Silver molecular ink with low viscosity and low processing temperature

This application relates to inks, particularly low viscosity printable molecular inks that have high silver loadings and can be sintered at relatively low temperatures.

Molecular inks based on silver neodecanoate have been formulated for screen printing. While these inks have good print quality and have shown excellent mechanical and electrical properties, they have at least two limitations.

First, due to their low solubility in solvents or carriers, the silver salts must be significantly diluted to form uniform inks. Low concentrations of silver salts result in thin silver deposits when printed. The resulting inks also have relatively high viscosities, greater than those required for many printing technologies (aerosol jet, inkjet printing, flexogravure printing). To print thick traces of silver neodecanoate ink, multiple layers are printed (inkjet or aerosol jet). If the printing technology requires a low viscosity ink, the silver neodecanoate ink must be diluted to reduce the ink's relative silver content, which in turn results in a very thin deposit. Additionally, printing multiple layers can be time consuming and degrade print quality.

Second, these inks require processing temperatures of about 220-240°C, so when seeking the highest conductivity, thermal sintering is generally only compatible with expensive substrates such as Kapton. . Silver neodecanoate ink traces can be sintered at lower temperatures, but only if longer processing times are used.

Accordingly, there is a need for silver salt ink formulations, particularly silver neodecanoate formulations, that allow higher silver salt loadings and/or allow the silver to be sintered at lower temperatures.

Molecular silver inks have been formulated that increase the dispersibility (eg, solubility) of silver salts in the ink, thereby increasing the loading of silver in the ink. The formulated ink can have a lower viscosity than existing silver inks without sacrificing silver content. Silver inks may also require lower processing temperatures than existing silver inks.

In one embodiment, a silver carboxylate, an organic amine, and said polymeric binder comprising a polyester, polyimide, polyetherimide or any mixture thereof having functional groups that render the polymeric binder compatible with said organic amine. A molecular ink is provided comprising:

In another aspect, a method of producing a conductive silver trace on a substrate, comprising the steps of depositing a molecular ink on the substrate to form a non-conductive trace of the ink on the substrate; and sintering said non-conductive traces of ink to form conductive silver traces.

In another aspect, a substrate is provided comprising conductive silver traces manufactured by the method as described above.

In another aspect, an electronic device is provided comprising a substrate having conductive silver traces manufactured by the method as described above.

Additional features will be described or will become apparent during the course of the detailed description below. Each feature described herein may be utilized in any combination with one or more of the other features described, each feature being used separately from another feature, except where it is obvious to one skilled in the art. It should be understood that it does not necessarily depend on the presence of

For a clearer understanding, preferred embodiments will be described in detail by way of example with reference to the accompanying drawings.

<figref num="1A">FIG. 1A shows a graph of viscosity (cP) of various inks as a function of silver neodecanoate (AgND) weight fraction (wt/wt) plotted on a linear scale (FIG. 1A).</figref><figref num="1B">FIG. 1B shows a graph of viscosity (cP) of various inks as a function of silver neodecanoate (AgND) weight fraction (wt/wt) plotted on a semi-logarithmic scale (FIG. 1B). The black dashed horizontal line at 500 cP viscosity in FIG. 1B indicates that inks I1, I2 and I3 have higher AgND loadings at 500 cP than inks C1 and C2.</figref><figref num="2">Sintering temperature (°C) for silver neodecanoate (AgND) inks of the present invention (Ink I1, Ink I2 and Ink I3) compared to other AgND inks with different formulations (Ink C1 and Ink C2). FIG. 4 is a graph of nominal 20 mil line sheet resistivity (mΩ/square/mil) as a function of inks sintered for 45 minutes.</figref><figref num="3">of the nominal 20 mil line as a function of AgND weight fraction (wt/wt) after heating traces of various inks (Ink I1, Ink I2, Ink I3, Ink C1 and Ink C2) to 200°C for 45 minutes. Cross-sectional area (mm²) is a graph of FIG.</figref>

Silver carboxylates contain silver ions and organic groups containing carboxylic acid moieties. The carboxylate preferably contains 1-20 carbon atoms, more preferably 6-15 carbon atoms, even more preferably 8-12 carbon atoms, such as 10 carbon atoms. The carboxylate is preferably an alkanoate. The silver carboxylate is preferably a silver salt of alkanoic acid. Some non-limiting examples of preferred silver carboxylates are silver ethylhexanoate, silver neodecanoate, silver benzoate, silver phenylacetate, silver isobutylacetate, silver benzoylacetate, silver oxalate, silver pivalate and their any mixture. Silver neodecanoate is particularly preferred. One or more silver carboxylates may be present in the ink. Silver carboxylate is preferably dispersed in the ink. Preferably, the ink does not contain flakes or particles of other metallic silver materials.

The silver carboxylate is preferably present in the ink in an amount that provides a silver loading of about 23% or more by weight in the ink, based on the total weight of the ink. More preferably, the silver carboxylate provides a silver loading of about 23.5 wt% or more, or about 25 wt% or more, or about 26.5 wt% or more, or about 27 wt% or more. When the silver carboxylate is silver neodecanoate, the silver neodecanoate is preferably about 61 wt% or more, or about 65 wt% or more, or about 68 wt% or more, or about 70 wt%, based on the total weight of the ink. % or more in the ink.

Organic amines are preferably alkylamines, hydroxyalkylamines or cyclic amines. The organic amine preferably contains 2-12 carbon atoms, more preferably 2-8 carbon atoms. Some non-limiting examples of alkylamines are 2-ethyl-1-hexylamine, 1-octylamine, 1-hexylamine, and the like. Some non-limiting examples of hydroxyalkylamines are 1,2-ethanolamine, 1-aminoisopropanol (amino-2-propanol), 1,3-propanolamine, 1,4-butanolamine, and the like. Some non-limiting examples of cyclic amines are pyridine, pyrimidine, pyrrole, pyrrolidine, oxazoline, piperidine, isoxazole, morpholine, and the like. One or more organic amines may be present in the ink.

The organic amine is present in any suitable amount, preferably in an amount of about 5 wt% or more, more preferably about 8 wt% or more, and preferably about 50 wt% or less, more preferably about 25 wt% or less, and More preferably, it may be present in the ink in an amount of up to about 20% by weight, all weights being based on the total weight of the ink. Exemplary preferred ranges are from about 5% to about 50%, or from about 10% to about 50%, or from about 5% to about 25% by weight.

The polymeric binder may comprise polyesters, polyimides, polyetherimides or any mixture thereof with functional groups that render the polymeric binder compatible with organic amines. Therefore, mixtures of organic amines in polymeric binders do not result in significant phase separation. The polymeric binder may be dispersible, eg soluble, in organic amines. The functional groups that render the polymeric binder compatible with organic amines are preferably one or more of polar groups, such as hydroxyl groups, carboxyl groups, amino groups and sulfonyl groups, which are capable of participating in hydrogen bonding. be. Preferably, the polymeric binder contains terminal hydroxyl groups and/or carboxyl groups. The polymeric binder preferably comprises a polyester having functional groups that render the polyester compatible with organic amines. More preferably, the polymeric binder comprises hydroxyl-terminated and/or carboxyl-terminated polyesters.

Other types of polymeric binders may be used. Such other types of polymeric binders may be homopolymers or copolymers. Such other types of polymeric binders may be thermoplastics or elastomers. Some examples of other polymeric binders include, for example, thermoplastic polyurethanes and silicone elastomers.

The polymeric binder may be present in the ink in any suitable amount, preferably within the range of about 0.1% to about 10% by weight based on the total weight of the ink. More preferably, the amount is about 0.5 wt% to about 10 wt%, or about 0.1 wt% to about 5 wt%, about 0.5 wt% to about 3 wt%, or about 1 wt% to about 2 wt%. Within range.

In a particularly preferred embodiment, the molecular ink contains about 61% or more by weight silver neodecanoate; about 5% to about 50% by weight amino-2-propanol, 2-ethyl-1-hexylamine, or 2-ethyl-2. - Oxazoline; containing from about 0.5% to about 3% by weight of hydroxyl-terminated and/or carboxyl-terminated polyester, all weights based on the total weight of the ink.

The molecular ink may optionally contain a solvent. The solvent is preferably compatible with one or both of the organic amine or polymeric binder. The solvent is preferably compatible with both the organic amine and the polymeric binder. The organic amine and/or polymeric binder is preferably dispersible, eg soluble, in the solvent. The solvent is preferably an organic solvent, more preferably a non-aromatic organic solvent. Non-aromatic organic solvents are, for example, glycol ethers (e.g. dipropylene glycol methyl ether), alcohols (e.g. methylcyclohexanol, octanol, heptanol), carbitols (e.g. 2-(2-ethoxyethoxy)ethanol) or any of them. including mixtures of alcohol is preferred, preferably C₁-C₁₀alkanol, more preferably C₆-C₈Alkanols such as octanol. Solvents, if used, may be present in the ink in any suitable amount, preferably within the range of about 1% to about 50% by weight based on the total weight of the ink. More preferably, the amount is from about 2 wt% to about 50 wt%, or from about 5 wt% to about 50 wt%, or from about 5 wt% to about 40 wt%, or from about 5 wt% to about 20 wt%. is within the range of If present, solvent generally makes up the remainder of the ink.

The ink can have a viscosity within the range of about 1 cP to about 50,000 cP. For example, the viscosity of the ink may be within the range of about 1 cP to about 15,000 cP.

The relative amounts of each component in the ink play an important role in tailoring the dispersibility (e.g., solubility) of the silver carboxylate in the ink while providing lower viscosity and lower processing temperatures than existing silver neodecanoate inks. can be fulfilled. Preferred embodiments of the amounts of each component in the ink result in inks with improved processing temperatures, particularly at lower viscosities and higher silver loadings.

The ink can be deposited on the substrate by any suitable method for forming non-conductive traces of ink on the substrate. The inks are particularly suitable for printing, such as screen printing, inkjet printing, flexographic printing (eg stamping), gravure printing, offset printing, airbrushing, aerosol printing, typesetting, plotting or any other method. Inks can be uniquely optimized for a variety of different printing technologies.

After deposition on the substrate, the conductive traces are formed by drying and decomposing the silver carboxylate in the non-conductive traces. Drying and decomposition can be accomplished by any suitable technique, the technique and conditions being guided by the type of substrate on which the traces are deposited and the type of silver carboxylate in the ink. For example, drying of the ink and decomposition of the silver carboxylate can be achieved by heating and/or photonic sintering.

In one technique, the traces are dried and sintered by heating the substrate to form the conductive traces. Sintering decomposes the silver carboxylate to form conductive particles (eg, nanoparticles) of silver. Advantageously, heating can be performed in a relatively low temperature range of less than about 185°C, especially about 150-185°C, or about 150-175°C, while producing relatively highly conductive silver traces. . The ability to sinter at lower temperatures is an advantage of the inks, but heating may be performed at higher temperatures if desired, such as temperatures above about 185°C or up to about 250°C.

Heating is preferably carried out for about 3 hours or less, more preferably about 2 hours or less, for example, about 1 to 180 minutes, or about 2 to 120 minutes. The heating is for a temperature and time balance sufficient to sinter the traces on the substrate to form conductive traces. The type of heating equipment also affects the temperature and time required for sintering. Sintering can be performed with the substrate under an oxidizing atmosphere (eg air) or an inert atmosphere (eg nitrogen and/or argon gas).

In another technology, photonic sintering systems can feature high intensity lamps (eg, pulsed xenon lamps) that deliver broadband spectrum light. Ramp is about 5~20J/cm to the trace²of energy can be delivered. The pulse width is preferably within the range of about 0.58-1.5 ms. The driving voltage is preferably in the range of about 1.6-2.8 kV. Photonic sintering can be performed under ambient conditions (eg, in air). Photonic sintering is particularly suitable for polyethylene terephthalate and polyimide substrates. lower energy (e.g. 10J/cm²) enhances ink compatibility on low temperature substrates such as polyethylene terephthalate and polyethylene naphthalate, and for amine-containing silver neodecanoate-based inks as described herein, substrate damage (e.g. melting and/or warping).

The conductive traces formed by drying and sintering the ink on the substrate can be of any desired thickness and width. Advantageously, the ink can be dried and sintered to form relatively thin and/or narrow conductive traces while maintaining relatively high electrical conductivity (ie, relatively low resistivity). Additionally, the sintered traces formed from the ink may be flexible and able to pass the ASTM F1683-02 flex and crease test without open circuit interruption (ie, no open circuit failure). Manufacturing applications require the lowest possible resistance change. Open circuit interruption is defined as total loss of conductivity (ie infinite resistivity).

The substrate may be any suitable surface, especially a printable surface. Printable surfaces include, among others, polyethylene terephthalate (PET) (eg Melinex), polyethylene naphthalate (PEN), polyolefins (eg silica-filled polyolefins (Teslin), polydimethylsiloxane (PDMS), polystyrene , acrylonitrile/butadiene/styrene, polycarbonates, polyimides (e.g. Kapton), thermoplastic polyurethanes (TPU), silicone membranes, wool, silk, cotton, flax, jute, modal, bamboo, nylon, polyester, acrylic, aramid, It may include spandex, polylactide, paper, glass, coated glass (eg, ITO coated glass), metals, dielectric coatings.

Conductive traces deposited on substrates can be used in electronic devices such as electrical circuits, conductive busbars (e.g. for solar cells), sensors (e.g. touch sensors, wearable sensors), antennas (e.g. RFID antennas), thin film transistors, diodes, smart For packaging (e.g. smart drug packaging), conformable inserts in equipment and/or vehicles, and multilayer circuits and MIM devices including low-pass filters, frequency selective surfaces, transistors and antennas on conformable surfaces that can withstand high temperatures. can be incorporated. Inks enable miniaturization of such electronic devices.

<p>Example 1 Silver Neodecanoate Inks A series of silver neodecanoate (AgND) based inks were formulated as described in Table 1. Inks I1, I2 and I3 are formulated according to the present invention, and Inks C1 and C2 are comparative samples of other formulations of AgND-based inks. Inks have different types of carriers that affect the decomposition temperature of the ink. Each ink has different components that make up the maximum weight fraction of the carrier: octanol (ink I1 and ink C2), alkylamine (ink I2), oxazoline (ink I3) and terpene alcohol (ink C1).</p><p><tables><img file="JP7242557B2_D0001.tif" /></tables></p><p>An ink containing 1-amino-2-propanol (hydroxyamine), 2-ethyl-1-hexylamine (alkylamine) and 2-ethyl-2-oxazoline (oxazoline) was first treated with silver neodecanoate in octanol. Prepared by preparing a concentrated suspension. 1-Amino-2-propanol, 2-ethyl-1-hexylamine or 2-ethyl-2-oxazoline was then slowly incorporated into the suspension using a mortar and pestle to form a clear, homogeneous and viscous solution. Mix until done. Other inks were prepared by combining all ingredients and mixing in a plenary mixer until the solution was uniform. One of two polymeric binders, Rokrapol 7075 (polyester) or ethyl cellulose 46 cP, was added to the ink.</p><p>Ink viscosity was determined as a function of AgND loading. For these tests, the silver neodecanoate component of the ink was diluted with the respective carrier and amine in the same proportions as for the formulations in Table 1. The viscosity of these inks was measured using a Brookfield RV-DV-III Ultrarheometer with a UL adapter at 20.5°C.</p><p>The four inks were applied onto an 8.5 x 11 inch sheet of Kapton HPP-ST using a screen with a mesh count of 400 (stainless steel screen with 19 µm thread diameter and 45 µm mesh openings). screen printed. The screen contained lines 10 cm long and 2-20 mils wide. The printed traces were thermally sintered in air at reflow temperatures (T) varying from 151 °C to 229 °C using the heating program described in Table 2 (the temperatures in Table 2 are the temperature of the furnace). corresponding to the target temperature). The temperatures used to obtain the resistivity data in Table 3 and Figure 2 are those measured by thermocouples attached to the Kapton substrates.</p><p><tables><img file="JP7242557B2_D0002.tif" /></tables></p><p>The electrical properties of the traces were characterized by measuring the resistance over a 10 cm long trace using an ohmmeter. The width and thickness of the sintered traces were measured using an optical profilometer (Cyber Technologies 3D Surface Profiler). The trace width can be used to determine the square of each 10 cm long trace, which can then be used to calculate the sheet resistance. The cross-sectional area of the trace was calculated by multiplying the measured width and thickness of the trace. The thickness measurements were used to calculate the sheet resistance of the traces. Electrical properties of the sintered traces are provided in FIG.</p><p>As is evident from Table 1, the silver neodecanoate loading for the inventive inks I1, I2, I3, I4 and I5 can be much higher than the silver neodecanoate loading for other AgND-based inks. As shown by the cross-sectional area of the traces in Table 3, higher silver neodecanoate loadings lead to higher silver deposits. Table 3 shows the resistance, line width, line thickness and cross-sectional area of 10 cm long silver traces made from Ink I1, Ink I2, Ink I3, Ink C1 and Ink C2 after heating at 200° C. for 45 minutes. and sheet resistance comparisons. Figure 3 shows the relationship between the silver neodecanoate loading in the ink and the cross-sectional area of the silver traces after sintering at 200°C for 45 minutes.</p><p>Based on Figure 2, inks with low viscosity (suitable for flexographic and plotter-based printing) and maintaining high silver neodecanoate loadings (about 48% to about 67%, depending on the amine) were selected. It is also clear that the ink can be formulated with the addition of additional amines and octanol to produce. Furthermore, it is clear from FIG. 2 that inks I1, I2 and I3 can be sintered at significantly lower temperatures than inks C1 and C2 while providing silver traces with good conductivity. Furthermore, photonic curing of these inks printed on low temperature substrates can be performed at lower energies with significantly less damage to the underlying substrate.</p><p><tables><img file="JP7242557B2_D0003.tif" /></tables></p><p>Three more experiments were performed using ink I3 with different sintering conditions and substrates.</p><p>In the first experiment, ink I3 was screen printed onto Kapton® HPP-ST using the method described above and sintered, except that sintering was at a temperature of 200° C. for 30 minutes instead of 45 minutes. went for a minute. The results are shown in Tables 4A and 4B.</p><p><tables><img file="JP7242557B2_D0004.tif" /></tables></p><p><tables><img file="JP7242557B2_D0005.tif" /></tables></p><p>In a second experiment, ink I3 was screen printed onto Kapton® using the method described above and sintered, except that the sintering was at a temperature of 180°C instead of 200°C for 45 minutes. Went for 30 minutes instead. Results are shown in Tables 5A and 5B. Tables 5A and 5B provide mechanical properties (flexibility by ASTM F1683-02 flex and crease test).</p><p><tables><img file="JP7242557B2_D0006.tif" /></tables></p><p><tables><img file="JP7242557B2_D0007.tif" /></tables></p><p>In a third experiment, ink I3 was screen printed onto Melinex® through a stainless steel screen with a mesh count of 360 counts per inch (SS360) and intense pulsed light (IPL) sintering (340 V/1500 μs). was photonic sintered using , followed by thermal sintering at a temperature of 160 °C for 30 min. Results are shown in Tables 6A and 6B.</p><p><tables><img file="JP7242557B2_D0008.tif" /></tables></p><p><tables><img file="JP7242557B2_D0009.tif" /></tables></p><p>The data in the table for Ink I3 show that the combination of 1-octanol and 2-ethyl-oxazoline allows the production of highly conductive traces (volume resistivity values of about 10 μΩ cm for most line widths). suggesting. This performance is believed to be due to the ability to convert the traces to conductive silver using less energy than ink C1, for example. The mechanical properties of the traces obtained from Ink 13 are also excellent, with no more than 3% increase in resistance after bending and crease testing (ASTM 1683-02) (Tables 5A and 5B).</p><p>Using a stainless steel screen with a mesh count of 360 counts per inch (SS360) and an emulsion thickness of approximately 710 µm, screen-print the ink I4 onto a glass substrate with an RMS roughness of 0.06 µm at 200 °C. and sintered for 30 minutes. The screen printed pattern had a 4B crosshatch. Table 7 shows the results.</p><p><tables><img file="JP7242557B2_D0010.tif" /></tables></p><p>The data suggest that the combination of polymeric binder and ink components adheres the silver traces very well (4B) to the glass substrate while remaining very smooth (RMS surface roughness ~0.06 µm). ing.</p><p>Ink I5 was screen printed onto Melinex® through a high resolution screen containing woven tungsten wire with a wire diameter of 13 μm, which had a mesh count of 430 counts/inch. The screen-printed ink was dried for 5 min, followed by heat sintering at 165 °C for 30 min. Table 8 shows the results. As seen in Table 8, traces with measured line widths of less than 50 μm can be readily fabricated with volume resistivities between 10 and 20 μΩ·cm. This suggests that the ink can be used for transparent conductive electrode (TCE) applications.</p><p><tables><img file="JP7242557B2_D0011.tif" /></tables></p><p>Novel features will become apparent to those of ordinary skill in the art upon review of the description. It is to be understood, however, that the claims should not be limited by the embodiments, but are to be accorded the broadest interpretation consistent with the language of the claims and the specification as a whole.</p>