Ink to improve printhead life

Abstract

The inkjet ink contains a water-based ink vehicle and 5-250 ppm of polyvinyl alcohol. This ink is useful for improving the lifespan of inkjet printheads, especially those equipped with inkjet nozzle devices that have resistance heating elements prone to corrosion failure.

Description

Technical Field

[0001] The present invention relates to an inkjet ink, which has been mainly developed to improve the life of a print head, particularly the life of a thermal inkjet print head.

Background Art

[0002] The present applicant has developed a number of high-speed inkjet printers employing a stationary Memjet® print head extending across the width of the media.

[0003] In page-width high-speed printing, compared to conventional types of inkjet print heads, there are necessarily further requirements placed on the design of the print head. The nozzle device needs to have a self-cooling design, a high ink replenishment rate, and high thermal efficiency. For this purpose, the present applicant has developed various thermal bubble type print heads including those having a suspended resistive heating element in a liquid (e.g., described in U.S. Patent No. 6,755,509; U.S. Patent No. 7,246,886; U.S. Patent No. 7,401,910; and U.S. Patent No. 7,658,977, the contents of which are incorporated herein by reference), and those having an embedded (''adhesive'') resistive heating element (e.g., described in U.S. Patent No. 7,377,623; U.S. Patent No. 7,431,431; U.S. Patent Application Publication No. 2006 / 250453; and U.S. Patent No. 7,491,911, the contents of which are incorporated herein by reference).

[0004] A nozzle device having an uncoated suspended heating element in a liquid provides the advantages of efficient heat transfer from the heating element to the ink and optimal self-cooling characteristics. However, an uncoated suspended heating element in a liquid typically has the disadvantage of a relatively short print head life because it is not as robust as an adhesive type.

[0005] Ink components can shorten the lifespan of a printhead through either corrosive or coagulation failure mechanisms. Dye-based inks tend to shorten their lifespan through corrosive failure mechanisms. On the other hand, inks containing polymers (e.g., pigment-based inks) tend to shorten their lifespan through coagulation failure mechanisms. However, in both dye-based and pigment-based inks, there is inevitably a balance between corrosive and coagulation failure mechanisms, depending, for example, on the type of heating element.

[0006] In multicolor printheads (e.g., CMYK), the printhead's lifespan is actually limited by the lifespan of the color channel with the shortest lifespan. For example, if black dye-based ink is found to be particularly corrosive to the heat-generating element, the printhead's lifespan will be determined by the lifespan of the black channel, even if all other color channels are still functioning well when the black color channel fails.

[0007] In the context of this invention, "failure" of a nozzle device means any change in droplet ejection characteristics that results in unacceptable print quality. For example, failure may be caused by a decrease in droplet velocity, poor droplet orientation (e.g., a directional deviation of more than 2 pixels), or failure to eject ink. Furthermore, the criteria for failure may also differ by color. For example, a decrease in print quality in the yellow channel may be more acceptable than a corresponding decrease in print quality in the black channel because black ink is more visible to the human eye (i.e., black ink is brighter on white paper). This, combined with the aggressive nature of many black dyes, means that the black channel of a Memjet® printhead is often the limiting color channel in terms of printhead lifespan.

[0008] One method to improve printhead lifespan is to coat the heating element with a protective coating layer. For example, U.S. Patent No. 6,719,406 (assigned to the applicant) describes a liquid-supported heating element with a conformal protective coating, which improves the rigidity of the heating element and thus extends printhead lifespan. However, protective coatings may be undesirable for several reasons, including reducing the efficiency of heat transfer from the resistive heating element to the surrounding ink, consequently affecting self-cooling characteristics, and creating further MEMS manufacturing challenges.

[0009] Another method to improve printhead lifespan is to introduce certain additives (e.g., corrosion inhibitors) into the ink formulation.

[0010] U.S. Patent No. 6,435,659 (assigned to Hewlett-Packard Company) describes an ink containing aluminum ions for inhibiting corrosion of heating elements. It has been reported that the metal ions form a protective film on the surface of the resistive heating element, thereby protecting the heating element from attack by corrosive components in the ink.

[0011] U.S. Patent No. 9,422,441 (the contents of which are incorporated herein by reference) describes Butoxyne® additives as means for reducing corrosion of printheads having resistive heating elements. While such additives are effective in extending the life of printheads, Butoxyne® presents supply challenges and is not desirable for the consistent mass production of ink for commercial use.

[0012] It would be desirable to improve the lifespan of thermal inkjet printheads using ink formulation additives as an alternative option. Such additives would also be desirable to be widely available and at least as effective as known additives in reducing corrosion and improving printhead lifespan. Furthermore, such additives would be desirable to be used in minimal amounts and to have minimal impact on other required ink properties. [Overview of the project]

[0013] In the first aspect: Water-based ink vehicle, and 5-250 ppm polyvinyl alcohol, Inkjet ink containing [the specified ingredient] is provided.

[0014] Inks according to the first embodiment exhibit a significant improvement in printhead life compared to similar inks that do not contain polyvinyl alcohol (PVA) additives or, in fact, other polymer additives. Typically, using inks according to the first embodiment can achieve printhead life improvements of at least 25%, at least 50%, at least 100%, or at least 200%. Surprisingly, inks according to the first embodiment exhibit a favorable improvement in printhead life even at very low concentrations of PVA additives. At such low concentrations, printhead failures via competing cogation mechanisms are minimized. Furthermore, the established balance of desirable ink properties does not change significantly even when very small amounts of PVA are added to the ink.

[0015] Preferably, polyvinyl alcohol (PVA) is present in an amount ranging from 10 to 200 ppm, or more preferably from 10 to 100 ppm.

[0016] Preferably, the polyvinyl alcohol has a molecular weight in the range of 5,000 to 15,000 g / mol, or more preferably 7,000 to 11,000 g / mol. From the viewpoint of solubility, relatively low molecular weight PVA is generally preferred, which not only provides optimal lifespan but also allows for easy ink formulation.

[0017] Preferably, the polyvinyl alcohol has a degree of hydrolysis in the range of 70-90%, or more preferably 75-85%. From the viewpoint of solubility, PVA with a relatively low degree of hydrolysis is generally preferred, and it allows for easy formulation of inks.

[0018] Typically, inks contain corrosive components, which may be, for example, water-soluble anions or organic compounds having anionic groups. Examples of corrosive components include chloride ions, bromide ions, iodide ions, sulfate ions, and nitrate ions, as well as organic compounds containing one or more sulfonate groups.

[0019] Typically, the corrosive components include dyes. Dyes may be present in amounts ranging from 0.01 to 5% by weight, or from 0.02 to 2% by weight.

[0020] In one preferred embodiment, the ink does not contain any polymer other than polyvinyl alcohol having a molecular weight greater than 5000 g / mol. The ink according to this preferred embodiment advantageously exhibits minimal cogation of the heating element, thereby maximizing the life of the printhead. In another preferred embodiment, the ink does not contain any polymer other than polyvinyl alcohol having a molecular weight greater than 3000 g / mol.

[0021] Notably, polymers with a molecular weight exceeding 5000 g / mol do not include, for example, alkoxylated (e.g., ethoxylated) surfactants or alkoxylated (e.g., ethoxylated) glycerols commonly used in inkjet inks. Typical examples of ethoxylated surfactants used in inkjet inks include ethoxylated acetylenediols, commercially available as Surfynols® (e.g., Surfynol 2502, Surfynol 420, Surfynol 440, Surfynol 465, Surfynol 485, etc., sold by Air Products), as well as ethoxylated silicones, commercially available as BYK-345, BYK-346, and BYK-349 (sold by BYK Japan KK), and Silface® SAG-002, SAG-005, SAG-008, SAG-KB, and SAG-503A (sold by Nissin Chemical Industry Co.). A typical example of ethoxylated glycerol is Liponic® EG-1 (26 molar equivalents of ethoxylate), a burn prevention additive commercially available from Lipo Chemicals.

[0022] Preferably, the ink vehicle contains 5 to 50% by weight of one or more cosolvents. The range of cosolvents is not particularly limited, and several cosolvents suitable for use in the present invention are described in more detail below. In some embodiments, the ink vehicle may contain Liponic® EG-1 to help minimize cogation.

[0023] Preferably, the ink vehicle contains 0.05 to 2% by weight of at least one surfactant, as described below. The range of surfactants is not particularly limited, and several surfactants suitable for use in the present invention are described in more detail below. For example, the surfactant may be anionic, cationic, nonionic, or zwitterionic.

[0024] In a second aspect, a method for improving the lifespan of an inkjet printhead is provided, the method comprising: supplying the above-described ink to a nozzle chamber of the printhead, each nozzle chamber having an associated actuator in contact with the ink; and operating one or more of the actuators to eject ink from the printhead, whereby.

[0025] The method according to the second aspect significantly improves the lifespan of the printhead as compared to an ink not containing PVA as described herein.

[0026] Preferably, each actuator comprises a resistive heating element which forms bubbles by overheating the ink and ejects the ink through a nozzle opening from the corresponding nozzle chamber.

[0027] In some embodiments, the heating element may not be coated such that the ink is in direct contact with the resistive heating element. Such heating elements are particularly vulnerable to corrosive attacks.

[0028] Preferably, the heating element is composed of a metal or a conductive ceramic material such as a metal nitride. As used herein, the term "metal" includes metal alloys containing a plurality of different metals. Preferably, the heating element is composed of a material selected from the group consisting of titanium alloys (e.g., titanium-aluminum alloy); titanium nitride; and nitrides of titanium alloys (e.g., titanium aluminum nitride).

[0029] In a third aspect, an inkjet printer is provided comprising: an inkjet printhead having a plurality of nozzle chambers, each nozzle chamber having an associated actuator for contact with ink; and an ink reservoir in fluid communication with the nozzle chambers and containing the above-described ink.

[0030] Preferred embodiments of the print head and ink should be readily apparent from the above.

[0031] In a fourth aspect, the use of the inks described herein is provided for improving the lifespan of an inkjet printhead.

[0032] As used herein, the term “ink” is interpreted to mean any printing fluid that can be printed from an inkjet printhead. Ink may or may not contain colorants. Therefore, the term “ink” may include conventional dye-based or pigment-based inks, infrared inks, fixatives (e.g., pre-coats and finishes), 3D printing fluids (e.g., binder fluids), functional fluids (e.g., solar inks, sensing inks, etc.), and biological fluids. Typically, ink refers to dye-based inks for use in thermal inkjet printheads. When referring to fluids or printing fluids, this is not intended to limit the meaning of “ink” as used herein. [Brief explanation of the drawing]

[0033] Hereinafter, various embodiments of the present invention will be described as mere examples with reference to the accompanying drawings.

[0034] [Figure 1] Figure 1 is a perspective view of a portion of a thermal inkjet printhead. [Figure 2] Figure 2 is a side view of one of the nozzle assemblies shown in Figure 1. [Figure 3] Figure 3 is a perspective view of the nozzle assembly shown in Figure 2. [Figure 4] Figure 4 is a perspective view of a thermal inkjet print engine. [Modes for carrying out the invention]

[0035] The inventors explored solutions to the problem of improving printhead lifespan by considering ink additives. As anticipated above, ink additives are an attractive solution to this problem because they do not require any changes to the printhead design.

[0036] Butoxyne™ (1,4-bis(2-hydroxyethoxy)-2-butyne) has been shown to improve printhead life in dye-based inks (see U.S. Patent No. 9,422,441), but the effectiveness of this additive is subject to supply constraints and some batch variability between different suppliers. Early attempts to find alternative additives with similar effects were generally unsuccessful. For example, based on previous research described in International Publication No. 2022 / 184478, it was hypothesized that zwitterionic compounds might be useful for protecting heating elements. It was thought that zwitterions could help repel anionic corrosive species through a bilayer effect on the heating element surface. However, additives such as betaine were found to be detrimental to the heating element's lifespan. Similarly, weak acids such as boric acid and ascorbic acid were ineffective or detrimental to the heating element's lifespan.

[0037] In light of batch variations in the Butoxyne® additive, we hypothesized that the active species extending the heating element lifespan is not small alkyne molecules, but rather water-soluble polymers that are transiently formed on the heating element surface during droplet ejection. The presence or absence of impurities in Butoxyne® (which may catalyze or inhibit polymerization) or microscopic variations on the surface of individual heating elements may explain the variability in the observed effect. However, polymers are known to be highly coagulating components in ink, and therefore were not expected to extend printhead lifespan.

[0038] Initial experiments using water-soluble ethoxylated silicone polymers confirmed the hypothesis that they are prone to coging. Adding Dow Corning Dowsil™ 8526 to dye-based inks at various concentrations resulted in rapid coging accumulation, as evidenced by poor droplet ejection characteristics (e.g., low ejection rate, droplet directional deviation). However, despite the unsuitability of such coging-prone polymers, the analysis of increased heat resistance during these experiments proved promising. Increased heat resistance is a strong indicator of corrosion, and the data demonstrated a clear protective effect of ethoxylated silicones (at the expense of coging) compared to similar formulations without ethoxylated silicones.

[0039] Based on this promising data, we attempted to reduce coging by decreasing the amount of silicone additive. While corrosion prevention was observed at very low additive concentrations (approximately 10 ppm), the silicone still exhibited unacceptable coging even at low concentrations. Adding known coging prevention additives (Liponic® EG-1, ethoxylated glyercol) did not significantly improve the performance of ethoxylated silicone in terms of coging.

[0040] Ethoxylated silicones were ineffective in improving printhead life due to coging, but their ability to limit corrosion at very low concentrations (presumably through a protective layer on the heating element surface) had been demonstrated. Therefore, the inventors turned their attention to other water-soluble polymers that may have similar corrosion-preventive effects at low concentrations but without the harmful coging effect exhibited by silicones.

[0041] Surprisingly, polyvinyl alcohol was found to be very effective at minimizing corrosion of heating elements at low concentrations, without the same cogation effects as silicone, thereby improving the overall lifespan of the heating elements. Notably, at concentrations of approximately 5–250 ppm, PVA exhibited excellent corrosion inhibition along with acceptable droplet discharge characteristics. At higher PVA concentrations, droplet discharge characteristics became unacceptable due to the onset of cogation, while at lower PVA concentrations, the corrosion inhibition effect was reduced.

[0042] PVA has the added advantage of being relatively mild and having little to no interaction with other ink components, and therefore does not affect the overall balance of ink properties at the required concentration.

[0043] All PVAs tested appeared to have similar resistance to corrosion, but generally, from the standpoint of ink formulation, more soluble PVAs were preferred. Therefore, PVAs with relatively low molecular weight (e.g., 5000-15000 g / mol) and relatively low degree of hydrolysis (e.g., 70%-90%) were generally preferred.

[0044] PVA has long been used in the field of inkjet technology, typically as a primer (see, e.g., U.S. Patent No. 10,414,189) or as part of the ink-receiving layer on media (see, e.g., U.S. Patent Application Publication No. 2011 / 0279554) to promote ink adhesion to the media. For these purposes, high-viscosity, high-molecular-weight PVA is used in high concentrations. To date, the use of PVA in ink at very low concentrations to extend printhead life has not been documented in the literature.

[0045] Colorants, ink vehicles, and print heads suitable for use in connection with the present invention are described in further detail below.

[0046] Coloring agents The ink used in this invention may be of any type, but is typically a dye-based ink known to be corrosive to thermal inkjet heating elements.

[0047] Inkjet dyes are well known to those skilled in the art, and the present invention is not limited to any particular type of dye. Examples of dyes suitable for use in the present invention include azo dyes such as Food Black 2 and K1600 (as described in U.S. Patent No. 8,834,620, the content of which is incorporated herein by reference), metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinone-imine dyes, xanthene dyes, cyanine dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes, phthalocyanine dyes (including naphthalocyanine dyes), and metallic phthalocyanine dyes (including metallic naphthalocyanine dyes such as those described in U.S. Patent No. 7,148,345).

[0048] Specific examples of suitable dyes include: CI Direct Black 4, 9, 11, 17, 19, 22, 32, 80, 151, 154, 168, 171, 194, and 195; CI Direct Blue 1, 2, 6, 8, 22, 34, 70, 71, 76, 78, 86, 142, 199, 200, 201, 202, 203, 207, 218, 236, and 287; CI Direct Red 1, 2, 4, 8, 9, 11, 13, 15, 20, 28, 31, 33, 37, 39, 51, 59, 62, 63, 73, 75, 80, 81, 83, 87, 90, 94, 95, 99, 101, 110, 189, 225, and 227; CI Direct Yellow 1, 2, 4, 8, 11, 12, 26, 27, 28, 33, 34, 41, 44, 48, 86, 87, 88, 132, 135, 142, and 144; CI Hood Black 1 and 2; CI Acid Black 1, 2, 7, 16, 24, 26, 28, 31, 48, 52, 63, 107, 112, 118, 119, 121, 172, 194, and 208; CI Acid Blue 1, 7, 9, 15, 22, 23, 27, 29, 40, 43, 55, 59, 62, 78, 80, 8 1, 90, 102, 104, 111, 185, and 254; CI Acid Yellow 1, 3, 4, 7, 11, 12, 13, 14, 19, 23, 25, 34, 38, 41, 42, 44, 53, 55, 61, 71, 76, and 79; CI Reactive Blue 1, 2, 3, 4, 5, 6, 7, 8, 9, 13, 14, 15, 17, 18, 19, 20, 21, 25, 26, 27, 28, 29, 31, 32, 33, 34, 37, 38, 39, 40, 41, 43, 44, and 46; CI Reactive Red 1, 2, 3, 4, 5, 6, 7, 8, 11, 12, 1 3, 15, 16, 17, 19, 20, 21, 22, 23, 24, 28, 29, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 49, 50, 58, 59, 63, 64, and 180; CI Reactive Yellow 1, 2, 3, 4, 6, 7, 11, 12, 13, 14, 15, 16, 17, 18, 22, 23, 24, 25, 26, 27, 37, and 42; CI Reactive Black 1, 3, 4, 5, 6, 8, 9, 10, 12, 13, 14, and 18; Pro-Jet® Fast Cyan 2 (Fujifilm Imaging Colorants);Examples include Pro-Jet® Fast Magenta 2 (Fujifilm Imaging Colorants), Pro-Jet® Fast Yellow 2 (Fujifilm Imaging Colorants), and Pro-Jet® Fast Black 2 (Fujifilm Imaging Colorants).

[0049] Colorants such as dyes may be used individually or in combination of two or more in inkjet inks. For example, the ink may contain a main dye and one or more tinting dyes to provide an optimal color gamut.

[0050] Ink Vehicle Ink vehicles for inkjet inks are well known to those skilled in the art, and the ink vehicle used in the present invention is not particularly limited. The ink vehicle used in the present invention is typically a conventional aqueous ink vehicle containing at least 40% by weight of water, at least 50% by weight of water, or at least 60% by weight of water. Typically, the amount of water present in an inkjet ink is in the range of 50% to 90% by weight, or optionally in the range of 60% to 80% by weight.

[0051] Aqueous inkjet ink compositions are known in the literature and may contain, in addition to water, other components such as cosolvents (including water-retaining agents, penetrating agents, wetting agents, etc.), surfactants, biocides, chelating agents, pH adjusters, and viscosity modifiers.

[0052] The cosolvent is typically a water-soluble organic solvent. Suitable water-soluble organic solvents include C 1-4Alkyl alcohols such as ethanol, methanol, butanol, propanol, 1-propanol, and 2-propanol; glycol ethers such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-isopropyl ether, diethylene glycol mono-isopropyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol mono-t-butyl ether, diethylene glycol mono-t-butyl ether, 1- Examples include methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-isopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-isopropyl ether, propylene glycol mono-n-butyl ether, and dipropylene glycol mono-n-butyl ether; formamide, acetamide, dimethyl sulfoxide, sorbitol, sorbitan, glycerol monoacetate, glycerol diacetate, glycerol triacetate, and sulfolane; or combinations thereof.

[0053] Other useful water-soluble organic solvents that can be used as cosolvents include polar solvents such as 2-pyrrolidone, N-methylpyrrolidone, ε-caprolactam, dimethyl sulfoxide, sulfolane, morpholine, N-ethylmorpholine, and 1,3-dimethyl-2-imidazolidinone, as well as combinations thereof.

[0054] Inkjet inks may contain a high-boiling point water-soluble organic solvent as a cosolvent, which can function as a wetting agent or water-retaining agent to impart water retention and wetting properties to the ink composition. Examples of such high-boiling point water-soluble organic solvents include those with a boiling point of 180°C or higher. Examples of water-soluble organic solvents with a boiling point of 180°C or higher include ethylene glycol, propylene glycol, diethylene glycol, pentamethylene glycol, trimethylene glycol, 2-butene-1,4-diol, 2-ethyl-1,3-hexanediol, 2-methyl-2,4-pentanediol, tripropylene glycol monomethyl ether, dipropylene glycol monoethyl glycol, dipropylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol, triethylene glycol monomethyl ether, tetraethyl These include polyethylene glycol, triethylene glycol, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, tripropylene glycol, polyethylene glycol with a molecular weight of 2000 or less, 1,3-propylene glycol, isopropylene glycol, isobutylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, glycerol, trimethylolpropane, erythritol, pentaerythritol, and combinations thereof.

[0055] Other suitable wetting or water-retaining agents include sugars (including monosaccharides, oligosaccharides, and polysaccharides) and their derivatives (e.g., maltitol, sorbitol, xylitol, hyaluronic acid, aldonic acid, uronic acid, etc.).

[0056] Inkjet inks may also contain a penetrant as one of the cosolvents to promote the penetration of the water-based ink into the recording medium. Suitable penetrants include polyhydric alcohol alkyl ethers (glycol ethers) and / or 1,2-alkyldiols. Examples of suitable polyhydric alcohol alkyl ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol mono-n-propyl ether, ethylene glycol mono-isopropyl ether, diethylene glycol mono-isopropyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, and ethylene glycol mono-t-butyl ether. These include diethylene glycol mono-t-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-t-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol mono-isopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol mono-isopropyl ether, propylene glycol mono-n-butyl ether, and dipropylene glycol mono-n-butyl ether. Suitable examples of 1,2-alkyldiols are 1,2-pentanediol and 1,2-hexanediol. Penetrants may also be selected from linear hydrocarbon diols such as 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol. Glycerol can also be used as a penetrating agent.

[0057] Typically, the amount of solvent present in the ink is in the range of approximately 5% to 50% by weight, or, if desired, 10% to 40% by weight.

[0058] Inkjet inks may also contain one or more surfactants ("surfactants"), such as anionic surfactants, zwitterionic surfactants, nonionic surfactants, or mixtures thereof. Useful anionic surfactants include sulfonic acid type alkanesulfonates, α-olefin sulfonates, alkylbenzene sulfonates, alkylnaphthalene sulfonic acid, acylmethyl taurine, and dialkyl sulfosuccinate; alkyl sulfate salts, sulfated oils, sulfated olefins, polyoxyethylene alkyl ether sulfate salts; carboxylic acid type fatty acid salts and alkyl sarcosine salts; and phosphate ester type alkyl phosphate salts, polyoxyethylene alkyl ether phosphate salts, and glycerophosphate salts. Specific examples of anionic surfactants include sodium dodecylbenzenesulfonate, sodium laurate, and polyoxyethylene alkyl ether ammonium sulfate.

[0059] Examples of zwitterionic surfactants include N,N-dimethyl-N-octylamine oxide, N,N-dimethyl-N-dodecylamine oxide, N,N-dimethyl-N-tetradecylamine oxide, N,N-dimethyl-N-hexadecylamine oxide, N,N-dimethyl-N-octadecylamine oxide, and N,N-dimethyl-N-(Z-9-octadecenyl)-N-amine oxide.

[0060] Examples of nonionic surfactants include ethylene oxide duct-type polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, polyoxyethylene alkyl esters, and polyoxyethylene alkylamides; polyol ester-type glycerol alkyl esters, sorbitan alkyl esters, and sugar alkyl esters; polyether-type polyhydric alcohol alkyl ethers; and alkanolamide-type alkanolamine fatty acid amides. Specific examples of nonionic surfactants include ethers such as polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene dodecylphenyl ether, polyoxyethylene alkyl allyl ether, polyoxyethylene oleyl ether, polyoxyethylene lauryl ether, and polyoxyalkylene alkyl ether (e.g., polyoxyethylene alkyl ether); and esters such as polyoxyethylene oleate, polyoxyethylene oleate ester, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan mono-oleate, sorbitan sesquioleate, polyoxyethylene mono-oleate, and polyoxyethylene stearate.

[0061] Acetylene glycol surfactants such as 2,4,7,9-tetramethyl-5-decine-4,7-diol; ethoxylated 2,4,7,9-tetramethyl-5-decine-4,7-diol; 3,6-dimethyl-4-octin-3,6-diol; or 3,5-dimethyl-1-hexyn-3-ol may also be used. Specific examples of nonionic surfactants that can be used in the present invention are Surfynol® 465 and Surfynol® 440 (available from Air Products and Chemicals, Inc.).

[0062] Surfactants are typically present in aqueous inkjet inks in amounts ranging from 0.05% to 2% by weight.

[0063] Water-based inkjet inks may also contain pH adjusters or buffers such as sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, lithium carbonate, sodium phosphate, potassium phosphate, lithium phosphate, potassium dihydrogen phosphate, dipotassium hydrogen phosphate, sodium oxalate, potassium oxalate, lithium oxalate, sodium borate, sodium tetraborate, potassium bitartrate, and potassium bitartrate; ammonia; and amines such as methylamine, ethylamine, diethylamine, trimethylamine, triethylamine, tris(hydroxymethyl)aminomethane hydrochloride, triethanolamine, diethanolamine, diethylethanolamine, triisopropanolamine, butyldiethanolamine, morpholine, propanolamine, 4-morpholineethanesulfonic acid, and 4-morpholinepropanesulfonic acid ("MOPS"). The amount of pH adjuster, if present, is typically in the range of 0.01 to 2% by weight or 0.05 to 1% by weight.

[0064] Water-based inkjet inks may also contain biocides such as benzoic acid, dichlorophene, hexachlorophene, sorbic acid, hydroxybenzoic acid esters, sodium dehydroacetate, 1,2-bentiazolin-3-one ("Proxel® GXL," available from Arch Chemicals, Inc.), 3,4-isothiazolin-3-one, or 4,4-dimethyloxazolidine. The amount of biocide, if present, is typically in the range of 0.01–2% by weight or 0.05–1% by weight.

[0065] Water-based inkjet inks may also contain chelating agents such as ethylenediaminetetraacetic acid (EDTA).

[0066] Inkjet printhead The inks according to the present invention are primarily intended for use with thermal inkjet printheads, but may also be used with other types of printheads, particularly those in which an actuator contacts the ink. For completeness, one of the thermal inkjet printheads by the applicant described in U.S. Patent No. 7,303,930, the contents of which are incorporated herein by reference, is briefly described below.

[0067] Referring to Figure 1, a portion of a printhead with multiple nozzle assemblies is shown. Figures 2 and 3 show one of these nozzle assemblies in a side section and a sectioned perspective view.

[0068] Each nozzle assembly comprises a nozzle chamber 24 formed on a silicon wafer substrate 2 by MEMS manufacturing technology. The nozzle chamber 24 is defined by a roof 21 and side walls 22 extending from the roof 21 to the silicon substrate 2. As shown in Figure 1, each roof is defined by a portion of a nozzle plate 56 that extends across the ejection surface of the print head. The nozzle plate 56 and side walls 22 are formed from the same material and deposited by PECVD on a sacrificial scaffold of photoresist during MEMS manufacturing. Typically, the nozzle plate 56 and side walls 21 are formed from ceramic materials such as silicon dioxide or silicon nitride. These rigid materials have excellent properties for print head rigidity, and their inherently hydrophilic nature is advantageous for supplying ink to the nozzle chamber 24 by capillary action.

[0069] Returning to the details of the nozzle chamber 24, we can see that the nozzle openings 26 are defined on the roof of each nozzle chamber 24. Each nozzle opening 26 is roughly elliptical and has an accompanying nozzle rim 25. The nozzle rim 25 assists in the directionality of droplets during printing and reduces, at least to some extent, ink overflow from the nozzle opening 26. The actuator for ejecting ink from the nozzle chamber 24 is a heating element 29 located below the nozzle opening 26 and supported in liquid across the pit 8. Current is supplied to the heating element 29 via electrodes 9 connected to a drive circuit in the underlying CMOS layer of the substrate 2. When current flows through the heating element 29, it rapidly overheats the surrounding ink, forming bubbles, which push the ink out of the nozzle opening 26. By supporting the heating element 29 in liquid, the heating element 29 is completely immersed in ink when the nozzle chamber 24 is filled with ink. This reduces heat dissipation to the substrate 2, allowing more input energy to be used for bubble generation, thus improving printhead efficiency. Typically, the heating element is made of a metal or conductive ceramic material. Examples of suitable materials include titanium nitride, titanium aluminum nitride, and titanium-aluminum alloys.

[0070] As is most clearly visible in Figure 1, the nozzles are arranged in a row, and an ink supply channel 27 extending longitudinally along the row supplies ink to each nozzle in the row. The ink supply channel 27 supplies ink to the ink inlet passage 15 of each nozzle, which in turn supplies ink from the side of the nozzle opening 26 through the ink conduit 23 in the nozzle chamber 24.

[0071] A MEMS manufacturing process for producing such printheads is described in detail in U.S. Patent No. 7,303,930, the contents of which are incorporated herein by reference.

[0072] The operation of a printhead having a liquid-supported heating element is described in detail in the applicant's U.S. Patent No. 7,278,717, the contents of which are incorporated herein by reference.

[0073] The applicant has also reported on thermal bubble inkjet printheads having bonded heating elements. Such printheads are described, for example, in U.S. Patent No. 7,246,876 and U.S. Patent Application Publication No. 2006 / 0250453, the contents of which are incorporated herein by reference.

[0074] As described above, the inkjet inks of the present invention function optimally in combination with the applicant's thermal inkjet printheads. However, their use is not limited to the applicant's thermal printheads. The inks described herein may also be used with other types of thermal bubble inkjet printheads, piezoelectric printheads, thermal-bend actuated printheads (for example, those described in U.S. Patents No. 7,926,915; No. 7,669,967; and No. 8,998,383, the contents of which are incorporated herein by reference).

[0075] For completeness, inkjet printers incorporating the applicant's thermal inkjet printheads are described, for example, in U.S. Patents 7,201,468; 7,360,861; 7,380,910; and 7,357,496, the contents of which are incorporated herein by reference.

[0076] Figure 4 shows a print engine 103 for a thermal inkjet printer as described in the applicant's U.S. Patent No. 8,066,359, the contents of which are incorporated herein by reference. The print engine 103 includes a removable print cartridge 102 with a page-width print head and a set of user-replaceable ink cartridges 128. Each color channel typically has its own ink reservoir 128 and a corresponding pressure regulating chamber 106 for regulating the hydrostatic pressure of the ink supplied to the print head. Thus, the print engine 103 has five ink reservoirs 128 and five corresponding pressure regulating chambers 106. Typically, the ink channels ("color channels") used in this five-channel print engine 103 are CMYK1K2. The order of the ink channels may be arranged to optimize a preferred ink color mixing effect at the nozzle plate of the print head, as described in U.S. Patent Application Publication No. 2013 / 0070024, the contents of which are incorporated herein by reference. For example, an ink channel sequence of CK1MK2Y may be used, in which cyan (C) is located furthest upstream and yellow (Y) is located furthest downstream.

[0077] Each ink cartridge 128 may contain the ink composition described herein. Although fluid connections between the various components are not shown in Figure 4, it will be understood that these connections are made, for example, using appropriate hoses in accordance with the fluid system described in U.S. Patent No. 8,066,359, the contents of which are incorporated herein by reference.

[0078] Experiment Section Accelerated life testing of the printhead was performed with various inks according to the method described below.

[0079] Printhead integrated circuits (PHICs) containing uncoated titanium aluminum nitride resistive heating elements were individually installed to operate in a modified printing device. The actuation pulse width was controlled to replicate the operation of an otherwise unmodified printer. The increase in the resistance of the heating element (expressed as a percentage increase from the start of the experiment) was recorded after 50 million actuations. The increase in resistance correlated with the corrosion rate of the heating element within the PHIC.

[0080] As shown in Table 1, a baseline ink formulation without additives was prepared and filtered (0.2 microns) before use. TIFF2026510262000002.tif591701.K1600 is a black disazo dye, as described in U.S. Patent No. 8,834,620. 2. Surfynol® 465 is ethoxylated 2,4,7,9-tetramethyl-5-decine-4,7-diol. 3. Proxel(registered trademark) GXL is 1,2-benzisothiazolin-3-one.

[0081] Inks 1-9 were prepared using the baseline ink formulation with various additives in the amounts shown in Table 2. Each ink was tested on the modified printing apparatus described above, and the resistance increase after 50 million ejections was measured for each ink (normalized to the baseline ink without additives). For some ink candidates, qualitative cogation observations were reported on a score from 1 to 5 (1 = baseline cogation, 5 = severe cogation / off-center droplets). The results of these printhead accelerated life tests are shown in Table 2. TIFF2026510262000003.tif94170

[0082] Table 2 shows that, with the exception of Butoxyne™, a known corrosion inhibitor, most of the additives tested had either a negligible or undesirable accelerating effect on the corrosion rate compared to a baseline formulation without any additives.

[0083] Interestingly, Dow Corning Dowsil™ 8526 (an ethoxylated silicone polymer with a molecular weight in the range of 6000-8000 g / mol) showed promising corrosion protection at relatively low concentrations. Presumably, this silicone polymer forms a protective layer on the heating element, minimizing corrosive attack by the dye species. However, coagulation was observed to be very poor, both from droplet ejection characteristics and visual inspection of the heating element. Therefore, this silicone polymer additive was clearly unacceptable for use in ink formulations, at both 0.3% by weight and 0.1% by weight.

[0084] However, based on its promising corrosion prevention performance, Dow Corning Dowsil® 8526 was selected as a candidate for further testing. It was hypothesized that coagulation could be mitigated at lower concentrations or by adding a known coagulation inhibitor (Liponic®-EG1). Table 3 shows the test results of Dow Corning Dowsil® 8526 compared to the baseline formulation. TIFF2026510262000004.tif82170

[0085] Unfortunately, all tested inks containing ethoxylated silicone (Dow Corning Dowsil® 8526) exhibited either unacceptable coaging or negligible corrosion protection. For example, ink 12 showed very good corrosion protection at a concentration of 0.005% by weight (50 ppm), but its coaging performance remained very poor. On the other hand, ink 13 showed acceptable coaging performance at a concentration of 0.001% by weight (10 ppm), but its corrosion protection was negligible. Therefore, there was no room for formulations in which the Dowsil® 8526 additive provided useful corrosion protection without unacceptable coaging.

[0086] Based on the theoretical basis that low concentrations of water-soluble polymers can provide corrosion protection through a protective film on heating elements, polyvinyl alcohol was identified as a candidate alternative to ethoxylated silicone. The results for various polyvinyl alcohol (PVA) additives and one polyvinylpyrrolidone (PVP) additive are shown in Table 4. TIFF2026510262000005.tif57170

[0087] PVA has similar solubility and molecular weight as Dow Corning Dowsil™ 8526, but PVA showed significantly improved cogasing results compared to ethoxylated silicone additives while maintaining excellent corrosion prevention performance. Comparison with a similar water-soluble polymer (PVP-10) demonstrated that corrosion and cogasing performance cannot be predicted solely by solubility and / or molecular weight, and ink 17 had worse corrosion and cogasing performance than inks 14-16. Fortunately, PVA interacts with the heating element in a way not seen with other polymers during droplet ejection, and therefore, inks containing PVA appear to be less prone to cogasing than inks containing other polymer additives. Naturally, it was impossible to investigate the interaction between individual polymers and the heating element under the high temperature and pressure environment inside the inkjet nozzle chamber during droplet ejection.

[0088] Comparing inks 14-16, it was observed that PVA with a lower molecular weight was preferable from the standpoint of ink formulation and corrosion / coagulation performance. Similarly, a lower degree of hydrolysis was preferred, which indicates that, in general, more soluble PVA is preferable for optimizing ink formulations to improve printhead life.

[0089] Compared to other polymer additives, PVA additives can switch the ink's failure mode from cogation (typical for most polymers) to corrosive failure, thereby extending its overall lifespan. However, PVA additives do not completely eliminate cogation, and therefore, it is desirable to minimize the amount of PVA in any ink formulation as much as possible. Minimizing the amount of PVA in the ink formulation achieves a desirable balance between corrosion and cogation, thereby optimizing both printhead life and print quality.

[0090] Table 5 shows the effect of increasing the amount of PVA on corrosion and coagulation performance in the standard ink formulations. The PVA added to each of inks 18-23 had a molecular weight of 9000 g / mol and a degree of hydrolysis of 80%. This series of experiments reports the actual lifespan until failure. TIFF2026510262000006.tif57170

[0091] The corrosion-preventive effect of PVA was observed at a low concentration of 10 ppm compared to the standard ink formulation. However, the corrosion-preventive effect of PVA was expected to decrease significantly at concentrations below approximately 5 ppm.

[0092] PVA concentrations up to 200 ppm were acceptable, but as expected, the overall coagulation performance deteriorated with increasing PVA concentration. At PVA concentrations of 500 ppm and 1000 ppm, coagulation became the dominant failure mode, resulting in a dramatic decrease in lifespan. While not bound by theory, the inventors understand that a threshold amount of PVA is required to coat the surface of the heating element to minimize corrosion. However, once the amount of PVA reaches the necessary "saturation" on the heating element surface, increasing the amount of PVA has little effect on the corrosion rate; rather, the lifespan decreases due to the coagulation failure mechanism.

[0093] Naturally, the optimal amount of PVA in any ink formulation depends on the aggressiveness of corrosive components (e.g., dyes) and other formulation components. Those skilled in the art will understand that the optimal PVA concentration within the range of 5 to 250 ppm can be experimentally determined for a given ink formulation, depending on the requirements for a balanced relationship between print quality and printhead life.

[0094] It will naturally be understood that the present invention is described merely as an example, and that detailed modifications can be made within the scope of the invention as defined in the appended claims.

Claims

1. Water-based ink vehicle, and 5-250 ppm polyvinyl alcohol, Inkjet ink containing ink.

2. The inkjet ink according to claim 1, wherein the polyvinyl alcohol is present in an amount within the range of 10 to 200 ppm.

3. The inkjet ink according to claim 1, wherein the polyvinyl alcohol has a molecular weight in the range of 5,000 to 15,000 g / mol.

4. The inkjet ink according to claim 1, wherein the polyvinyl alcohol has a degree of hydrolysis in the range of 70 to 90%.

5. The inkjet ink according to claim 1, further comprising a corrosive component.

6. The inkjet according to claim 5, wherein the corrosive component includes a dye.

7. The inkjet ink according to claim 1, wherein the ink vehicle contains 5 to 50% by weight of one or more cosolvents.

8. The inkjet ink according to claim 1, wherein the ink vehicle contains 0.05 to 2% by weight of at least one surfactant.

9. The inkjet ink according to claim 1, wherein it does not contain any polymer other than the polyvinyl alcohol having a molecular weight exceeding 5000 g / mol.

10. The inkjet ink according to claim 1, wherein it does not contain any polymer other than the polyvinyl alcohol having a molecular weight exceeding 3000 g / mol.

11. Methods to improve the lifespan of an inkjet printhead: A step of supplying the ink described in claim 1 to the nozzle chamber of the print head, wherein each nozzle chamber has an accompanying actuator that contacts the ink; and A step of operating one or more of the actuators to eject ink from the print head, Methods that include...

12. The method according to claim 11, wherein each actuator is equipped with a resistive heating element.

13. The aforementioned heating element is uncoated, and: Titanium alloy; Titanium nitride; and Titanium alloy nitrides, The method according to claim 12, comprising a material selected from the group consisting of the following.

14. The method according to claim 11, wherein the lifespan is improved compared to the polyvinyl alcohol-free ink.

15. The use of the ink according to claim 1 for improving the lifespan of an inkjet print head.

Images