(12) INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT)
`(19) World Intellectual Property
`Organization
`International Bureau
`
`(43) International Publication Date
`3 November 2016 (03.11.2016)
`
`WIPOI PCT
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`\9
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`(10) International Publication Number
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`WO 2016/175738 A1
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`(51)
`
`International Patent Classification:
`C09D 11/00 (2014.01)
`
`(21)
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`International Application Number:
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`PCT/US201 5/027743
`
`(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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`27 April 2015 (27.04.2015)
`
`English
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`English
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`Applicant: HEWLETT-PACKARD DEVELOPMENT
`COMPANY, LP. [US/US]; 11445 Compaq Center Drive
`W., Houston, Texas 77070 (US).
`
`Inventors: KASPERCHIK, Vladek; 1070 NE Circle
`Blvd., Corvallis, Oregon 97330-4239 (US). BUTLER,
`Thomas W.; 1070 NE Circle B1vd., Corvallis, Oregon
`97330—4239 (US). BRUINSMA, Paul Joseph; 16399 W.
`Bernardo Dr., San Diego, California 92127-1899 (US).
`
`Agents: FOUGERE, Jeffrey R. et al.; Hewlett-Packard
`Company, Intellectual Property Administration, 3404 E.
`Harmony Rd, Mail Stop 35, Fort Collins, Colorado 80528
`(US).
`
`Designated States (unless otherwise indicated, for every
`kind ofnational protection available): AE, AG, AL, AM,
`AO, AT, AU, AZ, BA, BB, BG, BH, BN, BR, BW, BY,
`
`BZ, CA, CH, CL, CN, CO, CR, CU, CZ, DE, DK, DM,
`DO, DZ, EC, EE, EG, ES, FI, GB, GD, GE, G11, GM, GT,
`HN, HR, HU, ID, IL, IN, 1R, IS, JP, KE, KG, KN, KP, KR,
`KZ, LA, LC, LK, LR, LS, LU, LY, MA, MD, ME, MG,
`MK, MN, MW, Mx, MY, MZ, NA, NG, N1, 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.
`
`(84) Designated States (unless otherwise indicated, for every
`kind of regional protection available): ARIPO (BW, GH,
`GM, KE, LR, LS, MW, MZ, NA, RW, SD, SL, ST, 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,
`GW, KM, ML, MR, NE, SN, TD, TG).
`Declarations under Rule 4.17:
`
`as to the identity ofthe inventor (Rule 4.1 7(i))
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`as to applicant’s 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)
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`Title: WHITE INKS
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`
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`(57) Abstract: The present disclosure provides a White ink including an aqueous ink vehicle, from 5 Wt% to 50 Wt% of a white metal
`oxide pigment having an average particulate size from 100 nm to 2,000 nm, from 0.1 wt% to 4 wt% of anionic oxide particulates
`having an average particulate size from 1 nm to 100 nm, from 2 Wt% to 30 Wt% of latex particulates having a glass transition temper—
`ature from 0 C to 130 C, and a non-ionic or predominantly non-ionic dispersant having an acid number not higher than 100mg
`KOH/g based on dry polymer weight. The White metal oxide pigment and anionic oxide particulates are present in the white ink at a
`weight ratio from 5:1 to 200: l.
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`WHITE 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 coupled with appreciable reduction in cost.
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`Today's ink-jet printers offer acceptable print quality for many commercial,
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`business, and household applications at lower costs than comparable products
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`available just a few years ago. Notwithstanding their recent success, research
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`and development efforts continue toward improving ink-jet print quality over a
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`wide variety of different applications.
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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 sometimes composed of water—soluble
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`organic solvents, surfactants, and colorants in a predominantly aqueous fluid.
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`Regarding the use of colorants, certain pigments can be more challenging than
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`other in achieving certain desirable properties. For example, ink opacity,
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`durability, and uniformity can be a challenge in certain circumstances.
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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 depicts examples where a cationic polymer is digitally printed
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`on a media substrate contemporaneously orjust before printing a white inkjet ink
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`thereon, and wherein the white inkjet ink is prepared in accordance with
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`examples of the present disclosure;
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`[0005] FIG. 2 depicts examples where a cationic polymer is applied to a
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`media substrate prior to (either digital or by analog application) printing a white
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`inkjet ink thereon, and wherein the white inkjet ink is prepared in accordance with
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`examples of the present disclosure;
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`[0006]F|G. 3 depicts examples of heat fusing an image printed as
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`described in FIGS. 1 or 2 in accordance with examples of the present disclosure;
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`[0007]F|G. 4 depicts a printed article, such as that shown in FIG. 3, after
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`heat fusing on the media substrate;
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`[0008]F|G. 5 is an image of a vertical drip test conducted using a Control
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`lnk;and
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`[0009]F|G. 6 is an image of a vertical drip test conducted using an ink
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`prepared in accordance with examples of the present disclosure.
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`[0010] 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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`[0011]The present disclosure is drawn to white inks, namely water-based
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`white inkjet inks that can be jetted from various types of inkjet printheads, but are
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`particularly friendly for use in thermal inkjet printheads. These inks, in some
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`instances with the assistance of a fixer coating layer or fixer ink, can be printed
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`not only on porous media, but also effectively on more challenging non-porous
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`polymer media.
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`[0012] In accordance with this, it has been realized that inks white metal
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`oxide pigments (e.g., zinc oxide, titanium dioxide such as rutile or anatase,
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`zirconium oxide, etc.) can be dispersed and effectivelyjetted from thermal inkjet
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`printheads with non-ionic or predominantly non-ionic dispersants. Unfortunately,
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`these inks also tend to produce coating of non-uniform thickness when dried on
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`non-porous substrates, which ultimately leads to poor quality prints. This problem
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`can be solved by adding a relatively small amount (around 1-2 orders of
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`magnitude less than the weight percentage of the white metal oxide pigment) of
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`anionic oxide particulates (e.g., precipitated silica dispersion, fumed silica
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`dispersion, anionically charged alumina-silicate particles dispersion, etc.). This, in
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`combination with latex for added durability, and typically, fixer applied to the
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`media substrate to temporarily fix the ink prior to heat fusion, can provide high
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`print quality and highly durable prints can be generated on smooth polymer
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`substrates. More specifically, the anionic oxide particulates of the white ink can
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`act to cross-link with cationic polymer (e.g., usually delivered with a digitally
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`printable or analog application fixer fluid) located at the surface of the media
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`substrate. This interaction temporarily freezes the white metal oxide pigment on
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`the print surface and prevents pigment shifting and print quality degradation
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`during drying. Then, in some examples, the latex can be fused with the ink to
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`provide durability to the printed image. Thus, by generating a more uniform print
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`layer (avoiding the Marangoni effect and severe coalescence), uniform and
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`adequate ink thickness can lend itself to greater uniformity and efficient opacity of
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`the printed image. Additionally, non-ionic stabilization of the white metal oxide
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`pigment provides for prevention of the formation of stable aggregates
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`(coagulation) during ink drying. Printing a relatively thick ink layer on non-porous
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`media surface in absence of strong cohesive forces between pigment particles
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`can lead to uncontrolled ink spread outside printed area boundaries and poor
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`edge definition. This can be avoided using the inks of the present disclosure. On
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`another note, in some examples, color gamut can be improved if this white ink is
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`used as part of a colored ink set, because these inks can also provide a method
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`of generating an on-demand white background for colored, black, or off-white
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`substrates.
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`[0013] In accordance with examples of the present disclosure, the white
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`ink formulations of the present disclosure can include an aqueous ink vehicle,
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`latex particulates, and two separate and distinct types of oxide particulates. For
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`example, the ink can include from 5 wt% to 50 wt% (or from 10 wt% to 35 wt%) of
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`a white metal oxide pigment having an average particulate size from 100 nm to
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`2000 nm. The ink can also include from 0.1 wt% to 4 wt% of anionic oxide
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`particulates having an average particulate size from 1 nm to 100 nm. The white
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`metal oxide pigment and anionic oxide particulates can be present in the white
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`ink at a weight ratio from 5:1 to 200:1. As also mentioned, the white ink can also
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`include from 2 wt% to 30 wt% of latex particulates having a glass transition
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`temperature from 0 °C to 130°C. The ink can also included a non-ionic or
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`predominantly non-ionic dispersant to disperse the pigment and other
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`particulates. The non—ionic or predominantly non—ionic dispersant can be defined
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`by having non—ionic to weak anionic character having an acid number, per dry
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`polymer, of not higher than 100mg KOH/g, or not higher than 50mg KOH/g, or in
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`some examples, not higher than 30mg KOH/g. The dispersant can likewise be
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`non-ionic without an appreciable acid number.
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`[0014] In another example, a method of making a white ink can include
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`steps of milling a white metal oxide pigment in a water—based carrier (which can
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`be a thick slurry or a thinner composition) with a non-ionic or predominantly non-
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`ionic dispersing agent (i.e. predominantly non-ionic/weak anionic character
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`having an acid number, per dry polymer, of not higher than 100mg KOH/g, or not
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`higher than 50mg KOH/g, or in some examples, not higher than 30mg KOH/g) to
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`form a white metal oxide pigment dispersion; and admixing water, organic co—
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`solvent, anionic oxide particulates, and latex particulates with the white metal
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`oxide pigment dispersion to form a white ink. The white ink can have a white
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`metal oxide pigment to anionic oxide particulate weight ratio from 5:1 to 200:1.
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`[0015] In another example, a white thermal inkjet ink can include an
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`aqueous ink vehicle, Ti02 pigment, and anionic oxide particulates. The Ti02
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`pigment can be present in the white thermal inkjet ink at from 10 wt% to 35 wt%,
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`and can have an average particulate size from 150 nm to 500 nm. The TiOz
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`pigment can be dispersed with a non-ionic or predominantly non-ionic dispersant
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`having an acid number not higher than 30 mg KOH/g based on dry polymer
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`weight. The anionic oxide particulates can be present in the white thermal inkjet
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`ink at from 0.1 wt% to 4 wt%, and can have an average particulate size from 1
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`nm to 50 nm. The white metal oxide pigment and anionic oxide particulates can
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`be present in the white thermal inkjet ink at weight ratio from 5:1 to 200:1.
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`[0016]These white inks can be used in forming white images on various
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`media substrate, including smooth polymer (non-porous) media substrate, and
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`can be printed in combination with a fixer coated on the surface of the media. For
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`example, a fixer with cationic polymer can be applied to the media substrate and
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`can be formulated so that its cationic polymer interacts with the anionic oxide
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`particulates to immobilize the white metal oxide pigment.
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`[0017] In each of these examples, there are several advantages related to
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`the inclusion of the anionic oxide particulates along with a more dominant
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`concentration of the white metal oxide pigment. The addition of anionic oxide
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`particulates provides a relatively strong to very strong electrostatic interaction
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`with cationic polymer that may be present on the media substrate, or as part of a
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`fixer fluid to be printed (digitally) or otherwise applied (analog application) on a
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`media substrate. The negative charge, small size, and relative large number of
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`these anionic oxide particulates provide a way of fixing relatively thick ink layer on
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`a smooth polymer surface for drying and/or subsequent heat fusing. For example,
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`these particulates have an opposite charge relative to that of the cationic polymer
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`present in a fixer coating or fixer fluid applied to the media substrate. Thus, these
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`inks can provide electrostatic cross-linking sites for cationic polymer molecules.
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`Mixing of white ink containing these particulates with cationic fixer or a fixer
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`coating can very quickly create a cross-linked network, trapping larger non-
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`ionically—stabilized Ti02 pigment (or other white metal oxide pigment).
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`[0018]F|G. 1 depicts an example where a digitally printed fixer is applied
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`just prior to or essentially simultaneously with an inkjet ink of the present
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`disclosure. FIG. 2 depicts an example where a fixer is applied to a media
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`substrate prior to application of an inkjet ink. The fixer in this latter example can
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`likewise be applied by digital printing, or alternatively, by analog application, e.g.,
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`roller, curtain coating, blade coating, Meyer rod coating, or any other coating
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`methodology suitable for producing thin layer of fixer on the printed substrate,
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`etc. As shown in FIGS. 1 and 2, an inkjet printing device 30 is adapted to digitally
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`print a white inkjet ink 10, and in some examples, a fixer composition 20, on a
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`media substrate 40. The media substrate can be a smooth, non-porous polymer
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`substrate that is othenNise difficult to print on with high image quality and high
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`durability. Specifically, FIG.
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`1 shows the fixer composition being printed digitally
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`from the printing device, and FIG. 2 shows the fixer composition being pre-
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`applied to the media substrate, either digitally or by an analog coating method. In
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`both examples, the white inkjet ink includes white metal oxide pigment 12,
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`anionic oxide particulates 14, latex particulates 16, and an ink vehicle 18 which
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`typically includes a non-ionic dispersant or dispersing agent. Water, organic
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`solvent, and/or other ingredients can likewise be present in the ink vehicle. The
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`fixer composition can include cationic polymer 22 that is interactive with the
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`anionic oxide particles of the white ink, thereby providing some immobilization or
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`freezing of the pigment and particles on the print media substrate.
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`[0019] In another example, the image printed or otherwise generated in
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`accordance with FIGS. 1 and 2 can be heat fused. More specifically, FIG. 3
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`shows a heat fusing device 50 which is used to apply heat 52 to the printed
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`article to form a heat fused printed article as shown in FIG. 4. Because of the
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`presence of both the white metal oxide pigment 12 and the latex particulates
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`16,16b appropriately spaced, there can be enhanced light scattering 60 and
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`lower transmittance 62 than even more densely packed white metal oxide
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`pigment, which thus provides enhanced opacity. This increased opacity can be
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`achieved by optically spacing the white metal oxide pigment from one another.
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`For example, drying of the inks without latex particulates such that all of the high
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`refractive index particulates are in close contact leads to formation of a densely
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`packed layer of the white metal oxide pigment, which reduces their light
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`scattering ability and overall opacity. On the other hand, using the fusible latex
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`particulates as shown, and typically applying heat to fuse the latex particulates,
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`the low refractive index optical spacing can boost the opacity of the printed
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`coating by from 0.1% to 25%, or more typically from 5% to 20% or from 5% to
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`25%. In other words, the crowding effect of tightly-packed high refractive index
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`(n) particulates with little or no voids decreases light scattering and increase
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`transparency of the coating. By optically spacing the white metal oxide pigment
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`with the low refractive index latex particulates (and typically heat fused after
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`printing) an increase in opacity can be realized. As a further point, fusion can add
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`enhanced durability to the printed article. In some cases the fusing of the latex
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`particulates may help the latex polymer distribute more evenly between light
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`scattering white metal oxide pigment and, hence, further improve opacity as well.
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`[0020] In accordance with this, a printed article can include up to 75, or up
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`to 50 gsm, of total fluids (white ink + fixer) applied to a media substrate. The term
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`"up to 75 gsm" or "up to 100 gsm" is used because typical inkjet images include
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`fully imaged areas as well as non-imaged and/or lower density areas. After water
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`and solvent(s) evaporation and fusing, the gsm roughly translates into 15-50 wt%
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`of the initial fluid dispersion flux density, i.e. thus less than 50 gsm. In one
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`example, full density inked area may be at from 30 to 50 gsm ink/fixer film, but
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`densities lower in the tone ramp will be lower than this, thus the use of the phrase
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`“up to” 75 gsm or "up to" 50 gsm. That being stated, though some areas on a
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`media substrate might be at 0 gsm under this definition (unprinted areas), there
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`will be areas that are imaged that range from greater than 0 gsm up to 50 gsm
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`(after drying or heat fusing). In a typical printed article, there is a portion of the
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`media that can be printed at from 5 gsm to 50 gsm.
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`[0021]Turning now to the various specific ingredients that are present in
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`the white ink, there can be a white metal oxide pigment. The “white” pigment
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`provides much of the white coloration to the ink, though without the other
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`ingredients in the ink, the pigment may have some transparency or translucency.
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`Examples of white metal oxide pigments that can be used include titanium
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`dioxide particulates, zinc oxide particulates, zirconium oxide particulates,
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`combinations thereof, or the like. Pigments with high light scatter capabilities,
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`such as these, can be selected to enhance light scattering and lower
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`transmittance, thus increasing opacity. White metal oxide pigments can have a
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`particulate size from about 100 nm to about 2000 nm, and more typically, from
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`about 125 nm to 700 nm, and in still another example, from about 150 nm to 500
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`nm. The combination of these pigments within these size ranges, appropriately
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`spaced from one another with ingredients such as latex, full opacity can be
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`achieved at relatively thin thickness, e.g., 5 gsm to 50 gsm after removal of water
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`and other solvent(s) from the printed ink and fixer film.
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`[0022]The white metal oxide pigment, among other solids that may be
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`present, can be dispersed using a non-ionic dispersing agent. Suitable non-ionic
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`dispersing agents can allow for suitable dispersibility and stability in an aqueous
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`ink environment, while having little to no impact on the viscosity of the liquid
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`phase of the ink as well as retaining good printhead reliability in thermal inkjet
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`printheads. Dispersants meeting these parameters are typically non-ionic or
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`predominantly non-ionic (only weakly anionic) in character. For definitional
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`purposes, these dispersants are referred to as non-ionic dispersants, provided
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`they are non-ionic or predominantly non-ionic in nature, i.e. the acid number of
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`the predominantly non—ionic/weak anionic dispersant, per dry polymer, is not
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`higher than 100mg KOH/g, and is typically less than 50mg KOH/g, most typically
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`less than 30mg KOH/g. That being state, in one example, non-ionic dispersing
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`agent with no anionic properties can be used one example.
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`[0023] Examples of non-ionic dispersants that are included in this definition
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`are water-hydrolysable silane coupling agents (SCAs) with relatively short
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`(oligomer length range of not longer than 50 units, not longer than 30 units, or not
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`longer than 15 units, e.g., 10 to 15 units) polyether chain(s), which are also
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`soluble in water. An example of such a dispersant includes Silquest® A1230
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`polyethylene glycol methoxysilane available from Momentive Performance
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`Materials. Other examples include soluble low-to-midrange M (e.g., usually
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`molecular mass of the polymer less than 15,000 Da) branched co—polymers of
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`comb-type structures with polyether pendant chains and acidic anchor groups
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`attached to the backbone, such as Disperbyk®-190 and Disperbyk®-199
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`available from BYK Chemie, as well as Dispersogen® PCE available from
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`Clariant.
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`[0024] In further detail regarding the dispersants that can be used, in one
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`example, reactive hydrophilic alkoxysilane dispersants that can be present, and
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`examples include, but are not limited to, hydrolysable alkoxysilanes with alkoxy
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`group attached to water-soluble (hydrophilic) moieties, such as water-soluble
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`polyether oligomer chains, phosphate groups, or carboxylic groups. In some
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`examples, the dispersant used to disperse white metal oxide pigment can be a
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`polyether alkoxysilane or polyether phosphate dispersant. Upon dissolution in
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`water with the white metal oxide pigment, the alkoxysilane group of the
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`dispersant often hydrolysis resulting in formation of silanol group. The silanol
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`group, in turn, may react or form hydrogen bonds with hydroxyl groups of metal
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`oxide particulate surface, as well as with silanol groups of other dispersant
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`molecules through hydrogen bonding. These reactions lead to bonding or
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`preferential absorption of the dispersant molecules to the metal oxide particulate
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`surfaces and also form bonds between dispersant molecules themselves. As a
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`result, these interactions can form thick hydrophilic coatings of reactive
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`dispersant molecules on surface of the white metal oxide pigment. This coating
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`can increase the hydrodynamic radius of the particulates and thus reduce their
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`effective density and settling rate. Furthermore, the dispersant coating prevents
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`agglomeration of the white metal oxide pigment upon settling so that when
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`sediment and settling does occur over time in the ink formulations, the settled
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`white metal oxide pigment remain fluffy and thus are easy to re-disperse upon
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`agitation. In still further detail, these dispersants have a relatively short chain
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`length and do not contribute significantly to the ink viscosity, even with relatively
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`high metal oxide particulate loads, e.g. over 30 wt% white metal oxide pigment in
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`the ink.
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`[0025]As mentioned, a suitable alkoxysilane dispersant can have an
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`alkoxysilane group which can be easily hydrolyzed in aqueous environment and
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`produce a silanol group, and a hydrophilic segment. The general structure of the
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`alkoxysilane group is —Si(OR)3, where R most can be methyl, ethyl, n-propyl,
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`isopropyl, or even a longer (branched or unbranched) alkane chain. It is noted
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`that the longer the hydrocarbon (R), the slower hydrolysis rate and rate of
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`interaction with dispersed metal oxide particulate surface. In a few highly practical
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`examples, structures with —Si(OR)3 where R is methyl or ethyl can typically be
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`used. The hydrophilic segment of the alkoxysilane dispersant can likewise be
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`large enough (relative to the whole molecule size) in order to enable dispersant
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`solubility in aqueous environment, as well as prevent agglomeration of the white
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`metal oxide pigment. In one example, the hydrophilic segment can be a polyether
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`chain, e.g., polyethylene glycol (PEG) or its co—polymer with polypropylene glycol
`
`(PPG). Polyether—based dispersant moieties have clean thermal decomposition,
`
`and thus, are good candidates for use. When heated above decomposition
`
`temperature, PEG and PPG-based molecules decompose into smaller molecular
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`fragments with high volatility or good water solubility. Thus, their decomposition
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`usually does not form noticeable amounts of solid residue on surface of
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`microscopic heaters used for driving thermal inkjet printheads (which can cause
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`thermal inkjet printheads to fail over time or render them non—operational in some
`
`instances).
`
`[0026] In further detail, examples polyether alkoxysilane dispersants that
`
`may be used to disperse white metal oxide pigment can be represented by the
`
`following general Formula (I):
`
`(I)
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`R1
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`
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`Rz—Sli
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`R3
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`(PE) — R4
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`1O
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`wherein:
`
`a) R1, R2 and R3 are hydroxy groups, or hydrolyzable linear or branched
`
`alkoxy groups. For hydrolyzable alkoxy groups, such groups can have 1 to 3
`
`carbon atoms; in one aspect, such groups can be —OCH3 and —OCH2CH3. In
`
`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 —OCH3 or —OCZH5.
`
`b) PE is a polyether oligomer chain segment of the structural formula
`
`[(CH2)n—CH(R)—O]m, attached to Si through Si—C bond, wherein n is an integer
`
`ranging from O to 3, wherein m is an integer superior or equal to 2 and wherein R
`
`is H or a chain alkyl group. R can also be a chain alkyl group having 1 to 3
`
`carbon atoms, such as CH3 or CzH5. In some examples, m is an integer ranging
`
`from 3 to 30 and, in some other examples, m is an integer ranging from 5 to 15.
`
`The polyether chain segment (PE) may include repeating units of polyethylene
`
`glycol (PEG) chain segment (—CH2CH2—O—), or polypropylene glycol (PPG)
`
`chain segment (—CH2—CH(CH3)—O—), or a mixture of both types. In some
`
`examples, the polyether chain segment (PE) contains PEG units (—CHZCH2—
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`0—); and
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`c) R4 is hydrogen, or a linear or a branched alkyl group. In some examples,
`
`R4 is an alkyl group having from 1 to 5 carbon atoms.
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`[0027] Other examples of dispersants used to disperse white metal oxide
`
`pigment can include polyether alkoxysilane dispersants having the following
`
`general Formula (II):
`
`OR’
`
`(11)
`
`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', R” and R'" are linear alkyl groups having from 1 to 3 carbon atoms
`
`in chain length. In some examples, R', R” and R"’—CH3 or —C2H5. R4 and PE are
`
`as described above for Formula (I); i.e. PE is a polyether oligomer chain segment
`
`of the structural formula: [(CH2) n—CH—R—O]m, wherein n is an integer ranging
`
`from O to 3, wherein m is an integer superior or equal to 2 and wherein R is H or
`
`a Chain alkyl group; and R4 is hydrogen, or a linear or a branched alkyl group. In
`
`some examples, R4 is CH3 or CzH5.
`
`[0028] In some examples, the white metal oxide pigment present in the ink
`
`composition are dispersed with polyether alkoxysilanes. Examples of suitable
`
`polyether alkoxysilanes include (CH30)3Si—(CH20HzO)n, H; (CH3CH20)3Si—
`
`(CHZCH20)n,H; (CH30)3Si—(CHZCHZO)n, CH3; (CH3CHZO)3Si—(CHZCHZO)n,
`
`CH3; (CH30)3Si—(CHZCH20)n, CH2CH3; (CH30H20)3Si—(CHZCHZO)n, CHchg;
`
`(CH30)3Si—(CHZCH(CH3)O)n, H; (CHgCHzO)3Si—(CH2CH(CH3) O)“, H;
`
`(CH30)3Si—(CHZCH(CH3) O)n, CH3; (CH3CH20)3Si—(CH20H(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.
`
`[0029] Commercial examples of the polyether alkoxysilane dispersants
`
`include, but are not limited to, the aforementioned Silquest®A—1230
`
`manufactured by Momentive Performance Materials, and Dynasylan® 4144
`
`manufactured by Evonik/Degussa.
`
`[0030]The amount of dispersant used to disperse the white metal oxide
`
`pigment and other solids may vary from about 1% by weight to about 300% by
`
`weight of the white metal oxide pigment content. In some examples, the
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`dispersant content range is from about 2 to about 150% by weight of the white
`
`metal oxide pigment content. In some other examples, the dispersant content
`
`range is from about 5 to about 100% by weight of the white metal oxide pigment
`
`content.
`
`[0031]A dispersion of white metal oxide pigment suitable for forming the
`
`white inks of the present disclosure can be prepared via milling or dispersing
`
`metal oxide powder in water in the presence of suitable dispersants. For example,
`
`the metal oxide dispersion may be prepared by milling commercially available
`
`inorganic oxide pigment having large particulate size (in the micron range) in the
`
`presence of the dispersants described above until the desired particulate size is
`
`achieved. The starting dispersion to be milled can be an aqueous dispersion with
`
`solid content up to 65% by weight of the white metal oxide pigment or pigments.
`
`The milling equipment that can be used may be a bead mill, which is a wet
`
`grinding machine capable of using very fine beads having diameters of less than
`
`1.0 mm (and, generally, less than 0.5 mm) as the grinding medium, for example,
`
`Ultra-Apex Bead Mills from Kotobuki Industries Co. Ltd. The milling duration, rotor
`
`speed, and/or temperature may be adjusted to achieve the dispersion particulate
`
`size desired.
`
`[0032]The anionic oxide particulates that are also included in the white ink
`
`can be any of a variety of anionic oxide particles, such as anionic semi-metal
`
`oxide particles, e.g., anionic silica particulates. One example is an anionically-
`
`stabilized colloidal silica dispersion. Other examples include precipitated silica
`
`dispersions, anionically charged alumina silicate particle dispersion, anionically-
`
`stabilized fumed silica dispersions (such as Cab—O—Sperse® silica series
`
`available from Cabot Corporation). Typically, in many colloidal silica dispersions,
`
`particulates have a strong anionic (negative) charge at about pH >7, and thus,
`
`can instantly or very quickly react with cationic polymer applied to a media
`
`substrate, forming a loose cross-linked network. Generally, the higher is the
`
`number of particulates per volume of the ink, the stronger is their cross-
`
`linking/pigment immobilization effect upon mixing with the fixer layer or fluid on
`
`the media substrate. Thus, in some examples, there are advantages for using
`
`small anionically charged silica, e.g., the same weight percentage of anionic
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`oxide particulates in an ink formulation at 3 nm would have roughly 103 times
`
`more particulates than a dispersion having 30 nm particulates. Thus, the use of
`
`small particles, e.g., from 1 nm to 100 nm, or more typically from 1 nm to 50 nm,
`
`relative to the size of the white metal oxide pigments, e.g., 100 nm to 2000 nm,
`
`can provide some advantage with respect to fixing an ink with a fixer coating or
`
`composition.
`
`[0033]Anionic oxide particulates, such as anionic colloidal silica in
`
`dispersion form, are commercially available, and examples include Snowtex®
`
`Colloidal Silicas available from Nissan Chemical Corporation, e.g., Snowtex® ST—
`
`S (spherical particulates; median particulate size ~2—3nm); Snowtex® ST-3OLH
`
`(spherical particulates; median particulate size ~30nm); and Snowtex® ST-UP
`
`(elongated particulates (particulate dimensions ~9-15/40-100 nm). Other anionic
`
`oxide particulates include IDISIL® colloidal silica available from Evonik Industries
`
`(particulate size 5—50nm); Ludox® colloidal silicas available from W.R. Grace &
`
`Co. such as Ludox® HS-3O (particulate size ~12nm); Ludox AM, Ludox® SM-AS,
`
`Ludox® AS-30, Ludox® AS-40 (particulate size ~12nm), etc.; Bindzil® and
`
`Levasi|® grades of colloidal silica available from Akzo Nobel N.V.
`
`[0034] It is also notable that there are advantages to adding the latex
`
`particulates to the inks of the present disclosure. For example, by combining
`
`white metal oxide pigment with latex particulates, opacity can be increased, even
`
`though la