A method for forming features by dispensing a metal nanoparticle composition from an inkjet printhead and a metal nanoparticle composition for inkjet printing.

Abstract

A method for forming features by dispensing a metal nanoparticle composition from an inkjet printhead is disclosed. An ejection waveform is applied to a piezoelectric actuator to dispense droplets of the metal nanoparticle composition through a nozzle opening. The droplet volume ranges from 0.5 picoliters to 2.0 picoliters. The ejection waveform includes an intermediate contraction waveform portion, a final contraction waveform portion following the intermediate contraction waveform portion, and an expansion waveform portion following the final contraction waveform portion. During the intermediate contraction waveform portion, the applied voltage increases from an initial low voltage to an intermediate voltage and then remains at the intermediate voltage. During the final contraction waveform portion, the applied voltage increases from the intermediate voltage to a maximum voltage and then remains at the maximum voltage. During the expansion waveform portion, the applied voltage decreases from the maximum voltage to a final low voltage.

Description

[0001] background

[0002] Industrial inkjet printers can be used to print a wide variety of materials. With recent advancements in nanoparticle technology, it is possible to prepare metal nanoparticles with predetermined characteristics. For novel electronic applications, the ability to print metal nanoparticle features with linewidths <100 μm and <50 μm is desirable. To achieve such small features via inkjet printing, metal nanoparticle compositions compatible with picoliter inkjet printheads and methods for dispensing these compositions from such printheads are required. Invention Overview

[0004] In one aspect, a method of forming a feature by dispensing a metal nanoparticle composition from an inkjet printhead includes: configuring the inkjet printhead and applying an ejection waveform to a piezoelectric actuator to dispense droplets of the metal nanoparticle composition through a nozzle opening. The droplet volume ranges between 0.5 picoliters and 2.0 picoliters. The ejection waveform includes an intermediate contraction waveform portion, a final contraction waveform portion following the intermediate contraction waveform portion, and an expansion waveform portion following the final contraction waveform portion. During the intermediate contraction waveform portion, the applied voltage increases from an initial low voltage to an intermediate voltage and then remains at the intermediate voltage. During the final contraction waveform portion, the applied voltage increases from the intermediate voltage to a maximum voltage and then remains at the maximum voltage. During the expansion waveform portion, the applied voltage decreases from the maximum voltage to a final low voltage.

[0005] In another aspect, the metal nanoparticle composition for inkjet printing comprises silver nanoparticles and a glycol ether solvent. The glycol ether solvent has a boiling point in the range of 200°C to 240°C, a viscosity in the range of 4 cP to 8 cP at 25°C, and a vapor pressure not exceeding 0.1 mm Hg at 25°C. The concentration of silver in the metal nanoparticle composition is in the range of 20 wt% to 40 wt%. Polyvinylpyrrolidone (PVP) is present on the surface of the silver nanoparticles.

[0006] The above summary of the invention is not intended to describe every disclosed embodiment or implementation of the invention. The following description illustrates illustrative embodiments in more detail. Guidance is provided by way of examples throughout this application, which can be used in various combinations. In each example listed, the enumerated list is used only as a representative group and should not be construed as an exclusive list. Attached Figure Description

[0007] This disclosure can be more fully understood in light of the following detailed description of various embodiments of the disclosure taken in conjunction with the accompanying drawings, in which:

[0008] Figure 1This is a flowchart of a method for forming features through inkjet printing.

[0009] Figure 2 This is a schematic top view of the sprayed pixels.

[0010] Figure 3 This is a schematic top view of the sprayed and non-sprayed pixels.

[0011] Figure 4 This is a schematic diagram illustrating the relationship between the jet waveform, the non-jet waveform, and the static waveform.

[0012] Figure 5 This is a schematic diagram showing the composition of the injection drive signal.

[0013] Figure 6 This is a schematic diagram showing the composition of the non-jet drive signal.

[0014] Figure 7 This is a schematic diagram illustrating the composition of another type of non-jet drive signal.

[0015] Figure 8 , 9 Figures 10, 11, 12, 13, 14, 15, and 16 are graphical representations of respective implementations of the drive signals.

[0016] Figure 17 This is a schematic top view illustrating an implementation of an inkjet printer.

[0017] Figure 18 , 19 Figures 20 and 21 are schematic cross-sectional views of the inkjet printhead in their respective actuated states.

[0018] Figure 22 This is a transmission electron microscope (TEM) image of silver nanoparticles at a low magnification.

[0019] Figure 23 This is a transmission electron microscope (TEM) image of silver nanoparticles at a high magnification.

[0020] Figure 24 It is an optical microscope image of features (including lines and dots) formed according to the present invention. Detailed Implementation

[0021] This disclosure relates to a method for forming features by dispensing a metal nanoparticle composition from an inkjet printhead and to a metal nanoparticle composition for inkjet printing.

[0022] In this disclosure:

[0023] The terms "preferred" and "ideally" indicate that embodiments of the present invention may provide certain benefits in certain circumstances. However, other embodiments may also be preferred in the same or other circumstances. Furthermore, the description of one or more preferred embodiments does not imply that other embodiments are useless and is not intended to exclude other embodiments from the scope of the present invention.

[0024] The term "comprising" and its variations are not restrictive when these terms appear in the specification and claims.

[0025] Unless otherwise stated, “a / an”, “the” and “at least one” are used interchangeably and mean one or more.

[0026] The description of the numerical range based on the endpoints includes all numbers contained in that range (for example, 1 to 5 includes 1, 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.).

[0027] For any method disclosed herein that includes discrete steps, these steps can be performed in any feasible order. Where appropriate, any combination of two or more steps can be performed simultaneously.

[0028] For the experiments described in this paper, we used a Fujifilm Polaris inkjet printer to dispense the metal nanoparticle composition. While there is considerable interest in using inkjet printing to dispense relatively narrow nanoparticle features (e.g., lines <100 μm or <50 μm in width), preparing suitable nanoparticle compositions has proven very difficult. There is a tendency for nanoparticles to aggregate in the printhead, leading to nozzle clogging. To reduce the likelihood of nanoparticle aggregation, nozzles (nozzle openings) that produce larger droplets than desired are typically used. In the example printer, with conventional nanoparticle compositions, printheads rated for dispensing 10 picoliters (pl) of droplets are typically used. However, the metal nanoparticle composition (silver nanoparticle composition) and printing method described in this paper enabled the use of a 1 pl printhead without any clogging over several weeks of use.

[0029] Figure 1This is a flowchart of a method 100 for forming features by inkjet printing. Method 100 includes steps 102, 104, 106, 108, 110, 112, and 114. In step 102, a metal nanoparticle composition is prepared. Step 102 includes the synthesis of silver nanoparticles, if they are not yet available. The synthesis of suitable silver nanoparticles is illustrated in Examples 1 and 2 below. Example 2 is the same as Example 1 in terms of the synthesis of silver nanoparticles. Typically, the synthesis of metal nanoparticles in solution employs three components: (1) a metal precursor (e.g., AgNO3 for silver nanoparticles); (2) a reducing agent (e.g., ethylene glycol for silver nanoparticles); and (3) a stabilizing (capping) agent (e.g., polyvinylpyrrolidone). Polyvinylpyrrolidone, abbreviated as PVP, is soluble in water and other polar solvents. When PVP is used effectively as a dispersant, stable colloidal silver nanoparticles with small size (<250 nm) covered (end-capped) with PVP polymer can be obtained because PVP reduces the aggregation of silver.

[0030] The average size of silver nanoparticles can be controlled within the range of 20 nm to 80 nm. Average particle size and dispersion can be controlled by manipulating thermodynamic and kinetic reaction parameters. Reaction temperature, temperature slope, and reaction time are important thermodynamic parameters. The reagent addition rate and the molar ratio of the metal precursor to the stabilizer (PVP) are important kinetic parameters. Appropriate combinations of these parameters result in nanoparticles exhibiting the desired properties of small particle size, low dispersion, and high dispersion stability (low aggregation rate).

[0031] Step 102 involves preparing a metal nanoparticle composition from metal nanoparticles (silver nanoparticles). Typically, the nanoparticles are separated to remove impurities and excess PVP and dispersed in a solvent or solvent mixture. The metal nanoparticle composition may optionally contain additives to better control its physicochemical properties. These additives include surfactants, binders, adhesion promoters, and defoamers.

[0032] The preparation of suitable metal nanoparticle compositions is illustrated in Examples 1 and 2 below. Typically, the composition comprises a glycol ether solvent having a boiling point in the range of 200°C to 240°C, a viscosity in the range of 4 cP to 8 cP at 25°C, and a vapor pressure not exceeding 0.1 mm Hg at 25°C. Preferably, the glycol ether solvent is 2-(2-butoxyethoxy)ethanol. An alternative name for 2-(2-butoxyethoxy)ethanol is diethylene glycol monobutyl ether. The 2-(2-butoxyethoxy)ethanol solvent has a boiling point of 230°C at 760 mm Hg, a viscosity of 6.0 cP at 25°C, a surface tension of 30.0 mN / m measured at 25°C, and a vapor pressure of 0.03 mm Hg at 25°C. Preferably, the combined concentration of water, methanol, ethanol, 1-propanol, and 2-propanol in the metal nanoparticle composition does not exceed 10.0 wt%. Preferably, the total concentration of solvents other than glycol ether solvents in the metal nanoparticle composition does not exceed 10.0 wt%. The concentration of silver in the metal nanoparticle composition is in the range of 20 wt% to 40 wt%. Preferably, the concentration of silver in the metal nanoparticle composition is in the range of 32 wt% to 39 wt%. Polyvinylpyrrolidone (PVP) is present on the surface of the silver nanoparticles. In the composition of Example 1, the concentration of silver is estimated to be in the range of 32 wt% to 34 wt%. The solid concentration is estimated to be higher, in the range of 34 wt% to 36 wt%, because solids other than silver, such as PVP, are present in the composition. In the composition of Example 2, the concentration of silver is estimated to be in the range of 37 wt% to 39 wt%. Both the compositions of Example 1 and Example 2 have been successfully used in the printing experiments described herein.

[0033] Preferably, the silver nanoparticles have an average particle size in the range of 20 nm to 80 nm. Preferably, the silver nanoparticles have an average particle size in the range of 35 nm to 50 nm. Preferably, the silver nanoparticles are approximately spherical. Figure 22 This is a transmission electron microscope (TEM) image of silver nanoparticles 330 synthesized according to Example 1 at a lower magnification. Figure 23 These are TEM images of the same silver nanoparticles at a high magnification. It can be seen that the silver nanoparticles are approximately spherical.

[0034] Example 1: The silver nanoparticle composition was measured to have a viscosity in the range of 26 cP to 30 cP, and a viscosity at 25°C for 100 s⁻¹. -1 The viscosity was measured at the shear rate. Example 2: The silver nanoparticle composition was measured to have a viscosity in the range of 50 cP to 60 cP at 25°C for 100 s⁻¹. -1 The viscosity was measured at a shear rate of 26 cP to 60 cP. Preferably, the silver nanoparticle composition has a viscosity in the range of 26 cP to 60 cP and a viscosity at 25°C for 100 s⁻¹. -1The surface tension of the silver nanoparticle composition is measured at a shear rate of 28 mN / m to 32 mN / m at 25°C.

[0035] Step 102 ( Figure 1 Preferably, this includes some additional treatments before pouring (injecting) the silver nanoparticle composition into the printhead. Such additional treatments include: (1) mixing the vial of the silver nanoparticle composition in an ultrasonic water bath for 10 minutes; (2) degassing the silver nanoparticle composition in a vacuum dryer for 15 minutes; and (3) filtering the silver nanoparticle composition through a 1 μm polyamide filter.

[0036] In step 104 ( Figure 1 ), configuring the inkjet printhead. This step 104 includes filling (injecting) the silver nanoparticle composition into the printhead and installing the printhead in the inkjet printer. Figure 17 This is a schematic top view of an inkjet printer implementation, in which a printhead 304 is suspended above a substrate 302. The printhead 304 includes nozzles 306. The nozzle opening (318, ...) of the printhead 304... Figure 18 The typical vertical distance between the printhead 304 and the substrate 302 ranges from 500 μm to 750 μm. In the example shown, 16 nozzles (drawn as dashed circles) are arranged in a one-dimensional array extending along the X-axis direction 122. During printing, the printhead 304 is laterally displaced relative to the substrate 302 along the Y-axis direction 124. The X-axis direction 122 and the Y-axis direction 124 are perpendicular to each other and perpendicular to the vertical direction (Z-axis direction). As the printhead 304 is laterally displaced along the Y-axis direction, each nozzle 306 prints a pixel. Figure 2 This illustration shows an example in which nozzle 306 has formed jetting pixels 130, 132, 134, 136, and 138 (collectively referred to as pixel 120). In the example shown, adjacent pixels overlap. Figure 3 Another example is shown in which nozzle 306 has formed spray pixels 150 and 158. Spray pixels 150 and 158 are separated by non-spray pixels 152, 154 and 156. The spray pixels (150, 158) and non-spray pixels (152, 154, 156) are collectively referred to as pixel 140.

[0037] From step 106 ( Figure 1 The inkjet printer begins printing. In step 106, the printhead positioning system moves the printhead to the next pixel (e.g., ...). Figure 3The position of pixel 150. In determination step 108, one of the following is selected: (a) the pixel is an ejected pixel (the "Yes" branch of determination step 108); and (b) the pixel is a non-ejected pixel (the "No" branch of determination step 108). A pixel to be ejected is called an ejected pixel, even though ejection has not yet occurred. A pixel not to be ejected is called a non-ejected pixel. If the pixel is an ejected pixel, an ejection drive signal is applied to the piezoelectric actuator of the printhead (step 110). After the ejection drive signal is applied, ink droplets are dispensed through the nozzle opening. In this case, the ink is a silver nanoparticle composition. In the example shown, the droplet volume ranges between 0.5 picoliters and 2.0 picoliters. If the pixel is a non-ejected pixel, a non-ejection drive signal is applied to the piezoelectric actuator of the printhead (step 112). After the non-ejection drive signal is applied, no ink is dispensed through the nozzle opening. In decision step 114, one of the following is selected: (a) printing of all pixels is complete (the "Yes" branch of decision step 114); and (b) printing of all pixels is not yet complete (the "No" branch of decision step 114). If printing of all pixels is complete (the "Yes" branch of decision step 114), the printing operation can end. If printing of all pixels is not yet complete (the "No" branch of decision step 114), the printhead positioning system moves the printhead to the next pixel (e.g., ...). Figure 3 The position of pixel 152). Repeat steps 106, 108, 110, 112 and 114 until all pixels are printed.

[0038] exist Figure 24 An example of a feature formed on a glass substrate by method 100 is shown. The printed features include lines 340 and dots (circles) 350. For lines, a line width of less than or equal to 40 μm is possible. For dots, a dot diameter of less than or equal to 40 μm is possible. The composition can be dispensed onto a substrate comprising polyimide, polyethylene terephthalate (PET), and glass. An example of a polyimide film is Kapton 500HN. Typically, the resulting feature has a diameter of approximately 3.95 × 10⁻⁶. -8 The resistivity is approximately 41% of the volumetric conductivity of silver (Ωm). After dispensing, the workpiece can be selectively sintered. Preferred sintering conditions are 250°C for 40 minutes in an air or nitrogen atmosphere.

[0039] During printing, both jet drive signals and non-jet drive signals are used. Figure 4The diagram schematically illustrates the typical relationship between the waveforms. When the nozzle opening is in a jetting pixel (e.g., 150, 158), a jetting drive signal 160 is applied to the piezoelectric actuator. When the nozzle opening is in a non-jetting pixel (e.g., 152, 154, 156), a non-jetting drive signal 180 is applied to the piezoelectric actuator. The jetting drive signal 160 includes a jetting waveform 170 and a static waveform 182 following the jetting waveform 170. The non-jetting drive signal 180 includes a non-jetting waveform 184 and a static waveform 182 following the non-jetting waveform 170. For example, if there are jetting pixels and non-jetting pixels immediately following the jetting pixels, the waveform sequence is as follows: jetting waveform 170, static waveform 182, non-jetting waveform 184, and static waveform 182. Considering an example with a maximum jetting frequency of 5 kHz, this means that for each nozzle opening, a jetting pixel is formed at a rate of 5 kHz or less, or one jetting pixel is formed every 200 μs or longer. For example, if the duration of the jet waveform is about 10 μs, the duration of the static waveform will be 190 μs or longer.

[0040] Figure 5 This is a schematic diagram illustrating some components of the jet drive signal. The jet drive signal 160 is applied after the static waveform 182A of the previous pixel. The jet drive signal includes a jet waveform 170 and a static waveform 182 following the jet waveform 170. The jet waveform 170 includes: an intermediate contraction waveform portion 174, a final contraction waveform portion 176 following the intermediate contraction waveform portion 174, and an expansion waveform portion 178 following the final contraction waveform portion 176. Optionally, the jet waveform 170 also includes a start-up waveform portion 172 preceding the intermediate contraction waveform portion 174.

[0041] Figure 8 , 9 Figures 10, 11, 12, 13, 14, 15, and 16 are graphical representations of respective implementations of the drive signals. Figure 8 , 9 Each of the following (10, 11, 12, 13, 14, 15, and 16) illustrates a respective drive signal implementation (210, 220, 230, 240, 250, 260, 270, 280, 290), which includes a respective injection waveform (212, 222, 232, 242, 252, 262, 272, 282, 292) and a respective non-injection waveform (214, 224, 234, 244, 254, 264, 274, 284, 294).

[0042]

[0043] Table 1: Characteristics of the jet waveform

[0044] use Figure 9 The injection waveform 222 is explained in detail with reference to Table 1. The injection waveform 222 includes an initiation waveform portion (part 1), an intermediate contraction waveform portion (part 2), a final contraction waveform portion (part 3), and an expansion waveform portion (part 4). At the zero point of the injection waveform, the applied voltage is the maximum voltage V. max 27%. In the following text, when voltage is expressed as a percentage, this refers to the maximum voltage V. max The percentage. This 27% applied voltage corresponds to the applied voltage during the duration of the static waveform applied before and after the injection waveform 222. During the start-up waveform section (section 1), the applied voltage decreases from the voltage level of the preceding static waveform (27% for injection waveform 222) to an initial low voltage (7% for injection waveform 222) and then remains at the initial low voltage for the remainder of the start-up waveform section. "Initial low voltage" is the voltage applied at the beginning of the intermediate contraction waveform section, as explained below. The initial low voltage does not exceed the maximum voltage V. max 30%. Preferably, the initial low voltage does not exceed the maximum voltage V. max 10%. In this example, the duration of the startup waveform portion is 2.56 μs. Preferably, the startup duration is in the range of 2.0 μs to 3.0 μs. In the example shown, the applied voltage changes (decreases) by 1.0V from the voltage level of the previous static waveform to the initial low voltage. max A conversion rate of / μs occurs. Preferably, during the start-up waveform portion, the applied voltage is 0.5V. max A slew rate of / μs or greater is used to reduce the voltage level from the previous static waveform to the initial low voltage.

[0045] During the intermediate contraction waveform portion (part 2), the applied voltage increases from an initial low voltage (7% for jet waveform 222) to an intermediate voltage (73% for jet waveform 222) and then remains at the intermediate voltage for the remainder of the intermediate contraction waveform portion. The intermediate voltage is at the maximum voltage V. max The voltage is in the range of 63% to 83%. Preferably, the intermediate voltage is within the range of the maximum voltage V. max The duration is in the range of 68% to 78%. In this example, the duration of the intermediate contraction waveform portion is 2.048 μs. Preferably, the duration of the intermediate contraction waveform portion is in the range of 1.7 μs to 2.2 μs. In the example shown, the applied voltage changes (increases) from an initial low voltage to the maximum voltage in increments of 1.0V. max The conversion rate occurs at a rate of / μs. Preferably, during the final contraction waveform portion, the applied voltage is 0.5V. max A conversion rate of / μs or greater is increased from the intermediate voltage to the maximum voltage V. max .

[0046] During the final contraction waveform portion (part 3), the applied voltage increases from the intermediate voltage (73% for jet waveform 222) to the maximum voltage V. max (100%) and then maintains the maximum voltage for the remainder of the final contraction waveform portion. In the example printer, the maximum voltage V max It can be set to a voltage range of 16V to 40V. However, we found that by adjusting the maximum voltage V... max Choosing a range of 22V to 27V or 24V to 25V will yield better results. Figure 8 , 9 The drive signal examples shown in 10, 11, 12, 13, 14, 15, and 16 use a maximum voltage V set in the range of 24V to 25V. max Perform the test. Preferably, the maximum voltage V max Within the range of 22V to 27V. Preferably, the maximum voltage V max Within the range of 24V to 25V. In this example, the duration of the final contraction waveform portion is 2.56μs. Preferably, the duration of the final contraction waveform portion is within the range of 1.0μs to 2.7μs. In the example shown, the applied voltage changes (increases) from the intermediate voltage to the maximum voltage in increments of 2.0V. max The conversion rate occurs at a rate of / μs. Preferably, during the final contraction waveform portion, the applied voltage is 0.5V. max The voltage is increased from the intermediate voltage to the maximum voltage at a conversion rate of / μs or greater. Preferably, during the final contraction waveform portion, the applied voltage is 1.5V. max A conversion rate of / μs or greater is increased from the intermediate voltage to the maximum voltage.

[0047] During the expansion waveform section (section 4), the applied voltage decreases from the maximum voltage (100%) to a final low voltage (27% for injection waveform 222). The final low voltage does not exceed the maximum voltage V. max 30% of the maximum voltage. Preferably, the final low voltage does not exceed the maximum voltage V. max 27%. In the example shown, the applied voltage is from the maximum voltage V. max The final low voltage change (decrease) is 1.0V. max A conversion rate of / μs occurs. Preferably, during the expansion waveform portion, the applied voltage is 0.5V. max A conversion rate of / μs or greater reduces the voltage from the maximum voltage to the final low voltage. Figure 9 In the example shown, the expansion waveform includes a voltage reduction segment 226 (during which the applied voltage decreases from the maximum voltage V). maxThe voltage is reduced to a final low voltage (during which the applied voltage remains at the final low voltage) and a constant voltage segment 228. In the example shown, the duration of the expansion waveform portion (including segments 226 and 228) is 2.56 μs (Table 1).

[0048] Following the jet waveform 184 is the static waveform 182. Figure 5 Preferably, the voltage applied during the static waveform does not exceed the maximum voltage V. max 30%. Preferably, the sum of the duration of the jet waveform and the duration of the static waveform is 0.2 milliseconds or longer. In an example of drive signal implementation 220 ( Figure 9 In the waveform, the applied voltage remains at a final low voltage (27%) during the static waveform period and during the constant voltage segment 228. Therefore, the voltage applied at time zero is also 27%, corresponding to the final low voltage. If the jet waveform includes a startup waveform portion, the applied voltage decreases from the time zero voltage to the initial low voltage. Therefore, the initial low voltage is preferably less than or equal to the final low voltage.

[0049] Jet waveform 272 ( Figure 14 ) and injection waveform 222 ( Figure 9 The similarity between the two waveforms is that both include an initiation waveform portion 172, an intermediate contraction waveform portion 174, a final contraction waveform portion 176, and an expansion waveform portion 178. (Ejection waveform 282) Figure 15 ) and 292 Figure 16 The waveform includes an intermediate contraction waveform portion 174, a final contraction waveform portion 176, and an expansion waveform portion 178, but excludes the initiation waveform portion 172. In the case of jet waveforms 282 and 292, the initial low voltage (at the beginning of the intermediate contraction waveform portion 174) remains unchanged compared to the voltage level during the static waveform and compared to the final low voltage (at the end of the expansion waveform portion 178).

[0050] Jet waveform 212 ( Figure 8 The waveform includes an initiation waveform portion 172 and an intermediate contraction waveform portion 174, but excludes a final contraction waveform portion. Instead, during the portion following the intermediate contraction waveform portion 174 (portion 3), the applied voltage decreases from an intermediate voltage (73%) to a low voltage (0%). The waveform shape of portion 3 resembles an expansion portion. However, portion 3 is not an expansion portion because the applied voltage decreases from an intermediate voltage rather than from a maximum voltage. Furthermore, during the portion 4 following portion 3, the applied voltage increases from a low voltage (0%) to a higher voltage (27%).

[0051] Jet waveform 232 ( Figure 10 ), 242 ( Figure 11 ) and 252 ( Figure 12Each includes its own startup waveform portion, while the injection waveform 262 ( Figure 13 This excludes any initiation waveform portion. During portion 2 of each of these waveforms, the applied voltage increases from an "initial low voltage" to an "intermediate voltage." However, the applied voltage does not remain at the "intermediate voltage." Therefore, in each of these injection waveforms, portion 2 does not have the characteristics of an intermediate contraction waveform portion. Subsequently, during portion 3 of each of these waveforms, the applied voltage increases from the intermediate voltage to the maximum voltage V. max And then it remains at the maximum voltage. Therefore, in each of these waveforms, portion 3 corresponds to the final contraction waveform portion. Subsequently, during portion 4 of each of these waveforms, the applied voltage decreases from the maximum voltage V. max The voltage is reduced to a final low voltage. Therefore, in each of these waveforms, part 4 corresponds to the expansion waveform part.

[0052] Figure 6 The composition of the non-jet drive signal 190 is shown, which includes a non-jet waveform 194 and a static waveform 182 following the non-jet waveform 194. The non-jet drive signal 190 is applied after the static waveform 182A of the previous pixel (such as a jetted pixel or a non-jet pixel). Figure 6 In this case, the non-jet waveform 194 is configured such that the applied voltage remains unchanged compared to the previous static waveform 182A and the subsequent static waveform 182. Non-jet waveform 214 ( Figure 8 ), 224 Figure 9 ), 234 Figure 10 ), 244 Figure 11 ), 254 Figure 12 ), 264 Figure 13 ) and 274 Figure 14 This belongs to this type of non-jet waveform 194. The voltage characteristics of these non-jet waveforms are listed in Table 2.

[0053]

[0054] Table 2: Characteristics of Non-Jet Waveforms

[0055] Figure 7 Another composition of the non-jet drive signal 200 is shown, which includes a non-jet waveform 204 and a static waveform 182 following the non-jet waveform 204. Figure 7 In this case, the non-jet waveform 204 is configured such that the applied voltage includes voltage pulses. Non-jet waveform 284 ( Figure 15 ) and 294 Figure 16 This belongs to this type of non-jet waveform 204. The voltage characteristics of these non-jet waveforms are listed in Table 2. During non-jet waveform 284, the applied voltage is 1.0V.max The slew rate per μs increased from 13% (voltage level during the previous static waveform 182A) to 27%, where V max This corresponds to the maximum voltage of the jet waveform 282. In the example shown, the duration of the voltage pulse is 3.968 μs. Preferably, the duration of the voltage pulse during the non-jet waveform is 6 μs or less. A suitable voltage pulse during the non-jet waveform may agitate the composition in the pumping chamber, resulting in more stable droplet formation during the subsequent jet waveform.

[0056] Figure 18 This is a schematic cross-sectional view of a printhead 304 in an actuated state. The printhead 304 includes a flow path body 312 and a piezoelectric actuator 320. Inside the flow path body 312 is a pumping chamber 314. The pumping chamber 314 has a fluid inlet 316 connected to a fluid source, such as a reservoir containing fluid. Figure 18 (Not shown in the image). The fluid outlet is a nozzle opening 318 connected to the pumping chamber 314. In this case, the fluid is a silver nanoparticle composition. A piezoelectric actuator 320 is mechanically coupled to the pumping chamber 314 to cause the pumping chamber 314 to expand and contract. In the example shown, a portion 322 of the flow path body is a mechanically deformable element and the piezoelectric actuator 320 is attached to or adhered to the deformable element 322. Figure 18 , 19 Figures 20 and 21 show the respective actuation states of the piezoelectric actuator 320 when a respective voltage signal is applied to the piezoelectric actuator 320. Figure 18 , 19 Figures 20 and 21 show the first, second, third, and fourth actuation states, respectively. (The last two lines appear to be incomplete and possibly contain errors.) Figure 19 , 20 Compared to the pumping chamber of 21), the pumping chamber in the first actuation state ( Figure 18 Expansion. Compared to the first, second, and third actuation states ( Figure 18 , 19 Compared to the pumping chamber of 20), the pumping chamber in the fourth actuation state ( Figure 21 The piezoelectric actuator 320 is mechanically connected to the pumping chamber 314, causing the pumping chamber to expand and contract.

[0057] Figure 18 , 19 Figures 20 and 21 show schematic cross-sectional views of the printhead in its respective actuated state, wherein the degree of contraction of the pumping chamber is determined in sequence. Figure 18 , 19The numbers 20 and 21 increase. While we do not know the actual actuation state of the printhead when any of the drive signals (210, 220, 230, 240, 250, 260, 270, 280, 290) are applied, we believe that the first actuation state, where the piezoelectric film is almost flat (in...) Figure 18 (Illustrated schematically) at low voltages close to 0V (e.g., maximum voltage V) max This occurs at 7% or less. The inward deformation of the piezoelectric actuator (towards the pump chamber) increases with increasing applied voltage. The inward deformation of the piezoelectric actuator corresponds to the contraction of the pump chamber. For example, in the fourth actuation state ( Figure 21 This can correspond to the maximum voltage V. max 100% of the applied voltage.

[0058] During the intermediate contraction waveform portion, the pumping chamber transitions from an expanded state (e.g., Figure 18 The fully expanded state or Figure 19 The slightly contracted state) quickly contracts to the intermediate contraction state (e.g., Figure 20 And remain in the intermediate contraction state. During the final contraction waveform portion, the pumping chamber contracts from the intermediate contraction state (e.g., Figure 20 Rapidly contract to the final contraction state (e.g., Figure 21 And remain in the final contracted state. During the final contraction waveform portion, droplets of the silver nanoparticle composition are ejected (dispensed) through the nozzle opening. We believe that the intermediate contraction waveform portion helps stabilize droplet formation. During the expansion waveform portion, the pumping chamber moves from the final contraction state (e.g., Figure 21 Rapidly expands to an expanded state (e.g., Figure 18 The fully expanded state or Figure 19 During the expansion waveform section, the silver nanoparticle composition is refilled into the pumping chamber 314. During the expansion waveform section, the silver nanoparticle composition flows from the storage chamber into the pumping chamber 314 via the fluid inlet 316. During the start-up waveform section, the pumping chamber transitions from a slightly contracted state (e.g., ...). Figure 19 Rapidly expands to a fully expanded state (e.g., Figure 18 During the initial waveform phase, the silver nanoparticle composition may flow from the storage chamber into the pumping chamber 314 via the fluid inlet 316.

[0059] Printing tests were conducted using the silver nanoparticle compositions from Examples 1 and 2. Figure 8 , 9 The printouts for each drive signal in 10, 11, 12, 13, 14, 15, and 16 were evaluated. The printouts are listed in Table 3. Figure 8 The example's printout is incorrect. In Figure 8In the example (jet waveform 212), some nozzles fail to eject (dispense) and the droplets are too small and slow. This jet waveform 212 does not include the final contraction waveform portion. The "maximum voltage" (V) is reached during the intermediate contraction waveform portion. max (73%). It is believed that the maximum voltage is related to the kinetic energy imparted to the droplet. Therefore, when the applied voltage is too low, the droplet velocity may be too low. Droplets that are too slow tend to be less stable, and therefore the droplet's flight direction may be unreproducible. Furthermore, it is believed that the duration of the contraction waveform portion (the sum of the durations of the intermediate and final contraction waveform portions) is related to the droplet size. Therefore, when the duration is too short, the droplet size may be too small. Preferably, the droplet has a sufficient size. When the droplet has a sufficient size, the likelihood of residual ink (silver nanoparticle composition) remaining at the nozzle opening (nozzle contamination) that would interfere with the flow of the composition through the nozzle opening is lower.

[0060]

[0061] Table 3: Printing Performance

[0062] Figure 11 and 12 The output of the example is incorrect. In Figure 11 In the example (jet waveform 242), the droplets are fast and stable and Figure 12 In the example (ejection waveform 252), the droplets are fast. However, the droplets each have a moderate tail (ejection waveform 242). Figure 11 ) and long tail (jet waveform 252, Figure 12 There may be a correlation between faster droplets and larger tails. A tail is a smaller portion of the droplet following the main droplet portion. If the tail is small enough, it is more likely to be "absorbed" into the main droplet portion during its trajectory from the nozzle opening to the substrate. Tails that are not absorbed into the main droplet portion can separate and create "satellite" droplet patterns on the substrate. Such satellite droplets degrade print quality. Therefore, it is preferable to make the tail small enough. In these jet waveforms 242, 252, there is no intermediate contraction waveform portion because the applied voltage is not maintained at an intermediate voltage.

[0063] Figure 10 and 13 The print results for these examples are of medium quality. In these examples, the respective jet waveforms (for...) Figure 10 For 232 and for Figure 13 (262) This excludes the intermediate contraction waveform portion because the applied voltage is not maintained at the intermediate voltage. Figure 10 In the example (ejection waveform 232), the droplet has a short tail and is large enough and Figure 13In the example (jet waveform 262), the droplets are round and have short tails. However, in Figure 10 In the example, the droplets were observed to be slow (jet waveform 232).

[0064] exist Figure 9 , 14 In the examples 15 and 16, the respective jet waveforms (222, 272, 282 and 292) include intermediate contraction waveform portions and final contraction waveform portions. Figure 9 , 14 The printing results for the 16th instance are good and Figure 15 The print results for these examples are of medium quality. In all of these examples (jet waveforms 222, 272, 282, and 292), the droplets have short tails. Figure 14 In the example (jet waveform 272), the droplets are spherical. Figure 15 In the example (jet waveform 282), the droplet is stable. Figure 16 In the example (jet waveform 292), the droplet exhibits good stability and reproducibility. Figure 15 The example is considered moderate rather than good because the droplets are too small and the droplet flight direction is not reproducible. Jet waveform 272 ( Figure 14 ) and 282 ( Figure 15 The jet waveforms include intermediate and final shrinkage waveform sections with similar voltage levels and durations. The main difference between these jet waveforms is that jet waveform 272 includes a starting waveform section preceding the intermediate shrinkage waveform section, while jet waveform 282 does not. Therefore, including the starting waveform section may contribute to better printing performance.

[0065] exist Figure 15 and 16 In the examples, the respective non-jetting waveforms (284, 294) include voltage pulses. We believe that a suitable voltage pulse during the non-jetting waveform may agitate the composition in the pumping chamber, resulting in more stable droplet formation during the subsequent jetting waveform. Figure 15 The non-jet waveform 284 in the example includes voltage pulses, while Figure 14 The non-jet waveform 274 in the example does not include voltage pulses.

[0066] Example

[0067] Example 1: Silver nanoparticle-based ink composition in 2-(2-butoxyethoxy)ethanol (solids content: 34-36 wt%)

[0068] Reagents:

[0069] AgNO3-12.5g

[0070] PVP (K30 level) - 100.2g

[0071] Ethylene glycol - 560ml

[0072] Acetone - 1520ml

[0073] 96% ethanol - 300ml

[0074] Triethylene glycol - 1.326 ml

[0075] 2-(2-Butoxyethoxy)ethanol - 25ml

[0076] 1) Synthesis

[0077] Two synthetic reactions were carried out in parallel. For each synthetic reaction: AgNO3 (12.5 g) was dissolved in 50 mL of ethylene glycol at room temperature. In a three-necked flask, PVP (100.2 g) was dissolved in 250 mL of ethylene glycol under reflux while heating at 140 °C. The AgNO3 solution was poured rapidly (through a funnel) into the hot PVP dissolved in ethylene glycol. The mixture was heated at 140 °C for 60 min with vigorous stirring. Finally, it was cooled in a cold water bath until room temperature was reached.

[0078] 2) Purification

[0079] Pour each synthesized mixture into a 2.5-liter beaker. Add 100 ml of ethylene glycol to a three-necked reaction flask, sonicate with stirring for 1 min, and combine with the previously mentioned fraction. Mix 1440 ml of acetone and 160 ml of ethylene glycol in a 2-liter beaker and pour with stirring into a beaker containing the Ag NPs suspension. Then add 40 ml of acetone, and then add...

[0080] Add 40 ml of acetone, and then a few ml of ethylene glycol to change the color of the suspension from dark green to brown. Pour the contents of the beaker evenly into six 500 ml centrifuge flasks and centrifuge at 4000 × g for 15 min. Discard the clear orange supernatant. Redisperse the silver particles in 40 ml of ethanol (per flask) under sonication and shaking (10 min). Pour the solution into two flasks and centrifuge at 12000 × g for 45 min. Redisperse the particles separately in 50 mL of EtOH under sonication and shaking (10 min).

[0081] 3) Preparation

[0082] The obtained dispersion in ethanol was transferred to a 60 ml syringe and filtered directly through a 1.0 μm PA filter into a 250 ml round-bottom flask made of PFA. 18.00 mL of 2-(2-butoxyethoxy)ethanol, 99%+, was added. The flask was placed on a rotary evaporator at 44 °C, 80 mbar for 10 min, 30 mbar for 25 min, and the dispersion was transferred to a 100 ml flask and evaporated at 35 mbar. When reached, the conditions were maintained for 5 min. The solids loading of the obtained ink concentrate was determined by gravimetric analysis – it should be approximately 45 wt%. The ink concentrate was diluted with a sufficient amount of 2-(2-butoxyethoxy)ethanol to obtain an ink with a solids content in the range of 34-36 wt% and a viscosity of 26-30 cP at 25 °C. Finally, the ink was transferred to a syringe and filtered through a 1 μm PA filter into a clean PP container. The pure silver content in the ink is estimated to be in the range of 32-34 wt%, determined by TGA or AAS methods.

[0083] Example 2: Silver nanoparticle-based ink composition in 2-(2-butoxyethoxy)ethanol (solids content: 39wt%-41wt%)

[0084] Reagents:

[0085] AgNO3-12.5g

[0086] PVP (K30 level) - 100.2g

[0087] Ethylene glycol - 560ml

[0088] Acetone - 1520ml

[0089] 96% ethanol - 300ml

[0090] Triethylene glycol - 1.326 ml

[0091] 2-(2-Butoxyethoxy)ethanol - 25ml

[0092] 1) Synthesis

[0093] Two synthetic reactions were carried out in parallel. For each synthetic reaction: AgNO3 (12.5 g) was dissolved in 50 mL of ethylene glycol at room temperature. In a three-necked flask, PVP (100.2 g) was dissolved in 250 mL of ethylene glycol under reflux while heating at 140 °C. The AgNO3 solution was poured rapidly (through a funnel) into the hot PVP dissolved in ethylene glycol. The mixture was heated at 140 °C for 60 min with vigorous stirring. Finally, it was cooled in a cold water bath until room temperature was reached.

[0094] 2) Purification

[0095] Pour each synthesized mixture into a 2.5-liter beaker. Add 100 ml of ethylene glycol to a three-necked reaction flask, sonicate for 1 min with stirring, and combine with the previously mentioned fraction. Mix 1440 ml of acetone and 160 ml of ethylene glycol in a 2-liter beaker and pour with stirring into a beaker containing the Ag NPs suspension. Then add 40 ml of acetone, followed by another 40 ml of acetone, and then a few ml of ethylene glycol to change the color of the suspension from dark green to brown. Pour the contents of the beakers equally into six 500 ml centrifuge flasks and centrifuge at 4000 × g for 15 min. Discard the clear orange supernatant. Redisperse the silver particles in 40 ml of ethanol (per flask) with sonication and shaking (10 min). Pour the solution into two flasks and centrifuge at 12000 × g for 45 min. Redisperse the particles separately in 50 mL of EtOH with sonication and shaking (10 min).

[0096] 3) Preparation

[0097] The obtained dispersion in ethanol was transferred to a 60 ml syringe and filtered directly through a 1.0 μm PA filter into a 250 ml round-bottom flask made of PFA. 18.00 mL of 2-(2-butoxyethoxy)ethanol, 99%+, was added. The flask was placed on a rotary evaporator at 44 °C, 80 mbar for 10 min, 30 mbar for 25 min, and the dispersion was transferred to a 100 ml flask and evaporated at 35 mbar. When reached, the conditions were maintained for 5 min. The solids loading of the obtained ink concentrate was determined by gravimetric analysis – it should be approximately 45 wt%. The ink concentrate was diluted with a sufficient amount of 2-(2-butoxyethoxy)ethanol to obtain an ink with a solids content in the range of 39-41 wt% and a viscosity of 50-60 cP at 25 °C. Finally, the ink was transferred to a syringe and filtered through a 1 μm PA filter into a clean PP container. The pure silver content in the ink is estimated to be in the range of 37-39 wt%, determined by TGA or AAS methods.

Claims

1. A method for forming features by dispensing a composition of metal nanoparticles from an inkjet printhead, the method comprising the steps of: The inkjet printhead is configured to include a pump chamber connected to a source of the metal nanoparticle composition, a piezoelectric actuator mechanically coupled to the pump chamber to expand and contract the pump chamber, and a nozzle opening connected to the pump chamber. At the jetting pixel, a jetting drive signal is applied to the piezoelectric actuator to dispense droplets of the metal nanoparticle composition through the nozzle opening, the droplets having a volume ranging from 0.5 picoliters to 2.0 picoliters, and the jetting drive signal including a jetting waveform; The jet waveform includes an intermediate contraction waveform portion, a final contraction waveform portion following the intermediate contraction waveform portion, and an expansion waveform portion following the final contraction waveform portion; During the intermediate contraction waveform portion, the applied voltage of the injection drive signal increases from an initial low voltage to an intermediate voltage and then remains at the intermediate voltage; During the final contraction waveform portion, the applied voltage increases from the intermediate voltage to the maximum voltage V. max And then maintain the maximum voltage V max ; During the expansion waveform portion, the applied voltage decreases from the maximum voltage V. max Reduce to the final low voltage; The intermediate voltage is at the maximum voltage V max The percentage is between 63% and 83%; and The initial low voltage and the final low voltage do not exceed the maximum voltage V. max 30%, The injection drive signal further includes a static waveform following the injection waveform, during which the applied voltage does not exceed the maximum voltage V. max 30% of the total duration of the jet waveform and the sum of the duration of the static waveform is 0.2 milliseconds or longer; The jet waveform also includes an initiation waveform portion preceding the intermediate contraction waveform portion; During the startup waveform portion, the applied voltage decreases from the voltage level of another static waveform to the initial low voltage and then remains at the initial low voltage; and The initial low voltage does not exceed the maximum voltage V. max 10%.

2. The method as described in claim 1, wherein, The applied voltage remains at the final low voltage during the static waveform.

3. The method as described in claim 1, wherein, The duration of the start-up waveform is in the range of 2.0 microseconds to 3.0 microseconds.

4. The method of claim 1, wherein, During the startup waveform portion, the applied voltage is 0.5V. max A conversion rate of / ms or greater is used to reduce the voltage level of the other static waveform to the initial low voltage.

5. The method of claim 1, wherein, The intermediate voltage is at the maximum voltage V max The percentage is between 68% and 78%.

6. The method of claim 1, wherein, The duration of the intermediate contraction waveform portion is in the range of 1.7 microseconds to 2.2 microseconds.

7. The method of claim 1, wherein, During the intermediate contraction waveform portion, the applied voltage is 0.5V. max A conversion rate of / ms or greater is increased from the initial low voltage to the intermediate voltage.

8. The method of claim 1, wherein, The maximum voltage V max Within the range of 22V to 27V.

9. The method of claim 8, wherein, The maximum voltage V max Within the range of 24V to 25V.

10. The method of claim 1, wherein, The duration of the final contraction waveform portion is in the range of 1.0 microseconds to 2.7 microseconds.

11. The method of claim 1, wherein, During the final contraction waveform portion, the applied voltage is 0.5V. max A conversion rate of / ms or greater is increased from the intermediate voltage to the maximum voltage V. max .

12. The method of claim 11, wherein, The conversion rate is 1.5V. max / ms or greater.

13. The method of claim 1, wherein, The final low voltage does not exceed the maximum voltage V. max 27%.

14. The method of claim 1, wherein, During the expansion waveform portion, the applied voltage is 0.5V. max A conversion rate of / ms or greater from the maximum voltage V max Reduce to the final low voltage.

15. The method of claim 1, wherein, The initial low voltage is less than or equal to the final low voltage.

16. The method of claim 1, wherein, The initial low voltage does not exceed the maximum voltage V. max 10%.

17. The method of claim 1, further comprising the following steps: At the non-jetting pixel, a non-jetting drive signal is applied to the piezoelectric actuator, the non-jetting drive signal including a non-jetting waveform and the static waveform.

18. The method of claim 17, wherein, Non-jet waveforms include voltage pulses with a duration of 6 microseconds or less.

19. The method of claim 1, wherein, The metal nanoparticle composition comprises silver nanoparticles and a glycol ether solvent having a boiling point in the range of 200°C to 240°C, a viscosity in the range of 4 cP to 8 cP at 25°C, and a vapor pressure not exceeding 0.1 mm Hg at 25°C. The concentration of silver in the metal nanoparticle composition is in the range of 20 wt% to 40 wt%, and polyvinylpyrrolidone is present on the surface of the silver nanoparticles.

20. The method of claim 19, wherein, The glycol ether solvent is 2-(2-butoxyethoxy)ethanol.

21. The method of claim 19, wherein, The silver nanoparticles have an average particle size in the range of 20 nm to 80 nm.

22. The method of claim 21, wherein, The silver nanoparticles have an average particle size in the range of 35 nm to 50 nm.

23. The method of claim 19, wherein, The silver nanoparticles are approximately spherical.

24. The method of claim 19, wherein, The viscosity of the metal nanoparticle composition is in the range of 26 cP to 60 cP, and it withstands a 100-second reaction time at 25°C. -1 Measured at the shear rate.

25. The method of claim 19, wherein, The surface tension of the metal nanoparticle composition is in the range of 28 mN / m to 32 mN / m and is measured at 25°C.

26. The method of claim 19, wherein, The total concentration of water, methanol, ethanol, 1-propanol and 2-propanol in the metal nanoparticle composition does not exceed 10.0 wt%.

27. The method of claim 19, wherein, The total concentration of solvents other than the glycol ether solvent in the metal nanoparticle composition does not exceed 10.0 wt%.

28. The method of claim 19, wherein, The concentration of silver in the metal nanoparticle composition is in the range of 32 wt% to 39 wt%.

29. The method of claim 1, wherein the ink used in the inkjet printing is a metal nanoparticle composition comprising: Silver nanoparticles; and The glycol ether solvent has a boiling point in the range of 200°C to 240°C, a viscosity in the range of 4 cP to 8 cP at 25°C, and a vapor pressure not exceeding 0.1 mm Hg at 25°C. The concentration of silver in the metal nanoparticle composition is in the range of 20 wt% to 40 wt%; and Polyvinylpyrrolidone is present on the surface of the silver nanoparticles.

30. The method of claim 29, wherein, The glycol ether solvent is 2-(2-butoxyethoxy)ethanol.

31. The method of claim 29, wherein, The silver nanoparticles have an average particle size in the range of 20 nm to 80 nm.

32. The method of claim 31, wherein, The silver nanoparticles have an average particle size in the range of 35 nm to 50 nm.

33. The method of claim 29, wherein, The silver nanoparticles are approximately spherical.

34. The method of claim 29, wherein, The viscosity of the metal nanoparticle composition is in the range of 26 cP to 60 cP, and it withstands a 100-second reaction time at 25°C. -1 Measured at the shear rate.

35. The method of claim 29, wherein, The surface tension of the metal nanoparticle composition is in the range of 28 mN / m to 32 mN / m and is measured at 25°C.

36. The method of claim 29, wherein, The total concentration of water, methanol, ethanol, 1-propanol and 2-propanol in the metal nanoparticle composition does not exceed 10.0 wt%.

37. The method of claim 29, wherein, The total concentration of solvents other than the glycol ether solvent in the metal nanoparticle composition does not exceed 10.0 wt%.

38. The method of claim 29, wherein, The concentration of silver in the metal nanoparticle composition is in the range of 32 wt% to 39 wt%.

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