WO2020132336A1

WO2020132336A1 - Process control and coating development for conformal inkjet printing of metalized patterns on substrates with conductive inks

Info

Publication number: WO2020132336A1
Application number: PCT/US2019/067625
Authority: WO
Inventors: Hasan Shahariar; Henry SOEWARDIMAN; Jesse S. Jur; Inhwan Kim
Original assignee: North Carolina State University
Priority date: 2018-12-19
Filing date: 2019-12-19
Publication date: 2020-06-25

Abstract

Described herein are methods for printing a conductive ink on a substrate, the method comprising printing on the substrate a conductive ink in pattern, wherein the conductive comprises conductive metal nanoparticles or particle-free metal organic compound. In one embodiment, the conductive ink is heated after the conductive ink is printed on the substrate. In another embodiment, wherein prior to printing the conductive ink on the substrate, coating the substrate with a coating receptive to the conductive ink. The methods described herein are useful in producing printed substrates such as textiles.

Description

PROCESS CONTROL AND COATING DEVELOPMENT FOR CONFORMAL INKJET PRINTING OF METALIZED PATTERNS ON SUBSTRATES WITH CON DU COVE

INKS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to co-pending U.S. Provisional Patent Application No. 62/781,665, filed on December 19, 2018, the contents of which are incorporated by reference herein in its entirety.

BACKGROUND

[0002] Electronic-textiles have gained great interest in research, especially for wearable applications. ^1-5 More recently, printing technology has been adopted to integrate textiles with electronics by depositing metal inks on textiles through screen-printing. ⁶ Screenprinting is widely used for fast prototyping methods to develop sensors, ^{7 8} and other electronics ⁹·¹⁰ onto various substrates, but it has limitations. Screen-printing requires viscous inks and results in a great amount of ink wastage. On the contrary, inkjet printing uses much less ink, and can deposit a thin layer of conductive or functional layers on the selected surface. Inkjet printing can also be advantageous over the conventional manufacturing process of electronic textiles with conductive yams or threads. It is a single step process, which can precisely print the shape of the desired pattern as required. In a majority of the literature and research work, functional metal nanoparticle inks are used for inkjet printing conductive patterns on polymeric films and textiles. 11,12

[0003] Inkjet printing nanopartide inks have a tendency to dog the nozzles on the inkjet printer, and thus the inks are limited to suffidently small partide sizes in order to flow through the nozzles. Moreover, due to the high surface roughness and porosity of the textile, a large number of print passes and high density metal partides are needed to create a conductive path¹³ or, an ink receptive thick coating layers need to be deposited on rough textiles before inkjet printing, which degrade the soft and pliable properties of textile materials. 14-19 Thus, there is a need for low cost and effident processes for applying conductive inks to substrates in the field of printed electronics. SUMMARY

[0004] Described herein are methods for printing a conductive ink on a substrate, the method comprising printing on the substrate a conductive ink in pattern, wherein the conductive comprises conductive metal nanoparticles or particle-free metal organic compound.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Further aspects of the present disclosure will be readily appreciated upon review of the detailed description of its various embodiments, described below, when taken in conjunction with the accompanying drawings.

[0006] Figures 1 (a)-(c) show the systematic of process flow for inkjet printing with reactive Ag ink on textile surfaces; (d) shows the images of printed traces on knit, Evolon® and woven fabric (face & back side) for in situ and ex situ heart curing process (e) the XRD characterization of inkjet printed conductive ink on PET knit compared with pristine knit samples.

[0007] Figures 2(a)-(f) show transmission optical microscopy at 10X resolution of in-situ heat cured (a-c) Evolon®, PET knit and woven fabrics whereas Figure (d-f) shows the corresponding interface areas between the printed and non-printed par of fabrics.

[0008] Figures 3(a)-(f) show the SEM images of (a) native knit fabric (b) knit fabric with ex situ heat curing (c) knit fabric with in situ heat curing and (d), (e) , (f) are the corresponding images with EDS mapping showing the silver coated areas.

[0009] Figures 4(a)-(f) show the SEM images of (a) native Evolon^® fabric (b) Evolon^® with ex situ heat curing (c) Evolon^® with in situ heat curing and (d), (e) , (f) are the corresponding images with EDS mapping showing the silver coated areas.

[0010] Figures 5(a)-(d) show the SEM images (a) native Woven fabric (b) Woven with ex situ heat curing and (c), (d) are the corresponding images with EDS mapping showing the silver-coated areas.

[0011] Figure 6(a)-(b) shows measured sheet resistances corresponding to the number of layers of reactive silver reactive ink printed on various substrates (Knit PET, Woven PET & Evolon^®) with the comparison of in-situ and ex situ heat curing and with oxygen- plasma treatment.

[0012] Figure 7(a)-(b) show SEM cross-section of the conformal coating of Ag ink during inkjet printing on a) the woven PET and b) knit PET fabrics.

[0013] Figures 8(a)-(d) show (a) IR images (top) of the inkjet printed knit textiles under tensile tension while applying a DC voltage (1V) to generate resistive heating, and their optical microscope images (bottom); (b) corresponding graph showing the decrease of the resistance under strain; (c) tensile properties of the pristine (bare) and inkjet printed knit textiles; and (d) change of normalized resistance of inkjet printed conductive knit over the bending cycles.

[0014] Figures 9(a)-(b) show (a) the accelerated washing procedure following AATCC test method 61 and (b) shows the change of resistance for knit (red) and woven (black) polyester fabric with different washing cycles.

[0015] Figure 10 shows coating formulation described herein.

[0016] Figure 11 shows roll-to-roll application process of coating substrates.

[0017] Figure 12 shows a systematic inkjet printing process on coated textiles with reactive silver ink.

[0018] Figure 13 shows the FTIR-ATR spectrum analysis of formulated ink receptive coating.

[0019] Figure 14 shows the contact angle measurement on coated-woven cotton fabric for (a) water, (b) n-dodecane & (c) dichloromethane.

[0020] Figures 15(a)-(c) show optical images showing the line resistance of printed pattern on (a) coated woven fabric and on (b) coated paper; (c) shows the SEM images of the microstructure of the applied coating.

[0021] Figures 16(a)-(b) show SEM images of the coverage of ink layer on (a) coated paper and (b) coated woven fabric.

[0022] Figure 17 shows the variation of sheet resistance with respect to the number of print layers applied on the paper and woven fabric. [0023] Figures 18(a)-(c) show (a) synthesized ink, (b) the cross-section image of different layers of printed inkjet printed textile, and (c) the conductive track printed on the coated textile.

[0024] Figure 19 provides an additional demonstration of conductive traces of silver nanopartide ink on coated textile substrates.

DETAILED DESCRIPTION

[0025] Before the present disdosure is described in greater detail, it is to be understood that this disdosure is not limited to particular embodiments described, and as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0026] Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context dearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the disdosure. The upper and lower limits of these smaller ranges may independently be induded in the smaller ranges and are also encompassed within the disdosure, subject to any specifically exduded limit in the stated range. Where the stated range indudes one or both of the limits, ranges exduding either or both of those induded limits are also induded in the disdosure.

[0027] Unless defined otherwise, all technical and sdentific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disdosure belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present disdosure, the preferred methods and materials are now described.

[0028] All publications and patents dted in this specification are dted to disdose and describe the methods and/or materials in connection with which the publications are dted. All such publications and patents are herein incorporated by references as if each individual publication or patent were spedfically and individually indicated to be incorporated by reference. Such incorporation by reference is expressly limited to the methods and/or materials described in the dted publications and patents and does not extend to any lexicographical definitions from the dted publications and patents. Any lexicographical definition in the publications and patents dted that is not also expressly repeated in the instant application should not be treated as such and should not be read as defining any terms appearing in the accompanying daims. The dtation of any publication is for its disdosure prior to the filing date and should not be construed as an admission that the present disdosure is not entitled to antedate such publication by virtue of prior disdosure. Further, the dates of publication provided could be different from the actual publication dates that may need to be independently confirmed.

[0029] As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present disclosure. Any recited method can be carried out in the order of events recited or in any other order that is logically possible.

[0030] It should be noted that ratios, concentrations, amounts, and other numerical data can be expressed herein in a range format. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is also understood that there are a number of values disdosed herein, and that each value is also herein disdosed as“about” that particular value in addition to the value itself. For example, if the value“10” is disdosed, then“about 10” is also disdosed. Ranges can be expressed herein as from“about” one particular value, and/or to“about” another particular value. Similarly, when values are expressed as approximations, by use of the antecedent“about,” it will be understood that the particular value forms a further aspect. For example, if the value “about 10” is disdosed, then“10” is also disdosed.

[0031] Where a range is expressed, a further aspect includes from the one particular value and/or to the other particular value. Where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit unless the context dearly dictates otherwise, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the disdosure. The upper and lower limits of these smaller ranges may independently be induded in the smaller ranges and are also encompassed within the disdosure, subject to any specifically exduded limit in the stated range. Where the stated range indudes one or both of the limits, ranges exduding either or both of those induded limits are also induded in the disdosure. For example, where the stated range indudes one or both of the limits, ranges exduding either or both of those induded limits are also induded in the disdosure, e.g. the phrase“x to y” indudes the range from‘x’ to y as well as the range greater than‘x’ and less than y. The range can also be expressed as an upper limit, e.g. ‘about x, y, z, or less’ and should be interpreted to indude the spedfic ranges of‘about x¹,‘about y’, and‘about t as well as the ranges of ‘less than x’, less than y’, and‘less than t. Likewise, the phrase‘about x, y, z, or greater¹ should be interpreted to indude the specific ranges of‘about x’,‘about y’, and‘about z’ as well as the ranges of‘greater than x¹, greater than y’, and‘greater than t. In addition, the phrase“about‘x’ to‘y’”, where‘x’ and y are numerical values, indudes“about‘x’ to about‘y’”.

[0032] It is to be understood that such a range format is used for convenience and brevity, and thus, should be interpreted in a flexible manner to include not only the numerical values explicitly redted as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly redted. To illustrate, a numerical range of “about 0.1% to 5%” should be interpreted to indude not only the explicitly redted values of about 0.1% to about 5%, but also indude individual values (e.g., about 1%, about 2%, about 3%, and about 4%) and the sub-ranges (e.g., about 0.5% to about 1.1%; about 5% to about 2.4%; about 0.5% to about 3.2%, and about 0.5% to about 4.4%, and other possible sub-ranges) within the indicated range.

[0033] As used in the specification and the appended daims, the singular forms“a,”“an,” and“the” indude plural referents unless the context dearly dictates otherwise.

[0034] As used herein, "about," "approximately,"“substantially,” and the like, when used in connection with a numerical variable, can generally refers to the value of the variable and to all values of the variable that are within the experimental error (e.g., within the 95% confidence interval for the mean) or within +/- 10% of the indicated value, whichever is greater. As used herein, the terms “about,” “approximate,” “at or about,” and “substantially” can mean that the amount or value in question can be the exact value or a value that provides equivalent results or effects as retited in the daims or taught herein. That is, it is understood that amounts, sizes, formulations, parameters, and other quantities and characteristics are not and need not be exact, but may be approximate and/or larger or smaller, as desired, reflecting tolerances, conversion factors, rounding off, measurement error and the like, and other factors known to those of skill in the art such that equivalent results or effects are obtained. In some drcumstances, the value that provides equivalent results or effects cannot be reasonably determined. In general, an amount, size, formulation, parameter or other quantity or characteristic is“about,” “approximate,” or“at or about” whether or not expressly stated to be such. It is understood that where“about,”“approximate,” or“at or about” is used before a quantitative value, the parameter also indudes the specific quantitative value itself, unless spedfically stated otherwise.

[0035] Before the embodiments of the present disclosure are described in detail, it is to be understood that, unless otherwise indicated, the present disclosure is not limited to particular materials, reagents, reaction materials, manufacturing processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes of describing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequence where this is logically possible unless the context dearly dictates otherwise.

[0036] Described herein are methods for printing a conductive ink on a substrate. Inkjet printing nanopartide inks have a tendency to dog the nozzles on the inkjet printer, and thus the inks are limited to suffidently small partide sizes in order to flow through the nozzles. Moreover, due to the high surface roughness and porosity of the textile, a large number of print passes and high density metal partides are needed to create a conductive path or, an ink receptive thick coating layers need to be deposited on rough textiles before inkjet printing, which degrade the soft and pliable properties of textile materials. The methods described herein address these shortcomings.

[0037] In one embodiment, the conductive ink is a metal-organic compound. The distinct term "metal organic compound" refers to metal-containing compounds lacking direct metal-carbon bonds. Examples of metal organic compounds include, but are not limited to, metal b-diketonates, metal alkoxides, metal dialkylamides, and metal phosphine complexes. In another embodiment, the conductive ink is a particle free metal-organic compound. In this aspect, the metal organic compound does not exist as individual particles but can be converted to free particles upon further processing (e.g., heating or sintering). In one embodiment, the conductive ink is a silver organic compound. In another embodiment, the conductive ink is a particle-free silver organic compound.

[0038] In another embodiment, the conductive ink can indude a plurality of nanopartides. For example, the conductive ink can be metallonanopartides induding, but not limited to, silver nanopartides. In another embodiment, the conductive ink indudes silver nanopartides having an average size of from about 20 nm to about 60 nm, or about 20mm , about 25 mm, about 30 mm, about 35 mm, about 40 mm, about 45 mm, about 50mm , about 55 mm„ or about 60 mm, where any value can be a lower and upper end-point of a range (e.g., about 25 mm to about 50 mm).

[0039] In one embodiment, the conductive ink comprises silver partides functionalized with -OH, -NH₂ or, -COOH groups. In one embodiment, groups such as -OH, -NH₂ or, -COOH can be covalently bonded directly to the silver atoms. In another embodiment, -OH, -NH₂ or, -COOH groups can be indirectly bonded to the silver atoms via a linker such as, for example, an organic linker. Not wishing to be bound by theory, the -OH, -NH₂ or, -COOH groups can enhance the particle dispersion and control the adhesion of the partides to the substrate.

[0040] In one embodiment, the conductive ink comprises a silver salt dissolved in in a solvent. The selection of the silver salt can vary depending upon the solvent selected. In one aspect, the silver salt is a water soluble salts such as, for example, silver nitrate. In one aspect, the conductive ink comprises a silver salt and water.

[0041] In another embodiment, the conductive ink can indude an amine compound. Examples of amine compounds indude primary, secondary, and tertiary amines. In another aspect, the amine compound is a salt of a primary, secondary, and tertiary amine. In another embodiment, the amine compound is an ammonium salt. In one embodiment, the conductive ink comprises silver salt in a solution comprising water and an amine compound. [0042] The conductive ink can include one or more additional components including, but not limited to, a reducing agent, a capping agent, a humectant, or any combination thereof. An example of a reducing agent is an alkanol amine (i.e., alkyl alcohol substituted with one or more substituted or unsubstituted amine groups) such as, for example, diethanolamine. An example of a capping agent includes polyacrylic acid or polymethacrylic acid. An example of a humectant includes an alkylene glycol such as, for example, ethylene glycol.

[0043] In one aspect, the conductive ink has a viscosity of about 3 cps to about 20 cps when determined at a 1 s^-1 shear rate, or about 3 cps, about 4 cps, about 5 cps, about 6 cps, about 7 cps, about 8 cps, about 9 cps, about 10 cps, about 11 cps, about 12 cps, about 13 cps, about 14 cps, about 15 cps, about 16 cps, about 17 cps, about 18 cps, about 19 cps, or about 20 cps, where any value can be a lower and upper end point of a range (e.g., about 5 cps to about 15 cps, etc.). In one embodiment, the conductive ink has an average particle size greater than or equal to 10 times smaller than an inkjet nozzle opening. In one aspect, when the conductive ink comprises silver particles, the silver particles have a particle size from about 20 nm to about 100 nm, or about 20 nm, about 25 nm, about 30 nm, about 35 nm, about 40 nm, about 45 nm, about 50 nm, about 55 nm, about 60 nm, about 65 nm, about 70 nm, about 75 nm, about 80 nm, about 85 nm, about 90 nm, about 95 nm, or about 100 nm, where any value can be a lower and upper end point of a range (e.g., about 30 nm to about 80 nm, etc.)

[0044] In one embodiment, when the conductive ink comprises silver particles, the silver particles have a concentration of from about 5 wt% to about 25 wt% of the conductive ink, or of about 5, 6, 7, 8, 9, 10, 11 , 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, or about 25 wt% of the conductive ink, or a combination of any of the foregoing values, or a range encompassing any of the foregoing values.

[0045] The conductive ink is printed on the substrate in a specified pattern as determined by the end-user. In one embodiment, an ink-jet printer is used to print the conductive ink on the substrate. Inkjet printing involves high resolution conductive patterning on substrates. The conductive ink can be printed through fine capillary nozzles, such as inkjet nozzles. The conductive ink can be jetted on without clogging the nozzle since there is no particle formation when the ink is at room temperature. In one aspect, the inkjet droplet diameter should be at least one-third of the textile fiber diameter. Ink-jet printers useful herein can be two-dimensional or three-dimensional printers, for example, FUJI FILM Dimatix Materials Printer DMP-2850, Mimaki® UJF-6042 Flatbed UV Printer (Mk1 or Mk2), or Mimaki® UJV500-160.

[0046] In one embodiment, the conductive ink can be applied to the substrate as a single layer (i.e., a single pass with the printer). In other embodiments, the conductive ink can be applied to the substrate in multiple layers (i.e., multiple passes with the printer). In one aspect, the conductive ink can be applied from 1 pass to 10 passes, or 1 , 2, 3, 4, 5, 6, 7, 8, 9, or 10 passes, where any value can be a lower and upper end point of a range (e.g., 2 passes to 8 passes, etc.). In one embodiment, the conductive ink has a thickness of from about 100 nm to about 10 mm, or of about 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, or about 10 mm, ora combination of any of the foregoing values, or a range encompassing any of the foregoing values when printed on the substrate.

[0047] In some embodiments, after the conductive ink has been printed on the substrate, the printed ink is heated. Upon heating, the silver particles are converted to elemental silver. Not wishing to be bound by theory, the heat process helps to minimize the wicking of the ink into the fiber bulk. In one embodiment, the conductive ink is heated after the conductive ink is printed on the substrate. In another embodiment, the conductive ink is heated while the conductive ink is printed on the substrate. This heating step is also referred to herein as in situ heating. In one embodiment, the conductive ink on the substrate is heated from about 40 ^eC to about 120 °C, or about 40 °C, about 50 °C, about 60 °C, about 70 °C, about 80 °C, about 90 °C, about 100 °C, about 110 X, or about 120 °C, where any value can be a lower and upper end point of a range (e.g., about 60 °C to about 100 °C, etc.). In another embodiment, the printed ink can be heated from about 0.5 minutes to about 30 minutes, or about 0.5 minutes, about 1 minute, about 2 minutes, about 3 minutes, about 4 minutes, about 5 minutes, about 6 minutes, about 7 minutes, about 8 minutes, about 9 minutes, about 10 minutes, about 15 minutes, about 20 minutes, about 25 minutes, or about 30 minutes, where any value can be a lower and upper end point of a range (e.g., about 1 minute to about 10 minutes, etc.). In certain embodiments, after the printed ink has been heated, the ink can be further cured by exposing the ink to IR light, a pulse light sintering process, or a combination of both. These optional steps can further reduce silver ions to elemental silver.

[0048] In another embodiment, the printed substrate can be treated with oxygen plasma during or after heating the printed substrate. Not wishing to be bound by theory, oxygen plasma treatment along with the in-situ heat curing process during inkjet printing can enhance the adhesion of the ink particles on to the substrate and create connected electrical network with enhanced percolation.

[0049] In certain embodiments, the substrate can be coated with an ink-receptive coating prior to printing the ink on the substrate. In one embodiment, the coating composition comprises a silica-loaded aliphatic polymer composition and a UV curable acrylic- urethane monomer. In one aspect, the aliphatic polymer can be a low molecular weight ester, ester acetate, acrylamide, or isoprene, with a nonionic, anionic, or cationic backbone. In another aspect, the aliphatic polymer can have a molecular weight of about 100 g/mol or of less than 100 g/mol, less than 95 g/mol, less than 90 g/mol, less than 85 g/mol, a combination of any of the foregoing values, or a range encompassing any of the foregoing values.

[0050] In one embodiment, the silica in the coating composition is amorphous silica. In one embodiment, the aliphatic polymer is a water soluble having a glass transition temperature less than 20 ^eC. In another embodiment, the aliphatic polymer is a nonionic polymer. In another embodiment, the UV curable acrylic-urethane monomer is water soluble.

[0051] In one embodiment, the silica-loaded aliphatic polymer composition comprises from about 20 weight percent to about 50 weight percent silica, or about 20 weight percent, about 25 weight percent, about 30 weight percent, about 35 weight percent, about 40 weight percent, about 45 weight percent, or about 50 weight percent, where any value can be a lower and upper end point of a range (e.g., about 25 weight percent to about 35 weight percent, etc.).

[0052] In one embodiment, the coating composition comprises from about 50 weight percent to about 80 weight percent silica-loaded aliphatic polymer composition, or about 50 weight percent, about 55 weight percent, about 60 weight percent, about 65 weight percent, about 70 weight percent, about 75 weight percent, or about 80 weight percent, where any value can be a lower and upper end point of a range (e.g., about 55 weight percent to about 75 weight percent, etc.).

[0053] In one embodiment, the coating composition comprises from about 20 weight percent to about 50 weight percent UV curable acrylic-urethane monomer, or about 20 weight percent, about 25 weight percent, about 30 weight percent, about 35 weight percent, about 40 weight percent, about 45 weight percent, or about 50 weight percent, where any value can be a lower and upper end point of a range (e.g., about 25 weight percent to about 45 weight percent, etc.).

[0054] In one embodiment, the weight ratio of the silica-loaded aliphatic polymer composition and UV curable acrylic-urethane monomer is 1 :9 to 9:1 , 1 :9, 1 :8, 1 :7, 1 :6, 1 :5, 1 :4, 1 :3, 1 :2, 1 :1 , 2:1 3:1 , 4:1 , 5:1 , 6:1 , 7:1 , 8:1 , or 9:1 , where any value can be a lower and upper end point of a range (e.g., 1 :8 to 5:1 , etc.).

[0055] The coating can be applied to the substrate using techniques known in the art including, but not limited, spraying or brushing the coating on the substrate. In one embodiment, the coating is applied on the substrate by knife-coating process.

[0056] In one embodiment, after applying the coating to the substrate, the coating is cured. In one embodiment, the coating is cured at an intensity of from about 50 watt/m³ to about 200 watt/m³, or about 50 watt/m³, about 75 watt/m³, about 100 watt/m³, about 125 watt/m³, about 150 watt/m³, about 175 watt/m³, or about 200 watt/m³, where any value can be a lower and upper end point of a range (e.g., about 75 watt/m³ to about 125 watt/m³, etc.). In another embodiment, after curing, the coating is heated at a temperature of from about 100 ^eC to about 150 °C, or about 100 °C, about 115 °C, about 120 °C, about 125 X, about 130 °C, about 135 °C, about 140 °C, about 145 °C, or about 150 °C, where any value can be a lower and upper end point of a range (e.g., about 110 °C to about 130 °C, etc.).

[0057] In one embodiment, the substrate is knit textile, a woven textile, or a nonwoven textile. Specific selection of knit fabric structure (single jersey or double jersey) can create stretchable network where the ink particles will not be strained since the reduced silver particles are conformally coated on the textile fibers. The textile can be a synthetic polymer comprising a polyester, polyamide, a copolyester, a copolyamide, cellulose and the same class of natural fibers.

[0058] The porous, cylindrical shaped fibers can be conformally coated using the methods described herein. When the droplets of the inkjet nozzles impinge on the fibers, the adjacent droplets of particle free reactive ink settle down on the fiber surfaces, spread and wet the fiber over time forming conformal films around the fiber surfaces. This conformal films of conductive ink around the fiber surfaces are converted to elemental silver upon heating. The mechanism of creating conductive pathways with the conductive ink on textiles is fundamentally different than that of partide-based ink. The partide- colloidal system is very different since the density of the ink is much higher due to high loading of metal nanopartides. Thus, the gravitational force is much higher, and the partides starts filling up the fiber gaps when the ink is printed on the textile surface. The printed substrates have a very low resistance. In one embodiment, the printed substrates produced herein have a sheet-resistance of about 0.2 W/sq. to about 1 W/sq., or about 0.2 W/sq., about 0.3 W/sq., about 0.4 W/sq., about 0.5 W/sq., about 0.6 Q/sq., about 0.7 W/sq., about 0.8 W/sq., about 0.9, or about 1 W/sq., where any value can be a lower and upper end point of a range (e.g., about 0.3 W/sq. to about 0.8 W/sq., etc.). The printed substrates are also very durable. For example, the enhanced adhesion of the ink to textile fibers will help the pattern last for up to 50 regular washing and drying cydes.

[0059] In a first aspect, disdosed herein is method for printing a conductive ink on a substrate, the method induding printing on the substrate a conductive ink in pattern, wherein the conductive indudes conductive metal nanopartides or partide-free metal organic compound.

[0060] In a second aspect, disdosed herein is the method of the first aspect, wherein the conductive ink indudes a metal organic compound.

[0061] In a third aspect, disdosed herein is method of the first aspect, wherein the conductive ink indudes a silver organic compound.

[0062] In a fourth aspect, disdosed herein is the method the first aspect, wherein the conductive ink indudes a partide-free silver organic compound.

[0063] In a fifth aspect, disdosed herein is the method of the first aspect, wherein the conductive ink indudes metallonanopartides. [0064] In a sixth aspect, disclosed herein is the method of the first aspect, wherein the conductive ink includes Ag particles functionalized with -OH, -NHa or, -COOH groups.

[0065] In a seventh aspect, disclosed herein is the method of the first aspect, wherein the conductive ink indudes a silver salt in water.

[0066] In an eighth aspect, disdosed herein is the method of the seventh aspect, wherein the silver salt can be silver chloride, silver nitrate, or silver acetate.

[0067] In a ninth aspect, disclosed herein is the method of the seventh or the eighth aspect, wherein the conductive ink further indudes a redudng agent, a capping agent, a humedant, or any combination thereof.

[0068] In a tenth asped, disdosed herein is the method of the first asped, wherein the conductive ink indudes silver salt in a solution also having water and an amine compound.

[0069] In an eleventh asped, disdosed herein is the method of the first asped, wherein the ink comprises silver partides and wherein the silver particles have a concentration of from about 5 wt% to about 25 wt%.

[0070] In a twelfth asped, disdosed herein is the method in any of the first through the eleventh aspeds, wherein the condudive ink has a thickness of from about 100 nm to about 10 mm when printed on the substrate.

[0071] In a thirteenth asped, disdosed herein is the method of any one of the first through the twelfth aspeds, wherein the condudive ink has a viscosity of about 3 cps to about 20 cps when determined at a 1 s^-1 shear rate.

[0072] In a fourteenth asped, disdosed herein is the method of any one of the first through the thirteenth aspeds, wherein the condudive ink has an average partide size greater than or equal to 10 times smaller than an inkjet nozzle opening.

[0073] In a fifteenth asped, disdosed herein is the method in any one of the first through the fourteenth aspeds, wherein the condudive ink on the substrate is heated from about 40 °C to about 120 °C.

[0074] In a sixteenth asped, disclosed herein is the method of the fifteenth asped, wherein the condudive ink is heated after the condudive ink is printed on the substrate.

[0075] In a seventeenth asped, disdosed herein is the method of the fifteenth aspect, wherein the condudive ink is heated while the conductive ink is printed on the substrate. [0076] In an eighteenth aspect, disclosed herein is the method in any of the first through the seventeenth aspects, wherein conductive ink is further cured by IR, a pulse light sintering process, or a combination of both.

[0077] In a nineteenth aspect, disclosed herein is the method in any one of the first through the eighteenth aspects, wherein conductive ink is printed on the substrate by an inkjet printer.

[0078] In a twentieth aspect, disclosed herein is the method in any one of the first through the nineteenth aspects, further including applying oxygen plasma treatment to the printed substrate during or after heating the printed substrate.

[0079] In a twenty-first aspect, disclosed herein is the method in any one of the first through the twentieth aspects, wherein prior to printing the conductive ink on the substrate, the substrate is coated with a coating composition that includes a silica-loaded aliphatic polymer composition and a UV curable acrylic-urethane monomer.

[0080] In a twenty-second aspect, disclosed herein is the method of the twenty-first aspect, wherein the aliphatic polymer is a water soluble having a glass transition temperature less than 20 °C.

[0081] In a twenty-third aspect, disclosed herein is the method of the twenty-second aspect, wherein the UV curable acrylic-urethane monomer is water soluble.

[0082] In a twenty-fourth aspect, disclosed herein is the method in any one of twenty- first through the twenty-third aspects, wherein the silica-loaded aliphatic polymer composition includes from about 20 weight percent to about 50 weight percent silica and from about 50 weight percent to about 80 weight percent aliphatic polymer.

[0083] In a twenty-fifth aspect, disclosed herein is the method of any of the twenty-first through the twenty-fourth aspects, wherein the weight ratio of the silica-loaded aliphatic polymer composition and UV curable acrylic-urethane monomer is 1 :9 to 9:1.

[0084] In a twenty-sixth aspect, disclosed herein is the method of the twenty-first through the twenty-fifth aspects, wherein the coating is applied on the substrate by knife-coating process.

[0085] In a twenty-seventh aspect, disclosed herein is the method of any of the twenty- first through the twenty-sixth aspects, wherein the coating is and UV cured for 1 minute with subsequent heat-press process at about 100 °C to about 150 °C. [0086] In a twenty-eighth aspect, disclosed herein is the method in any one of the first through the twenty-seventh aspects, wherein the substrate can be a textile.

[0087] In a twenty-ninth aspect, disclosed herein is the method of the twenty-eighth aspect, wherein the textile is a knit textile, a woven textile, or a nonwoven textile.

[0088] In a thirtieth aspect, disclosed herein is the method of the twenty-eighth aspect, wherein the textile can be a synthetic polymer including a polyester, polyamide, a copolyester, a copolyamide, cellulose and the same class of natural fibers.

[0089] In a thirty-first aspect, disclosed herein is the method of any one of the first through the thirtieth aspects, wherein the substrate includes paper.

[0090] In a thirty-second aspect, disclosed herein is a printed substrate produced by the method in any one of first through the thirty-first aspects.

[0091] In a thirty-third aspect, disclosed herein is a method of printing of low viscous conductive ink that can be patterned on textile substrates, wherein the conductive ink can be comprised with conductive metal nanoparticles; or reactive organometallic particle free solutions, wherein the conductive ink has a viscosity of about 3 cps to about 20 cps when determined at a 1 s^-1 shear rate; wherein the conductive Ag particles can be functionalized with -OH, -NH₂ or, -COOH groups for enhancing the particle dispersion and controlling the adhesion of the particles to the textile substrates; wherein the conductive particles size can be at least 10 times smaller than the inkjet nozzle opening; wherein the conductive ink can also be a class of commercially available organometallic reactive compound which is soluble in aqueous vehicle. In another aspect, the ink is typically a silver salt in aqueous amine solution with a dissolved reducing agent. In a still further aspect, these kinds of commercial reactive metal inks are particle free but can turn into pure metal once heated to a temperature when the silver salt can be reduced. In a further aspect, the inkjet droplet diameter should be at least one-third of the textile fiber diameter.

[0092] In a thirty-fourth aspect, disclosed herein is the method of the thirty-third aspect, wherein the inkjet printing involves high resolution conductive patterning on textile substrates.

[0093] In a thirty-fifth aspect, disclosed herein is the method of the thirty-third or thirty fourth aspects, wherein the substrate can be or include a textile material made of synthetic polymers such as polyester, polyamide, their copolymer, cellulose and the same class of natural fibers.

[0094] In a thirty-sixth aspect, disclosed herein is the method of any one the thirty-third through the thirty-fifth aspects, wherein the textile substrate is stretchable.

[0095] In a thirty-seventh aspect, disclosed herein is the method of any one of the thirty- third through the thirty-sixth aspects, wherein the ink can be printed through fine capillary nozzles, such as, for example, inkjet nozzles.

[0096] In a thirty-eighth aspect, disclosed herein is the method of any one of the thirty- third through the thirty-seventh aspects, wherein the ink can be jetted on without clogging the nozzle. In a further aspect, no particle formation occurs for this kind of ink when the ink is at room temperature.

[0097] In a thirty-ninth aspect, disclosed herein is the method of any one of the thirty- third through the thirty-eighth aspects, wherein the printed ink on textile substrates can be cured (from 40 °C - 120 °C) to allow the ink to start solidifying. In another aspect, this process is referred to as an in situ heat curing process and, in a further aspect, the solidification process of the above in situ heat curing process can help to minimize the wicking of the ink into the fiber bulk. In still another aspect, this process also helps to maximize the print resolution.

[0098] In a fortieth aspect, disclosed herein is the method of any one of the thirty-third through the thirty-ninth aspects, wherein the printed and in situ heat cured ink on textile can be further cured by IR or pulse light sintering process, or a combination of both, to fully reduce the silver salt on to textile substrates.

[0099] In a forty-first aspect, disclosed herein is the method of any one of the thirty-third through the fortieth aspects, wherein the structure of the textile substrate can be knit, woven, or nonwoven.

[00100] In a forty-second aspect, disclosed herein is the method of any one the thirty- third through the forty-first aspects, further including oxygen plasma treatment processing of the synthetic fabrics along with the in situ heat curing process during inkjet printing enhance the adhesion of the ink particles on to the synthetic textile fibers and create connected electrically network with enhanced percolation. [00101] In a forty-third aspect, disclosed herein is the method any of the thirty-third through the forty-second aspects, wherein the textile substrate can be coated with ink- receptive coating where the coating includes a homogenous mixture of silica loaded aliphatic synthetic polymer solution and UV polymerizable acrylic-urethane monomer.

[00102] In a forty-fourth aspect, disclosed herein is the method of the forty-third aspect, wherein the aliphatic polymer can be water soluble and can have a glass transition temperature lower than 20 °C

[00103] In a forty-fifth aspect, disclosed herein is the method of the forty-fourth aspect, wherein the UV polymerizable acrylic-urethane monomer is water soluble.

[00104] In a forty-sixth aspect, disclosed herein is the method of process of the forty- third or forty-fourth aspect, wherein the amorphous silica loaded polymer solution and acrylic-based urethane monomer can be mixed in different ratios (1 :9 to 9:1) to modify the surface energy of the coating.

[00105] In a forty-seventh aspect, disclosed herein is the method of the claims from forty- third through the forty-sixth aspects, wherein the coating can be applied on any textile substrate using a knife-coating process and can further be UV cured for 1 minute with subsequent heat-press processing at 120 ^eC.

[00106] kin a forty-eighth aspect, disclosed herein is the method of any of the forty-third through the forty-seventh aspects, wherein the coated textile substrates can be used as inkjet printing media to printing functional silver particle based or particle free metal inks described in the thirty-third through the forty-second aspects.

EXAMPLES

[00107] Now having described the embodiments of the present disclosure, in general, the following Examples describe some additional embodiments of the present disclosure. While embodiments of the present disclosure are described in connection with the following examples and the corresponding text and figures, there is no intent to limit embodiments of the present disclosure to this description. On the contrary, the intent is to cover all alternatives, modifications, and equivalents included within the spirit and scope of embodiments of the present disclosure. The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to perform the methods and use the probes disclosed and claimed herein. Efforts have been made to ensure accuracy with respect to numbers (e.g., amounts, temperature, etc.), but some errors and deviations should be accounted for. Unless indicated otherwise, parts are parts by weight, temperature is in ^eC, and pressure is at or near atmospheric. Standard temperature and pressure are defined as 20 ^eC and 1 atmosphere.

Example 1

Substrates

[00108] Three very different types of textile substrates with different structures were selected. The selected fabrics are - plain-woven fabric made with PET (polyethylene terephthalate) yams, single jersey Knit fabric made with PET yams and Evolon^® nonwoven fabric made with bi-component PET and polyamide fibers.

Reactive Silver Ink

[00109] A commercially available reactive metal (silver) ink with a curing temperature of 100 ^eC to 150 °C (Liquid X, Pittsburgh, PA) was used for inkjet printing. The ink is a silver salt in an aqueous amine solution. At room temperature, the amine compound can form a dissolvable complex ion with silver salt to form a particle-free solution. The reactive metal inks can then react to form Ag once heated to a temperature when the silver complex can be reduced. The other bi-components of the reaction are released as volatile gases. The particle free formulation of reactive silver ink allows it to eject from the inkjet printer nozzles without clogging. The physical properties of the reactive Ag ink was tuned to achieve viscosity and surface tension that are suitable for inkjet printing. The viscosity and the surface tension of the ink ranges from 5 to 20 cps and 20 - 40 dyne/cm.

InkJet printing process

[00110] A commercial inkjet printer was used for inkjet printing the reactive inks. The Botfactory Squink is a thermal drop-on-demand printer capable of printing patterns on a 127mm by 127mm area, and has an adjustable Z-direction to accommodate for thick substrates. The resolution of the printing was set 90 DPI (drop-per-inch). The ink cartridge is made from polycarbonate and has a foam insert to facilitate the printing of dilute reactive inks, but prevents nanoparticle inks from being printed. The cartridge consists of twelve nozzles that can be adjusted via the software to eject or not eject. The silver reactive ink was deposited into the cartridge using a syringe and needle to penetrate the foam. A syringe filter with the porosity of 0.22 mm was used to filter the ink before using for inkjet printing.

[00111] Two different modes of printing were selectively chosen for the experiment. The surface of the printer bed can be heated to 40-80 ^eC during the printing time. When printing with in-situ heating, the software allows the plate to be heated to 40-80 ^eC, on which the substrate is placed. Printing on textile surfaces without selecting the in-situ heat-curing feature was also used. The number of layers printed was varied from 1 to 8 and is adjustable via software. After printing, the conductive traces were heat cured at 140 °C for 5 minutes. This curing process was recommended by the ink manufacturer, and was done once all layers were printed onto the textile substrate.

Characterizations

[00112] Optical transmission microscopy was used to observe the ink coverage on all substrates for different print layers. Sheet resistance measurements were taken for each substrate with and without in-situ heating while printing. Sheet resistances were calculated by measuring the resistance of each sample using the two-point probe method and measuring the length and width of each sample. To further analyze the ink microstructure, ink coverage, and the ink conformity on fibers, printed samples were characterized by Scanning Electron Microscope (SEM) with Energy Dispersive X-ray Spectroscopy (EDS) mode and XRD analysis.

Result and Discussion

[00113] XRD analysis of inkjet printed PET knit sample showed three distinct diffraction peaks at 38.2°, and 44.4^e in Figure 1 (d), which represent the [1 11 ] and [200] Miller indices of cubic face-centered silver. The pristine PET knit fabric in Figure 1 (d) did not show any characteristic silver peaks. No silver oxide was observed in the XRD analysis. The coverage of the ink on fibers of different substrates is shown in the transmission optical microscope images in Figure 2. It can be seen that the knit has the most open structure and the Evolon^® has the tightest structure. The woven fabric has a tighter structure than the knit and it is constituted with fibers that have a larger diameter than that of other substrates. Ink is seen to be concentrated on the denser area where the fibers pack. The uncoated fibers are visible as transparent in the images in Figure 1 (a) and 1 (b). The arrow shows concentration of ink on a bundle of fibers while in situ heat curing was done. A similar trend is observed for woven fabric samples. The ink concentrated on the fibers when in situ heat curing was selected. In comparison with knit and woven fabric, woven fabrics seem to have more coverage of the ink due to its tighter structure and larger fiber diameter. Evolon^® fabric has the finest constituent fibers and appeared to have the best coverage of ink on both ex situ and in situ heat cured samples.

[00114] Figures 2(a)-2(f) show the magnified optical images using a 3D laser confocal microscope of silver traces produced by inkjet printing of the particle-free reactive inks. It can be seen that the knit fabric has the most open structure and the Evolon® nonwoven has a very dense, randomly oriented fabric structure. The woven fabric has a tighter structure than the knit and it is constituted with fibers that have a largest diameter than that of other substrates. All the fabric samples, Evolon® fabric, PET knit, and woven fabrics seem to have good coverage of the ink on the surface as observed in Figure 2(d), (e), and (f). The edge pattern of the coating, visible in in Figure 2(d), (e) and (f) demonstrate that the ink was coated on the fibers of the fabric without blocking the open structure of textile fibers. This is the unique phenomenon of inkjet printing with particle- free reactive ink.

[00115] Further analysis of the printed sample had been done using SEM with EDS mode. Figures 3, 4 and 5 shows the SEM images of inkjet printed substrates with EDS mapping. The images also compare the ink coverage on the fibers for the in situ heat- cured and the ex situ heat-cured samples with a control native fabric (unprinted area). From Figures 3 (a, b & c), it was observed that the silver coverage of the fibers on the knit PET substrate is better when the sample was in situ heat cured during printing. The corresponding images in Figures 3(d)-3(f) show the EDS mapping where silver areas are colored as purple. Similarly, Figure 4 shows the comparison of SEM images and EDS mapping of printed areas on Evolon^® substrate. Evolon^® has more distributed coverage of ink on the fibers than that on the fibers of knit fabric. Interestingly, the ink resides on the edges of fibers on Evolon^® fabrics, shown in both Figures 4(e) and 4(f). This migration of ink is possibly due to the cylindrical shape of the fibers. Additionally, the ink areas on Figure 4(f) correspond to the in situ heat cured printed area on Evolon^®, seem more dense and brighter than ex situ heat cured substrate shown in Figure 4(e). In case of woven samples, it is seen that the ink also resides on the ridges and edges between the fibers, shown in Figures 5(b) and 5(d).

[00116] In general, the SEM and EDS mapping images that the ink density and coverage on the fibers is more prominent for in situ heat cured samples. In situ heat curing would mitigate the ink penetration in to the fiber bulk as the solvent evaporates during the time of printing. Thus, all the ejected ink during printing can reside on the top layer of the fabric. On the contrary, there is more penetration of ink in to the fiber bulk when there is no heat curing during the printing time. The partide free ink migrates easily in the in-plane and through-plane direction of the fabric surface by the capillary wicking effect. It is also noteworthy that for all of the fabric samples, the ink mostly resides at the edges and junctions between the fibers. Not wishing to be bound by theory, it is hypothesized that the ink migrates from the upper surface areas of the fibers to the lower areas of junctions among the fibers during the heat curing phase. There can be several explanations on the phenomenon of the ink residing in the fiber junctions. The low surface energy of the PET fibers may restrict the spreading of the ink on the fibers. Additionally, the selected drop size of the ink (~35 pico-liter) is larger (corresponds to ~40.6 mm of drop diameter) than the diameter of the fibers of knit and Evolon^® fabric. Thus, it is possible the drop impacting on the multiple fibers and their crossover points experience a capillary force (created by the capillary spadng between fibers) and the liquid ink tends to reside at the fiber junctions by the capillary force and gravitational force. Increasing the surface energy and decreasing the droplet size would help to conformally coat the fibers with conductive ink.

Sheet Resistances

[00117] Sheet resistances were determined for each sample by measuring resistance using a two-point probe and measuring the length and width of each printed pattern. Figures 6A-6B shows the sheet resistance of the printed lines on all the selected fabric surfaces with respect to the number of layers of ink printed. Due to the high porosity and surface roughness, the knit fabric required a higher number of print passes (6 layers) to achieve low sheet resistance, while it was ex situ heat cured. Evolon^® had a similar trend although it has a very tight fiber structure. However, the finer diameter of the fibers increased the capillary force to allow the ink to flow both in the in-plane and through-plane directions. The penetration of the ink in the z-direction of the fabric thickness disrupted the electrical percolation network. Thus, the sheet resistance is higher for the knit and Evolon^® fabric while they are ex situ heat cured than when they are in situ heat cured. The in situ heat cured traces on Evolon^® and knit require less print passes to achieve sheet resistance that is two orders of magnitude lower than ex situ heat cured samples. On the other hand, due to large fiber diameter and the tight fabric structure (low porosity) of the woven fabric, the ejected ink stays on the top layer of the fabric and creates a better electrical percolation network than that of the other fabrics. Thus, the woven fabric achieved the lowest sheet resistance of about ~ 1 W/p after 4 print passes for both in situ and ex situ heat cured procedures. The in situ heat curing process did not dramatically reduce the sheet resistance (0.2 W/p) for the woven fabric as compared to the knit and Evolon^®. Figure 6B shows the effect of oxygen plasma treatment with respect to sheet resistance.

[00118] One of the great advantages of particle free reactive silver ink over partide based is that the porous, cylindrical shaped textile fibers can be conformally coated by inkjet process. This process is very similar to a dyeing process where the dyes can be coated just on to the fiber surface and can also diffuse to the fiber to some extent. When the droplets of the inkjet nozzles impinge on the fibers, the adjacent droplets of partide free reactive ink settle down on the fiber surfaces, spread and wet fiber over time forming conformal films around the fiber surfaces. This conformal films of reactive ink around the fiber surfaces get sintered to form elemental silver upon annealing process. The mechanism of creating conductive pathways with the reactive ink on textiles is fundamentally different than that of partide-based ink. The partide-colloidal system is very different since the density of the ink is much higher due to high loading of metal nanopartides. Thus, the gravitational force is much higher, and the partides starts filling up the fiber gaps when the ink is printed on the textile surface.

[00119] Figures 7(a) and (b) provide cross-sectional SEM imaging of the silver coating on the knit and woven fabric, respectively. Both figures show that the silver is conformally coated around the fiber surfaces without filling the areas spaced among fibers. The thickness of the Ag after seven print passes ranged from 150 nm to 1 mm, which can be influenced by a number of factors induding interiadng points between fibers, fiber’s waviness and the porosity in the textile. Thus, inkjet printing with partide free reactive silver ink retains the feel/hand of pristine textile fabric.

[00120] An electromechanical analysis of printed patterns on PET knit fabric was performed to understand the change of mechanical function of the fabric after printing. In this analysis, the PET woven fabric and Evolon^® nonwoven is not stretchable because of the inherent fabric structure. Therefore, only the PET knit fabric was examined. An interconnect pattern of 30 mm x 4 mm was printed with 7 repeating print passes on the PET knit fabric. Figure 8(a) shows the infrared images and the optical images of the printed interconnect while it was stretched to 180% of the initial length (30 mm) using the Instron mechanical tester. The printed conductive pattern with interconnects were connected to a power source to generate resistive joule-heating. Additionally, the real time change of the resistance was recorded when the conductive pattern was stretched using the digital multimeter. It is noteworthy that the interconnect kept heating when the fabric was stretched to 100% of the initial length. This proves the current is flowing through the path of fabric in the stretched condition. The knit loops of the fabric get closer and create closer pack of conductive fibers, as shown in the optical images in Figure 8(a). This characteristic of knit structure helps to decrease the resistance while the knit fabric is stretched. Figure 8(b) shows the change of electrical resistance of the interconnect printed on a knit fabric with the increase of strain rate. Figure 8(c) compares the load- elongation curve for pristine knit fabric with inkjet printed interconnects on the same fabric. The data dearly suggests that there is no significant difference in the mechanical properties of textiles after the demonstrated inkjet printing process. The result confirms that inkjet printing of partide-free reactive ink does not alter the structural and physical properties of textile (see demonstration in supporting information). Figure 8(d) shows the change of normalized resistance over 10,000 bending cydes for inkjet printed conductive knit. The fabric was bent in the course direction along the continuous knit loops. There was no significant increase or change of the resistance observed over 10,000 bending cydes, which is unprecedented for printed conductive textiles. This example confirms a significant advantage of inkjet printing of particle free reactive ink directly on knit textile (without any coating or film lamination) over any other process.

[00121] Apart from the features such as conductivity, preserving the comfort of textile, the wash durability/fastness of the inkjet printed conductive patterns on textile fabric is an unavoidable requirement for many E-textiles applications, but is still rarely reported following industry standards. Figure 4 shows the change of resistance of the printed patterns on knit and woven fabric after 5, 10, 15, 20 and 25 regular wash cycles, following AATCC test method 61 (Figure 9). The fabric swatch is dipped in a cylindrical canister where 0.24 gm of detergent powder is added in 150 ml of water. Fifty steel balls are also added in the canister to intensify the mechanical agitation. The canister is then rotated for 45 minutes at 49° C water bath in the washing machine. After the washing process, the sample is rinsed and dried at 50° C for 15 minutes. It needs to be mentioned that one accelerated wash cycle as defined by the method is equivalent to 5 regular wash cycles. The conductive pattern on nonwoven increased the resistance 50x after a single wash (2.3 W ± 0.2 to >100 W). The resistance of the conductive pattern on knit fabric increased 2x after 15 regular washing and drying cycles. After 20 washes, the resistance increased to > 1 kW. The conductive pattern on woven fabric showed the highest wash-durability showing little change of the through 15 washing cycles. The conductive woven sample showed a reasonable amount of change of resistance (~3.5x increase) after 25 wash cycles. This wash durability results of the inkjet printed conductive patterns on knit, woven and Evolon^® further confirms that large diameter and high surface area of fibers in woven fabric enhance the adhesion of the conductive ink and hence improves the wash durability. On the other hand, the concentrated ink portions on to the fiber junctions on Evolon^® are loosely attached to the fibers. Thus, it can be surmised that the ink particles were washed off during the first wash cycle.

Example 2

Substrates

[00122] Two different types of cellulosic substrates with different surface structures were selected. The selected substrates are - plain-woven fabric (100% cellulose) and regular A-4 size printing paper. Both of this substrate are used coating and printing without any chemical treatment and modification.

Ink

[00123] The commercially available reactive metal (silver) ink with a curing temperature of 100^eC to 150° C was used for inkjet printing. The particle free formulation of reactive silver ink allows it to eject from the inkjet printer nozzles without dogging. The physical properties of the reactive Ag ink was tuned to achieve viscosity and surface tension that are suitable for inkjet printing. The viscosity and the surface tension of the ink ranges from 5 to 20 cps and 20 - 40 dyne/cm.

Experimental

Coating formulation for reactive particle free silver ink

[00124] Formulation 1 is amorphous silica (20-50) wt% loaded with water soluble synthetic polymer binder with glass transition temperature lower than 30 °C. Along with this, the formulation 2 is a UV curable cationic polyurethane coating dissolved in water.

[00125] The reactive silver ink forms into metal silver at 140 ^eC. The aliphatic polyurethane film from formulation 2 deforms in the elevated temperature like 140^eC. Thus, the ink cannot work or reduced on formulation 2. Formulation 1 is a water-based pretreatment with ~ 30wt% of amorphous silica suspended in aqueous nonionic polymer. The ink also cannot form metal silver on the film from formulationl because of its porous microstructure which sieve the partide free ink by the imbibition process. The ink spreads and sinks into the coating structure, which disrupts the resolution.

[00126] The reactive conductive ink worked very well on the coating when formulation 1 and formulation 2 were mixed in optimum ratio. 50-80 wt% of the formulation 1 and 20- 50 wt% of formulation 2 were mixed for 10 minutes with magnetic stirrer, then applied using a glass rod on our selected printing substrates (cotton fabric & paper). The coated substrates were UV cured for 2 minutes with an intensity of 100 (watt/m³) and followed by a heat-press process at 120 ^eC. The UV curing and heat press process creates a smooth coating on the top of the fabric and paper. The ink cured and formed metal silver on the coated surface. As both of the coating solutions are water base, the mixture creates a homogenous solution as shown in Figure 10. The UV curing process cures the reactive urethane monomer in the formulation 2, which coats and binds the amorphous silica and restricts the absorption of partide free ink into the substrate. Upon using 70 wt% of formulation 1 , the final formulated coating become stable at the curing temperature of the ink. The newly formulated coating is very easy to apply and process on a roll-to-roll manufacturing process (Figure 1 1).

InkJet printing process

[00127] Once the fabric and paper substrates are coated with the novel formulated coating, these are ready to use as a print media for any printing process. A Botfactory Squink inkjet printer was used for inkjet printing the reactive inks. A commercial inkjet printer, capable of printing patterns on a 127mm by 127mm area, has been used. The printed has an adjustable Z-direction to accommodate for thick substrates. The resolution of the printing was set 90 DPI (drop-per-inch). The ink cartridge is made from polycarbonate and has a foam insert to facilitate the printing of dilute reactive inks, but prevents nanopartide inks from being printed. The cartridge consists of twelve nozzles that can be adjusted via the Squink software to eject or not eject. The reactive silver ink was deposited into the cartridge using a syringe and needle to penetrate the foam. A syringe filter with the porosity of 0.22 mm was used to filter the ink before using for inkjet printing. The number of layers printed was varied from 1 to 3 and is adjustable via software. After printing, the conductive traces were Infrared (IR) cured for 1.5 minutes. During the IR curing process, the temperature of the chamber ramp to 130 °C to 160 ^eC. The inkjet printing and curing process is shown in Figure 12.

Characterization

[00128] The newly formulated coating was analyzed using FTIR-ATR spectrum analysis to identify the functional groups at the surface. The surface energy of the coated surface is calculated by measuring the contact angles of water, n-dodecane and dichloromethane using Goniometer. Optical transmission microscopy was used to observe the ink coverage on the substrates. Sheet resistance measurements were taken for each substrate with respect to print layer. Sheet resistances were calculated by measuring the resistance of each sample using the two-point probe method and measuring the length and width of each sample. To further analyze the ink microstructure, ink coverage printed samples were characterized by Scanning Electron Microscope (SEM).

Results and Discussion

[00129] Figure 13 shows the FTIR-ATR analysis spectrum analysis of the formulated coating materials. The observed peak at wave number 1076.66 cm·¹ confirms the Si-0 bond of amorphous silica. The sharp peak at 1729.81 cm^-1, 1372 cm^"1 attribute to the formate or carboxylate anion and cyanide (C-N) groups of polyurethane, respectively. The peak at 1235.35 cm^"1 attribute to the stretching of C-0 bond. Thus, FTIR-ATR peaks confirm the presence of polyurethane and amorphous silica in the formulated coating.

[00130] Figure 14 shows the contact angle of water, n-dodecane and dichloromethane on the coated substrates calculated using goniometer. The values of the contact angles and surface tension of the solvents are used to calculate the surface energy of the surface using the software available in Goniometer. The total surface energy of the substrate is 26.46 mN/m, where dispersive energy is 25.58 mN/m and polar energy is 0.89 mN/m. The calculated total surface energy of the coated surface is very close to the surface tension of the ink (~28 mN/m). This helps the adhesion of the reactive silver ink on the coated surface and enhance resolution. The optical microscope in Figures 15(a)-(c) show the resolution of printed traces on coated cotton fabric and cellulosic paper. In spite of having higher surface roughness for the woven structure, the resolution of printed traces is very similar to the print resolution on coated paper. Figure 15(c) shows morphology of the coating layer applied on the woven fabric and paper substrates. The visible structure of the coating is possibly picturizing the amorphous silica present in the coating material.

[00131] Figures 16(a) and (b) show SEM images of the microstructure of the ink layer printed on both coated paper and coated fabric. The white area is representing the conductive ink area. The ink has a smooth film type structure on both of the substrates, which proves a good coverage and adhesion between the coating and the ink.

[00132] The sheet resistance of the printed pattern has been measured and compared with the number of print passes (Figure 17). Due to having higher surface roughness, the coated woven fabric is not highly conductive after the first print pass. The resistance drops down to 6 order of magnitude lower as the second print pass was done on the coated fabric. However, the coated paper is very conductive (with sheet resistance below 1 W/D) in one printing pass. The sheet resistance decreased with the increase of the print passes. After three print passes, both of the coated substrates achieved the sheet resistance dose to 0.1 Q/D.

Example 3

[00133] The coating was formulated in a similar process as described in Example 2 and applied on a nonwoven fabric by knife coating process. The silver nanopartide ink is synthesized using the procedure by Russo A, Ahn BY, Adams JJ, Duoss EB, Bernhard JT, Lewis JA. Pen-on-paper flexible electronics. Advanced materials. 201 1 Aug 9;23(30):3426-30 using silver nitrate as salt, polyacrylic add with 5000 gm/mole as capping agent, diethanolamine as redudng agent and water as solvent. Ethylene glycol is used as the humectant. The partide size of the ink varied from 20-100 nm. The ink was filtered and used to inkjet print conductive pattern on coated Evolon^® fabric. Figure 18 (a) shows synthesized ink, 18(b) shows the cross-section image of different layers of printed inkjet printed textile, and 18(c) demonstrates the conductive track printed on the coated textile. The conductivity of the printed ink on the coated Evolon^® fabric was achieved as 1.503 X 10^® S/m. Figure 19 provides an additional demonstration of conductive traces of silver nanopartide ink on coated textile substrates.

[00134] From the foregoing, it will be seen that aspects herein are well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the structure.

[00135] It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the daims.

[00136] Since many possible aspects may be made without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

[00137] Various modifications and variations can be made to the compounds, compositions and methods described herein. Other aspects of the compounds, compositions and methods described herein will be apparent from consideration of the specification and practice of the compounds, compositions and methods disclosed herein. It is intended that the specification and examples be considered as exemplary.

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Claims

1. A method for printing a conductive ink on a substrate, the method comprising printing on the substrate a conductive ink in pattern, wherein the conductive comprises conductive metal nanoparticles or particle-free metal organic compound.

2. The method of claim 1 , wherein the conductive ink comprises a metal organic compound.

3. The method of claim 1 , wherein the conductive ink comprises a silver organic compound.

4. The method of daim 1 , wherein the conductive ink comprises a partide-free silver organic compound.

5. The method of daim 1 , wherein the conductive ink comprises a metallonanopartides.

6. The method of daim 1 , wherein the conductive ink comprises Ag partides functionalized with -OH, -NH₂ or, -COOH groups.

7. The method of daim 1 , wherein the conductive ink comprises silver salt in water.

8. The method of daim 7, wherein the silver salt comprises silver chloride, silver nitrate, or silver acetate.

9. The method of daim 7, wherein the condudive ink further comprises a reducing agent, a capping agent, a humedant, or any combination thereof.

10. The method of daim 1 , wherein the condudive ink comprises silver salt in a solution comprising water and an amine compound.

11. The method of daim 1 , wherein the condudive ink comprises silver partides, wherein the silver partides have a concentration of from about 5 wt% to about 25 wt%.

12. The method of daim 1 , wherein the condudive ink has a thickness of from about 100 nm to about 10 mm when printed on the substrate.

13. The method of daim 1 , wherein the condudive ink has a viscosity of about 3 cps to about 20 cps when determined at a 1 s^-1 shear rate.

14. The method of daim 1 , wherein the condudive ink has an average particle size greater than or equal to 10 times smaller than an inkjet nozzle opening.

15. The method in any one of claims 1-14, wherein the conductive ink on the substrate is heated from about 40 °C to about 120 °C.

16. The method of claim 15, wherein the conductive ink is heated after the conductive ink is printed on the substrate.

17. The method of claim 15, wherein the conductive ink is heated while the conductive in is printed on the substrate.

18. The method of claim 1 , wherein conductive ink is further cured by IR, a pulse light sintering process, or a combination of both.

19. The method of claim 1 , wherein conductive ink is printed on the substrate by an inkjet printer.

20. The method of claim 1 , further comprising applying oxygen plasma treatment to the printed substrate during or after heating the printed substrate.

21. The method of claim 1 , wherein prior to printing the conductive ink on the substrate, coating the substrate with a coating composition comprising a silica-loaded aliphatic polymer composition and a UV curable acrylic-urethane monomer.

22. The method of claim 21 , wherein the aliphatic polymer is a water soluble having a glass transition temperature less than 20 °C.

23. The method of claim 21 , wherein the UV curable acrylic-urethane monomer is water soluble.

24. The method of claim 21 , wherein the silica-loaded aliphatic polymer composition comprises from about 20 weight percent to about 50 weight percent silica and from about 50 weight percent to about 80 weight percent aliphatic polymer.

25. The method of claim 21 , wherein the weight ratio of the silica-loaded aliphatic polymer composition and UV curable acrylic-urethane monomer is 1 :9 to 9: 1.

26. The method of claim 21 , wherein the coating is applied on the substrate by knifecoating process.

27. The method of claim 21 , wherein the coating is and UV cured for 1 minutes with subsequent heat-press process at about 100 °C to about 150 °C.

28. The method of claim 1 , wherein the substrate comprises a textile.

29. The method of claim 28, wherein the textile is a knit textile, a woven textile, or a nonwoven textile.

30. The method of claim 28, wherein the textile comprises a synthetic polymer comprising a polyester, polyamide, a copolyester, a copolyamide, cellulose and the same class of natural fibers.

31. The method of claim 1 , wherein the substrate comprises paper.

32. A printed substrate produced by the method in any one of claims 1-31.