A-95 were completely dissolved. The TMD and A-95 solution was added to the pre-polymer solution at 50°C with vigorous stirring over 5 minutes. The solution became viscous and slight hazy. Stirring was continued for about 30 minutes at 50°C. Then, about 201.7 g of cold deionized water was added to polymer mixture in a 4-neck round bottom flask over 10 minutes with good agitation to form the non-UV-reactive polyurethane binder A dispersion. The agitation was continued for 60 minutes at 50°C. The non-UV-reactive polyurethane binder A dispersion was filtered through 400 mesh stainless sieve. Acetone was removed with rotorvap at 50°C (added 2 drops (20mg) BYK-011 de-foaming agent to control foaming). The final non-UV-reactive polyurethane binder A dispersion was filtered through fiber glass filter paper. The D50 particle size measured by Malvern Zetasizer is 156.8 nm. The pH was 7.0. The solid content was 34.5%. DLN-SD - can you provide this synthesis?

[0164] Non-UV-reactive polyurethane binder B

[0165] Non-UV reactive polyurethane binder B was the commercially available IMPRANIL® DLN-SD (from Covestro AG). This is an anionic aliphatic polyester- polyurethane.

[0166] Formulations

[0167] The formulations for the example fixer fluid (Ex. FF 1) and the comparative fixer fluid (Comp. Ex. FF 2) are shown in Table 1. The comparative example fixer fluid included a multi-valent calcium salt instead of the cationic polyurethane.

[0168] The formulations for the example magenta ink (Ex. Ink M) and the two different comparative example magenta inks (Comp. Ex. Ink M1 and Comp. Ex. Ink M2) are shown in Table 2, and the formulation for the example black ink (Ex. Ink K) and the two different comparative example black inks (Comp. Ex. Ink K1 and Comp. Ex. Ink KM2) are shown in Table 3. The comparative inks included one of the non-UV- reactive polyurethane binders instead of the UV light curable polyurethane binder. [0169] The weight percentages in Tables 1 through 3 represent active amounts of the particular components, unless otherwise stated.

TABLE 1 - Fixer Fluids

TABLE 2 - Magenta Inks

TABLE 3 - Black Inks

[0170] Print Generation

[0171] The example and comparative example fixer fluids and example and comparative example magenta and black inks were printed on different textile fabrics in different combinations. The fixer fluids were thermally inkjet printed at 1.5 dpp (drop per pixel) and the inkjet inks were thermally inkjet printed at 3 dpp. The textile fabrics were T-shirt media: Pakistan roll #1 (50:50 cotton/polyester blend, 175 GSM, knit), Pakistan roll # 4 (100% cotton, 150 GSM, knit), and Gildan 780 (100% cotton).

[0172] Some of the prints were exposed to thermal heating conditions, and some of the prints were exposed to UV curing conditions. For thermal heating, a heat press alone was used, and the prints were exposed to 150°C for 3 minutes. For UV curing, a 395 nm light emitting diode (Hereaus lamp) was used. When operated at 50% power, the light source emitted 6.62 W/cm². 0.5 second pulses were used, and the curing time varied. [0173] Optical Density

[0174] The initial optical density (initial OD) of print (after heating or curing) was measured. Then, the prints washed 5 times in a Kenmore 90 Series Washer (Model 110.28922791) with warm water (at about 40°C) and detergent. Each print was allowed to air dry between each wash. Then, the optical density (OD after 5 washes) of each print was measured, and the percent change in optical density (%D OD) was calculated for print. A smaller change in optical density indicates that the color of the print has less fading.

[0175] Washfastness

[0176] The prints were also tested for washfastness. The L^*a^*b^* values of a color (e.g., cyan, magenta, yellow, black, red, green, blue, white) before and after the 5 washes were measured. L* is lightness, a* is the color channel for color opponents green-red, and b* is the color channel for color opponents blue-yellow. The color change was then calculated using both the CIEDE1976 color-difference formula (Tables 4 and 5) and the CIEDE2000 color-difference formula (Tables 6 and 7). [0177] The CIEDE1976 color-difference formula is based on the CIELAB color space. Given a pair of color values in CIELAB space L*₁ ,a^* ₁,b^*1 and L*₂,a*₂,b*₂, the CIEDE1976 color difference between them is as follows:

It is noted that ΔE₇₆is the commonly accepted notation for CIEDE1976.

[0178] The CIEDE2000 color-difference formula is based on the CIELAB color space. Given a pair of color values in CIELAB space L*₁ ,a^* ₁,b^*1 and L*₂,a*₂,b*₂, the CIEDE2000 color difference between them is as follows:

It is noted that ΔE₀₀is the commonly accepted notation for CIEDE2000. With either calculation, a smaller change in ΔE indicates that the print is more durable. [0179] Results

[0180] Table 4 illustrates the optical density and washfastness results for example and comparative example prints on Pakistan roll #1 using no fixer fluid, Ex. FF 1, or Comp. Ex. FF 2 with Ex. Ink M, Comp. Ex. Ink M1 , or Comp. Ex, Ink M2, and one of the heating or UV curing conditions. The UV curing time in Table 4 represents the total exposure time using 0.5 second pulses. The prints are identified by the fixer and ink and the heating/curing condition that was used.

TABLE 4 - Magenta Prints and Results

[0181] The results for Comp. Prints 1 and 2 illustrate that without any fixer fluid, the non-reactive binder based magenta inks (Comp. Ink M2 and Comp. Ink M1) resulted in average wash durability (ΔE around 13) with heating at 150°C for 3 minutes.

[0182] When the salt-based Comp. Ex. FF 2 was used with the non-reactive binder based magenta inks (Comp. Ink M2 or Comp. Ink M1) (see Comp. Prints 3 and 4) and heating at 150°C for 3 minutes, the wash durability became much worse with DE around 22 to 26. Similarly, Comp. Print 5, which was printed with Comp. Ex. FF 2 and the reactive binder example magenta ink (Ex. Ink M), exhibited poor wash durability with ΔE around 24. The salt fixing agent in Comp. Ex. FF 2 is completely water soluble, which may be contributing to the poor washfastness.

[0183] With UV LED curing conditions, the prints generated with Comp. Ex. FF 2 were just as bad as those exposed to thermal heating, or worse. For example, Comp. Prints 6 and 7, which were printed with Comp. Ex. FF 2 and the non-reactive binder based magenta inks (Comp. Ink M2 and Comp. Ink M1) had very poor wash durability ΔE over 40. Comp. Print 8, which was printed with Comp. Ex. FF 2 and the reactive binder example magenta ink (Ex. Ink M) and was exposed to UV curing, exhibited better durability, with ΔE around 10. At the same LED curing condition, Ex. Prints 9 and 10 (printed with the cationic polyurethane based fixer fluid (Ex. FF 1) and the reactive binder example magenta ink (Ex. Ink M)) exhibited improved wash durability, with ΔE of 5.0 with just 2.5 seconds of LED curing, or ΔE of 3.1 with 5 seconds of LED curing. The dispersability of the cationic polymeric fixer may desirably impact wash durability.

[0184] Table 5 illustrates the optical density and washfastness results for example and comparative example prints on Pakistan roll #1 using no fixer fluid, Ex. FF 1 , or Comp. Ex. FF 2 with Ex. Ink K, Comp. Ex. Ink K1 , or Comp. Ex, Ink K2, and one of the heating or UV curing conditions. The UV curing time in Table 5 represents the total exposure time using 0.5 second pulses. The prints are identified by the fixer and ink and the heating/curing condition that was used. TABLE 5 - Black Prints and Results

[0185] The results for Comp. Prints 11 and 12 illustrate that without any fixer fluid, the non-reactive binder based black inks (Comp. Ink K2 and Comp. Ink K1) resulted in average wash durability (ΔE around 15) with heating at 150°C for 3 minutes.

[0186] When the salt-based Comp. Ex. FF 2 was used with the non-reactive binder based black inks (Comp. Ink K2 or Comp. Ink K1) (see Comp. Prints 13 and 14) and heating at 150°C for 3 minutes, the wash durability became much worse with DE around 26 to 33. Similarly, Comp. Print 15, which was printed with Comp. Ex. FF 2 and the reactive binder example black ink (Ex. Ink K), exhibited average wash durability with ΔE around 15.

[0187] With UV LED curing conditions, the prints generated with Comp. Ex. FF 2 were just as bad as those exposed to thermal heating, or worse. For example, Comp. Prints 16 and 17, which were printed with Comp. Ex. FF 2 and the non-reactive binder based black inks (Comp. Ink K2 and Comp. Ink K1) had poor wash durability ΔE ranging from 26 to 30. Comp. Print 18, which was printed with Comp. Ex. FF 2 and the reactive binder example black ink (Ex. Ink K) and was exposed to UV curing, exhibited better durability, with ΔE around 3. At the same LED curing condition, Ex. Prints 19 and 10 (printed with the cationic polyurethane based fixer fluid (Ex. FF 1) and the reactive binder example black ink (Ex. Ink K)) exhibited significantly improved wash durability, with ΔE of 1.9 with just 2.5 seconds of LED curing, or ΔE of 0 with 5 seconds of LED curing.

[0188] Tables 6A, 6B, and 6C illustrates the optical density and washfastness results for example prints and comparative example prints generated, respectively, on the textile fabrics Pakistan roll #1 , Pakistan roll # 4, and Gildan 780. The example prints were generated using Ex. FF 1 and Ex. Ink M or Ex. FF 1 and Ex. Ink K. The example prints were generated using Ex. FF 1 and Comp. Ink M1 or Comp. Ink M2 or Ex. FF 1 and Comp. Ink K1 or Comp. Ink K2. For these prints, the UV curing time was 2.5 seconds (i.e., five 0.5 second pulses) or 5 seconds (i.e., ten 0.5 second pulses).

TABLE 6A - Example Prints on Pakistan roll #1

TABLE 6B - Example Prints on Pakistan roll #4

TABLE 6C - Example Prints on Gildon 780

[0189] The results in Tables 6A, 6B, and 6C illustrate that the combination of the cationic polyurethane fixer fluid (Ex. FF 1) and either of the examples inks (Ex. Ink K or Ex. Ink M) and UV curing is efficient to cure the reactive UV light curable polyurethane binder on different type of T-shirt media without additional cross-linkers. After 10 pulses of LED (0.5 seconds) exposures (total exposure of 5 seconds), Ex. Print 21 with a combination of Ex. FF 1 and Ex. Ink M had a ΔE down to 2.5 for Pakistan roll #1 , 2.2 for Pakistan #4, and 2.5 for Gildan 780. After 10 pulses of LED (5 seconds) exposures, Ex. Print 22 with a combination of Ex. FF 1 and Ex. Ink K had a ΔE down to 1.4 for Pakistan roll #1 , 2.2 for Pakistan #4, and 2.2 for Gildan 780.

[0190] When the example fixer fluid (Ex. FF 1 ) was printed with any of the comparative inks (Comp. Ex. M1 , M2, K1 , K2), the wash durability was worse. More specifically, at the two different UV LED curing times, Comp. Prints 23 and 27, which were printed with Ex. FF 1 and the Comp. Ex. Ink M2 had average wash durability, with ΔE ranging from 13 to 16 across the different media. Comp. Prints 24 through 26 and 28 through 30, which were printed with Ex. FF 1 and one of Comp. Ex. Ink K2, Comp. Ex. Ink M1, Comp. Ex. Ink K1, exhibited even worse durability at both curing times, with ΔE ranging from 30 to 46.

[0191] These results demonstrate a synergistic affect between the cationic polyurethane in the fixer fluid disclosed herein with the UV light curable polyurethane binder in the inkjet ink disclosed herein.

[0192] The example inks, Ex. Ink M and Ex. Ink. K, were also tested for print performance. While the results are not reproduced herein, each of the example inks exhibited good decap results (after 1 second and 7 seconds of being uncapped), exceptional percentage of missing nozzles (ranging from 0 to 1%), good drop weight and drop velocity, and exceptional decel.

[0193] It is to be understood that the ranges provided herein include the stated range and any value or sub-range within the stated range, as if such values or subranges were explicitly recited. For example, from about 1 wt% to about 15 wt% should be interpreted to include not only the explicitly recited limits of from about 1 wt% to about 15 wt%, but also to include individual values, such as about 2.35 wt%, about 3.5 wt%, about 10 wt%, about 13.5 wt%, etc., and sub-ranges, such as from about 2.5 wt% to about 14 wt%, from about 4.5 wt% to about 12.5 wt%, etc. Furthermore, when “about” is utilized to describe a value, this is meant to encompass minor variations (up to +/- 10%) from the stated value. [0194] Reference throughout the specification to “one example", “another example", “an example", and so forth, means that a particular element (e.g., feature, structure, and/or characteristic) described in connection with the example is included in at least one example described herein, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any example may be combined in any suitable manner in the various examples unless the context clearly dictates otherwise.

[0195] In describing and claiming the examples disclosed herein, the singular forms “a", “an”, and “the" include plural referents unless the context clearly dictates otherwise.

[0196] While several examples have been described in detail, it is to be understood that the disclosed examples may be modified. Therefore, the foregoing description is to be considered non-limiting.

Claims

What is claimed is:

1. A fluid set, comprising: a fixer fluid, including: a cationic polyurethane including a phosphonium salt; and an aqueous fixer vehicle; and an inkjet ink, including: a colorant; an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group; a polymeric UV absorber; and an aqueous ink vehicle.

2. The fluid set as defined in claim 1 wherein the cationic polyurethane including the phosphonium salt is present in the fixer fluid in an amount ranging from about 1 wt% to about 15 wt%, based on a total weight of the fixer fluid.

3. The fluid set as defined in claim 1 wherein the cationic polyurethane is water dispersible.

4. The fluid set as defined in claim 1 wherein the aqueous fixer vehicle includes water and any of a co-solvent, a surfactant, an acid, or combinations thereof.

5. The fluid set as defined in claim 1 wherein the polymeric UV absorber includes a functionalized anthrone moiety, a polyether chain, and an amide linkage or an ether linkage attaching one end of the polyether chain to the functionalized anthrone moiety.

6. The fluid set as defined in claim 1 wherein the UV reactive group and the ionic stabilization group are positioned at terminal ends of the UV light curable polyurethane binder, and the UV light curable polyurethane binder further includes a second UV reactive group attached along a backbone of the UV light curable polyurethane binder.

7. The fluid set as defined in claim 6 wherein: the UV reactive group is an organic group that includes an acrylate, a methacrylate, an acrylamide, a methacrylamide, a styrene, an allyl, or an amine functional group; the ionic stabilization group is an amino carboxylic acid or an amino sulfonic acid; and the second UV reactive group an organic group containing an acrylate, a methacrylate, an acrylamide, or a methacrylamide functional group.

8. The fluid set as defined in claim 1 wherein: the cationic polyurethane includes a polyurethane backbone with pendent side chain groups along the polyurethane backbone and end cap groups terminating the polyurethane backbone; and the pendent side chain groups and the end cap groups of the cationic polyurethane collectively include the phosphonium salt and a polyalkylene oxide.

9. A textile printing kit, comprising: a textile fabric; a fixer fluid, including: a cationic polyurethane including a phosphonium salt; and an aqueous fixer vehicle; and an inkjet ink, including: a colorant; an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group; a polymeric UV absorber; and an aqueous ink vehicle.

10. The textile printing kit as defined in claim 9, wherein the textile fabric is selected from the group consisting of polyester fabrics, polyester blend fabrics, cotton fabrics, cotton blend fabrics, nylon fabrics, nylon blend fabrics, silk fabrics, silk blend fabrics, wool fabrics, wool blend fabrics, and combinations thereof.

11. A printing method, comprising: applying a fixer fluid to a textile fabric, the fixer fluid including: a cationic polyurethane including a phosphonium salt; and an aqueous fixer vehicle; applying an inkjet ink to the textile fabric, the inkjet ink including: a colorant; an ultraviolet (UV) light curable polyurethane binder including a UV reactive group and an ionic stabilization group; a polymeric UV absorber; and an aqueous ink vehicle; and exposing the textile fabric, having the fixer fluid and the inkjet ink thereon, to UV light from a UV light source for a total exposure time of 30 seconds or less.

12. The printing method as defined in claim 11 wherein the inkjet ink is applied to the textile fabric while the fixer fluid is wet.

13. The printing method as defined in claim 11 wherein the UV light source is a light emitting diode that emits emission wavelengths ranging from about 365 nm to about 400 nm.

14. The printing method as defined in claim 11 wherein the exposing of the textile fabric to the UV light involves intermittent light source on events and light source off events, and wherein each light source on event is a fraction of the total exposure time.

15. The printing method as defined in claim 11 , further comprising setting the UV light source so that energy density applied during the exposing ranges from about 2 J/cm² to about 28 J/cm².