Water-based inkjet inks and ink sets

Abstract

To provide an aqueous inkjet ink composition useful for an ink jet printing process, and capable of being utilized individually or as part of an inkjet ink set.SOLUTION: Each aqueous inkjet ink composition has a dynamic viscosity of 5 centipoise (5 mPa-sec) or lower at 25°C, and essentially includes: (a) a polymer dispersion-type pigment colorant, 0.9-6 mass%; (b) a composition including a compound expressed by a structural formula (I) (in the formula, R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group), 0.5-2 mass%; and (c) a water soluble water retention agent, cosolvent or both, 20 mass% or less. Each polymer dispersion-type pigment colorant has 50 percentile particle diameter of less than 70 nm and 95 percentile particle diameter of less than 150 nm, measured using a dynamic light scattering grain size analyzer. The aqueous inkjet ink composition can be used in a method and a system for ink jet printing, specifically continuous ink jet printing.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to aqueous inkjet ink compositions and inkjet ink sets, and inkjet printing processes, such as continuous inkjet printing processes, in which such aqueous inkjet ink compositions and inkjet ink sets can be used. The aqueous inkjet ink compositions of the present invention contain a unique set of preservatives that prevent the growth of microorganisms. [Background technology]

[0002] Inkjet printing of substrates intended for direct contact with food or skin requires careful consideration of the toxicity and potential unintended side effects of human exposure to chemicals contained in the inkjet ink. Most toxic chemicals in aqueous inkjet ink compositions tend to be industrial biocides used to prevent the growth of bacterial, yeast, and mold pathogens and extend the shelf life of the composition. For example, isothiazolinones and formaldehyde released from precursors or donors are generally safe and have high antimicrobial efficacy within their prescribed use levels. Nevertheless, such compounds have recently been found to be undesirable in certain products intended for skin contact, as sensitive users may experience skin irritation and dermatitis even after exposure to trace levels. Regulatory agencies and advocacy groups are increasingly influential regarding which chemicals are used in such consumer products. Furthermore, consumer groups are becoming more aware of the use of common preservatives in various products and are increasingly preferring products that do not contain them.

[0003] There remains a need to provide alternative preservatives (or biostats and biocides) with proven safety and tolerability in skin contact applications that are effective in inhibiting the growth of pathogenic contaminants in aqueous inkjet ink compositions without destabilizing pigment or dye-based colorants or in any other way impairing the high quality printing process.

[0004] US Patent Application Publication No. 2017 / 0073535A1 (Kusukame et al.) discloses piezoelectric drop-on-demand (DOD) inkjet inks using selected conventional and non-conventional ingredients.

[0005] US Patent 6,071,334 (Wider et al.) discloses the use of 2-phenoxyethanol (identified as ethylene glycol phenyl ether) in continuous ink jet printing (CIJ) processes using aqueous dye-based and pigment-based inks.

[0006] As disclosed in U.S. Patent 5,749,952 (Tsang et al.), ethylene glycol phenyl ether is described as approximately 3% by weight of a substantially water-insoluble oil in a thermal DOD black inkjet ink composed of a self-dispersed carbon black pigment.

[0007] As described in U.S. Patent 6,726,757 B2 (Sarkisian et al.), pigmented thermal DOD inkjet ink compositions using self-dispersed black pigments and acrylate polymer binders experience reduced "deceleration" (decrease in drop velocity during prolonged nozzle firing periods) when a deceleration mitigating component selected from the group of materials including ethylene glycol phenyl ether is incorporated into the ink.

[0008] U.S. Patent 6,123,757 (Yang et al.) discloses the use of 2-phenylethanol (identified as β-phenylethyl alcohol) in a fragranced aqueous ink-jet ink composition intended to impart a rose scent. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent Application Publication No. 2017 / 0073535A1 (Kusukame et al.) [Patent Document 2] U.S. Patent 6,071,334 (Wider et al.) [Patent Document 3] U.S. Patent 5,749,952 (Tsang et al.) [Patent Document 4] U.S. Patent 6,726,757B2 (Sarkisian et al.) [Patent Document 5] U.S. Patent 6,123,757 (Yang et al.) [Patent Document 6] U.S. Patent 5,026,427 (Mitchell et al.) [Patent Document 7] U.S. Patent 5,141,556 (Matrick) [Patent Document 8] U.S. Patent 5,160,370 (Suga et al.) [Patent Document 9] U.S. Patent 5,169,436 (Matrick) [Patent Document 10] U.S. Patent 8,173,215 (Sowinski et al.) [Patent Document 11] U.S. Patent Application Publication No. 2007 / 0043144 (House et al.) [Patent Document 12] U.S. Patent 9,828,513 (Lussier et al.) [Patent Document 13] U.S. Patent 8,430,492 (Falkner et al.) [Patent Document 14] U.S. Patent Application Publication No. 2008 / 0207811 (Brust et al.) [Patent Document 15] U.S. Patent 8,455,570B2 (Lindstrom et al.) [Patent Document 16] U.S. Patent Application Publication No. 2014 / 231674 (Cook) [Patent Document 17] U.S. Patent 7,219,989 (Uerz et al.) [Patent Document 18] U.S. Patent Application Publication No. 2018 / 0051184 (Lussier et al.) [Patent Document 19] U.S. Application No. 2005 / 0075415 (Harz et al.) [Patent Document 20] U.S. Patent 6,045,917 (Missell et al.) [Patent Document 21] U.S. Patent 5,605,750 (Romano et al.) [Patent Document 22] U.S. Patent 5,723,211 (Romano et al.) [Patent Document 23] U.S. Patent 5,789,070 (Shaw-Klein et al.) [Patent Document 24] U.S. Patent 9,067,448 (Dannhauser et al.) [Patent Document 25] U.S. Patent 5,526,026 (Bowers) [Patent Document 26] EP 0597628B1 (Loyd et al.) [Patent Document 27] U.S. Patent 7,221,440 (McCann et al.) [Patent Document 28] EP 0571784B1 (McCann et al.) [Patent Document 29] EP 1,013,450B1(Woolard et al.) [Patent Document 30] U.S. Patent 6,588,888 (Jeanmaire et al.), [Patent Document 31] U.S. Patent 6,554,410 (Jeanmaire et al.) [Patent Document 32] U.S. Patent 6,682,182 (Jeanmaire et al.) [Patent Document 33] U.S. Patent 6,793,328 (Jeanmaire et al.) [Patent Document 34] U.S. Patent 6,866,370 (Jeanmaire et al.) [Patent Document 35] U.S. Patent 6,575,566 (Jeanmaire et al.) [Patent Document 36] U.S. Patent 6,517,197 (Hawkins et al.) [Patent Document 37] U.S. Patent Application Publication No. 2002 / 0202054 (Jeanmaire et al.) [Patent Document 38] U.S. Patent 6,079,821 (Chwalek et al.) [Patent Document 39] U.S. Patent 6,505,921 (Chwalek) [Patent Document 40] U.S. Patent 6,817,705 (Crockett et al.) [Patent Document 41] U.S. Patent 9,010,909 (Nelson et al.) [Patent Document 42] U.S. Patent 8,585,189 (Marcus et al.) [Patent Document 43] US Patent 8,651,632 (Marcus et al.) [Patent Document 44] US Patent 8,696,094 (Marcus et al.) [Patent Document 45] U.S. Patent 8,888,256 (Marcus) [Patent Document 46] U.S. Patent 9,969,178 (Roberts et al.) [Non-patent literature]

[0010] [Non-Patent Document 1] A Method for Determining Surface and Interfacial Tension Using a Wilhelmy Plate, Colloid and Polymer Science, 255 (7), pages 675-681 [Non-patent document 2] Glossary of Basic Terms in Polymer Science, the International Union of Pure and Applied Chemistry ("IUPAC"), Pure Appl. Chem. 68, 2287-2311 (1996) [Non-patent document 3] Particle Size Characterization", the National Institute of Standards and Technology ("NIST"), Special Publication 960-1, 93-139 (2001) Summary of the Invention [Problem to be solved by the invention]

[0011] Despite these various innovations, there remains an unmet need for aqueous inkjet ink compositions and particle-free fluids that are substantially free of common preservatives or biocides, yet retain the desired continuous inkjet printing (CIJ) features and high quality images. [Means for solving the problem]

[0012] The present invention provides an aqueous inkjet ink composition having a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25°C as measured using a falling ball viscometer, comprising: (a) one or more polymer-dispersed pigment colorants in a total amount of at least 0.9% and no more than 6% by weight, inclusive, based on the total weight of the aqueous inkjet ink composition; (b) a total amount of at least 0.5% and no more than 2% by weight, inclusive, of the following structure (I): HO-CH2-CH2-R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). a composition comprising one or more compounds represented by (c) one or more compounds selected from a water-soluble humectant, a cosolvent, and both a water-soluble humectant and a cosolvent in an amount of 20% by weight or less based on the total weight of the aqueous inkjet composition; consists essentially of An aqueous inkjet ink composition is provided, wherein each of the one or more polymer-dispersed pigment colorants has a 50th percentile particle diameter of less than 70 nm and a 95th percentile particle diameter of less than 150 nm, all particle diameters measured using a dynamic light scattering particle size analyzer.

[0013] The present invention also provides ink sets comprising two or more different aqueous inkjet ink compositions, each of which is an embodiment of the invention described herein.

[0014] The present invention further provides a fluid set comprising two or more aqueous particle-free fluids each independently having a dynamic viscosity of 5 centipoise (5 mPa-seconds) or less at 25°C, wherein each of the two or more different aqueous particle-free fluids independently comprises: (b) a total amount of at least 0.5% and no more than 2% by weight, inclusive, of the following structure (I): HO-CH2-CH2-R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). A composition comprising one or more compounds represented by a fluid set consisting essentially of:

[0015] Additionally, the aqueous particle-free fluids of the present invention have a dynamic viscosity of 5 centipoise (5 mPa-seconds) or less at 25°C; (b) a total amount of at least 0.5% and no more than 2% by weight, inclusive, of the following structure (I): HO-CH2-CH2-R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). and a composition comprising one or more compounds represented by a sorbosurfactant in an amount of at least 0.1% by weight and no more than 20% by weight, inclusive All amounts are based on the total weight of the aqueous particle-free fluid.

[0016] The inkjet printing method of the present invention comprises: providing a substrate; inkjet printing the first aqueous inkjet ink composition from a printhead onto the surface of a substrate in a controlled manner to provide an inkjet printed image on the surface of the substrate. and the aqueous inkjet ink composition is an optional embodiment of the present invention.

[0017] In some embodiments, the methods of the present invention further comprise: ceasing inkjet printing of the first aqueous inkjet ink composition; delivering an aqueous particle-free fluid from a maintenance fluid delivery station to the printhead; and ejecting an aqueous particle-free fluid from the printhead and purging the first aqueous ink-jet ink composition from the printhead. Further comprising: The aqueous particle-free fluid has a dynamic viscosity of 5 centipoise (5 mPa-seconds) or less at 25°C; a (b) composition that is the same as or different from that present in the first aqueous inkjet ink composition, and a solvosurfactant in an amount of at least 0.1% and no more than 20% by weight, inclusive, based on the total weight of the aqueous particle-free fluid; It essentially consists of:

[0018] The present invention further provides a method of printing an image using a continuous ink jet printer system, comprising: providing a substrate; providing a jetting module having a plurality of nozzles, the nozzles being in fluid communication with a main fluid delivery containing a first aqueous-based ink-jet ink composition; forming droplets of the first aqueous ink-jet ink composition during ejection of the first aqueous ink-jet ink composition from a nozzle in fluid communication with a main fluid delivery portion by droplet stimulation in response to a time-varying electrical signal; providing a capture region including a droplet contact surface; using a deflection mechanism to deflect at least some of the droplets of the first aqueous ink-jet ink composition onto a droplet contact surface of the trap while allowing other droplets of the first aqueous ink-jet ink composition to pass through the trap and be deposited on the surface of the substrate; and causing the droplets of the aqueous inkjet ink composition in contact with the droplet contact surface to flow along the droplet contact surface. wherein the first aqueous inkjet ink composition is any embodiment described herein.

[0019] Further, the continuous ink jet printing method of the present invention comprises: delivering a first aqueous inkjet ink composition, any embodiment described herein, to a primary fluid delivery section of a continuous inkjet printer; ejecting a continuous stream of droplets of a first aqueous inkjet ink composition from a droplet generating mechanism; in response to electrical signals received from a control mechanism, selecting between print droplets for imaging onto a substrate and non-print droplets that are collected and returned to a main fluid delivery section, both types of droplets being from the first aqueous-based ink-jet ink composition; and (b) replenishing the main fluid delivery section with an aqueous particle-free fluid containing composition as a function of the resistivity of the first aqueous ink-jet ink composition in the main fluid delivery section. Includes.

[0020] Stable aqueous pigment dispersions and inkjet ink compositions according to the present invention exhibit improved resistance to pathogen growth and are acceptable for skin contact when commonly used industrial biocide preservatives, such as isothiazolinone derivatives and formaldehyde-releasing agents, are refrained from incorporation into such formulations due to the presence of 2-phenoxyethanol, 2-phenylethanol, or combinations thereof. These ethanol derivatives, used individually or in combination, were effective in inhibiting the growth of a representative mixture of Gram-negative and Gram-positive bacteria during in vitro challenge testing of the inkjet ink compositions. When combined with an appropriate supplemental antimicrobial compound, the susceptibility of the compositions to the growth of a wide range of pathogenic organisms can be sufficiently minimized during long-term challenge testing. A method of continuous inkjet (CIJ) printing according to the present invention is provided for recycling ink using an aqueous particle-free fluid containing 2-phenoxyethanol, 2-phenylethanol, or other alternative preservatives when the aqueous inkjet ink composition is used and replenished in the CIJ printer fluid system. The printed substrates obtained by the present invention may be porous matte media (e.g., paper), woven media (e.g., textiles), and porous or non-porous films (e.g., polymer sheets) that have been pre-treated or pre-coated to improve acceptance and bonding of the printed inkjet ink to the medium or article being printed.

[0021] Further details and advantages of the present invention can be understood from the teachings provided below. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following discussion is directed to various embodiments of the present invention, and while some embodiments may be desirable for particular uses, the disclosed embodiments should not be interpreted or considered as limiting the scope of the invention as claimed below. Moreover, those skilled in the art will appreciate that the following disclosure has broader applications than are expressly set forth in the discussion of any embodiment.

[0023] definition As used herein to define the various components of the aqueous organic pigment dispersions, aqueous inkjet ink compositions, and other materials used in the practice of the present invention, unless otherwise indicated, the singular forms "a," "an," and "the" are intended to include one or more of the components (i.e., include plural referents).

[0024] Each term not expressly defined in this application should be understood to have the meaning generally accepted by one of ordinary skill in the art. If a term becomes meaningless or essentially meaningless in the context due to its construction, the term should be construed as having its standard dictionary meaning.

[0025] The use of numerical values ​​in the various ranges specified herein, unless expressly indicated otherwise, is considered to be approximations, as if both the minimum and maximum values ​​within the stated ranges were preceded by the term "about." In this manner, small variations above or below the stated ranges may be useful to achieve substantially the same results as values ​​within the ranges. Furthermore, the disclosure of these ranges contemplates continuous ranges, including all values ​​between the minimum and maximum values, as well as the endpoints of the ranges.

[0026] As used herein, the parameter "acid number" (also known as acid value) is defined as the milligrams (mg) of potassium hydroxide required to neutralize 1 g of acidic polymer.

[0027] The term "aqueous" in the aqueous organic pigment dispersion and aqueous inkjet ink composition according to the present invention means that the water content is greater than 60% by weight based on the total amount of solvent, and thus water is the predominant solvent in the aqueous medium.

[0028] The dynamic viscosity of inks and fluids can be measured by any of the well-known techniques. Preferred methods include measuring the time of mass flow through a capillary, as in a capillary viscometer, or measuring the falling velocity of a sphere through a fluid, for example, using a falling-ball viscometer. Both capillary flow viscometers and the commercially available Anton Paar Automated MicroViscometer (AMVn), which uses the falling-ball method, can be used to measure the dynamic viscosities reported herein. Dynamic viscosity values ​​for all inks disclosed herein were measured at approximately 24°C to 26°C under gravity-induced shear. The values ​​referred to are reported in centipoise (cP) or millipascal-seconds (mPa-sec), with 1 cP = 10 -3 Pascal-second (Pa-s) = 10 -2 dyne-s / cm 2 It is recognized that viscosity can be measured with high precision, but viscosity values ​​herein are reported to only one or two decimal places, and these are typically rounded values, not truncated values. All claims reciting ink viscosities are intended to be interpreted in terms of mPa-second values, typically rounded to one decimal place. Accordingly, various aqueous inkjet ink compositions may have viscosities of 10 centipoise (10 mPa-second) or less, inclusive.

[0029] The Wilhelmy plate method is a well-known technique for measuring the static surface tension of a liquid ink or feed fluid at a solid interface. This technique utilizes a plate of known dimensions, typically selected from a roughened platinum alloy, suspended from a balance. The plate is brought into contact with the solution of interest and a normal force is applied to the plate, forming a meniscus of liquid between the solution and the plate. The resulting surface tension is calculated using Equation (1): (1)σ=F / L cos(θ) where σ is the surface tension of the liquid, F is the force acting on the balance (in milli-Newtons / meter), L is the wetting length of the plate in millimeters, and θ is the contact angle between the plate and the solution. is given by

[0030] Typically, roughened platinum results in a contact angle very close to zero, with the cosine of θ being 1. A complete theoretical treatment of the method can be found, for example, in "A Method for Determining Surface and Interfacial Tension Using a Wilhelmy Plate," Colloid and Polymer Science, 255 (7), pages 675-681. While many commercially available instruments are known for measuring surface tension, the instrument used to report surface tension values ​​in this invention is a Kruss Model K10ST tensiometer.

[0031] The pigment colorants used in various embodiments of the present invention are generally not self-dispersing, i.e., they require the presence of one or more organic polymeric pigment dispersants attached to a portion of the surface of the pigment particle in order to remain suspended in the aqueous medium.

[0032] The terms "water soluble" and "water-soluble" mean that 1 part by weight of a solute material can be dissolved in as little as less than 1 part by weight (i.e., relatively soluble) solutes, and in as much as 1,000 parts by weight (i.e., less soluble) distilled water at 25°C to produce a homogeneous and visibly clear solution.

[0033] The term "sorbosurfactant" refers to a compound or combination of compounds that is an effective solvent for the dried "ink" and is a volatile solvent that has a boiling point at sea level of less than 200° C. and can reduce the surface tension and self-cohesion of the fluid. Further details of such compounds are provided below.

[0034] For clarification of the definition of any term relating to polymers, reference should be made to the "Glossary of Basic Terms in Polymer Science," Pure Appl. Chem. 68, 2287-2311 (1996), published by the International Union of Pure and Applied Chemistry ("IUPAC"). However, any definitions explicitly set forth herein should be considered to prevail. The polymers can be prepared from ethylenically unsaturated polymerizable monomers using free radical or acid-catalyzed polymerization processes, or by the reaction of suitable condensation monomers (e.g., diols and diisocyanates) using known condensation polymerization processes.

[0035] Unless otherwise indicated, the terms "polymer" and "polymeric" refer to the stated mass distribution average molecular weight (M), as measured using gel permeation chromatography (polystyrene standard). w ) or number distribution average molecular weight (M n ) refers to both homopolymers and copolymers, each having the same structure.

[0036] The term "copolymer" refers to a polymer derived from two or more different monomers in a random or predetermined order (e.g., block) along the polymer backbone, i.e., each copolymer contains at least two repeat units with different chemical structures.

[0037] The term "backbone" refers to a chain of atoms in a polymer to which multiple pendant groups can be attached. An example of such a backbone is an "all-carbon" backbone resulting from the polymerization of one or more ethylenically unsaturated polymerizable monomers. However, other backbones can contain heteroatoms, in which case the polymer is formed by a condensation reaction or some other means.

[0038] Water-based organic pigment dispersions The (a) polymer-dispersed pigment colorants useful in the practice of the present invention can be used alone or in combinations of two or more different polymer-dispersed pigment colorants to produce any desired color or shade. For example, a polymer-dispersed carbon black pigment may be combined with a differently colored polymer-dispersed organic pigment in the same aqueous pigment dispersion or aqueous inkjet ink composition. The exact choice of polymer-dispersed pigment colorant depends on the specific application, performance, color reproduction, and image stability desired. Useful polymer-dispersed pigment colorants are described, for example, in U.S. Patents 5,026,427 (Mitchell et al.), 5,141,556 (Matrick), 5,160,370 (Suga et al.), and 5,169,436 (Matrick).

[0039] Useful pigment colorants that can be dispersed by organic polymers include, but are not limited to, azo pigments, monoazo pigments, disazo pigments, azo metalloorganic pigments, β-naphthol pigments, naphthol AS pigments, benzimidazolone pigments, disazo condensation pigments, metal complex pigments, isoindolinone and isoindoline pigments, quinacridone pigments, polycyclic pigments, phthalocyanine pigments, perylene and perinone pigments, thioindigo pigments, anthrapyrimidone pigments, flavanthrone pigments, anthanthrone pigments, dioxazine pigments, triarylcarbonium pigments, quinophthalone pigments, diketopyrrolopyrrole pigments, titanium dioxide, iron oxide, and carbon black. Representative useful yellow, black, green, brown, red, magenta, cyan, blue, orange, and purple pigment colorants are described in U.S. Patent 8,173,215 (Sowinski et al.), columns 7 (line 48) to 8 (line 5).

[0040] Useful pigment colorants may be accompanied by or dispersed using suitable polymeric dispersants (such as those mentioned above) known in the art. Exemplary useful organic polymeric dispersants can be prepared from at least one anionic hydrophilic monomer, such as an acrylic or methacrylic acid monomer, or a combination thereof, and at least one monomer comprised of, for example, a hydrophobic methacrylate or acrylate monomer having an aliphatic chain with 12 or more carbon atoms, as described, for example, in U.S. Patent Application Publication 2007 / 0043144 (House et al.). Useful Monomer Repeat Units, Monomer Amounts and M w Further details of useful organic polymeric dispersants, including are provided in column 5 (line 45) through column 6 (line 31) of US Pat. No. 8,173,215 (supra).

[0041] Many useful organic polymeric dispersants have a mass average (M) viscosity of at least 500 daltons and less than 100,000 daltons, more suitably less than or equal to 15,000 daltons, inclusive, or less than or equal to 10,000 daltons, inclusive. w ) molecular weight of at least one anionic hydrophilic monomer as described above.

[0042] The one or more organic polymeric dispersants for the pigment colorants may be present in amounts that will be readily apparent to one skilled in the art, depending on the aqueous medium, the organic pigment selected, and the other components of the aqueous inkjet ink composition.

[0043] In addition to the polymeric dispersant, a nonionic or anionic surfactant, as known in the art, may be present with the pigment colorant. Representative materials of this type include, but are not limited to, sodium dodecyl sulfate or sodium oleyl methyl taurate, as described in U.S. Patent 8,173,215 (noted above), column 7 (lines 15-23).

[0044] The particle size of each useful polymer-dispersed pigment colorant is as follows:

[0045] The particle size of various polymer-dispersed pigment colorants refers to the approximate diameter of a substantially spherical pigment particle or the approximate largest characteristic dimension of a non-spherical particle. More specifically, the diameter of a sphere having the same volume as the particle is determined (i.e., the equivalent spherical diameter). The desired median particle diameter (or 50th percentile particle diameter) of each pigment-based colorant used according to the present invention may be less than 300 nm, less than 150 nm, less than 70 nm, or even less than 60 nm, so that 50% of the particle volume is composed of particles having a diameter smaller than the specified diameter. Furthermore, at least 95% of the total primary particles of each polymer-dispersed pigment colorant used according to the present invention have a particle diameter smaller than 500 nm, less than 300 nm, less than 150 nm, or even less than 110 nm. This refers to the 95th percentile particle diameter, which is a categorized particle size distribution in which 95% of the volume of organic pigment particles is contributed by particles having a diameter smaller than the specified diameter. Particle size (or particle volume) can be easily measured using a conventional dynamic laser light scattering particle size analyzer. Instrumental techniques for analyzing and reporting nanoparticle size are usefully described in "Particle Size Characterization," Special Publication 960-1, 93-139 (2001), published by the National Institute of Standards and Technology ("NIST").

[0046] The (b) composition used in the practice of the present invention has the following structure (I): HO-CH2-CH2-R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). For example, R can be either an unsubstituted phenyl group or an unsubstituted phenoxy group. Mixtures of compounds represented by structure (I) can also be used.

[0047] Therefore, either or both of 2-phenoxyethanol and 2-phenylethanol can be advantageously used in the practice of the present invention due to the advantages described above. 2-Phenoxyethanol is also known as ethylene glycol phenyl ether, ethylene glycol monophenyl ether, and 1-hydroxy-2-phenoxyethane, and is available from various commercial sources as DOWANOL PhE, DOWANOL EPh, or DOWANOL EP. 2-Phenylethanol is also known as phenylethanol, 2-phenylethan-1-ol, phenethyl alcohol, β-hydroxyethylbenzene, phenylethyl alcohol, β-phenylethanol, and benzyl carbinol, and is available from various commercial sources.

[0048] The aqueous medium, such as water and any water-miscible organic solvent, may be present in any desired amount that provides the viscosity and other physical properties desired for storage of the aqueous pigment dispersion or its use to make an aqueous inkjet ink composition.

[0049] The aqueous pigment dispersions according to the present invention can be prepared by any method commonly used in the art and typically involve two steps: (a) a dispersing or milling step to break up agglomerates of one or more pigment colorants into primary particles, where a primary particle is defined as the smallest identifiable fraction in a particulate system, and (b) a dilution step in which the pigment colorant dispersion from step (a) is diluted by the addition of an aqueous medium and any other additives. Details of milling are described, for example, in U.S. Pat. No. 8,173,215 (cited above), column 6 (line 58) to column 7 (23).

[0050] Aqueous inkjet ink composition Aqueous inkjet ink compositions according to the present invention generally have a dynamic viscosity of 5 centipoise (5 mPa-sec) or less, or at least 1 centipoise (1 mPa-sec) and 3 centipoise (3 mPa-sec) or less, inclusive, all measured at 25° C. using a falling ball or capillary viscometer and known procedures. Parameters may vary between different aqueous inkjet ink compositions.

[0051] Aqueous inkjet ink compositions also typically have a pH of at least 7.5 and no more than 11, inclusive, or more suitably at least 8 and no more than 9, inclusive. When the aqueous inkjet ink composition is used on hardware having nickel or nickel-plated device parts, a corrosion inhibitor such as the sodium salt of 2- or 5-methyl-1-H-benzotriazole may be added and the pH may be adjusted to at least 10 and no more than 11, inclusive. When printheads made from silicon are used for inkjet printing, the pH of the aqueous inkjet ink composition may be adjusted to at least 7.5 and no more than 10, inclusive, or at least 8 and no more than 9.5, inclusive.

[0052] The aqueous inkjet ink composition according to the present invention comprises one or more of the same or different (a) polymer-dispersed pigment colorants in a total amount of at least 0.9% and no more than 6% by weight, inclusive, or at least 1.5% and no more than 5% by weight, inclusive, based on the total weight of the aqueous inkjet ink composition. Useful polymer-dispersed pigment colorants and useful particle size parameters are described above. If desired, two or more polymer-dispersed pigment colorants can be used to impart a desired hue or color to the resulting inkjet printed image.

[0053] The (b) composition, comprising one or more compounds represented by Structure (I), is present in the aqueous ink-jet ink composition in a total amount of at least 0.5% and no more than 2% by weight, inclusive, or even at least 1% and no more than 1.8% by weight, inclusive, based on the total weight of the aqueous ink-jet ink composition. The (b) composition may be the same or different from the various aqueous ink-jet ink compositions.

[0054] Each aqueous inkjet ink composition according to the present invention comprises (c) one or more compounds selected from a water-soluble humectant, a cosolvent, and both a water-soluble humectant and a cosolvent. Cosolvents are generally water-soluble or water-miscible organic solvents having a viscosity greater than 1 centipoise (1 mPa-second), and possibly even greater than 40 centipoise (40 mPa-seconds), as measured at 25°C using a standard falling-ball, capillary, or spinning-plate viscometer. Any water-soluble humectant or cosolvent known in the inkjet art that is compatible with the other requirements of the present invention may be used. While individual humectants may be used, mixtures of two or more humectants, each providing useful properties, may also be used. Representative humectants are described, for example, in U.S. Patent No. 9,828,513 (Lussier et al.) and include classes of compounds such as (1) monoalcohols, (2) polyhydric alcohols, (3) lower mono- and dialkyl ethers derived from polyhydric alcohols, (4) nitrogen-containing compounds such as urea, 2-pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone, and (5) sulfur-containing compounds such as 2,2'-thiodiethanol, dimethyl sulfoxide, and tetramethylene sulfone. Useful cosolvents are also included within the scope of such classes of compounds. The same or different (c) compounds may be used in various aqueous inkjet ink compositions.

[0055] The one or more (c) humectants, co-solvents or both humectants and co-solvents may be present in an amount of less than 20% by weight, or at least 0.5% by weight, or at least 1% and no more than 15% by weight, inclusive, or at least 3% and no more than 10% by weight, inclusive, all based on the total weight of the aqueous inkjet ink composition. Highly preferred levels of the one or more (c) humectants, co-solvents or both humectants and co-solvents are at least 4% and at most 8% by weight.

[0056] The same or different (d) supplemental antimicrobial agent(s) may be present in the aqueous ink-jet ink composition, and such materials are different from the (b) composition described above and represented by structure (I). Representative materials include, but are not limited to, iodopropynyl butylcarbamate (CAS 55406-53-6), piroctone olamine (CAS 68890-66-4), 2,4-dichlorobenzyl alcohol (CAS 1777-82-8), boric acid (CAS 10043-35-3) and monovalent and divalent metal ion salts derived from boric acid, and combinations of these materials. A useful amount of the one or more supplemental antimicrobial agents is at least 0.01% and up to 3% by weight, inclusive, based on the total weight of the aqueous ink-jet ink composition.

[0057] Each aqueous inkjet ink composition according to the present invention may further comprise one or more anionic polyurethanes, each having an acid number of at least 50, or at least 60 and no more than 150, inclusive, or even at least 55 and no more than 90, inclusive; these acidic polymers are described in more detail below. The anionic polyurethanes may be the same or different in the various aqueous inkjet ink compositions.

[0058] Alternatively, or in addition to the anionic polyurethane, the aqueous inkjet ink composition may comprise one or more anionic non-aromatic acrylic or anionic styrene-acrylic polymers, which may be the same or different, each having an acid number of at least 50, or at least 120 and no more than 240, inclusive, or even at least 160 and no more than 220, inclusive; these acidic polymers are described in more detail below. Mixtures of two or more of such materials may be used if desired.

[0059] Representative examples of both types of anionic polymers are described, for example, in U.S. Patents 8,430,492 (Falkner et al.) and 9,783,553 (supra). Particularly useful anionic polyurethanes contain polyether diol units and may be identified as polyether polyurethanes. Such anionic polyether polyurethanes generally have a molecular weight (M) of at least 10,000 daltons and up to 30,000 daltons, inclusive, or at least 15,000 daltons and up to 25,000 daltons, inclusive. w For example, certain useful polyether polyurethanes are individually represented by structure (I) in U.S. Pat. No. 9,783,553 (noted above).

[0060] Useful water-soluble or water-dispersible anionic polyether polyurethanes can be prepared, for example, as described in U.S. Patent Application Publication No. 2008 / 0207811 (Brust et al.) at paragraphs

[0045] to

[0049] . The acidic groups of the anionic polyether polyurethanes may be at least partially, and up to 100%, neutralized (converted to salts) using a monovalent inorganic base such as an alkali metal hydroxide or an organic amine such as dimethylethanolamine.

[0061] Representative anionic non-aromatic acrylic polymers and anionic styrene acrylic polymers useful in the present invention are also described, for example, in U.S. Patent Application Publication No. 2008 / 0207811 (noted above), under paragraph 0061. Examples of useful anionic styrene acrylic polymers include those commercially available under the trademarks JONCRYL® (BASF Corp.), TRUDOT® (formerly available from Mead Westvaco Co.), and VANCRYL® (Allnex USA, Inc.).

[0062] Useful amounts of such anionic polymers are readily known in the art and can be up to 15% by weight, inclusive, or up to 10% by weight, inclusive, all based on the total weight of the aqueous inkjet ink composition. A particularly useful amount range of anionic polymers is at least 1% by weight and up to 5% by weight, inclusive, including anionic non-aromatic acrylic polymers and anionic styrene acrylic polymers used as pigment dispersants.

[0063] Additionally, modified polysiloxanes may be present in the aqueous inkjet ink composition. Examples of such materials include ethoxylated or propoxylated silicone-based "surfactants" commercially available under the trademarks SILWET® (CL Witco) and BYK® (Byk Chemie), such as BYK® 348 and 381, and Dow Corning DC67, DC57, DC28, DC500W, and DC51. Non-silicone surfactants, including anionic, cationic, nonionic, or amphoteric surfactants, such as those commercially available as SURFYNOL® surfactants (Evonik Corp.), including, but not limited to, SURFYNOL® 440 and 465 alkynediol surfactants, may also be used. Useful amounts of such materials will be readily apparent to those skilled in the art. Particularly useful amounts of selected surfactants are described in U.S. Patent 8,455,570 B2 (Lindstrom et al.).

[0064] It may be useful to include one or more "accelerators," the same or different, in the aqueous ink-jet ink composition to (b) potentially enhance the effectiveness of the compound represented by structure (I) of the composition. Such materials are generally alkanediols, each having at least 7 carbon atoms and no more than 12 carbon atoms, inclusive, particularly at least 7 carbon atoms and no more than 10 carbon atoms, inclusive. Representative useful compounds that may be used alone or in combination as accelerators include, but are not limited to, 1,7-heptanediol, 1,2-heptanediol, 2-ethyl-1,3-hexanediol, 1,2-octanediol, 3,6-octanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,2-nonanediol, 1,10-decanediol, 1,12-dodecanediol, and others that will be readily apparent to those skilled in the art. 1,2-octanediol is particularly useful in this regard.

[0065] The one or more accelerators may be present in the aqueous inkjet ink composition in a total amount of 1.5% by weight or less, or 1.25% by weight or less, based on the total weight of the aqueous inkjet ink composition. The minimum amount may be at least 0.3% by weight.

[0066] A colorless fluorescent colorant (dye or pigment) may also be present in the aqueous inkjet ink composition in an amount that will be readily apparent to one skilled in the art; examples of such compounds are described in U.S. Patent Application Publication 2014 / 231674 (Cook).

[0067] Other additives that may be present in the aqueous ink-jet ink composition in amounts readily apparent to one skilled in the art include, but are not limited to, TERGITOL® 15-S and TMN series nonionic surfactants, BRIJ® series nonionic surfactants, TRITON® series nonionic surfactants, ZONYL® fluorosurfactants, PLURONIC® nonionic surfactants, TETRONIC® nonionic surfactants, SILWET® nonionic surfactants, and SURFY® nonionic surfactants. Other surfactants for adjusting the surface tension of the composition, including NOL® nonionic surfactants, as well as various anionic and cationic surfactants mentioned in U.S. Patent 8,173,215 (noted above), column 10, lines 64 to column 11, line 14, thickeners, conductivity enhancers, drying agents, water resistance agents, viscosity modifiers, pH buffers, foam suppressants, wetting agents, corrosion inhibitors, foam inhibitors and defoamers (such as SURFYNOL® DF-110L, PC, MD-20 and DF-70), UV radiation absorbers, antioxidants and light stabilizers available under the trademarks TINUVIN® (BASF Corp.) and IRGANOX® (BASF Corp.), and other additives described in U.S. Patent 8,455,570 (noted above), column 17 (lines 11-36). Useful amounts of such materials will be readily apparent to one skilled in the art using routine experimentation.

[0068] Water is typically present in each aqueous inkjet ink as the primary aqueous medium in a suitable amount such as at least 75% by weight, or at least 80% by weight, and typically up to 90% by weight, based on the total weight of the aqueous inkjet ink composition.

[0069] Each aqueous inkjet ink composition described herein can be prepared by dispersing a suitable polymer-dispersed pigment colorant in water and mixing it with other described ingredients, such as (b) a compound represented by Structure (I), (c) a humectant or co-solvent, and any adjuvants, accelerators, supplemental antimicrobial agents, and suitable amounts of additional materials.

[0070] Ink set The present invention can provide an ink set, which may include two or more different aqueous inkjet ink compositions, each containing at least one visible polymer-dispersed pigment colorant (described above) to impart a desired color or hue. For example, each ink set may include a variety of useful aqueous inkjet ink compositions having different hues or "colors," such as various shades of orange, red, purple, green, cyan, yellow, black, magenta, brown, pink, and blue, and thus may contain one or more suitable polymer-dispersed pigment colorants suitable for imparting the desired hue. By proper use and blending of suitable polymer-dispersed pigment colorants, any desired hue, defined, for example, using known a* and b* CIELAB values, can be imparted. An aqueous "white" inkjet ink composition may also be useful in certain situations and may be included in the ink set. As described above, a wide variety of organic and inorganic pigments may be used individually or in combination in such aqueous inkjet ink compositions, which may have the desired pigment particle size, as described above. The polymer-dispersed pigment colorant may be present in any suitable amount, as described above for aqueous inkjet ink compositions according to the present invention.

[0071] In addition to the polymer-dispersed pigment colorant, one or more of the aqueous color inkjet ink compositions in the ink set may contain one or more water-soluble dyes known in the art, for example, as described in column 12 (lines 4-55) of U.S. Pat. No. 8,455,570 (noted above).

[0072] The aqueous inkjet ink compositions in the ink set may be formulated similarly or differently to those described above.

[0073] Each aqueous colour inkjet ink composition in the ink set may have a desired pH of at least 7.5 and no more than 11, inclusive, as described above, or at least 8 and no more than 10, inclusive, using a suitable base and buffer system.

[0074] Additionally, each aqueous color inkjet ink composition may have a suitable dynamic viscosity of at least 1 centipoise (1 mPa-second) and less than 5 centipoise (5 mPa-seconds) measured at 25°C.

[0075] Each of the aqueous inkjet ink compositions in the ink set is as described above and independently comprises (the same or different) (a) a polymer-dispersed pigment colorant (as described above) in an amount of at least 0.9% and no more than 6% by weight, inclusive, based on the total weight of the aqueous inkjet ink composition, (b) a composition consisting of a compound represented by Structure (I), and (c) at least one water-soluble humectant, co-solvent, or combination of water-soluble humectant and co-solvent, all in the amounts described above.

[0076] For example, an ink set according to the present invention may comprise two or more of the following specific types of aqueous inkjet ink compositions: (i) an aqueous inkjet ink composition comprising a polymer-dispersed cyan pigment colorant; (ii) an aqueous inkjet ink composition comprising a polymer-dispersed magenta pigment colorant; (iii) an aqueous inkjet ink composition comprising a polymer-dispersed yellow pigment colorant; and (iv) An aqueous inkjet ink composition comprising a polymer-dispersed black pigment colorant.

[0077] Many ink sets have all four of the aqueous inkjet ink compositions (i) through (iv) present.

[0078] In some embodiments, ink sets according to the present invention may further comprise particle-free, colorless ink jet compositions (or aqueous particle-free fluids), such as those described in U.S. Patent No. 8,764,161 (noted above). Such compositions may be known in the art as "fluids" and may have various purposes or functions, such as use as printhead maintenance, reservoir, flushing or cleaning, or replenishment fluids. Details of such fluids are provided in the referenced patents, the disclosures of which are incorporated herein by reference. "Particle-free" means that such compositions are intentionally free of any type of colorless or colored particulate matter or pigment. Further details of useful such fluids are provided below in the discussion of the individual aqueous particle-free "fluid sets."

[0079] Such particle-free colorless inkjet compositions may also include a (b) composition consisting of a compound represented by Structure (I) described above, which may be the same or different from those used in two or more aqueous inkjet ink compositions in an ink set containing a polymer-dispersed pigment colorant. For example, such particle-free colorless inkjet compositions may contain 2-phenoxyethanol, 2-phenylethanol, or both 2-phenoxyethanol and 2-phenylethanol (such as when R is 2-phenyl or 2-phenoxy in Structure (I)) in an amount of at least 0.5% and up to 2% by weight, inclusive, based on the total weight of the particle-free colorless inkjet composition.

[0080] The durability, gloss, and other properties of inkjet-printed images can be improved by applying a colorless polymer overcoat composition, which may be considered an aqueous particle-free inkjet composition according to the present invention. Examples of such compositions are provided in U.S. Patent 7,219,989 (Uerz et al.). To achieve the high inkjet printing speeds and throughput associated with CIJ printing, such overcoat compositions can be applied using a CIJ printhead followed by one or more printheads of droplet-forming nozzles that dispense a "pigmented" aqueous inkjet ink composition. Further details regarding such applications are provided in column 17 (lines 16-48) of U.S. Patent 8,173,215 (cited above).

[0081] Additional aqueous particle-free inkjet compositions (or inks) that may be part of the ink set include those described in U.S. Patent Application Publication No. 2018 / 0051184 (Lussier et al.), the disclosure of which is incorporated herein by reference, and which may be inkjet printed to produce colorless or colored coatings. Such compositions may comprise at least one or more of the anionic polyether polyurethanes or anionic acrylic or styrene-acrylic polymers described above, and a suitable foam suppressor or defoamer to reduce foaming tendency. Such aqueous particle-free inkjet compositions may further comprise a (b) composition having a compound defined by structure (I) described above.

[0082] Each component or composition present in the ink set, whether colored or colorless, may contain various other additives that will be readily apparent to one skilled in the art, such as antifoam agents, surfactants, conductivity enhancers, drying agents, water resistance agents, chelating agents, thickeners, anti-kogation agents, stabilizers and buffers.

[0083] Aqueous particle-free fluid Aqueous particle-free fluids may be designed for a variety of purposes and used in the practice of the present invention. Each of these aqueous particle-free fluids generally independently have a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25° C., as measured, for example, using a falling ball viscometer or a capillary viscometer and standard procedures. Each of these aqueous particle-free fluids is colorless or otherwise intentionally free of particles and can be used for a variety of purposes or functions in inkjet printing methods, as described below.

[0084] If desired, two or more different aqueous particle-free fluids with different purposes and compositions can be combined into a "fluid set" for commercialization. Alternatively, one or more of the aqueous particle-free fluids may be included within an ink set as described above.

[0085] Each aqueous particle-free fluid may independently have a pH similar to the aqueous ink-jet ink compositions described above, i.e., at least 5 and no more than 11, inclusive. The pH may be controlled for each aqueous particle-free fluid using the teachings of U.S. Patent 8,764,161 (noted above), columns 11 (line 58) to 12 (line 26). In some embodiments, the pH is at least 10 and no more than 11, inclusive, and may be controlled by the presence of one or more bases as described below.

[0086] Each of the aqueous particle-free fluids according to the present invention independently consists essentially of a (b) composition consisting of one or more compounds represented by Structure (I) described above. Individual aqueous particle-free fluids in the set of fluids may have the same or different (b) compositions. One or more compounds of the (b) composition, e.g., where R is 2-phenyl or 2-phenoxy, may be present in the aqueous particle-free fluid in an amount of at least 0.5% and no more than 2% by weight, inclusive, based on the total weight of the aqueous particle-free fluid.

[0087] In certain embodiments, aqueous particle-free fluids can have different general compositions in addition to their (b) composition, making them suitable for two or more different print supply functions. For example, a "replenisher" aqueous particle-free fluid can be used to replace evaporated solvent from an aqueous inkjet ink composition in an ink tank, restoring the composition to its previous colorant concentration. Such aqueous particle-free fluids generally consist essentially of the (b) composition described above. However, such aqueous particle-free fluids can also include humectants, cosolvents, supplemental antimicrobial agents, surfactants, accelerators, or any combination thereof, as described in more detail below. For example, such aqueous particle-free fluids may also desirably contain volatile organic solvents that are lost to evaporation upon ink recycling, or weak organic bases (e.g., alkanolamines) to mitigate pH fluctuations due to carbonic acid formation resulting from carbon dioxide uptake. Because the continuous ink jet printer's fluid system's method of determining the relative concentration of ink in the ink tank is to measure the ink's ionic conductivity (or alternatively its resistivity), it is undesirable to significantly alter the fluid properties and ionic content of the recovered ink by cumulative contributions from repeated replenisher additions. Thus, it is desirable to minimize the replenisher aqueous particle-free fluid content of, for example, organic solvents, humectants, pH and ionic conductivity modifying additives, polymeric compounds, surfactants, and foam suppressors.

[0088] Printhead cleaner and reservoir fluids that are "maintenance" aqueous particle-free fluids may be used to redissolve, redisperse, or solubilize dried ink deposits that form on and around the nozzles of the nozzle plate and interfere with inkjet straightness and inkjet stability. In this case, the fluids can be used to purge the ink channels and exterior surfaces of the printhead, flushing the ink away. Aqueous particle-free fluids are also suitable for keeping the wetted parts ready for efficient start-up after long storage periods, although the various printhead and fluid system maintenance functions of flushing, cleaning, and reservoiring may be accomplished by specialized individual aqueous particle-free fluids as desired.

[0089] In addition to the (b) composition, printhead cleaners and reservoired aqueous particle-free fluids according to the present invention may desirably comprise organic solvents that improve the effectiveness of the fluid vehicle (water) in penetrating and solvating the dried pigment particles in the dried aqueous inkjet ink composition deposit. The fluid may further contain optional additives, including, but not limited to, solubilizers, cosolvents, viscosity modifiers, bases, acids, pH buffers, chelating agents, dispersants, water-soluble or water-dispersible polymers, corrosion inhibitors, viscosity modifiers, penetrating agents, wetting agents, foam suppressors, and defoaming agents. Solvents effective for the dried aqueous inkjet ink composition may be selected from the class of dynamic surface tension-reducing cosolvents, also known in the art as penetrants; polar dynamic surface tension-reducing cosolvents are also considered functional surface tension modifiers (i.e., aptly termed "solvosurfactants," which are low molecular weight volatile solvents that can reduce the surface tension of a fluid and include amphiphilic compositions capable of self-coalescence). On a molar and mass fraction basis, such sorbosolvents are surface modifiers that are less effective than conventional surfactants at reducing equilibrium surface tension. The sorbosurfactants used in removing dried aqueous inkjet ink compositions desirably comprise an asymmetric polyhydric alcohol or a monoalkyl ether derived from a polyhydric alcohol. Specific examples of lower (C1-C4) monoalkyl ethers and derivatives derived from polyhydric alcohols include, but are not limited to, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, polyethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, and diethylene glycol monobutyl ether acetate, all distributed as the DOWANOL, CELLUSOLVE®, and CARBITOL® series by Dow Chemical Co., among others.Such sorbosurfactants may be used alone or in combination in an amount of at least 0.1% and no more than 20% by weight, inclusive, or even in an amount of at least 3% and no more than 6% by weight, inclusive, all based on the total weight of the aqueous particle-free fluid.

[0090] Increasing the fluid pH can be beneficial in removing dried aqueous inkjet ink compositions, and the pH of aqueous particle-free printhead cleaners is optionally raised with organic bases such as hydroxyl-substituted aliphatic amines (e.g., alkanolamines), including monoethanolamine, diethanolamine, 3-amino-1-propanol, N-methylethanolamine, N-benzyl-N-methylethanolamine, 2-(2-aminoethoxy)ethanol, N,N-dimethyl-2-(2-aminoethoxy)ethanol, N-methyldiethanolamine, N,N-dimethylethanolamine, and triethanolamine. High pH aqueous particle-free fluids may have a pH of at least 10 and up to and including 11.

[0091] Wetting of contaminated printhead parts is important for successful cleaning. If sufficient sorbosurfactant is used, additional dynamic or static surface tension modifiers may not be required. Otherwise, surfactants may be included. Representative compounds of these types are described in column 12 (lines 27-62) of U.S. Patent 8,764,161 (noted above), the disclosure of which is incorporated herein by reference. One or more surfactants, which may be anionic, cationic, amphoteric, or nonionic in nature, may be present in the aqueous particle-free fluid in an amount of at least 0.01% by weight and no more than 10% by weight, inclusive, based on the total weight of the aqueous particle-free fluid. While any agent that acts to control surface tension over long surface ages may be usefully employed, the surfactant desirably has a mass-normalized molecular weight of less than about 1,000 Daltons. While charged surfactants may diffuse relatively slowly in aqueous fluids due to the aggregation of water of hydration, which effectively increases their binding mass, useful nonionic surfactants desirably have a molecular weight greater than about 350 Daltons, greater than about 400 Daltons, or even greater than about 500 Daltons, thereby ensuring slow diffusion in the bulk of the ink and allowing for well-defined control of the static or equilibrium surface tension.Examples of suitable nonionic surfactants include, but are not limited to, linear or secondary alcohol ethoxylates (such as the TERGITOL® 15-S and TERGITOL® TMN series of compounds available from Dow Chemical Company, and the BRIJ® series of compounds from Croda International Plc.), ethoxylated alkylphenols (such as the TRITON® series of compounds from Dow Chemical Company), fluorosurfactants (such as the ZONYL® compounds from DuPont and the FLUORAD® compounds from 3M), fatty acid ethoxylates, fatty acid amide ethoxylates, ethoxylated and propoxylated block copolymers (such as the PLURONIC® and TETRONIC® series of compounds from BASF Corp.), ethoxylated and propoxylated silicone-based surfactants (such as the SILWET® series of compounds from Momentive), alkyl polyglycosides (such as the BASF® series of compounds from Momentive), alkyl ...BASF® series of compounds from Momentive), alkyl phenols (such as the BASF® series of compounds from Momentive), alkyl phenols (such as the BASF® series of compounds from Momentive), alkyl phenols (such as the BASF® series of compounds from Momentive), alkyl phenols (such as the BASF® series of compounds from Momentive), alkyl phenols (such as the BASF® series of compounds from Mo Polymeric surfactants include acetylenic diol polyethylene oxide surfactants (such as the GLUCOPONS compounds from Evonik Corp.) as well as acetylenic diol polyethylene oxide surfactants (such as the SURFYNOL® family of compounds from Evonik Corp.). Polymeric surfactants can be water-soluble or water-dispersible, depending in part on their tendency to aggregate. A useful surfactant blend suitable for dispersing pigments and redispersing dried aqueous inkjet ink compounds is ZETASPERSE® 1600 (Evonik Corp.).

[0092] Additionally, styrene-acrylic polymers can be used in printhead cleaners and reservoir fluids. The water-soluble or water-dispersible polymer component may be the same or similar to the polymers described above used as polymeric dispersants for pigment colorants or the anionic polymers incorporated into aqueous inkjet ink compositions. Such materials are present in aqueous inkjet ink compositions to improve the physical durability of inkjet-printed images or to enhance other characteristics of the composition, such as colloidal stability against gear pump-mediated recirculation filtration. For example, such water-soluble or water-dispersible polymer components may be random or block copolymers having both hydrophilic and hydrophobic repeat units derived from corresponding ethylenically unsaturated polymerizable monomers. These may be "acrylic" and "styrene-acrylic" based primarily on styrene monomers and (meth)acrylic acid or (meth)acrylate ester monomers. Some useful water-soluble or water-dispersible polymer components may be derived from various monomers and teachings provided in U.S. Patent 8,764,161 (cited above), columns 7 (line 24) to 8 (line 55). Other useful (3) water-soluble or water-dispersible polymeric compounds may be, for example, the water-soluble polymers and water-dispersible polyurethanes having poly(ethylene oxide) segments described in U.S. Patent No. 8,764,161 (noted above), column 10 (lines 24-46). Mixtures of two or more of the same or different classes of these materials may be used if desired.

[0093] The one or more water-soluble or water-dispersible polymer components may be independently present in each aqueous particle-free fluid in an amount of 20% by weight or less, inclusive, or at least 0.2% and 10% by weight or less, inclusive, or even at least 0.5% and 8% by weight or less, inclusive, or more suitably at least 2% and 5% by weight or less, inclusive, all based on the total weight of the aqueous particle-free fluid.

[0094] Aqueous particle-free fluids used for printhead cleaning and reservoir supply desirably contain a humectant, a cosolvent, or both to facilitate inkjet printing startup after extended periods without printing. Any water-soluble humectant or cosolvent known in the inkjet art and compatible with the other requirements of the present invention may be used. By water-soluble, it is meant that the mixture of humectant or cosolvent used with water is sufficiently homogeneous and does not spontaneously phase separate. While individual humectants or cosolvents may be used, useful aqueous particle-free fluid compositions may also use mixtures of two or more humectants and cosolvents, each of which imparts useful properties. Representative examples of humectants and cosolvents used in aqueous-based ink compositions include: (1) alcohols such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, isobutyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; (2) ethylene glycol, di(ethylene glycol), tri(ethylene glycol), tetra(ethylene glycol), propylene glycol, di(propylene glycol), poly(ethylene glycol)s having an average molecular weight in the range of 200 to about 5,000 daltons (particularly poly(ethylene glycol)-400 (an average M of about 400)); n , herein for convenience referred to as PEG-400), polypropylene glycols having an average molecular weight in the range of 200 to about 5000 daltons (particularly poly(propylene glycol)-425 (an average M of about 425) n)), 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 1,2,4-butanetriol, 3-methyl-1,3-butanediol, 2-methyl-1,3-propanediol, 1,5-pentanediol, 1,6-hexanediol, 2-methyl-2,4-pentanediol, 1,7-heptanediol, 2-ethyl-1,3-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, 1,8-octanediol, glycerol, 1,2,6-hexanetriol, 2- Polyhydric alcohols such as ethyl-2-hydroxymethyl-propanediol, 2-methyl-2-hydroxymethyl-propanediol, sugars and sugar alcohols, and thioglycols; (3) polyoxide polyols and their derivatives such as diglycerol, polyglycerol, glycerol ethoxide, glycerol propoxide, glycerides, alkylated and acetylated glycerides; sorbitol or fructose; sugars such as pentaerythritol, pentaerythritol ethoxide, and pentaerythritol propoxide, and their alkylated and acetylated derivatives. Particularly desirable ingredients that act primarily as humectants, retard the drying of aqueous particle-free fluids, and aid in the redispersibility of aqueous ink-jet ink compositions include glycerol, ethylene glycol, diethylene glycol, triethylene glycol, related polyols, and desirable polyhydric alcohol derivatives thereof. Triethylene glycol is particularly useful. The total level of humectants and co-solvents in a fluid or ink is the sum of the individual contributions of the humectants or miscible polar organic co-solvents, DST-modified co-solvents (solvosurfactants), and any other co-solvent sources that may include humectants or organic co-solvents added directly or incidentally during the formulation of the overall aqueous particle-free fluid or ink (e.g., co-solvents accompanying commercial pigment dispersion preparations that may be present as a supplemental ingredient in commercial biocide preparations or to prevent so-called "paint flakes" - dried pigment cakes - from forming around bottle caps, as described in U.S. Application No. 2005 / 0075415 (Harz et al.)).The one or more (c) humectants, co-solvents, or both humectants and co-solvents may be present in the aqueous particle-free fluid in an amount of less than 20% by weight, or at least 0.5% by weight, or at least 1% and no more than 15% by weight, inclusive, or at least 3% and no more than 10% by weight, inclusive, all based on the total weight of the aqueous particle-free fluid. More desirably, the total level of humectants and co-solvents is no more than 10% by weight.

[0095] Each aqueous particle-free fluid may further contain (b) one or more accelerators for one or more compounds in the composition to potentially enhance the effectiveness of the compound represented by structure (I). As described above, such accelerators are generally alkanediols, each having at least 7 carbon atoms and no more than 12 carbon atoms, inclusive, particularly at least 7 carbon atoms and no more than 10 carbon atoms, inclusive. Representative useful compounds that may be used alone or in combination as accelerators are described above. In this regard, 1,2-octanediol is particularly useful as an accelerator.

[0096] The one or more accelerators may be present in each aqueous particle-free fluid in a total amount of 1.5% by weight or less, or 1.25% by weight or less, based on the total weight of the aqueous ink-jet ink composition. The minimum amount may be at least 0.3% by weight.

[0097] One or more (d) supplemental antimicrobial compounds may also be independently present in each aqueous particle-free fluid of the fluid set, and such materials are different from the (b) composition described above. Representative materials include, but are not limited to, iodopropynyl butylcarbamate (CAS 55406-53-6), piroctone olamine (CAS 68890-66-4), 2,4-dichlorobenzyl alcohol (CAS 1777-82-8), boric acid (CAS 10043-35-3), and monovalent and divalent metal ion salts derived from boric acid, and any combination of these materials. A useful amount of the one or more supplemental antimicrobial agents is at least 0.01% and up to 3% by weight, inclusive, based on the total weight of the aqueous particle-free fluid.

[0098] Inkjet printing methods Although numerous publications provide details regarding various methods and apparatus useful for inkjet printing, none of these publications describe the methods as practiced using the (b) composition having a compound represented by structure (I) as defined above, or the advantages achieved by the present invention.

[0099] The method according to the present invention is carried out by first providing a suitable substrate (also known in the art as a "receiver" or "receiver element"), which is understood to have at least one surface with "printable" areas onto which the aqueous ink-jet ink composition can be ink-jetted using suitable equipment and processes.

[0100] Suitable substrates are typically essentially planar, having two opposing surfaces or supporting sides, one or both of which are inkjet printed to impart the same or different images. The substrate may have a single "layer" or level, or may be composed of multiple layers or levels composed of the same or different materials. In most cases, the substrate will have a primary material, such as a cellulosic material, coated with or layered with one or more other types of materials, such as a polymeric coating.

[0101] For example, exemplary substrates can include, but are not limited to, photoglossy receivers such as high-brightness white inkjet paper available from a variety of commercial sources, or plain paper receivers (e.g., as described in U.S. Pat. No. 8,187,371 (supra), column 13, lines 28-34). Photoglossy receivers (also known as expandable or microporous media) can be manufactured with a coated layer on an underlying paper support and are useful for imparting photographic-quality inkjet printed images. Some details of such substrates are provided in U.S. Pat. No. 8,187,371 (supra), column 13, lines 37-51. Plain paper may be treated with a multivalent salt during or after manufacture, as is well known in the art. Other useful substrates are described in U.S. Patents 6,045,917 (Missell et al.), 5,605,750 (Romano et al.), 5,723,211 (Romano et al.), and 5,789,070 (Shaw-Klein et al.).

[0102] Useful paper substrates include plain bond paper, surface-treated paper, coated or calendared commercial glossy paper, resin-coated paper, laminated substrates containing both a paper layer and a polymeric film layer, such as a polyester film layer, and cardboard base stock. Fabrics, cardboard or paperboard materials, organic or inorganic polymeric materials, microporous materials, nonwoven composites, and any other substrate material known in the art for forming inkjet printable substrates can also be used. The substrate may be transparent, translucent, or opaque and may be prepared for inkjet printing in the form of a rigid or semi-rigid sheet, cut or continuous film or web, or wound roll.

[0103] The durability and other properties of inkjet-printed color images can be improved by using a substrate that has been pretreated with a composition to enhance the quality of the resulting image. This pretreatment typically occurs before the substrate is incorporated into an inkjet printing apparatus (such as a continuous inkjet printing apparatus), although in some cases the substrate may be pretreated in the apparatus with one or more aqueous inkjet ink compositions prior to inkjet printing. One or both opposing surfaces (planar sides) of the substrate may be pretreated, or one support surface may be pretreated and the opposite support surface may remain untreated.

[0104] For example, the substrate may be pretreated with a pretreatment composition containing a water-soluble polyvalent metal ion salt, such as a salt containing one or more polyvalent cations, including, but not limited to, calcium, magnesium, barium, zinc, and aluminum cations, with calcium and magnesium cations being particularly useful. Examples of useful polyvalent metal cation salts for providing such cations are known in the art, so that useful salts can be determined by those skilled in the art. Details of such pretreatment procedures and compositions are provided, for example, in U.S. Patent 9,067,448 (Dannhauser et al.).

[0105] Each aqueous inkjet ink composition according to the present invention (having the required viscosity and all of (a) the polymer-dispersed pigment colorant, (b) the composition consisting of the compound of structure (I), and (c) the compound, as described above) can be inkjet printed in a controlled manner from a suitable printhead onto at least one surface of a substrate to provide an inkjet printed image on that surface of the substrate.

[0106] While the aqueous inkjet ink compositions according to the present invention may be useful in one or more DOD printing systems, advantages are particularly apparent when the present invention is practiced using CIJ printing processes and equipment. There are multiple CIJ printing processes known in the art, and the present invention is not limited to any one CIJ process, although certain CIJ processes may be more useful in practicing the present invention than others. Generally, such CIJ processes use one or more aqueous inkjet ink compositions ejected from one or more printheads (containing nozzles), with unprinted aqueous inkjet ink compositions being collected and reused multiple times by the printing system until depleted. Additionally, CIJ printing systems may have built-in replenishment systems. Details of such CIJ processes and equipment are provided, for example, in U.S. Patent No. 8,173,215 (noted above).

[0107] Thus, in most CIJ inkjet printing processes, each aqueous inkjet ink composition according to the present invention is ejected or printed from a dedicated main fluid delivery section as a continuous stream of aqueous inkjet ink composition that is separated into both printing and non-printing droplets. The non-printing droplets of each aqueous inkjet ink composition may be collected using a suitable collection means, such as a "catcher," and returned to its respective main fluid delivery section. This entire situation may be carried out using a single (first) aqueous inkjet ink composition alone or in combination with one or more "additional" aqueous inkjet ink compositions having the same or different "color" or shade as the first aqueous inkjet ink composition. In this case, the multiple aqueous inkjet ink compositions are inkjet printed in a controlled manner, in a selected order that can be controlled by specific software and digital input, to impart a multicolor inkjet-printed image to the surface of a substrate.

[0108] Furthermore, inkjet printing of an aqueous "colorless" or aqueous particle-free composition or fluid (as described above) may be performed simultaneously or sequentially with inkjet printing of a "colored" aqueous inkjet ink composition. For example, according to U.S. Patent Application Publication No. 2018 / 0051184 (Lussier et al.), a colorless lacquer or protective coating may be applied over a single-color or multi-color inkjet printed image.

[0109] As provided herein, each aqueous inkjet ink composition, fluid aqueous colorless composition, or aqueous particle-free composition used in such a process may be designed hereby to contain the described (a) one or more polymer-dispersed pigment colorants (in the case of aqueous inkjet ink compositions only), the described (b) composition consisting of a compound defined by structure (I), and the described (c) compound. However, all such aqueous compositions used in a method according to the present invention may further contain one or more (d) supplemental antimicrobial compounds that are all different from the (b) composition.

[0110] Useful CIJ printing processes and equipment may include replenishment systems that measure the electrical resistivity of the ink and are described, for example, in U.S. Patent 5,526,026 (Bowers) and EP 0597628B1 (Loyd et al.). Useful CIJ printing processes and equipment that use other means for detecting ink concentration are disclosed in U.S. Patent 7,221,440 (McCann et al.), EP 0571784B1 (McCann et al.), and EP 1,013,450B1 (Woolard et al.).

[0111] In one embodiment, basic replenishment is performed as follows: a fluid system contains an ink resistivity measurement cell, and an aqueous ink-jet ink composition passes through the measurement cell as it is recirculated through the ink-handling portion of the system, including the printhead. A circulation means determines the resistance of the ink resistivity cell. A logic and control unit responsive to the circulation means controls the movement of the aqueous ink-jet ink composition from a supplemental "ink" delivery and the movement of an aqueous particle-free fluid ("carrier fluid") from a supplemental carrier fluid delivery to the main fluid delivery of the system to maintain a desired resistivity of the aqueous ink-jet ink composition. The volume of the aqueous ink-jet ink composition is monitored by a float valve position, and when a predetermined volume is depleted, the predetermined volume is replaced either by aqueous ink-jet ink composition from the supplemental "ink" delivery or by carrier fluid from a supplemental carrier fluid delivery.

[0112] Thus, the first and any additional aqueous ink-jet ink compositions may each be supplemented with a first and any additional aqueous ink-jet ink composition each consisting essentially of the same or different (a), (b) and (c) components described above, in particular the (b) composition consisting of a compound defined by the same or different structure (I) described above.

[0113] In another example, the method according to the present invention may further comprise the step of replenishing the primary fluid supply with an aqueous particle-free fluid having a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25° C., the aqueous particle-free fluid comprising: (b) composition, which may be the same or different from that present in the first aqueous inkjet ink composition described above; It essentially consists of:

[0114] Such aqueous particle-free fluids may further comprise a (d) supplemental antimicrobial compound, as described above, that is different from the (b) composition. For example, the (d) supplemental antimicrobial compound can be iodopropynyl butylcarbamate, piroctone olamine, 2,4-dichlorobenzyl alcohol, boric acid, or a combination of these compounds.

[0115] The aqueous particle-free fluid used for replenishment may also contain one or more accelerators for the one or more (b) compounds, each of which is an alkanediol having at least 7 carbon atoms and no more than 12 carbon atoms, inclusive, in an amount of no more than 1.5% by weight, based on the total weight of the aqueous ink-jet ink composition. For example, the accelerator can be 1,2-octanediol.

[0116] In some embodiments, the method according to the present invention is carried out using a plurality of printing droplets formed from a continuous fluid stream, with non-printing droplets of a different volume than the printing droplets being diverted by a droplet deflection means into a "gutter" for collection and recycling. Details regarding such CIJ printing systems and equipment are provided in, for example, U.S. Patents 6,588,888 (Jeanmaire et al.), 6,554,410 (Jeanmaire et al.), 6,682,182 (Jeanmaire et al.), 6,793,328 (Jeanmaire et al.), 6,866,370 (Jeanmaire et al.), 6,575,566 (Jeanmaire et al.), and 6,517,197 (Hawkins et al.) and U.S. Patent Application Publication No. 2002 / 0202054 (Jeanmaire et al.).

[0117] In other embodiments, the aqueous inkjet ink compositions may be printed using an apparatus capable of controlling the direction of formed printing and non-printing droplets by asymmetrically applying heat to a fluid stream, which acts to initiate droplet breakup and direct the resulting droplets, as described, for example, in U.S. Pat. Nos. 6,079,821 (Chwalek et al.) and 6,505,921 (Chwalek). Useful agitation, heat distribution, printhead, and fluid filtration means for CIJ printing are described, for example, in U.S. Pat. No. 6,817,705 (Crockett et al.), the disclosure of which is incorporated herein by reference.

[0118] A simplified schematic diagram of a CIJ printing system is provided in FIG. 1 of US Pat. No. 8,764,161 (noted above).

[0119] Furthermore, in some embodiments, the method according to the present invention further comprises: ceasing inkjet printing of the first aqueous inkjet ink composition; delivering an aqueous particle-free fluid (described above) to the printhead from a maintenance fluid delivery station; and ejecting an aqueous particle-free fluid from the printhead and purging the first aqueous ink-jet ink composition from the printhead. wherein the aqueous particle-free fluid has a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25°C as measured using a falling ball viscometer; a (b) composition that is the same as or different from that present in the first aqueous inkjet ink composition, as described above; It essentially consists of:

[0120] Such aqueous particle-free fluids may further contain up to 15% by weight, based on the total weight of the aqueous particle-free fluid, of one or more compounds selected from water-soluble humectants, co-solvents, and both water-soluble humectants and co-solvents.

[0121] Additionally, the aqueous particle-free fluid may further contain (b) one or more accelerators for the composition, each of which is an alkanediol having at least 7 carbon atoms and no more than 12 carbon atoms, inclusive, in an amount of no more than 1.5% by weight, based on the total weight of the aqueous particle-free fluid.

[0122] The aqueous particle-free fluid used in this sequence may be considered a "maintenance fluid" used to clean the printhead at selected intervals or when a print job is completed or interrupted for any reason. The maintenance fluid may be stored in the printhead for a period of time, after which delivery of the first or additional aqueous ink-jet ink compositions from the main and any other respective fluid delivery units to the respective printheads may be resumed for a new printing sequence.

[0123] Further details regarding the use of aqueous particle-free compositions as maintenance fluids in this manner are provided in US Pat. No. 8,764,161 (noted above).

[0124] According to some embodiments of the present invention, a method of printing an image using a continuous inkjet printer system comprises: providing a substrate (as described above); providing a jetting module having a plurality of nozzles, including nozzles in fluid communication with a primary fluid delivery portion containing a first aqueous ink-jet ink composition (such equipment is readily known to those skilled in the art in view of the teachings of U.S. Pat. No. 9,010,909 (Nelson et al.)); forming droplets of the first aqueous ink-jet ink composition during ejection of the first aqueous ink-jet ink composition from a nozzle in fluid communication with a main fluid delivery portion by droplet stimulation in response to a time-varying electrical signal (the equipment used to perform this function will be readily apparent to one skilled in the art in view of the teachings of U.S. Pat. No. 9,010,909 (Nelson et al.)); providing a capture region comprising a droplet contact surface (known to those skilled in the art in view of the teachings of U.S. Pat. No. 9,010,909 (noted above)); using a deflection mechanism to deflect at least some of the droplets of the first aqueous ink-jet ink composition onto the droplet contact surface of the trap while allowing other droplets of the first aqueous ink-jet ink composition to pass through the trap and be deposited on the surface of the substrate (as will be known to those skilled in the art in view of the teachings of U.S. Pat. No. 9,010,909 (noted above)); and causing a droplet of the aqueous ink-jet ink composition in contact with the droplet contact surface to flow along the droplet contact surface (known to those skilled in the art in view of the teachings of U.S. Pat. No. 9,010,909 (noted above)); wherein the first aqueous inkjet ink composition has a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25°C; (a) one or more polymer-dispersed pigment colorants (as described above) in a total amount of at least 0.9% and no more than 6% by weight, inclusive, based on the total weight of the aqueous inkjet ink composition; (b) a total amount of at least 0.5% and no more than 2% by weight, inclusive, of the following structure (I): HO-CH2-CH2-R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). a composition comprising one or more compounds represented by the formula: (c) 15% by weight or less of one or more compounds selected from water-soluble humectants, cosolvents, and both water-soluble humectants and cosolvents (described above), based on the total weight of the aqueous inkjet composition. consists essentially of Each of the one or more polymer-dispersed pigment colorants has a 50th percentile particle diameter of less than 70 nm and a 95th percentile particle diameter of less than 150 nm, all particle diameters measured using a dynamic light scattering particle size analyzer.

[0125] In some embodiments, at least some of the droplets of the first aqueous inkjet ink composition used in the described methods (deflected droplets) are smaller than other droplets of the first aqueous inkjet ink composition (non-deflected and deposited droplets).

[0126] In yet another embodiment, at least some of the droplets of the first aqueous inkjet ink composition (the deflected droplets) are larger than other droplets of the first aqueous inkjet ink composition (the non-deflected and deposited droplets).

[0127] Furthermore, the method according to the invention for continuous ink jet (CIJ) printing comprises having a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25°C for use in the main fluid delivery section of a continuous ink jet printer (as known in the art); (a) one or more polymer-dispersed pigment colorants (as described above) in a total amount of at least 0.9% and no more than 6% by weight, inclusive, based on the total weight of the aqueous inkjet ink composition; (b) a total amount of at least 0.5% and no more than 2% by weight, inclusive, of the following structure (I): HO-CH2-CH2-R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). a composition comprising one or more compounds represented by the formula: (c) 15% by weight or less of one or more compounds selected from water-soluble humectants, cosolvents, and both water-soluble humectants and cosolvents (described above), based on the total weight of the aqueous inkjet composition. delivering a first aqueous inkjet ink composition (described above) consisting essentially of: each of the one or more polymer-dispersed pigment colorants having a 50th percentile particle diameter of less than 70 nm and a 95th percentile particle diameter of less than 150 nm, all particle diameters measured using a dynamic light scattering particle size analyzer; ejecting a continuous stream of droplets of a first aqueous inkjet ink composition from a droplet-generating mechanism (as known in the art); in response to electrical signals received from a control mechanism, sorting print droplets for imaging onto a substrate and non-print droplets that are collected and returned to a main fluid delivery section, both types of droplets being from the first aqueous-based ink-jet ink composition; and replenishing the main fluid delivery section as a function of the resistivity of the first aqueous-based ink-jet ink composition in the main fluid delivery section. Replenishing may be accomplished using replenishing the first aqueous ink-jet ink composition described above, or replenishing an aqueous particle-free fluid.

[0128] Further details of CIJ printing processes and useful CIJ apparatus are described, for example, in U.S. Patents 8,585,189 (Marcus et al.), 8,651,632 (Marcus et al.), 8,696,094 (Marcus et al.), 8,888,256 (Marcus), and 9,969,178 (Roberts et al.).

[0129] printed matter The resulting inkjet print (or printed receptor element) can have a single color or multicolor image on at least one supporting surface of an article including, but not limited to, a document, banknote, postage stamp, packaging material, fabric, polymeric film or sheet, nonwoven web or sheet, clothing, a label for a perfume or wine bottle, a raffle ticket, a passport, a driver's license, and other articles or documents that would be readily apparent to one skilled in the art using the teachings provided herein.

[0130] The following examples are presented to illustrate the practice of one or more aspects and embodiments of the present invention.

[0131] In the preparations and examples that follow, the reported pigment content of the pigment dispersions is based on the weight percent of colorant as received in the final dispersion.

[0132] Preparation of aqueous inkjet ink and feed fluid compositions Preparation of polymeric dispersants and additives: Polymer Dispersant P-1 In a typical procedure, a 5-liter, three-necked round-bottom flask equipped with a mechanical stirrer, reflux condenser, and gas inlet was charged with 225 g of 1-methoxy-2-propanol and purged with nitrogen. The initiator, PERKADOX® AMBN-GR (1.9 g) from Akzo-Nobel Chemicals, Inc., was added with stirring. A reactant reservoir was charged with 225 g of 1-methoxy-2-propanol, 23.4 g of 1-dodecanethiol, 203.5 g of benzyl methacrylate, 165.0 g of stearyl methacrylate, and 181.5 g of methacrylic acid, and the solution was degassed with nitrogen sparging. PERKADOX® AMBN-GR (7.7 g) was added to the solution and mixed. The reactor temperature was increased to 77°C, and the reactants were pumped from the reservoir at approximately 2.3 ml / min for 360 minutes. The reaction mixture was then stirred for at least 12 hours at approximately 77°C. The resulting polymer was fully neutralized with N,N-dimethylethanolamine and stirred for 45 minutes. The reaction mixture was diluted with 2,580 g of water and filtered through a Pall Corp. ULTIPLEAT® polypropylene cartridge filter. The final polymer solution of Polymeric Dispersant P-1 had a concentration of approximately 20% solids by weight and a pH of 8.6. The weight average molecular weight of the polymer was 9,070 daltons.

[0133] Polymer Dispersant P-2 Polymeric Dispersant P-2 was prepared in a manner similar to P-1, except that instead of using 1 equivalent of N,N-dimethylethanolamine during the neutralization step, 90% of the acid was reacted with potassium hydroxide. The final polymer solution of Polymeric Dispersant P-2 had a concentration of approximately 17% solids by weight.

[0134] Polymer Additive P-3 A benzyl methacrylate-methacrylic acid copolymer having a monomer weight ratio of 77:23 and an acid value of about 137 was neutralized 90% with potassium hydroxide to obtain an aqueous solution. The final polymer solution of polymer additive P-3 had a concentration of about 25% solids by weight.

[0135] Polymer Additive P-4 JONCRYL® HPD696, a styrene-acrylic copolymer from BASF Dispersions & Pigments North America with a weight average molecular weight Mw of 16,000 Daltons, was neutralized 90% with potassium hydroxide to obtain an aqueous solution. The final polymer solution of polymer additive P-4 had a concentration of approximately 20% solids by weight.

[0136] Polymer Additive P-5 A 50-liter round-bottom flask equipped with a thermometer, stirrer, water condenser, nitrogen inlet, and vacuum outlet was charged with 1,454.4 g of TERATHANE® 2000 polyether glycol, 670.5 g of 2,2-bis(hydroxymethyl)propionic acid, 313.2 g of 1,4-butanediol, and 3,771 g of ethyl acetate. The temperature was adjusted to 65°C, and when a homogeneous solution was obtained, 1,840.9 g of isophorone diisocyanate was added, followed by 184 g of ethyl acetate. The temperature was raised to 78°C and maintained for 22 hours to complete the reaction. The reaction mixture was then diluted with 86 g of 2-propanol and neutralized with 467.9 g of N,N-dimethylethanolamine. 18 kg of distilled water was added under high shear, and the organic solvent was then removed by distillation under vacuum. The resulting aqueous dispersion was filtered and determined to have a non-volatile solids concentration of about 25% by weight and a pH of about 8.0. The weight average molecular weight (Mw) of the polyurethane dispersion was found to be about 19,800 by size exclusion chromatography.

[0137] Preparation of pigment dispersion: Pigment Dispersion KD-1 Water (1,000 g) and a solution of polymeric dispersant P-1 (1,000 g of a 19.9 wt.% solution) were added to a 2.5-gallon (9.46 liter), 9-inch (22.9 cm) diameter, 12-inch (30.5 cm) deep, double-walled stainless steel mixing vessel containing four baffle plates. A nominal 4-inch (10.2 cm) ring disperser impeller (Hockmeyer Equipment Corp. D-blade) driven by a Charles Ross & Son Co. Model HSM-100LH-2 high shear mixer was centered 2 inches (5.1 cm) above the bottom of the mixing vessel and agitation was initiated. Cabot Corp. BLACK PEARLS® 900 carbon black pigment (500 g) was slowly mixed into the fluid. As the impeller speed increased, milling media (3,000 g) containing beads of polystyrene resin (a copolymer derived from styrene and a divinylbenzene / ethylvinylbenzene mixture) with an average particle diameter of 50 μm was slowly added. The mixture was milled at an impeller blade tip speed of approximately 19 m / s for approximately 20 hours at an internal temperature of 25-35°C. Samples were periodically removed, diluted, and filtered for particle size determination using a Microtrac Inc. NANOTRAC® NPA150 Dynamic Light Scattering Particle Size Analyzer. Upon milling completion, the dispersion / media mill mixture was further diluted with aqueous solution (1,667 g) to a final pigment concentration of approximately 12 wt. %, a polymeric dispersant concentration of approximately 4.8 wt. % including counterion, and a theoretical dispersion batch size of approximately 4,167 g. The impeller was removed, and the milling media was separated from the dispersion by filtration. Final filtration through a Pall Corp. PROFILE II® depth filter with 0.3 μm removal efficiency yielded roughly 4 kg of dispersion, with an approximate yield of 80%. As characterized by a NANOTRAC® NPA150 dynamic light scattering particle sizer, the volume-weighted particle 50th percentile particle size distribution diameter was approximately 55 nm and the 95th percentile particle size distribution diameter was approximately 99 nm.

[0138] Pigment Dispersion MD-1 Magenta pigment dispersion MD-1 was prepared in a manner similar to pigment dispersion KD-1, except that CINQUASIA® Magenta D4500J from BASF Dispersions & Pigments North America was used instead of the carbon black pigment. The resulting dispersion had approximately 12 wt. % pigment and 6.1 wt. % polymeric dispersant containing a counterion. As characterized by a NANOTRAC® NPA150 dynamic light scattering particle sizer, the volume-weighted median particle size was approximately 16 nm, and the 95th percentile particle size distribution diameter was approximately 59 nm.

[0139] Pigment Dispersion CD-1 Cyan pigment dispersion CD-1 was prepared in a manner similar to pigment dispersion KD-1, except that Pigment Blue 15:4 and Pigment Green 7 were used in a 3.75:1 ratio in place of carbon black pigment, and polymeric dispersant P-2 was used in place of P-1, in the presence of Lubrizol Corp.'s SOLSPERSE® 12000 and polymeric additive P-3. The resulting dispersion had approximately 12 wt.% pigment and 8.5 wt.% polymeric dispersant containing a counterion. As characterized by a NANOTRAC® NPA150 dynamic light scattering particle sizer, the volume-weighted 50th percentile particle size distribution diameter was approximately 28 nm, and the 95th percentile particle size distribution diameter was approximately 86 nm.

[0140] Pigment Dispersion YD-1 To a 10-gallon (37.85 liter), 13-inch (33 cm) diameter, 17-inch (43.2 cm) deep, double-walled stainless steel mixing vessel containing four baffles, 2,560 g of water and 2,400 g of a 15% solution of polymeric dispersant P-2 were added. A nominal 6-inch (15.2 cm) circular dispersing impeller (D-blade from Hockmeyer Equipment Corp.) driven by a Hockmeyer Model HBI-7.5-11-99 high-shear mixer was centered 3 inches (7.6 cm) above the bottom of the mixing vessel and agitation was initiated. Sun Chemical Co. Pigment Yellow 74 (1,200 g) was slowly added to the fluid. With the impeller speed increasing, grinding media containing polymeric beads (7,200 g) with an average particle diameter of 50 μm derived from styrene and a divinylbenzene / ethylvinylbenzene mixture was slowly added. The mixture was milled at an impeller blade tip speed of approximately 20 meters / second for approximately 20 hours at an internal temperature of 25-30°C. The dispersion / media mixture was further diluted with water (6,000 g) to a final pigment concentration of approximately 12% by weight and a polymer additive P-2 concentration of approximately 4.1% by weight. The impeller was removed, and the dispersion was separated from the milling media by filtration. Final filtration through a Pall Corp. PROFILE II® depth filter with a 0.3 μm particle removal rating yielded roughly 10.6 kg of dispersion. The volume-weighted 50th percentile particle size distribution diameter of the dispersion was approximately 11 nm, and the 95th percentile particle size distribution diameter was approximately 16 nm, as determined by a NANOTRAC® NPA150 dynamic light scattering sizer.

[0141] Preparation of continuous inkjet ink and feed fluid compositions: Water-based black inkjet ink composition A black pigment-based CIJ aqueous inkjet ink composition KA(E) was prepared using pigment dispersion KD-1 by combining the ingredients in the relative proportions reported in TABLE I below. In a typical procedure, 15.0 kg of the aqueous inkjet ink composition was mixed by individually adding the ingredients to a 30-liter cross-linked high-density polyethylene flat-bottom tank, using a 2-inch (5.1 cm) impeller rotating at approximately 1,000 rpm to provide good mixing. The ingredients (if so indicated) were added in the following order of functional ingredients: water, acid or acid solution, amine salt solution, humectant and organic cosolvent, amine base, metal corrosion inhibitor, preservative or biocide, sorbosurfactant, soluble azo dye, pigment dispersion, surfactant, and defoamer. The aqueous inkjet ink composition was mixed for approximately 2 minutes between component additions, and then stirred for 1 hour after the final addition of surfactant or defoamer. The aqueous inkjet ink composition was filtered through a Pall Corp. ULTIPOR® N66 cartridge filter medium with an effective pore size of 0.2 μm at a rate of approximately 0.5 liters / minute / inch (0.2 liters / minute / cm) of medium. The pigment particles in the resulting aqueous inkjet ink composition had a volume-weighted 50th percentile particle size of 53 nm and a 95th percentile particle size of 79 nm, a pH of approximately 8.6, an electrical conductivity of 1.14 mS / cm, a dynamic viscosity of 1.60 mPa-sec at 25° C., and a viscosity of 1.035 g / cm at 25° C. 3 and a static surface tension of 37.2 mN / m at 25°C.

[0142] [Table 1]

[0143] Water-based cyan inkjet ink composition Aqueous cyan CIJ inkjet ink compositions CA through CC were prepared from pigment dispersion CD-1 by combining the components in the relative proportions shown in TABLE II below in a manner similar to that described for aqueous inkjet ink composition KA. These inkjet ink compositions exhibited the physical properties reported in TABLE III below.

[0144] [Table 2]

[0145] [Table 3]

[0146] Water-based magenta inkjet ink composition Water-based magenta CIJ inkjet ink compositions MA through MC were prepared from pigment dispersion MD-1 by combining the components in the relative proportions reported in TABLE IV below in a manner similar to that described for water-based black inkjet ink KA. These water-based magenta inkjet ink compositions exhibited the physical properties reported in TABLE V below.

[0147] [Table 4]

[0148] [Table 5]

[0149] Water-based yellow inkjet ink composition Aqueous yellow CIJ inkjet ink composition YA(E) was prepared from pigment dispersion YD-1 by combining the components in the relative proportions reported in TABLE VI below in a manner similar to that described for aqueous inkjet ink composition KA.

[0150] [Table 6]

[0151] The pigment particles in this aqueous inkjet ink composition had a volume-weighted 50th percentile particle size of 12 nm and a 95th percentile particle size of 31 nm as characterized by a NANOTRAC® NPA150 dynamic light scattering particle sizer. It had a pH of about 8.4, an electrical conductivity of 2.26 mS / cm, a dynamic viscosity of 1.62 mPa-sec at 25°C, and a viscosity of 1.020 g / cm at 25°C. 3 and a static surface tension of 36.3 mN / m at 25°C.

[0152] Replenishment fluid for continuous inkjet printing (CIJ) CIJ replenisher fluids RA(E) and RB(E) were prepared in a manner similar to that described for aqueous black inkjet ink composition KA by combining the components in the relative proportions shown in TABLE VII below. These aqueous particle-free fluids exhibited the physical properties shown in TABLE VIII below.

[0153] [Table 7]

[0154] [Table 8]

[0155] Continuous Ink Jet Printing (CIJ) Printhead Cleaner and Reservoir Fluid CIJ printhead cleaner and reservoir fluids SA (C) and SB (E) were prepared in a manner similar to that described for aqueous black inkjet ink composition KA by combining the ingredients in the relative proportions shown in TABLE IX below. These aqueous particle-free fluids exhibited the physical properties shown in TABLE X below.

[0156] [Table 9]

[0157] [Table 10]

[0158] Microbial growth susceptibility testing: The aqueous inkjet ink compositions described above were subjected to ten-way stress preservative efficacy tests using cultures of specific microorganisms. The test organisms were individually cultured to known concentrations of colony-forming units (CFU), which were then mixed together and inoculated into 50 grams of test samples of the aqueous inkjet ink composition. At specified time intervals, the inoculated samples were tested. The viable population of the inoculum was assessed by streaking 10 μl of the thoroughly mixed sample onto a trypticase soy agar plate and incubating. The presence of microorganisms was recorded using the growth grading shown in TABLE XI below. Each sample was re-inoculated and evaluated up to 10 times during the study, during which any changes in the physical appearance of the sample were observed.

[0159] [Table 11]

[0160] TABLE XII below reports the results of a 10-way stress growth rating test on the aqueous inkjet ink compositions ("inks") described above, where the initial baseline growth rating for microorganisms in the as-received compositions was determined to be "1." The column identified with "R-OH" represents the absence or presence of the sorbosurfactants 2-phenoxyethanol (PhE) or 2-phenylethanol (PEA) in the samples.

[0161] [Table 12]

[0162] The results, shown in TABLE XII, indicate that significant microbial growth (high colony counts) was observed in comparative compositions ("inks") CA(C) and MA(C) after the initial small inoculation. The data in TABLE XII also demonstrate that the presence of 2-phenoxyethanol (PhE) in inventive compositions ("inks") CB(E) and MB(E), or 2-phenylethanol (PEA) in inventive compositions ("inks") CC(E), MC(E), YA(E), and KA(E), resulted in minimal or undetectable microbial growth across all 10 challenges.

[0163] In the same manner as the aqueous inkjet ink compositions, the aqueous particle-free fluids were subjected to ten stress preservative efficacy tests using the same culture strains of specific microorganisms. TABLE XIII below shows the results of the ten stress growth rating tests on these fluids, where the initial baseline growth rating for the microorganisms in the as-received fluids was determined to be "1." The column identified with "R-OH" represents the absence or presence of the sorbosurfactant 2-phenoxyethanol (PhE) or 2-phenylethanol (PEA) in the fluid.

[0164] [Table 13]

[0165] The results reported in TABLE XIII show that although significant microbial growth (increased colony counts) was observed with the inventive replenisher fluids RA(E) and RB(E) after a small initial inoculation, the results are expected to be superior to replenisher fluids containing pure water without any sorbosurfactant. The results in TABLE XIII also show that virtually no microbial growth was observed with the comparative printhead cleaning and reservoir fluid SA(C), which contained the sorbosurfactant diethylene glycol monobutyl ether as the dry ink cleaning agent, with only Load No. 7 producing significant growth, a rating of 3. However, the presence of 2-phenoxyethanol (PhE) in the inventive printhead cleaning and reservoir fluid SB(E) produced undetectable microbial growth across all 10 loads.

[0166] It will be appreciated that embodiments of the aqueous inkjet ink composition and aqueous particle-free fluid according to the present invention may be suitably resistant to the growth of contaminating microorganisms and do not contain, i.e. are substantially free of, any substantial amount of commonly used preservatives, such as isothiazolinone compounds and formaldehyde-releasing compounds (e.g., 2-bromo-2-nitropropane-1,3-diol and hexamethylenetetramine chloroallyl chloride) and biocides currently listed on the List of Approved Active Substances (Article 95 list) published by the European Chemical Agency (ECHA), a government agency of the European Union.

[0167] Continuous inkjet printing of aqueous inkjet ink compositions: In a representative procedure, the ink reservoir of a continuous ink jet printing test stand fixture was loaded with the aqueous cyan ink jet ink composition CC(E) of the present invention. Repeated cycles of draining, flushing, and filling the ink reservoir and fluid lines with CC(E) were performed to ensure that the new composition was not contaminated by previous inks in the equipment. The equipment consisted of the following elements: (1) (a) pressurizing the composition ("ink") to greater than 60 psig (0.41 MPa) to produce an ink volumetric flow rate of up to about 2 liters / minute; (b) delivering the pressurized ink to the drop generator of a continuous ink jet printhead; (c) returning unprinted ink to an ink reservoir in a fluidic system under vacuum; (d) detecting the ink concentration in the ink reservoir by electrical resistivity measurement, and replenishing the ink with a replenishment fluid RB(E) of the present invention if it has become concentrated due to evaporation of water, or conversely, adding more aqueous ink jet ink composition CC(E) to the ink reservoir if it has become depleted through use in printing but is at the correct concentration; (e) a fluidic system that can provide a printhead cleaning and reservoir fluid SB(E) of the present invention to the printhead to flush the nozzles and duct system and shut down the system for a safe reservoir for a significant duration to restore accurate printing after contamination due to accumulation of dried ink; (2) a vacuum drum capable of supporting a sheet of porous media (e.g., uncoated free-sheet paper) or non-porous media (e.g., coated or uncoated polymer film) and continuously spinning it at a precise speed synchronized by a control unit to simulate web transport of a print substrate in a roll format; (3) (a) a KODAK PROSPER Press Jetting Module having a MEMS silicon-based drop generator that forms ink droplets and a Coanda gutter that captures non-printing droplets when the printer is not printing an image file or when it is not printing a given pixel even when it is printing an image file;(b) a continuous ink jet printhead PIC box assembly including (b) a non-printing drop deflector that creates a zone of intersection with the drop curtain provided by the positive and negative air duct assemblies and directs those drops into the Coanda gutter, and (c) ink return lines to the ink reservoir; and (4) a print controller that (a) controls the print drum speed and synchronizes the drum position with the data feed to the jetting module, and (b) conveys electrical signals to the jetting module CMOS circuitry that uses nozzle plate heater pulse patterns with optimized waveforms to translate the rasterized image into pixel-by-pixel ink stream stimulation instructions to generate non-printing trapped drops and printing drops of ink that are delivered to pixel locations on the print substrate surface as required;

[0168] The fluidic system used a Micropump Inc. MICROPUMP® Series GJ-N23DB380A gear pump to deliver ink through a Pall Corp. disposable filter assembly capsule filter DFA4201ZU0045 containing ULTIPOR® GF-HV glass fiber media with a nominal effective pore size of 0.45 μm at a pressure drop of approximately 65 psid (0.45 MPa) at the nozzle plate, generating a uniform droplet velocity of approximately 20 m / s at the nozzle plate. The fluidic system's gear pump speed setting was continuously adjusted to provide and maintain constant fluid pressure at the jetting module, generating the desired uniform droplet velocity per system specifications. The system parameter settings required for proper jetting and accurate ink replenishment were determined and recorded in a computer file called an "inkdex" to enable printing on other systems, such as the KODAK® PROSPER S10 Imprinting Systems, a two-up web press adapted for production. The deflected non-printing ink droplets were captured in a Coanda gutter and returned to the fluid system ink tank under vacuum. Continued operation of the printer in the non-printing droplet capture mode gradually evaporated the aqueous ink solvent vehicle. When the ink concentration became concentrated above about 5% based on the ink's electrical resistivity determination, it was maintained within about 5% of the original ink concentration by adding aqueous, pigment-free replenisher fluid to the ink. The test target was a raster image processed to generate digital print signal indications for each pixel location with an addressability of 600 x 600 pixels per inch (ppi) (236 x 236 pixels per centimeter (ppcm)) for speeds up to about 1,000 FPM, at a suitable transport speed of the test substrate. NewPage STERLING® Ultra Gloss paper and / or uncoated, untreated free-sheet paper (e.g., International Paper 20-lb (75 g / m)) was used. 2A DATASPEED® Laser MOCR was mounted on a rotating drum at a constant speed synchronized with the print data controller. Various test images were printed at different substrate transport speeds to profile the system's functional print speed capability using a 600 nozzles per inch PROSPER Press Jetting Module with a near-production printhead assembly configuration, resulting in a jet curtain print width of 4.25 inches (10.8 cm). Operational stability and startup robustness ("viability") were also investigated by printing into a catch pan to evaluate time-dependent jet linearity and long-term print ruggedness, and by performing multiple shutdown and startup sequences to evaluate the time to achieve the first acceptable print and any required interventions (service cleaning (cross-flushing with ink), duct cleaning (flushing with reservoir fluid), and nozzle plate wiping). The aqueous inkjet ink composition CC(E) was found to be viable and was mounted on a production-matched two-up web press, the KODAK PROSPER S10 Imprinting Systems, for long-term testing.

[0169] The present invention has been specifically illustrated above for use in a continuous ink jet printer system employing a gas flow drop deflection mechanism, a thermal drop stimulation device, and a nozzle plate fabricated from silicon. However, the present invention can also be used in continuous ink jet printer systems employing an electrostatic drop deflection mechanism, a pressure regulating or vibration physical stimulation device, and a nozzle plate fabricated from other types of materials. The electrostatic deflection can be of a type that includes separate drop charging and drop deflection electrodes, or can be of a type that incorporates both functions into a single electrode.

Claims

1. A fluid set comprising two or more different aqueous particle-free fluids, each independently having a dynamic viscosity of 5 centipoise (5 mPa-seconds) or less at 25°C, each of the two or more different aqueous particle-free fluids independently comprising: (b) a total amount of at least 0.5% and no more than 2% by weight, inclusive, of the following structure (I), based on the total weight of the aqueous particle-free fluid: HO-CH 2 -CH 2 -R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). A composition comprising one or more compounds represented by A fluid set comprising: at least one of the two or more different aqueous particle-free fluids further comprises a sorbosurfactant in an amount of at least 0.1% and no more than 20% by weight, inclusive, based on the total weight of at least one of the two or more different aqueous particle-free fluids; 1. A fluid set, wherein the sorbosurfactant is selected from ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, polyethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, diethylene glycol monobutyl ether acetate, and combinations thereof.

2. 10. The fluid set of claim 1, wherein at least one of the two or more different aqueous particle-free fluids further comprises (d) a supplemental antimicrobial agent different from the composition of (b).

3. 3. The fluid set of claim 2, wherein the supplemental antimicrobial agent in (d) is iodopropynyl butylcarbamate, piroctone olamine, 2,4-dichlorobenzyl alcohol, boric acid or a metal ion salt derived from boric acid, or a combination of these compounds.

4. 4. The fluid set of any one of claims 1 to 3, wherein at least one of the two or more different aqueous particle-free fluids further comprises one or more accelerators for the one or more compounds of structure (I) in the composition of (b), each accelerator being an alkanediol having at least 7 carbon atoms and no more than 12 carbon atoms, inclusive, in an amount of no more than 1.5% by weight, based on the total weight of at least one of the two or more different aqueous particle-free fluids.

5. 5. The fluid set of claim 1, wherein at least one of the two or more different aqueous particle-free fluids further comprises a non-ionic surfactant in an amount of at least 0.1% by weight and no more than 10% by weight, inclusive, based on the total weight of at least one of the two or more different aqueous particle-free fluids.

6. 6. The fluid set of claim 1, wherein at least one of the two or more different aqueous particle-free fluids further comprises a water retention agent, an organic solvent that solvates the dried pigment particles, a metal corrosion inhibitor, or a styrene acrylic polymer.

7. an aqueous particle-free fluid having a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25°C, Based on the total mass of the aqueous particle-free fluid, (b) a total amount of at least 0.5% and no more than 2% by weight, inclusive, of the following structure (I): HO-CH 2 -CH 2 -R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). and a composition comprising one or more compounds represented by a sorbosurfactant in an amount of at least 0.1% by weight and no more than 20% by weight, inclusive Including, 1. An aqueous particle-free fluid, wherein the sorbosurfactant is selected from ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, polyethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monopropyl ether, diethylene glycol monobutyl ether acetate, and combinations thereof.

8. 8. The aqueous particle-free fluid of claim 7, wherein the compound represented by structure (I) is 2-phenoxyethanol or 2-phenylethanol.

9. 9. The aqueous particle-free fluid of claim 7 or 8, wherein the sorbosurfactant is present in an amount of at least 3% and no more than 6% by weight, inclusive, based on the total weight of the aqueous particle-free fluid.

10. 10. An aqueous particle-free fluid according to any one of claims 7 to 9, having a pH of at least 10 and no more than 11, inclusive.

11. 11. The aqueous particle-free fluid of any one of claims 7 to 10, further comprising a non-ionic surfactant having a molecular weight greater than 350 Daltons and less than 1,000 Daltons.

12. providing a substrate; inkjet printing one or more aqueous inkjet ink compositions from a printhead onto a surface of a substrate in a controlled manner to provide an inkjet printed image on the surface of the substrate; and supplementing any of said one or more aqueous ink-jet ink compositions with an aqueous particle-free fluid.

1. A method of continuous ink jet printing comprising: any of the one or more aqueous inkjet ink compositions having a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25°C; (a) one or more polymer-dispersed pigment colorants in a total amount of at least 0.9% and no more than 6% by weight, inclusive, based on the total weight of the aqueous inkjet ink composition; (b) a total amount of at least 0.5% by weight and no more than 2% by weight, inclusive, of the following structure (I): HO-CH2-CH2-R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). a composition comprising one or more compounds represented by (c) one or more compounds selected from a water-soluble humectant, a cosolvent, and both a water-soluble humectant and a cosolvent in an amount of 20% by weight or less based on the total weight of the aqueous inkjet composition; Including, each of the one or more polymer-dispersed pigment colorants has a 50th percentile particle diameter of less than 70 nm and a 95th percentile particle diameter of less than 150 nm, all particle diameters measured using a dynamic light scattering particle size analyzer; and the aqueous particle-free fluid has a dynamic viscosity of 5 centipoise (5 mPa-sec) or less at 25°C; (b) a total amount of at least 0.5% and no more than 2% by weight, inclusive, of the following structure (I), based on the total weight of the aqueous particle-free fluid: HO-CH2-CH2-R (I) (wherein R is a substituted or unsubstituted phenyl group or a substituted or unsubstituted phenoxy group). A composition comprising one or more compounds represented by 1. A method of continuous ink jet printing, comprising:

13. inkjet printing onto a substrate with the aqueous inkjet ink composition delivered from a printhead; ceasing inkjet printing of the aqueous inkjet ink composition from said printhead; delivering an aqueous particle-free fluid according to any one of claims 7 to 11 from a maintenance fluid delivery section to the printhead; ejecting the aqueous particle-free fluid from the printhead and purging the printhead of the aqueous ink-jet ink composition to provide a cleaned printhead; and optionally, resuming inkjet printing of the aqueous inkjet ink composition from said cleaned printhead.

1. A method for starting up continuous inkjet printing, comprising:

Images