Ink for improving printhead lifetime

Abstract

An inkjet ink comprises a water-based ink vehicle and 5 to 250 ppm of a polyvinyl alcohol. The ink can be used to improve the lifetime of inkjet printheads, particularly printheads with inkjet nozzle devices having resistive heater elements that are susceptible to failure due to corrosion.

Description

Field of the Invention

[0001] The present invention relates to an inkjet ink that has been developed primarily to improve the life of printheads, and in particular thermal inkjet printheads. Background of the Invention

[0003] The applicant of the present invention has developed a number of methods for using fixed A high-speed inkjet printer with a print head that extends across the width of the media.

[0004] Compared to conventional inkjet printheads, high-speed page width printing necessarily places additional demands on the design of the printhead. The nozzle arrangement must have a self-cooling design, a high ink refill rate, and high thermal efficiency. To this end, the applicant has developed a series of thermal bubble formation printheads, including those with suspended resistive heater elements (as described, for example, in US 6,755,509; US 7,246,886; US 7,401,910; and US 7,658,977, the contents of which are incorporated herein by reference) and those with embedded ("bonded") resistive heater elements (as described, for example, in US 7,377,623; US 7,431,431; US ​​2006 / 250453; and US 7,491,911, the contents of which are incorporated herein by reference).

[0005] Nozzle arrangements with uncoated suspended heater elements offer the advantages of efficient heat transfer from the heater element to the ink and optimal self-cooling characteristics. However, they suffer from the disadvantage of relatively short printhead life because uncoated suspended heater elements are typically less robust than their bonded counterparts.

[0006] Ink components can shorten printhead life through corrosion or kogative failure mechanisms. Dye-based inks tend to shorten life through the corrosion failure mechanism. On the other hand, inks containing polymers (e.g., pigment-based inks) tend to shorten life through the kogative failure mechanism. However, depending on, for example, the type of heater element, there is inevitably a balance between the corrosion and kogative failure mechanisms in both dye-based and pigment-based inks.

[0007] In a multi-color printhead (e.g., CMYK), the printhead life is effectively limited by the life of the color channel with the shortest life. For example, if a black dye-based ink is found to be particularly aggressive to the heater elements, the life of the printhead will be determined by the life of the black channel, even if all other color channels perform well when the black channel fails.

[0008] In the context of the present invention, "failure" of a nozzle arrangement means any change in the droplet ejection characteristics that results in unacceptable print quality. For example, a failure may be caused by a drop in droplet velocity, poor droplet directionality (e.g., greater than 2 pixel misdirection), or ink not ejected. Furthermore, the criteria for failure may be different for different colors. For example, a decrease in print quality in the yellow channel may be more tolerable 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 has a higher brightness on white paper). Combined with the erosive nature of many black dyes, this means that in terms of printhead life, The black channel in a printhead is typically the limiting color channel.

[0009] One approach to improving printhead life is to coat the heater element with a protective coating. For example, US Pat. No. 6,719,406 (attributed to the present applicant) describes a suspended heater element with a conformal protective coating that improves the robustness of the heater element and improves printhead life. However, protective coatings can be undesirable for a number of reasons: they reduce the efficiency of heat transfer from the resistive heater element to the surrounding ink; they therefore affect self-cooling characteristics; and they introduce additional MEMS manufacturing challenges.

[0010] Another approach to improving printhead life is to introduce certain additives (such as anti-corrosion additives) into the ink formulation.

[0011] US 6,435,659 (attributed to Hewlett-Packard Company) describes inks containing aluminum ions for inhibiting heater corrosion. The metal ions reportedly form a film on the surface of the resistive heater, thereby protecting the heater element from corrosion by corrosive components in the ink.

[0012] US 9,422,441 (the contents of which are incorporated herein by reference) describes Butoxyne TM Additives as a means to reduce corrosion in printheads having resistive heater elements. While such additives are effective in increasing printhead life, Butoxyne TM This is undesirable for the continued manufacture of large quantities of ink for commercial use, subject to challenging supply issues.

[0013] It would be desirable to use alternative ink formulation additives to improve the life of thermal inkjet printheads. It would be further desirable that such additives be widely available and at least as effective as known additives in reducing corrosion and improving printhead life. It would be further desirable that such additives be used in minimal amounts and have minimal impact on other desired ink characteristics. SUMMARY OF THE INVENTION

[0015] In a first aspect, there is provided an inkjet ink comprising:

[0016] a water-based ink vehicle; and

[0017] 5 to 250 ppm of polyvinyl alcohol.

[0018] The ink according to the first aspect exhibits a significant improvement in printhead longevity compared to similar inks lacking a polyvinyl alcohol (PVA) additive or indeed other polymeric additives. Typically, at least 25%, at least 50%, at least 100% or at least 200% improvement in printhead longevity can be achieved by employing the ink according to the first aspect. Surprisingly, the ink according to the first aspect exhibits a beneficial improvement in printhead longevity at very low concentrations of PVA additive. At these low concentrations, printhead failure via the competing fouling mechanism is minimised. Furthermore, by adding very small amounts of PVA to the ink, the established balance of desirable ink characteristics is not significantly altered.

[0019] Preferably, the polyvinyl alcohol (PVA) is present in an amount in the range 10 to 200 ppm, or preferably 10 to 100 ppm.

[0020] Preferably, the polyvinyl alcohol has a molecular weight in the range 5000 to 15,000 g / mol, or preferably 7000 to 11,000 g / mol. Relatively low molecular weight PVA is generally preferred from the perspective of solubility, enabling the ink to be conveniently formulated and optimal longevity.

[0021] Preferably, the polyvinyl alcohol has a degree of hydrolysis in the range 70% to 90%, or preferably 75% to 85%. PVA with a relatively low degree of hydrolysis is generally preferred from the perspective of solubility, enabling the ink to be conveniently formulated.

[0022] Typically, the ink contains a corrosive component, which can for example be a water-soluble anion or an organic compound having an anionic group. Examples of corrosive components include chloride, bromide, iodide, sulphate and nitrate ions, and organic compounds containing one or more sulphonate groups.

[0023] Typically, the corrosive component comprises a dye. The dye can be present in an amount in the range 0.01 to 5 wt.% or 0.02 to 2 wt.%.

[0024] In a preferred embodiment, the ink is free of any polymers having a molecular weight greater than 5000 g / mol, other than polyvinyl alcohol. The ink according to this preferred embodiment advantageously exhibits minimal fouling of the heater element, thereby maximizing printhead life. In another preferred embodiment, the ink is free of any polymers having a molecular weight greater than 3000 g / mol, other than polyvinyl alcohol.

[0025] Notably, polymers having a molecular weight greater than 5000 g / mol do not include, for example, alkoxylated (e.g., ethoxylated) surfactants or alkoxylated (e.g., ethoxylated) glycerols, which are often used in inkjet inks. Examples of typical ethoxylated surfactants used in inkjet inks include: ethoxylated acetylenic diols, which are used as Commercially available (e.g., Surfynol 2502, Surfynol 420, Surfynol 440, Surfynol 465, Surfynol 485, etc., sold by Air Products); and ethoxylated silicones, which are sold as BYK-345, BYK-346, and BYK-349 (sold by BYK Japan KK) and Silface TM SAG-002, SAG-005, SAG-008, SAG-KB and SAG-503A (sold by Nissin Chemical Industry Co.) are commercially available. Typical examples of ethoxylated glycerols are anti-fouling additives. EG-1 (26 molar equivalents of ethoxylate), commercially available from Lipo Chemicals.

[0026] Preferably, the ink vehicle comprises 5 to 50 wt.% of one or more co-solvents. The range of co-solvents is not particularly limited, and some suitable co-solvents for use in the present invention are described in more detail below. In some embodiments, the ink vehicle may comprise EG-1 to help minimize scaling.

[0027] Preferably, the ink vehicle comprises 0.05 to 2 wt% of at least one surfactant, as described below. The range of surfactants is not particularly limited, and some suitable surfactants for use in the present invention are described in more detail below. For example, the surfactant can be an anionic, cationic, nonionic, or zwitterionic surfactant.

[0028] In a second aspect, there is provided a method for improving the life of an inkjet print head, the method comprising the steps of:

[0029] supplying ink as described above to nozzle chambers of a printhead, each nozzle chamber having an associated actuator in contact with the ink; and

[0030] One or more of the actuators are actuated to eject ink from the printhead.

[0031] As described herein, the method according to the second aspect significantly improves printhead life compared to inks in which the PVA is not present.

[0032] Preferably, each actuator comprises a resistive heater element that superheats the ink so as to form a bubble and eject the ink from the corresponding nozzle chamber through the nozzle opening.

[0033] In some embodiments, the heater element may be uncoated, so that the ink is in direct contact with the resistive heater element.Such heater elements are particularly susceptible to corrosive attack.

[0034] Preferably, the heater 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 heater element is composed of a material selected from the group consisting of: a titanium alloy (e.g., a titanium-aluminum alloy); titanium nitride; and a nitride of a titanium alloy (e.g., titanium aluminum nitride).

[0035] In a third aspect, there is provided an inkjet printer comprising:

[0036] an inkjet printhead having a plurality of nozzle chambers, each nozzle chamber having an associated actuator for contacting ink; and

[0037] An ink reservoir is in fluid communication with the nozzle chamber, the ink reservoir containing ink as described above.

[0038] Preferred aspects of the printhead and ink will become readily apparent from the foregoing.

[0039] In a fourth aspect, there is provided the use of an ink as described herein for improving the life of an inkjet printhead.

[0040] As used herein, the term "ink" means any printing fluid that can be printed from an inkjet printhead. The ink may or may not contain a colorant. Accordingly, the term "ink" may include conventional dye-based or pigment-based inks, infrared inks, fixatives (e.g., pre-coating and finishing agents), 3D printing fluids (e.g., adhesive fluids), functional fluids (e.g., solar inks, sensing inks, etc.), biofluids, etc. Typically, ink is a dye-based ink for a thermal inkjet printhead. Where a fluid or printing fluid is mentioned, this is not intended to limit the meaning of "ink" herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Various embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:-

[0042] Figure 1 is a perspective view of a portion of a thermal inkjet print head;

[0043] Figure 2 yes Figure 1 a side view of one of the nozzle assemblies shown;

[0044] Figure 3 yes Figure 2 A perspective view of the nozzle assembly shown; and

[0045] Figure 4 It is a three-dimensional diagram of a thermal inkjet print engine. DETAILED DESCRIPTION

[0046] The inventors of the present invention have sought a solution to the problem of improving printhead life by investigating ink additives. As mentioned above, ink additives are an attractive solution to this problem because they do not require any modifications to the design of the printhead.

[0047] Although Butoxyne TM (1,4-bis(2-hydroxyethoxy)-2-butyne) has previously been shown to improve print head life in dye-based inks (see US 9,422,441), but the effectiveness of this additive exhibits some batch variability between different suppliers, as well as supply limitations. Initial efforts to find alternative additives with similar efficacy were generally unsuccessful. For example, based on early work described in WO 2022 / 184478, it was hypothesized that zwitterionic compounds could help protect heater elements. It was believed that zwitterions could help repel anionic corrosive species via a double layer effect at the heater surface. However, additives such as betaine were in fact found to be detrimental to heater life. Similarly, weak acids such as boric acid and ascorbic acid were ineffective or detrimental to heater life.

[0048] Given Butoxyne TM Due to batch variability in additives, it has been hypothesized that the active species that extends heater life is not the small alkyne molecule, but rather a water-soluble polymer that forms transiently on the heater surface during droplet ejection. TM The presence or absence of impurities in the ink (which may catalyze or hinder polymerization) or microscopic variations in the surface of individual heaters may explain the observed variability in efficacy. However, polymers are known to be highly kogogenic components in inks and would not be expected to be effective in extending printhead life.

[0049] Preliminary experiments with water-soluble ethoxylated silicone polymers confirmed the scaling hypothesis. TM When 8526 was added to a dye-based ink, rapid accumulation of kogation was observed, as evidenced by poor droplet jetting characteristics (e.g., low jet velocity, misdirected droplets). However, while such a kogation polymer is unsuitable, analysis of the heater resistance rise during those experiments was encouraging. Heater resistance rise is a strong indicator of corrosion, and the data showed a clear protective effect from the ethoxylated silicone (albeit at the expense of kogation) compared to a similar formulation lacking the ethoxylated silicone.

[0050] With these encouraging data, attempts were made to reduce scaling by lowering the amount of silicone additive. Although anti-corrosion effects were observed at very low additive concentrations (about 10 ppm), silicone still exhibited unacceptable scaling even at low concentrations. Addition of known anti-scaling additives ( EG-1, ethoxylated glycerin) is not particularly effective in improving the performance of ethoxylated silicones with respect to scaling.

[0051] While ethoxylated silicones are not effective in improving printhead life due to scaling, their effectiveness in limiting corrosion at very low concentrations (presumably via a protective layer at the heater surface) has been demonstrated. Therefore, the present inventors turned their attention to other water-soluble polymers that might have similar anti-corrosion effects at low concentrations, but without the detrimental scaling effects exhibited by silicones.

[0052] Surprisingly, polyvinyl alcohol was found to be very effective at minimizing corrosion of heater elements at low concentrations, but without the same scaling impact as silicone, thereby improving heater life overall. Remarkably, at concentrations of approximately 5 to 250 ppm, PVA exhibited excellent anti-corrosion effects along with acceptable droplet ejection characteristics. At higher PVA concentrations, droplet ejection characteristics became unacceptable due to the onset of scaling, while at lower PVA concentrations, it became less effective in reducing corrosion.

[0053] PVA has the added advantage of being relatively friendly, with little or no interaction with other ink components, and therefore does not affect the overall balance of ink properties at the desired concentration.

[0054] While all tested PVAs appear to have similar anti-corrosion effectiveness, from an ink formulation perspective, more soluble PVAs are generally preferred. Thus, PVAs with relatively low molecular weights (e.g., 5000 to 15,000 g / mol) and relatively low degrees of hydrolysis (e.g., 70% to 90%) are generally preferred.

[0055] Although PVA has been used in the field of inkjet technology before, it has typically been used as a primer fluid (see, for example, US 10,414,189) or as part of an ink-receiving layer on a medium (see, for example, US 2011 / 0279554) to promote adhesion of the ink to the medium. For this purpose, high-viscosity, high-molecular-weight PVA is used at high concentrations. To date, the use of very low concentrations of PVA in inks to increase printhead life has not been described in the literature.

[0056] Colorants, ink vehicles, and printheads suitable for use in combination with the present invention are described in further detail below.

[0057] Colorants

[0058] The inks used in the present invention may be of any type, but are typically dye-based inks which are known to be corrosive to thermal inkjet heater elements.

[0059] Inkjet dyes will be well known to those skilled in the art, and the present invention is not limited to the dye of any specific type. For example, dyes suitable for use in the present invention include azo dyes (such as Food Black 2 and K1600 (as described in US 8,834,620, the contents of which are 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 metal phthalocyanine dyes (including metal naphthalocyanine dyes, such as those described in US 7,148,345).

[0060] 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 Food 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, 7 8, 80, 81, 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, 13, 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; Fast Cyan 2 (Fujifilm Imaging Colorants); Fast Magenta2 (Fujifilm Imaging Colorants Co., Ltd.); Fast Yellow 2 (Fujifilm Imaging Colorants Co., Ltd.); and Fast Black 2 (Fujifilm Imaging Colorants Co., Ltd.)

[0061] Colorants such as dyes can be used in inkjet inks alone or in combinations of two or more thereof. For example, the ink can contain a primary dye and one or more shading dyes to provide an optimal color gamut.

[0062] ink carrier

[0063] Ink vehicles for inkjet inks will be well known to those skilled in the art, and there are no particular limitations on the ink vehicles used in the present invention. The ink vehicle used in the present invention is typically a conventional aqueous ink vehicle comprising at least 40 wt % water, at least 50 wt % water, or at least 60 wt % water. Typically, the amount of water present in the inkjet ink is in the range of 50 wt % to 90 wt %, or alternatively in the range of 60 wt % to 80 wt %.

[0064] Aqueous inkjet ink compositions are well known in the literature and may contain, in addition to water, other components such as co-solvents (including humectants, penetrants, wetting agents, etc.), surfactants, biocides, chelating agents, pH adjusters, viscosity modifiers, etc.

[0065] The cosolvent is typically a water-soluble organic solvent. Suitable water-soluble organic solvents include C 1-4 Alkyl 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 monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-tert-butyl ether, 1-methyl-1- - methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-tert-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, propylene glycol mono-n-butyl ether, and dipropylene glycol mono-n-butyl ether; formamide, acetamide, dimethyl sulfoxide, sorbitol, sorbitan, glyceryl monoacetate, glyceryl diacetate, glyceryl triacetate, and sulfolane; or a combination thereof.

[0066] Other useful water-soluble organic solvents that can be used as co-solvents include polar solvents such as 2-pyrrolidone, N-methylpyrrolidone, ε-caprolactam, dimethyl sulfoxide, sulfolane, morpholine, N-ethylmorpholine, 1,3-dimethyl-2-imidazolidinone, and combinations thereof.

[0067] The inkjet ink may contain a high boiling point water-soluble organic solvent as a co-solvent, which may act as a wetting agent or moisturizer for imparting water retention and wetting properties to the ink composition. Such high boiling point water-soluble organic solvents include organic solvents having a boiling point of 180°C or higher. Examples of water-soluble organic solvents having a boiling point of 180°C or higher are 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 monoethylene glycol, dipropylene glycol monoethyl ether, dipropylene glycol monomethyl ether, dipropylene glycol, triethylene glycol monomethyl ether. , tetraethylene glycol, triethylene glycol, diethylene glycol monobutyl ether, diethylene glycol monoethyl ether, diethylene glycol monomethyl ether, tripropylene glycol, polyethylene glycol having 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.

[0068] Other suitable humectants or moisturizers include sugars (including monosaccharides, oligosaccharides, and polysaccharides) and their derivatives (eg, maltitol, sorbitol, xylitol, hyaluronate, aldonic acid, uronic acid, etc.).

[0069] The inkjet ink may also contain a penetrant (as one of the co-solvents) for promoting the penetration of the aqueous ink into the recording medium. Suitable penetrants include polyol alkyl ethers (glycol ethers) and / or 1,2-alkyl diols. Examples of suitable polyol alkyl ethers are 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, ethylene glycol mono-n-propyl ether, ethylene glycol monoisopropyl ether, diethylene glycol monoisopropyl ether, ethylene glycol mono-n-butyl ether, diethylene glycol mono-n-butyl ether, triethylene glycol mono-n-butyl ether, ethylene glycol mono-tert-butyl ether, diethylene glycol mono-tert-butyl ether, 1-methyl-1-methoxybutanol, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol mono-tert-butyl ether, propylene glycol mono-n-propyl ether, propylene glycol monoisopropyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monoethyl ether, dipropylene glycol mono-n-propyl ether, dipropylene glycol monoisopropyl ether, propylene glycol mono-n-butyl ether, and dipropylene glycol mono-n-butyl ether. Examples of suitable 1,2-alkyl diols are 1,2-pentanediol and 1,2-hexanediol. The penetrant may also be selected from linear hydrocarbon diols such as 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, and 1,8-octanediol. Glycerol may also be used as a penetrant.

[0070] Typically, the amount of co-solvent present in the ink is in the range of about 5 wt% to 50 wt%, or alternatively 10 wt% to 40 wt%.

[0071] The inkjet ink may also contain one or more surface active agents (surfactants), such as anionic surfactants, zwitterionic surfactants, nonionic surfactants, or mixtures thereof. Useful anionic surfactants include sulfonic acid types, such as alkanesulfonates, α-olefinsulfonates, alkylbenzenesulfonates, alkylnaphthalenesulfonic acids, acylmethyltaurine, and dialkylsulfosuccinic acid; alkyl sulfates, sulfated oils, sulfated olefins, polyoxyethylene alkyl ether sulfates; carboxylic acid types, for example, fatty acid salts, and alkyl sarcosinates; and phosphates, such as alkylphosphates, polyoxyethylene alkyl ether phosphates, and glycerophosphates. Specific examples of anionic surfactants are sodium dodecylbenzenesulfonate, sodium laurate, and ammonium polyoxyethylene alkyl ether sulfates.

[0072] 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.

[0073] Examples of the nonionic surfactant include ethylene oxide adduct types such as polyoxyethylene alkyl ether, polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ester, and polyoxyethylene alkylamide; polyol ester types such as glycerol alkyl ester, sorbitan alkyl ester, and sugar alkyl ester; polyether types such as polyol alkyl ether; and alkanolamide types such as alkanolamine fatty acid amide. Specific examples of the nonionic surfactants are 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 ethers (e.g., polyoxyethylene alkyl ether); and esters such as polyoxyethylene oleate, polyoxyethylene oleate ester, polyoxyethylene distearate, sorbitan laurate, sorbitan monostearate, sorbitan monooleate, sorbitan sesquioleate, polyoxyethylene monooleate, and polyoxyethylene stearate.

[0074] Acetylene glycol surfactants, such as 2,4,7,9-tetramethyl-5-decyne-4,7-diol; ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol; 3,6-dimethyl-4-octyne-3,6-diol or 3,5-dimethyl-1-hexyne-3-ol, may also be used. Specific examples of nonionic surfactants that can be used in the present invention are 465 and 440 (available from Air Products and Chemicals, Inc.).

[0075] Surfactants are typically present in aqueous inkjet inks in amounts ranging from 0.05 wt% to 2 wt%.

[0076] The aqueous inkjet ink may also contain a pH adjuster or buffer, 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 hydrogen phthalate, and potassium hydrogen tartrate; 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"). When present, the amount of the pH adjuster is typically in the range of 0.01 to 2 wt.% or 0.05 to 1 wt.%.

[0077] The aqueous inkjet ink may also contain biocides such as benzoic acid, dichlorophen, hexachlorophene, sorbic acid, hydroxybenzoates, sodium dehydroacetate, 1,2-benzothiazoline-3-one (" GXL", available from Arch Chemicals, Inc.), 3,4-isothiazolin-3-one or 4,4-dimethyloxazolidine. When present, the amount of biocide is typically in the range of 0.01 to 2 wt.% or 0.05 to 1 wt.%.

[0078] Aqueous inkjet inks may also contain chelating agents, such as ethylenediaminetetraacetic acid (EDTA).

[0079] inkjet print heads

[0080] The inks according to the present invention are primarily intended for use in combination with thermal inkjet printheads, although they can be used with other types of printheads, particularly those in which the actuator contacts the ink. For the sake of completeness, a brief description of one of the applicant's thermal inkjet printheads, as described in U.S. Patent No. 7,303,930, the contents of which are incorporated herein by reference, will be provided below.

[0081] refer to Figure 1 , showing a portion of a print head including a plurality of nozzle assemblies. Figure 2 and Figure 3 One of these nozzle assemblies is shown in side section and cutaway perspective.

[0082] Each nozzle assembly includes a nozzle chamber 24 formed on a silicon substrate 2 by MEMS manufacturing technology. The nozzle chamber 24 is defined by a top 21 and a sidewall 22 extending from the top 21 to the silicon substrate 2. Figure 1 As shown, each top portion is defined by a portion of a nozzle plate 56 that spans the ejection face of the printhead. The nozzle plate 56 and sidewalls 22 are formed from the same material, deposited by PECVD on a sacrificial support of photoresist during MEMS fabrication. Typically, the nozzle plate 56 and sidewalls 21 are formed from a ceramic material such as silicon dioxide or silicon nitride. These hard materials have excellent properties for printhead robustness, and their inherent hydrophilicity is beneficial for supplying ink to the nozzle chamber 24 via capillary action.

[0083] Returning to the details of the nozzle chambers 24, it will be seen that a nozzle opening 26 is defined in the top of each nozzle chamber 24. Each nozzle opening 26 is generally oval in shape and has an associated nozzle rim 25. The nozzle rim 25 aids in droplet direction during printing and reduces, at least to some extent, the overflow of ink from the nozzle opening 26. The actuator for ejecting ink from the nozzle chamber 24 is a heater element 29, which is positioned below the nozzle opening 26 and suspended across the recess 8. Current is supplied to the heater element 29 via an electrode 9 connected to a driver circuit in the CMOS layer of the underlying substrate 2. When current passes through the heater element 29, the heater element rapidly superheats the surrounding ink to form a bubble, which forces the ink through the nozzle opening 26. By suspending the heater element 29, the heater element is completely immersed in the ink when the nozzle chamber 24 is primed. This improves printhead efficiency because less heat is dissipated into the underlying substrate 2 and more of the input energy is used to generate the bubble. Typically, the heater element is constructed of metal or a conductive ceramic material. Examples of suitable materials include titanium nitride, titanium aluminum nitride, and titanium-aluminum alloys.

[0084] As in Figure 1As best seen in the drawing, the nozzles are arranged in a row and ink is supplied to each nozzle in the row by an ink supply channel 27 extending longitudinally along the row. The ink supply channel 27 delivers ink to the ink inlet passage 15 of each nozzle, which is supplied with ink from the side of the nozzle opening 26 via the ink conduit 23 in the nozzle chamber 24.

[0085] MEMS fabrication processes for making such printheads are described in detail in US Pat. No. 7,303,930, the contents of which are incorporated herein by reference.

[0086] The operation of a printhead having suspended heater elements is described in detail in US Pat. No. 7,278,717 to the present applicant, the contents of which are incorporated herein by reference.

[0087] The applicant has also described a thermal bubble formation inkjet printhead having an integrated heater element. Such printheads are described in, for example, US 7,246,876 and US 2006 / 0250453, the contents of which are incorporated herein by reference.

[0088] The inkjet inks of the present invention are best used in combination with the applicant's thermal inkjet printheads as described above. However, their use is not limited to the applicant's thermal printheads. The inks described herein can be used in other types of thermal bubble formation inkjet printheads, piezoelectric printheads, thermal bend actuated printheads (as described, for example, in US Pat. Nos. 7,926,915; 7,669,967; and 8,998,383, the contents of which are incorporated herein by reference), and the like.

[0089] For the sake of completeness, inkjet printers incorporating the applicant's thermal inkjet printheads are described, for example, in US 7,201,468; US 7,360,861; US ​​7,380,910; and US 7,357,496, the contents of each of which are incorporated herein by reference.

[0090] Figure 4A print engine 103 for a thermal inkjet printer is shown, as described in Applicant's US 8,066,359, the contents of which are incorporated herein by reference. The print engine 103 includes a removable print cartridge 102 (including a pagewidth printhead) 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 printhead. Thus, the print engine 103 has five ink reservoirs 128 and five corresponding pressure regulating chambers 106. Typically, the ink channels ("color channels") employed in this five-channel print engine 103 are CMYK1K2. The ink channel sequence can be arranged so as to optimize the preferred ink color mixing effect at the nozzle plate of the printhead, as described in US 2013 / 0070024 (the contents of which are incorporated herein by reference). For example, an ink channel order of CK1MK2Y may be employed, in which cyan (C) is positioned most upstream and yellow (Y) is positioned most downstream.

[0091] Each ink cartridge 128 may contain an ink composition as described herein. Although fluid connections between the various components are not provided in the drawings, Figure 4 8,066,359, the contents of which are incorporated herein by reference, are shown, but it will be appreciated that these connections are made with suitable hoses in accordance with the fluid system described in, for example, US 8,066,359.

[0092] Experimental part

[0093] Accelerated printhead life testing was performed on various inks according to the method described below.

[0094] A printhead integrated circuit (PHIC) with an uncoated titanium aluminum nitride resistive heater element was individually installed and operated in a modified printing setup. The actuation pulse width was controlled to replicate operation in an otherwise unmodified printer. The heater resistance rise (expressed as a percentage increase from the start of the experiment) was recorded after 50 million actuations. This resistance rise correlates with the corrosion rate of the heater element in the PHIC.

[0095] A baseline ink formulation without additives was prepared as shown in Table 1 and filtered (0.2 microns) before use.

[0096] Table 1. Baseline ink formulations used for accelerated printhead life testing

[0097]

[0098]

[0099] 1. K1600 is a black disazo dye as described in US 8,834,620

[0100] 2. 465 is ethoxylated 2,4,7,9-tetramethyl-5-decyne-4,7-diol

[0101] 3. GXL is 1,2-benzisothiazolin-3-one

[0102] Inks 1-9 were prepared using a baseline ink formulation with various additives in the amounts shown in Table 2. Each ink was tested in the modified printing rig described above, and the resistance rise of each ink was measured after 50 million jets (normalized relative to the baseline ink without additives). For some ink candidates, qualitative kogation observations were reported as a score from 1 to 5 (1 = baseline kogation; 5 = heavy kogation / misdirected drops). The results from these accelerated printhead life tests are shown in Table 2.

[0103] Table 2. Accelerated Printhead Life Tests of Various Additives

[0104]

[0105] As can be seen from Table 2, compared with the baseline formulation without additives, in addition to the known anti-corrosion additive Butoxyne TM Besides, most of the additives tested had either negligible effect or undesirable accelerating effect on the corrosion rate.

[0106] Interestingly, Dow Corning TM 8526 (an ethoxylated silicone polymer with a molecular weight in the range of 6000 to 8000 g / mol) showed promising anti-corrosion performance at relatively low concentrations. It is hypothesized that the silicone polymer forms a protective layer on the heater element that minimizes corrosive attack by the dye species. However, fouling was observed to be very poor both via droplet ejection characterization and visual inspection of the heater element. Therefore, the use of this silicone polymer additive in ink formulations at either 0.3 wt% or 0.1 wt% is clearly unacceptable.

[0107] However, Dow Corning TM The promising anti-corrosion properties of 8526 identified it as a candidate for further testing. It was hypothesized that fouling could be prevented at lower concentrations or with the addition of known anti-fouling additives ( Table 3 shows the effect of Dow Corning Dowsil on the TM 8526 test results.

[0108] Table 3. Dow Corning TM 8526 Accelerated Printhead Life Test

[0109]

[0110] Disappointingly, all the tested silicones containing ethoxylated silicones (Dow Corning TM 8526) have either unacceptable scaling or negligible anti-corrosion effects. For example, Ink 12 has excellent anti-corrosion performance at a concentration of 0.005 wt.% (50 ppm), but still has very poor scaling performance. On the other hand, Ink 13 has acceptable scaling performance at a concentration of 0.001 wt.% (10 ppm), but negligible anti-corrosion effect. Therefore, for Dowsil TM 8526 additive, there is no formulation solution that provides useful anti-corrosion effect without unacceptable scaling.

[0111] Based on the rationale that low concentrations of water-soluble polymers can provide an anti-corrosion effect via a protective coating on heater elements, polyvinyl alcohol was identified as a replacement candidate for ethoxylated silicone. The results for various polyvinyl alcohol (PVA) additives and one polyvinyl pyrrolidone (PVP) additive are shown in Table 4.

[0112] Table 4. Accelerated Printhead Life Testing of PVA and PVP Additives

[0113]

[0114] Although PVA has the same TM Despite similar solubility and molecular weight to 8526, PVA exhibited significantly improved fouling results compared to the ethoxylated silicone additives while maintaining excellent corrosion resistance. Comparison with a similar water-soluble polymer (PVP-10) indicated that corrosion and fouling performance cannot be simply predicted based on solubility and / or molecular weight alone, with Ink 17 exhibiting worse corrosion and fouling performance than Inks 14-16. Incidentally, it appears that PVA interacts with the heater element during droplet ejection in a way that other polymers do not, making inks containing PVA less prone to fouling than inks containing other polymer additives. Of course, it is not possible to study the interaction of each polymer with the heater element under the high temperature and pressure environment of the inkjet nozzle chamber during droplet ejection.

[0115] Comparing inks 14-16, it is observed that lower molecular weight PVA is preferred from both the perspective of ink formulation and corrosion / fouling performance. Similarly, lower degrees of hydrolysis are preferred, indicating that more soluble PVA is generally preferred to optimize ink formulations with improved printhead life.

[0116] Compared to other polymer additives, PVA additives can shift the failure mode of inks from kogation (typical of most polymers) to corrosion, thereby extending overall life. However, kogation cannot be completely eliminated with PVA additives, and therefore it is desirable to minimize the amount of PVA in any ink formulation to the extent possible. Minimizing the amount of PVA in an ink formulation achieves a desirable balance between corrosion and kogation in order to optimize both printhead life and print quality.

[0117] Table 5 shows the effect of increasing the amount of PVA on the corrosion and kogation performance of the reference ink formulations. The PVA added to each of inks 18 to 23 had a molecular weight of 9000 g / mol and a degree of hydrolysis of 80%. In this series of experiments, the actual life before failure is reported.

[0118] Table 5. Actual print head life test of PVA additives

[0119] Ink number additive life Failure Mode refer to none 120M corrosion Ink 18 PVA (10ppm) 240M corrosion Ink 19 PVA (50ppm) 260M corrosion Ink 20 PVA (100ppm) 300M corrosion Ink 21 PVA (200ppm) 260M corrosion Ink 22 PVA (500ppm) 50M Scaling Ink 23 PVA (1000ppm) 50M Scaling

[0120] Compared to the reference ink formulation, the anti-corrosion effect of PVA can be observed at concentrations as low as 10 ppm. However, the anti-corrosion effect of PVA is expected to decrease significantly at concentrations below about 5 ppm.

[0121] While PVA concentrations up to 200 ppm can be tolerated, as expected, fouling performance generally deteriorates with increasing PVA concentration. At PVA concentrations of 500 ppm and 1000 ppm, fouling failure mode dominates, and lifetime is significantly reduced due to fouling. Without wishing to be bound by theory, the inventors understand that a threshold amount of PVA is required to coat the surface of the heater element in order to minimize corrosion. However, once the amount of PVA reaches the necessary "saturation" on the surface of the heater element, increasing the amount of PVA has little effect on the corrosion rate, but instead reduces lifetime via the fouling failure mechanism.

[0122] Of course, the optimal amount of PVA for any ink formulation will depend on the aggressiveness of the corrosive components (e.g., dyes) and other formulation components. Those skilled in the art will appreciate that an optimal PVA concentration within the range of 5 to 250 ppm can be empirically determined for a given ink formulation, depending on the balance between print quality and printhead life.

[0123] It will of course be understood that the present invention has been described by way of example only and modifications of detail may be made within the scope of the invention as defined in the appended claims.

Claims

1. An inkjet ink comprising: a water-based ink vehicle; and 5 to 250 ppm of polyvinyl alcohol.

2. The inkjet ink according to claim 1, wherein The polyvinyl alcohol is present in an amount ranging from 10 to 200 ppm.

3. The inkjet ink according to claim 1, wherein The polyvinyl alcohol has a molecular weight ranging from 5000 to 15,000 g / mol.

4. The inkjet ink according to claim 1, wherein The polyvinyl alcohol has a degree of hydrolysis ranging from 70% to 90%. The inkjet ink of 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 wt. % of one or more co-solvents.

8. The inkjet ink according to claim 1, wherein The ink vehicle comprises 0.05 to 2 wt % of at least one surfactant.

9. The inkjet ink according to claim 1, wherein The ink is free of any polymer other than the polyvinyl alcohol having a molecular weight greater than 5000 g / mol.

10. The inkjet ink of claim 1, which is absent any polymer other than the polyvinyl alcohol having a molecular weight greater than 3000 g / mol.

11. A method for improving the life of an inkjet print head, the method comprising the following steps: supplying the ink of claim 1 to nozzle chambers of the printhead, each nozzle chamber having an associated actuator in contact with the ink; as well as One or more of the actuators are actuated to eject ink from the printhead.

12. The method of claim 11, wherein: Each actuator includes a resistive heater element.

13. The method of claim 12, wherein: The heater element is uncoated and comprises a material selected from the group consisting of: titanium alloys; titanium nitride; and Nitrides of titanium alloys.

14. The method of claim 11, wherein: The lifetime is improved compared to corresponding inks in which the polyvinyl alcohol is not present.

15. Use of the ink according to claim 1 for improving the life of an inkjet print head.

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