(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(19) World Intellectual Property
`Organization
`International Bureau
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`(10) International Publication Number
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`g
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`(43) International Publication Date
`WO 2015/134020 A1
`11 September 2015 (11.09.2015) WIPOI PCT
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`(51)
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`International Patent Classification:
`C09D 11/30 (2014.01)
`B41M 5/00 (2006.01)
`B41J 2/01 (2006.01)
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`(21)
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`International Application Number:
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`PCT/US2014/021066
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`(22)
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`International Filing Date:
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`(25)
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`(26)
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`(71)
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`(72)
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`(74)
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`(81)
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`Filing Language:
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`Publication Language:
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`6 March 2014 (06.03.2014)
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`English
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`English
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`Applicant: HEWLETT-PACKARD DEVELOPMENT
`COMPANY, LP. [US/US]; 11445 Compaq Center Drive
`VV., Houston, Texas 77070 (US).
`
`Inventor: ADAMIC, Raymond; 1070 NE Circle B1vd.,
`Corvallis, Oregon 97330-4239 (US).
`
`Agents: RIETH, Nathan et al.; Hewlett-Packard Com-
`pany, Intellectual Property Administration, 3404 E. IIar-
`mony Rd., Mail Stop 35, Fort Collins, Colorado 80528
`(US).
`
`Designated States (unless otherwise indicated, for every
`kind of national protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BVV, BY,
`BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM,
`
`DO, DZ, EC, EE, EG, Es, FI, GB, GD, GE, GH, GM, GT,
`HN, HR, HU, ID, IL, IN, IR, 15, JP, KE, KG, KN, KP, KR,
`KZ, LA, LC, LK, LR, LS, LT, LU, LY, MA, MD, ME,
`MG, MK, MN, MW, MX, MY, MZ, NA, NG, NI, NO, NZ,
`OM, PA, PE, PG, PH, PL, PT, QA, RO, RS, RU, RW, SA,
`SC, SD, SE, SG, SK, SL, SM, ST, SV, SY, TH, TJ, TM,
`TN, TR, TT, TZ, UA, UG, US, UZ, VC, VN, ZA, ZM,
`ZW.
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`(84)
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`Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LR, LS, MW, MZ, NA, RWY, SD, SL, SZ, TZ,
`UG, ZM, ZW), Eurasian (AM, AZ, BY, KG, KZ, RU, TJ,
`TM), European (AL, AT, BE, BG, CH, CY, CZ, DE, DK,
`EE, Es, FI, FR, GB, GR, HR, HU, IE, IS, IT, LT, LU, Lv,
`MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM,
`TR), OAPI (BF, BJ, CF, CG, CI, CM, GA, GN, GQ, GVV,
`KM, ML, MR, NE, SN, TD, TG).
`Declarations under Rule 4.17:
`
`as to the identity ofthe inventor (Rule 4.1 7(1))
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`as to applicanth entitlement to applyfor and be granted a
`patent (Rule 4.1 7(ii))
`Published:
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`with international search report (Art. 21(3))
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`(54) Title: NON-NEVVTONIAN INKJET INKS
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`Optical Density Measurements on HP Brochure Media (2 Hour Scratch)
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`2—-_AverageofODScratch_Average 0! OD Off Scratch
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`Ink 1
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`FIG. 4
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`(57) Abstract: The present disclosure provides non-Newtonian inkjet inks and related methods. In one example, a non-Newtonian
`inkjet ink can comprise a gelator in an amount ranging from 0.1% to 10% by weight based on the total weight of the non-Newtonian
`inkjet ink; a, salt in an amount of 0.05% to 20% by weight based on the total weight of the non-Newtonian inkjet ink; a, sugar alcohol
`in an amount of 1% to 25% by weight based on the total weight of the non—Newtonian inkjet ink; and an organic solvent. The gelator
`and the salt can form a structured network, where the inkjet ink has a first dynamic viscosity ranging from 25 cps to 10,000 cps at a
`first state and a second dynamic Viscosity ranging from 1 cps to 50 cps at a second state.
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`NON-NEWTONIAN INKJET INKS
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`BACKGROUND
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`[0001]The use of ink—jet printing systems has grown dramatically in recent
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`years. This growth may be attributed to substantial improvements in print
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`resolution and overall print quality. Today's ink-jet printers offer acceptable print
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`quality for many commercial, business, and household applications at costs much
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`lower than comparable products availablejust a few years ago. Notwithstanding
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`their recent success, intensive research and development efforts continue toward
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`improving ink-jet print quality, while further lowering cost to the consumer.
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`[0002]An ink—jet image is formed when a precise pattern of dots is ejected
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`from a drop-generating device known as a "printhead" onto a printing medium.
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`Inks normally used in ink-jet recording are commonly composed of water-soluble
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`organic solvents (humectants, etc.), surfactants, and colorants in a predominantly
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`aqueous fluid. When a recording is made on plain paper, the deposited colorants
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`retain some mobility, which can be manifest in poor bleed, edge acuity,
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`feathering, and inferior optical density/chroma (due to penetration on the paper).
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`These features adversely impact text and image quality. Other systems include
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`using a coated paper or coating the paper immediately before printing with the
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`inkjet ink. The coatings generally contain various components such as fixers to
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`reduce colorant mobility. However, such systems can be costly, can lower print
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`quality, and can be limiting as the media is typically matched to the inks.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`[0003]Additional features and advantages of the disclosure will be
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`apparent from the detailed description which follows, taken in conjunction with the
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`accompanying drawings, which together illustrate, by way of example, features of
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`the technology; and, wherein:
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`[0004] FIG. 1
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`is a flow chart of a method in accordance with an example of
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`the present disclosure;
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`[0005] FIG. 2 is a flow chart of another method in accordance with an
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`example of the present disclosure;
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`[0006] FIG. 3 is a bar graph depicting curl measurements in accordance
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`with an example of the present disclosure;
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`[0007] FIG. 4 is a bar graph depicting optical density (OD) measurements
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`at 2 hours for scratch resistance in accordance with an example of the present
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`disclosure; and
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`[0008] FIG. 5 is a bar graph depicting optical density (OD) measurements
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`at 24 hours for scratch resistance in accordance with an example of the present
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`disclosure.
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`[0009] Reference will now be made to the exemplary embodiments
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`illustrated, and specific language will be used herein to describe the same. It will
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`nevertheless be understood that no limitation of the scope of the disclosure is
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`thereby intended.
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`DETAILED DESCRIPTION
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`[0010] Non-Newtonian inkjet inks can be prepared where the viscosity of
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`the inks can be manipulated by physical or thermal forces allowing for printing of
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`the inks via inkjet technologies at desirable viscosities. Notably, the reformation
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`of a structured network after printing can allow for the present non-Newtonian
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`inkjet inks to provide better optical density and other properties than achieved by
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`traditional Newtonian inkjet inks. Additionally, in accordance with the present
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`technology, the non-Newtonian inkjet inks of the present disclosure include a
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`sugar alcohol that provides curl and rub/scratch resistance not achieved by many
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`traditional inks including gel-based inks.
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`[0011] Examples in accordance with the disclosure are directed to non—
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`Newtonian inkjet inks that are useful in standard inkjet printing systems. The
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`present non—Newtonian inkjet inks can be inkjet printed as the viscosity of the
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`non-Newtonian inkjet inks are lowered using thermal control or mechanical
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`control within a printing system, e.g., an inkjet printhead. Once exiting the
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`printhead, the viscosity of the present non-Newtonian inkjet inks rapidly increases
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`(e.g. within 30 seconds) via self—assembly of a structured network within the non—
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`Newtonian inkjet inks. Generally, the structured network can be assembled
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`between a gelator, e.g., a low molecular weight organic gelator or metal oxide,
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`and a salt within the non-Newtonian inkjet inks disclosed herein.
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`[0012] It is noted that when discussing the present compositions and
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`methods, each of these discussions can be considered applicable to each of
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`these embodiments, whether or not they are explicitly discussed in the context of
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`that embodiment. Thus, for example, in discussing a low molecular weight
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`organic gelator used in a non-Newtonian inkjet ink, such a low molecular weight
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`organic gelator can also be used in a method of manufacturing a non-Newtonian
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`inkjet ink and/or a method of printing a non-Newtonian in kjet in k, and vice versa.
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`[0013] It is also noted that when referring to an "ink" or an "inkjet ink," this
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`does not infer that a colorant necessarily be present. Inks, as defined herein, can
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`be colorant free or can alternatively include colorant.
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`[0014] Generally, recording media and/or inkjet inks can have a variety of
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`additives and coatings to provide acceptable quality when used in printing
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`applications. However, utilizing the present non-Newtonian inkjet inks can
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`eliminate the use of some layers, can eliminate costly additives, and/or can
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`eliminate the amounts of materials used in the media sheets and/or inks.
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`[001 5] With the above in mind, a non-Newtonian inkjet ink can comprise a
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`gelator in an amount ranging from 0.1 % to 10% by weight based on the total
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`weight of the non-Newtonian inkjet ink; a salt in an amount of 0.1% to 20% by
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`weight based on the total weight of the non—Newtonian inkjet ink; a sugar alcohol
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`in an amount of 1% to 25% by weight based on the total weight of the non-
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`Newtonian inkjet ink; and an organic solvent. Water can optionally be present,
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`and in some examples, the ink can be an aqueous ink. Once printed, the gelator
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`and the salt can form a structured network. Further, the inkjet ink generally has a
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`first dynamic viscosity ranging from 25 cps to 10,000 cps at a first state and a
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`second dynamic viscosity ranging from 1 cps to 50 cps at a second state. The
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`first dynamic viscosity is generally higher than the second dynamic viscosity. It is
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`noted that for all viscosity measurements herein, unless othenNise stated, 25 °C
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`is the temperature that is used.
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`[0016] Regarding the present states, such states generally refer to the
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`non-Newtonian inkjet ink at a first state, e.g. proximate in time when at rest
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`(subject to shear rate of 5 s1) or at room temperature (23 °C), and at a second
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`state, e.g. proximate in time to when at high shear (10,000 s'1) or at elevated
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`temperature (50 °C). As such, the present non—Newtonian inkjet inks can be
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`subject to thinning under shear and/or heat to reduce the viscosity and allow for
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`the inks to be processed in an inkjet printing apparatus. In one example, the
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`viscosity of the first state can be higher than 10,000 cps, such as at least 20,000
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`cps, at least 100,000 cps, or even at least 500,000 cps. Thus, shearing and/or
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`heating can alter, e.g. lower, the viscosity profiles of the present inks.
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`[0017]As used herein, “structured network” refers to the three dimensional
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`structure formed by a gelator (e.g., a low molecular weight organic gelator or
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`metal oxide) and dissolved salt via electrostatic interactions and/or physical
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`interactions in the non-Newtonian inkjet ink. In one example, the three
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`dimensional structure can be dependent upon mechanical and/or thermal forces.
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`Such mechanical and/or thermal forces, such as shear energy or heat energy,
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`weaken the structured network such that the viscosity changes based on the
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`amount of force applied, as discussed herein. In one example, the structured
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`network can be free of polymers in that the three dimensional structure does not
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`comprise polymers. However, such an example does not preclude polymers to be
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`present within the non-Newtonian inkjet ink, or even trapped or contained within
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`the structured network. For example, the present non-Newtonian inkjet inks can
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`further comprise a polymeric surfactant that does not self—assemble as part of the
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`three dimensional structure, but can be present or become trapped within such a
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`structure. In one specific example, the structured network can be a gel.
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`[0018] Regarding the present description as it relates to "non—Newtonian,"
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`a non-Newtonian fluid is one in which the viscosity changes as the applied force
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`changes in magnitude, e.g. thermal or mechanical shear, resulting in a viscosity
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`which may not be well—defined. As such, in one aspect, the present non-
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`Newtonian fluids can be thinned by increasing the temperature of the fluids. In
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`another aspect, the present non-Newtonian fluids can be thinned by shearing the
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`fluids. Typically, in inkjet printing applications, ink is moved between a fluid
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`container and the printhead of an inkjet device. In these applications, the present
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`non-Newtonian inkjet inks can be heated at the fluid container, between the fluid
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`container and the printhead, or in the printhead, thereby decreasing viscosity
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`allowing for inkjet printing followed by rapid cooling and structured network
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`reformation on a recording medium. Additionally, in another example, such inks
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`can be sheared in the printhead thereby decreasing the viscosity allowing for
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`inkjet printing followed by structured network reformation on the recording
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`medium.
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`[0019] In an aspect of these non-Newtonian inkjet inks that may not be
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`intuitive to some, the colorants, e.g. dispersed pigments which may even be large
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`and dense pigments, show little or no settling in the fluid container or printhead
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`during the times when the ink is not moving through the system or when the ink is
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`not heated. When little or no dynamic pressure is being applied to the ink to move
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`it through the system or when no heat is being applied to the ink, the ink has a
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`viscous consistency. However, when the normal amount of dynamic pressure (at
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`least about 10,000 Pascals) is applied to the ink to move it through the inkjet
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`system or when the ink is heated to 50 °C, the ink's viscosity may even change to
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`something more resembling classical Newtonian inkjet inks, e.g. from 1 to 5 cps.
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`[0020]Thus, when such inks are ejected at a high frequency from the fluid
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`container of an inkjet fluid dispensing device, the dynamic viscosities of the inks
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`are at a low level that does not interfere with the ejection process of the inkjet
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`system. Generally, during the time when the ink is not moving or being heated,
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`settling may also be completely prevented or slowed down by several orders of
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`magnitude, for example.
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`[0021] In one example, the ink and resultant structured network can
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`comprise a low molecular weight organic gelator. As used herein, “low molecular
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`weight organic gelator” refers to an organic molecule or oligomer that is able to
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`form a three dimensional structure with a salt in the presence of an organic
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`solvent and/or water to form a structured network. As used herein “oligomer”
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`refers to a compound comprised of no more than 10 monomer units. Regarding
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`low molecular weight, in one example, the present low molecular weight organic
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`gelators can have a weight average molecular weight of 50 to 10,000 Mw. For
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`oligomers, the present molecular weights refer to weight average molecular
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`weights. In one aspect, the weight average molecular weight can be from 100 to
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`2,000 Mw.
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`[0022]The present low molecular weight organic gelators can include
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`amino acids. Such amino acids can be included as part of peptides and cyclic
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`peptides.
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`In one example, the amino acids can have a protecting group, e.g., an
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`amine protecting group. In another example, the amino acid can be an aliphatic
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`amino acid such as glycine, alanine, valine, Ieucine, or isoleucine. In another
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`example, the amino acid can be a hydroxyl or sulfur/selenium-containing amino
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`acid such as serine, cysteine, selenocysteine, threonine, or methionine. In still
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`another example, the amino acid can be a cyclic amino acid such as proline or a
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`cyclic peptide. In yet another example, the amino acid can be an aromatic amino
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`acid such as phenylalanine, tyrosine, or tryptophan. In still another example, the
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`amino acid can be a basic amino acid such as histidine, lysine, or arginine. In still
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`yet another example, the amino acid can be an acidic amino acid or amide—
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`containing amino acid such as aspartate, glutamate, asparagine, or glutamine.
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`Such amino acids can be individually functionalized with the presently disclosed
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`protecting groups or can be combined into peptides, including cyclic peptides,
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`with such functionalization. Regarding the amine protecting groups, in one
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`example, the amine protecting group can be a fluorenyl methoxy carbonyl group.
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`In another example, the amine protecting group can be an aromatic protecting
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`group. Other derivatives can include naphthalene or naphthyl based peptides. In
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`one specific example, the low molecular weight organic gelator can be N—(9—
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`fluorenylmethoxycarbonyl)-L-phenylalanine. In another example, the low
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`molecular weight organic gelator can be a dipeptide of N-(9-
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`fluorenylmethoxycarbonyl)—L—phenylalanine. Other examples include naphthalene
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`derivatives of N-(9-fluorenylmethoxycarbonyl)—L-phenylalanine.
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`Fluorenylmethoxycarbonyl peptide derivative materials can be obtained from
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`BaChem Chemicals Co.
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`[0023]As discussed herein, the low molecular weight organic gelator can
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`generally be present in the non-Newtonian inkjet ink in an amount ranging from
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`0.1% to 10% by weight based on the total weight of the non—Newtonian inkjet ink.
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`In one example, the low molecular weight organic gelator can be present in an
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`amount of 1% to 5% by weight, and in one aspect, 0.5% to 2% by weight; based
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`on the total weight of the non-Newtonian inkjet ink.
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`[0024] Without intending to be bound by any particular theory, particularly
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`with respect to low molecular weight organic gelators, a gel structure can be
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`formed by pi-pi stacking of aromatic groups present in the low molecular weight
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`organic gelators and hydrogen bonding. The salt can shield the repulsive
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`electrostatic charge between charged low molecular weight organic gelator
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`species and allow them to interact. Such interaction can result in cylindrical fiber
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`formation, and in some examples, the fibers can entangle and swell via water
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`and/or solvent and create a gel structure. The salts can also act to strengthen
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`the fibers or structured network primarily on the recording media. Thus, some
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`treated papers, e.g. ColorLok® papers, which include additional calcium ions, can
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`interact with fibers that form using the low molecular weight organic gelator. Upon
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`heating, the fibers can separate forming discrete domains, thereby minimizing
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`interactions between fibers and decreasing viscosity. After sufficient heating, the
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`fibers can be reduced to monomer units of the low molecular weight organic
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`gelators. In the “monomer” form, the viscosity can be expected to be quite low
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`because the size of the structure is much smaller.
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`[0025] In another example, the ink and resultant structured network can
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`comprise a metal oxide as the gelator. As used herein, “metal oxide” refers to a
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`molecule comprising at least one metal or semi—metal (e.g. Si) atom and at least
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`one oxygen atom which in a particulate form is able to form a three dimensional
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`structure in the presence of salt dissolved in an organic solvent and/or water,
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`thereby forming a structured network. As used herein “semi—metal” includes
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`boron, silicon, germanium, arsenic, antimony, and tellurium, for example. In one
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`example, the metal oxide can include with limitation aluminum oxide, silicon
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`dioxide, zinc oxide, iron oxide, titanium dioxide, indium oxide, zirconium oxide, or
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`mixtures thereof. As discussed herein, the metal oxide (again which is defined to
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`include both metal and semi-metal oxides) can generally be present in the non-
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`Newtonian inkjet ink in an amount ranging from 0.1% to 10% by weight based on
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`the total weight of the non—Newtonian inkjet ink. In one example, the metal oxide
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`can be present in an amount at from 1% to 5% by weight, and in one aspect, at
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`from 0.5% to 2% by weight, based on the total weight of the non-Newtonian inkjet
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`ink. Additionally, the particle size of the metal oxide can be varied depending on
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`the desired properties of the non—Newtonian inkjet ink. For example, the bigger
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`the particle size, the less viscous the non-Newtonian inkjet ink tends to be. In one
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`example, the particle size can be from 5 nm to 50 nm. In another aspect, the
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`particle size can be from 10 nm to 25 nm.
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`[0026] Metal oxide particles, e.g. F9304, can be dispersed with
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`dispersants. Examples of suitable dispersants include, but are not limited to,
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`water-soluble anionic species of low and high molecular weight such as
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`phosphates and polyphosphates, phosphonates and polyphosphonates,
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`phosphinates and polyphosphinates, carboxylates (such as citric acid or oleic
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`acid), polycarboxylates (such as acrylates and methacrylates). Other examples
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`include hydrolysable alkoxysilanes with alkoxy group attached to water-soluble
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`(hydrophilic) moieties such as water—soluble polyether oligomer chains,
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`phosphate group or carboxylic group. In some examples, the dispersant used to
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`disperse metal oxide particles can be a polyether alkoxysilane or polyether
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`phosphate dispersant.
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`[0027] Examples of polyether alkoxysilane dispersants used to dispersed
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`metal oxide particles can be represented by the following general Formula (I):
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`(1)
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`R1
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`Rz—Ti—(PE)—R4
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`R3
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`wherein:
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`a) R1, Rzand R3 are hydroxy groups, or hydrolyzable linear or branched
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`alkoxy groups. For hydrolyzable alkoxy groups, such groups can have 1 to 3
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`carbon atoms; in one aspect, such groups can be —OCH3 and —OCHZCH3. In
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`some examples, R1, R2 and R3 are linear alkoxy groups having from 1 to 5 carbon
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`atoms. In some other examples, R1, R2 and R3 groups are iOCHe, or 70C2H5.
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`b) PE is a polyether oligomer chain segment of the structural formula
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`[(CH2)n—CH(R)—O]m, attached to Si through Si—C bond, wherein n is an integer
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`ranging from O to 3, wherein m is an integer superior or equal to 2 and wherein R
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`is H or a chain alkyl group. R can also be a chain alkyl group having 1 to 3
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`carbon atoms, such as CH3 or C2H5. In some examples, m is an integer ranging
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`from 3 to 30 and, in some other examples, m is an integer ranging from 5 to 15.
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`The polyether chain segment (PE) may include repeating units of polyethylene
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`glycol (PEG) chain segment (—CH2CH2—O—), or polypropylene glycol (PPG)
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`chain segment (—CH2—CH(CH3)—O—), or a mixture of both types. In some
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`examples, the polyether chain segment (PE) contains PEG units (—CH20H2—
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`0—); and
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`c) R4is hydrogen, or a linear or a branched alkyl group. In some examples,
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`R4 is an alkyl group having from 1 to 5 carbon atoms.
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`[0028] Other examples of dispersants used to disperse metal oxide
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`particles can include polyether alkoxysilane dispersants having the following
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`general Formula (ll):
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`OR’
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`(11)
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`OR”—Si— (PE)—R4
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`OR":
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`wherein R', R" and R'" are linear or branched alkyl groups. In some examples, R’,
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`R" and R'" are linear alkyl groups having from 1 to 3 carbon atoms in chain
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`length. In some examples, R', R" and R"’—CH3 or —CzH5. R4 and PE are as
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`described above for Formula (I); i.e. PE is a polyether oligomer chain segment of
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`the structural formula: [(CHZ) n—CH—R—O]m, wherein n is an integer ranging
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`from O to 3, wherein m is an integer superior or equal to 2 and wherein R is H or
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`a chain alkyl group; and R4 is hydrogen, or a linear or a branched alkyl group. In
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`some examples, R4 is CH3 or C2H5.
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`[0029] In some examples, the metal oxide particles present in the ink
`
`composition are dispersed with polyether alkoxysilanes. Examples of suitable
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`polyether alkoxysilanes include (CH30)3Si—(CH2CH20)n, H; (CH3CH20)3Si—
`
`(CH2CH20)n,H; (CH30)3Si—(CH2CH20)n, CH3; (CH3CH20)3Si—(CH2CH20)n,
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`CH3; (CH30)3Si—(CH2CH20)n, CH2CH3; (CH3CH20)3Si—(CH2CH20)n, CH2CH3;
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`(CH30)3Si—(CH2CH(CH3)O)n, H; (CH3CH20)3Si—(CH2CH(CH3) O)“, H;
`
`(CH30)3Si—(CH2CH(CH3) 0)“, CH3; (CH3CH20)3Si—(CH2CH(CH3) 0)“, CH3;
`
`wherein n' is an integer equal to 2 or greater. In some examples, n' is an integer
`
`ranging from 2 to 30 and, in some other examples, n' is an integer ranging from 5
`
`to 15.
`
`[0030] Commercial examples of the polyether alkoxysilane dispersants
`
`include, but are not limited to, Silquest®A—1230 manufactured by Momentive
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`Performance Materials and Dynasylan® 4144 manufactured by Evonik/Degussa.
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`[0031]The amount of dispersant used in the metal oxide dispersion may
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`vary from about 1% by weight to about 300% by weight of the metal oxide
`
`particles content. In some examples, the dispersant content range is between
`
`about 2 to about 150% by weight of the metal oxide particles content. In some
`
`other examples, the dispersant content range is between about 5 to about 100%
`
`by weight of the metal oxide particles content. The dispersion of metal oxide
`
`particles can be prepared via milling or dispersing metal oxide powder in water in
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`the presence of suitable dispersants.
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`[0032] The metal oxide dispersion may be prepared by milling
`
`commercially available inorganic oxide pigment having large particle size (in the
`
`micron range) in the presence of the dispersants described above until the
`
`desired particle size is achieved. The starting dispersion to be milled can be an
`
`aqueous dispersion with a solids content up to 40% by weight of the metal oxide
`
`pigment. The milling equipment that can be used is a bead mill, which is a wet
`
`grinding machine capable of using very fine beads having diameters of less than
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`1.0 mm (and, generally, less than 0.3 mm) as the grinding medium, for example,
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`Ultra- Apex Bead Mills from Kotobuki Industries Co. Ltd. The milling duration,
`
`rotor speed, and/or temperature may be adjusted to achieve the dispersion
`
`particle size desired. In one example, commercially available colloidal metal
`
`oxide dispersions of particle sizes from 10 to 50 nm, such as silica and alumina,
`
`can be received from companies such as Nissan Chemical American Corporation
`
`and US Research Nanomaterials, Inc, among others.
`
`[0033]Generally, the ink and resultant structured network comprises a
`
`salt. In one example, the salt can be an organic salt (e.g. tetraethyl ammonium,
`
`tetramethyl ammonium, acetate salts, etc.). In another aspect, the salt can
`
`include salts of carboxylic acids (e.g. sodium or potassium 2—pyrrolidinone-5-
`
`carboxylic acid), sodium or potassium acetate, salts of citric acid or any organic
`
`acid including aromatic salts, and mixtures thereof. In another example, the salt
`
`can be an inorganic salt (e.g., sodium nitrate). In one aspect, the salt can be a
`
`monovalent salt. Such monovalent salts can include sodium, lithium, potassium
`
`cations and nitrate, chloride, acetate anions, and mixtures thereof. In another
`
`aspect, the salt can be multivalent, e.g. divalent, and can include calcium nitrate,
`
`magnesium nitrate, and mixtures thereof.
`
`[0034]As discussed herein, the salt can generally be present in the non—
`
`Newtonian inkjet ink in an amount ranging from 0.05% to 20% by weight based
`
`on the total weight of the non-Newtonian inkjet ink.
`
`In one example, the salt can
`
`be present in an amount of 1% to 10% by weight, and in some aspects, 0.5% to
`
`4%, 0.5% to 3%, or 1% to 2%, by weight, based on the total weight of the non—
`
`Newtonian inkjet ink.
`
`It is noted that the salts used with each type of gelator (e.g.
`
`metal oxide or low molecular weight organic gelator) can be distinct, e.g., an
`
`inorganic and organic salt. However, in one example, the salts can be the same.
`
`As such, each type of gelator can be used with any type of salt as discussed
`
`herein.
`
`[0035]The inclusion of a salt, particularly a dissolved salt in gelator ink,
`
`can contribute to the structure of the ink. In the case of metal oxide gelators, a
`
`salt can act to shield the electrostatic repulsion between particles and permit the
`
`van der Waals interactions to increase, thereby forming a stronger attractive
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`potential and resulting in a structured network by providing elastic content to a
`
`predominantly fluidic system. As mentioned, these structured systems show non-
`
`Newtonian flow behavior, thus providing useful characteristics for implementation
`
`in an ink-jet ink because their ability to shear or thermal thin for jetting. Once
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`jetted, this feature allows the jetted drops to become more elastic—, mass—, or gel—
`
`like when they strike the media surface. These characteristics can also provide
`
`improved media attributes such as colorant holdout on the surface.
`
`[0036] Regarding the inks of the present disclosure (with or without
`
`colorant), the role of salt can impact both the jettability and the response after
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`jetting. When comparing two gelator inkjet ink (with or without salt, but otherwise
`
`identical), the ink with salt will typically have a lower viscosity over a range of
`
`shear rates. In one example, the salt can be added such that its presence in this
`
`system is just enough to make an appreciable difference in the printing
`
`characteristics of the ink, but not so much that the ink becomes too low in
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`viscosity. This amount can be determined by routine experimentation. For
`
`example, the salted gelator ink can be designed so that the ink can refill quickly
`
`and produce a higher quality print. Higher quality printing can be determined in
`
`one aspect by improved optical density (when a colorant is present in the ink).
`
`Typically, inks with salt can have higher optical densities, while retaining good
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`jettability properties and other properties, such as ink structure, rheological
`
`behavior, shear thinning, and jetting of ink drops. Furthermore, salt can also
`
`contribute to the gelator inks of the present disclosure having decreased
`
`restructuring time after shear or thermal thinning for printing. Higher pre—shear
`
`rates can often result in a likewise faster response in the presence of salt. In
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`these instances, a fast restructuring of the ink can mean more solid-like behavior
`
`on the media surface in less time with less fluid penetration, and thus better
`
`colorant holdout and greater ink efficiency.
`
`[0037]The properties of the structured network, e.g., viscosity, gel
`
`strength, conductivity, particle size, etc. and the page attributes, optical density,
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`ink efficiency, media independence, etc., can be affected by a number of
`
`variables including the type of low molecular weight organic gelator or metal
`
`oxide, the type of salt, the type of solvents, the amounts of these components,
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`pH, ionic strength, etc. Regarding viscosity, as discussed herein, the viscosity for
`
`non-Newtonian fluids are not discrete but change based on the thermal or
`
`mechanical energy applied to the fluid. As used herein, “viscosity” refers to
`
`dynamic viscosity unless otherwise stated. For the present inks, the viscosity can
`
`generally be measured at two states: proximate to an at rest state; i.e., at room
`
`temperature (23 °C) or at a low shear rate (5 s4), and proximate to a processing
`
`state; i.e., at an elevated temperature (e.g. 50 °C) or at a high shear rate (10,000
`
`8'1). In one example, the present inks can have a dynamic viscosity ranging from
`
`100 cps to 10,000 cps at rest and a dynamic viscosity ranging from 1 cps to 25
`
`cps at a processing state. In one example, the dynamic viscosity can be 100 cps
`
`to 1000 cps at a rest state and can be 1 cps to 15 cps at a processing state.
`
`[0038]Additionally, the gelator and the salt can be present in the ink at a
`
`ratio that allows for formation of the structured network. In one example, the low
`
`molecular weight organic gelator and the salt can be present at a low molecular
`
`weight organic gelator to salt ratio ranging from 1:1 to 1:5 by weight. In one
`
`aspect, the ratio can be from 0.5:1 to 2:1. In another example, the metal oxide
`
`and the salt can be present at a metal oxide to salt ratio ranging from 0.5:1 to 5:1
`
`by weight. In one aspect, the ratio can be from 2:1 to 3:1.
`
`[0039]Generally, the present structured network is formed in an organic
`
`solvent. As used herein, “organic solvent” refers to any organic solvent or mixture
`
`thereof. As such, the term organic solvent includes systems of solvents. The
`
`present organic solvents are in addition to any water present in the non-
`
`Newtonian inkjet ink. Typical organic solvents