IMPROVED CONDUCTIVE INK COMPOSITIONS
Cross-reference to Related Application
[0001] This application claims the benefit of U.S. Application No. 63/622,489, filed on January 18, 2024, the disclosure of which is incorporated herein by reference in its entirety.
Field of the Invention
[0002] The present disclosure relates generally to novel conductive ink compositions and their methods of preparation and use. More particularly, the present disclosure relates to improved particle-free ink compositions comprising silver carboxylates that form conductive structures at low temperature.
Background of the Invention
[0003] The electronics, display, and energy industries rely on the production and use of coatings and patterns of conductive materials to form circuits on organic and inorganic substrates. Printed electronics offer an attractive alternative to conventional technologies by enabling the creation of large-area, flexible devices at low cost. There is a great need for high-conductivity materials with fine-scale features in modem electronics such as solar cell electrodes, flexible displays, radio frequency identification tags, antennas, and many more. In efforts to make these high-technology devices increasingly affordable, the substrates used typically have relatively little temperature resilience and require low processing temperatures to maintain integrity.
[0004] The vast majority of commercially produced conductive inks are specifically designed for inkjet, screen-printing, or roll-to-roll processing methods in order to process large areas with fine-scale features in short time periods. These inks have disparate viscosities and synthesis parameters. Particle-based inks are based on conductive metal particles, which are typically synthesized separately and then incorporated into an ink formulation. The resulting ink is then tuned for specific particle process.
[0005] Typically, precursor-based inks are based on thermally unstable precursor complexes that undergo reduction to a conductive metal upon heating. Prior particle- and precursor-based methods generally rely on high temperatures to form conductive coatings and thus may not be compatible with substrates that require low processing temperatures to maintain integrity. For example, silver compounds with carbamate or other relatively low molecular weight ligands (compared to polymer stabilizers) have been synthesized that decompose at temperatures near 150 °C, yielding electrical conductivities approaching that of bulk silver. Unfortunately, even these temperatures can render the ink incompatible with many plastic and paper substrates commonly used in flexible electronic and biomedical devices.
[0006] International Publication No. WO2015/160938 provides conductive ink compositions, methods of production and use, and conductive structures prepared using the ink compositions. Among the ink compositions are examples comprising a silver carboxylate, at least one dissolving agent, and a catalyst that decarboxylates the silver carboxylate to form a conductive structure. The decarboxylation reaction can occur at low temperatures.
[0007] European Patent No. EP 3597707 Bl provides conductive ink compositions for inkjet or screen printing processes. The conductive ink compositions comprise a silver carboxylate, a terpene, and at least one carboxylic acid as a further component. The ink compositions can be used in methods for producing a pattern on a substrate.
[0008] International Publication Nos. WO2015/192248 Al and WO2018/146617 Al provide conductive ink compositions containing a silver carboxylate, a solvent, and a polymer binder.
[0009] International Publication No. WO2023/168452 A2 provides conductive ink compositions, methods of production and use, and conductive structures prepared using the ink compositions. Among the ink compositions are examples comprising a silver decanoate and at least one dissolving agent, wherein the at least one dissolving agent comprises a terpene, a terpenoid, or a combination thereof. Some of the ink compositions comprise an adhesion promoter, and some of the ink compositions comprise an acid stabilizer.
[0010] Despite these and other advances in the field, there continues to be a need for particle-free conductive ink compositions with improved properties. Therefore, it is an object of the present invention to provide improved, stable, particle-free conductive ink compositions and methods for their preparation and use, in particular compositions that can form conductive structures at low temperatures and ideally without catalysts. It is also an object of the present invention to provide improved, stable, particle-free conductive ink compositions and methods for their preparation and use, wherein the compositions have considerable adhesion to a variety of substrates for a variety of purposes. Such purposes can include those involving epoxy molding compound (EMC), solder resist functionality, silver nanowire substrates (SNW), and so forth, with both thin and thick inkjet printing layers. Such conductive inks can be used on a variety of substrates to form conductive structures with superior physical, mechanical, and electrical properties. of the Invention
[0011] The instant disclosure addresses these and other considerations by providing the following:
[0012] In some aspects, the techniques described herein relate to a conductive ink composition including: a silver decanoate; a cyclic azasilane adhesion promoter; and at least one dissolving agent.
[0013] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the cyclic azasilane adhesion promoter is a compound of formula wherein each Ri is independently hydrogen, C -Cs alkyl, or
Ci-Cs alkoxy; R2 is hydrogen or an optionally substituted Ci-Cs alkyl or alkylene; and R3 is each independently hydrogen, Ci-Cs alkyl, or Ci-Cs alkoxy.
[0014] In some aspects, the techniques described herein relate to a conductive ink composition, wherein each Ri is independently hydrogen or C1-C3 alkyl, R2 is hydrogen or C1-C3 alkyl, and each R3 is independently hydrogen or C1-C3 alkyl. [0015] In some aspects, the techniques described herein relate to a conductive ink composition, wherein each Ri, R2, and R3 is independently hydrogen or methyl.
[0016] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the compound of formula (I) is:
[0017] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the silver decanoate includes at least one a-branched silver decanoate isomer.
[0018] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the silver decanoate includes a plurality of a-branched silver decanoate isomers.
[0019] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the silver decanoate is a compound of formula (IIB): wherein Ri' and R2' is each independently an alkyl group, wherein R3’ is either hydrogen or an alkyl group, and wherein Ri', R2', and R3’ together include eight total carbon atoms.
[0020] In some aspects, the techniques described herein relate to a conductive ink composition, wherein Ri' and R2' is each independently methyl or ethyl.
[0021] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the silver decanoate includes silver 2,2-dimethyloctanoate, silver 2,2,3,5-tetramethylhexanoate, silver 2,4-dimethyl-2-isopropylpentanoate, silver 2,5- dimethyl-2-ethylhexanoate, silver 2,2-diethylhexanoate, silver 2-butylhexanoate, or a combination thereof.
[0022] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the at least one dissolving agent includes a terpene, a terpenoid, or a [0023] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the terpene is a purified terpene or the terpenoid is a purified terpenoid.
[0024] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the terpene is a pinene or a limonene.
[0025] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the terpenoid is a terpineol.
[0026] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the at least one dissolving agent includes a limonene and a terpineol. [0027] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the limonene is a purified limonene and the terpineol is a purified terpineol.
[0028] In some aspects, the techniques described herein relate to a conductive ink composition, further including an acid stabilizer or a non-acid stabilizer.
[0029] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the acid stabilizer is a Ce-i2 a-branched alkanoic acid.
[0030] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the acid stabilizer is an a-branched decanoic acid isomer.
[0031] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the acid stabilizer is 2,2-dimethylhexanoic acid or 2,2- dimethylnonanoic acid.
[0032] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the non-acid stabilizer is a |3-diketone stabilizer.
[0033] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the non-acid stabilizer is a compound of formula (III): wherein each R4 group is independently a Ci-Ce straight-chain or branched-chain alkyl group, optionally substituted with an aryl group, or is an aryl group, and wherein each R5 group is independently -H, a Ci-Ce straight-chain or branched- chain alkyl group, optionally substituted with an aryl group, or wherein two R5 groups, taken together, form a double bond that is optionally substituted with a Ci-Ce straight- chain or branched-chain alkyl group, optionally further substituted with an aryl group, or is optionally substituted with an aryl group.
[0034] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the non-acid stabilizer is 2, 2, 6, 6 tetramethyl 3,5-heptanedione. [0035] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the silver decanoate includes at least one a-branched silver decanoate isomer, the at least one dissolving agent includes a limonene and a terpineol, and the cyclic azasilane adhesion promoter is N-methyl-aza-2,2,4- trimethylsilacyclopentane.
[0036] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the conductive ink composition is particle free.
[0037] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the conductive ink composition has a concentration of about 1 to about 50 weight percent silver decanoate.
[0038] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the conductive ink composition has a viscosity from about 5 centipoise to about 50 centipoise.
[0039] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the conductive ink composition has a viscosity from about 50 centipoise to about 1000 centipoise.
[0040] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the silver decanoate is decarboxylated at a temperature of 250 °C or less to form a conductive structure.
[0041] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the conductive structure has a sheet resistance of no more than 5 ohms per square, no more than 2 ohms per square, no more than 1 ohm per square, or no more than 0.5 ohms per square.
[0042] In some aspects, the techniques described herein relate to a conductive ink composition, wherein the conductive structure has a bulk silver content of at least 1%. [0043] In some aspects, the techniques described herein relate to a method of making a conductive ink composition, including: dissolving a silver decanoate and a cyclic azasilane adhesion promoter in at least one dissolving agent to form a conductive ink composition. [0044] In some aspects, the techniques described herein relate to a method, wherein the cyclic azasilane adhesion promoter is a compound of formula wherein each Ri is independently hydrogen, Ci-Cs alkyl, or Ci-Cs alkoxy; R2 is hydrogen or an optionally substituted Ci-Cs alkyl or alkylene; and R3 is each independently hydrogen, Ci-Cs alkyl, or Ci-Cs alkoxy.
[0045] In some aspects, the techniques described herein relate to a method, wherein each
Ri is independently hydrogen or C1-C3 alkyl, R2 is hydrogen or C1-C3 alkyl, and each R3 is independently hydrogen or C1-C3 alkyl.
[0046] In some aspects, the techniques described herein relate to a method, wherein each
Ri , R2, and R3 is independently hydrogen or methyl.
[0047] In some aspects, the techniques described herein relate to a method, wherein the compound of formula (I) is:
[0048] In some aspects, the techniques described herein relate to a method, wherein the silver decanoate includes at least one a-branched silver decanoate isomer.
[0049] In some aspects, the techniques described herein relate to a method, wherein the silver decanoate includes a plurality of a-branched silver decanoate isomers.
[0050] In some aspects, the techniques described herein relate to a method, wherein the silver decanoate is a compound of formula wherein R and R2' is each independently an alkyl group, wherein R3' is either hydrogen or an alkyl group, and wherein Ri', R2’, and R3' together include eight total carbon atoms.
[0051] In some aspects, the techniques described herein relate to a method, wherein R and R2' is each independently methyl or ethyl. [0052] In some aspects, the techniques described herein relate to a method, wherein the silver decanoate includes silver 2,2-dimethyloctanoate, silver 2, 2,3,5- tetramethylhexanoate, silver 2,4-dimethyl-2-isopropylpentanoate, silver 2,5-dimethyl-2- ethylhexanoate, silver 2,2-diethylhexanoate, silver 2-butylhexanoate, or a combination thereof.
[0053] In some aspects, the techniques described herein relate to a method, wherein the at least one dissolving agent includes a terpene, a terpenoid; or a combination thereof.
[0054] In some aspects, the techniques described herein relate to a method, wherein the terpene is a purified terpene or the terpenoid is a purified terpenoid.
[0055] In some aspects, the techniques described herein relate to a method, wherein the terpene is a pinene or a limonene.
[0056] In some aspects, the techniques described herein relate to a method, wherein the terpenoid is a terpineol.
[0057] In some aspects, the techniques described herein relate to a method, wherein the at least one dissolving agent includes a limonene and a terpineol.
[0058] In some aspects, the techniques described herein relate to a method, wherein the limonene is a purified limonene and the terpineol is a purified terpineol.
[0059] In some aspects, the techniques described herein relate to a method, including the further step of dissolving an acid stabilizer or a non-acid stabilizer in the at least one dissolving agent.
[0060] In some aspects, the techniques described herein relate to a method, wherein the acid stabilizer is a Ce-12 a-branched alkanoic acid.
[0061] In some aspects, the techniques described herein relate to a method, wherein the acid stabilizer is an a-branched decanoic acid isomer.
[0062] In some aspects, the techniques described herein relate to a method, wherein the acid stabilizer is 2,2-dimethylhexanoic acid or 2,2-dimethylnonanoic acid.
[0063] In some aspects, the techniques described herein relate to a method, wherein the non-acid stabilizer is a 0-diketone stabilizer.
[0064] In some aspects, the techniques described herein relate to a method, wherein the non-acid stabilizer is a compound of formula ( wherein each R4 group is independently a Ci-Ce straight-chain or branched-chain alkyl group, optionally substituted with an aryl group, or is an aryl group, and wherein each R5 group is independently -H, a Ci-Cr, straight-chain or branched-chain alkyl group, optionally substituted with an aryl group, or wherein two R5 groups, taken together, form a double bond that is optionally substituted with a Ci-G, straight-chain or branched-chain alkyl group, optionally further substituted with an aryl group, or is optionally substituted with an aryl group.
[0065] In some aspects, the techniques described herein relate to a method, wherein the non-acid stabilizer is 2, 2, 6, 6 tetramethyl 3, 5 -heptanedione.
[0066] In some aspects, the techniques described herein relate to a method, wherein the silver decanoate includes at least one a-branched silver decanoate isomer and the at least one dissolving agent includes a limonene and a terpineol, and the cyclic azasilane adhesion promoter is N-methyl-aza-2,2,4-trimethylsilacyclopentane.
[0067] In some aspects, the techniques described herein relate to a method, including the further step of dissolving an acid stabilizer or a non-acid stabilizer in the at least one dissolving agent.
[0068] In some aspects, the techniques described herein relate to a method, wherein the conductive ink composition has a concentration of about 1 to about 50 weight percent silver decanoate.
[0069] In some aspects, the techniques described herein relate to a method, wherein the conductive ink composition has a viscosity from about 5 centipoise to about 50 centipoise. [0070] In some aspects, the techniques described herein relate to a method, wherein the conductive ink composition has a viscosity from about 50 centipoise to about 1000 centipoise.
[0071] In some aspects, the techniques described herein relate to a method, wherein the silver decanoate is decarboxylated at a temperature of 250 °C or less to form a conductive structure.
[0072] In some aspects, the techniques described herein relate to a method, wherein the conductive ink composition is particle-free.
[0073] In some aspects, the techniques described herein relate to a method of forming a conductive structure comprising applying any of the above conductive ink compositions to a substrate; and heating the conductive ink composition on the substrate to a temperature of about 250 °C or less to form the conductive structure.
[0074] In some aspects, the techniques described herein relate to a method, wherein the conductive ink composition is applied by slot die coating, spin coating, roll-to-roll printing, including gravure, flexography, rotary screen printing, screen printing, aerosol jet printing, inkjet printing, airbrushing, Mayer rod coating, flood coating, 3D printing, dispenser, or electrohydrodynamic printing.
[0075] In some aspects, the techniques described herein relate to a method, wherein the conductive structure has a sheet resistance of no more than 5 ohms per square, no more than 2 ohms per square, no more than 1 ohm per square, or no more than 0.5 ohms per square.
[0076] In some aspects, the techniques described herein relate to a method, wherein the conductive structure has a bulk silver content of at least 1%.
Brief Description of the Drawings
[0077] FIG. 1 shows results from printing Formulation 1 on a nightmare epoxy and on a standard EMC substrate.
[0078] FIG. 2 shows reliability testing of Formulation 1 printed on a nightmare epoxy and on a standard EMC substrate.
[0079] FIG. 3 shows results from printing Formulation 2 on a nightmare epoxy and on a standard EMC substrate.
[0080] FIG. 4 compares reliability testing with Formulation 1 and Formulation 2 printed on a nightmare epoxy and on a standard EMC substrate.
[0081] FIGs. 5A and 5B provide images of an inkjet printer nozzle plate in the process of printing fresh preparations of two ink formulations of the disclosure at day 0.
[0082] FIG. 6 shows the stability of Formulation 1 over time at elevated temperatures.
Detailed Description of the Invention
[0083] Ink compositions derived from silver metal precursors have been described in PCT International Publication No. WO2013/096664A1, which is incorporated herein by reference in its entirety. Further conductive ink compositions are described, for example, in PCT International Publication No. WO2015/160938A1, which is also incorporated herein by reference in its entirety. Although these ink compositions are advantageously free of metallic particles, they typically require a catalyst, for example an amine- containing catalyst, to facilitate decarboxylation of the silver complexes, and thus formation of the conductive metallic structures at low temperatures.
[0084] Disclosed herein are improved conductive ink compositions formed by making silver complexes that do not require high decomposition temperatures. The disclosed conductive ink compositions advantageously comprise a silver decanoate comprising at least one a-branched silver decanoate isomer. In preferred embodiments, the improved conductive ink compositions do not require a catalyst to decarboxylate the silver complex. By employing lower decomposition temperatures and reduced tack times to form the conductive structures, the improved conductive ink compositions are compatible with more substrates that do not require high processing temperatures to maintain integrity. Furthermore, the methods for making the conductive ink compositions are both simple and result in a high yield of conductive structures.
[0085] The conductive ink compositions may possess low viscosity so that they are compatible with a broad range of patterning techniques, including slot die coating, spin coating, roll-to-roll printing, including gravure, flexography, rotary screen printing, screen-printing, aerosol jet printing, inkjet printing, airbrushing, Mayer rod coating, flood coating, 3D printing, and electrohydrodynamic printing. In particular, the inks are compatible with inkjet printing, dip coating, and spray coating. The patterned features may be highly conductive at room temperature and achieve bulk conductivity upon decomposing at mild temperatures (e.g., in some cases at less than about 100 °C). Finally, the ink compositions may remain stable at room temperature for months without particle precipitation.
[0086] Accordingly, conductive ink compositions (also referred to as “conductive inks” or “inks”) have been created for printing highly conductive features at low temperatures. Such inks may be stable, particle-free, and suitable for a wide range of patterning techniques. In some embodiments, a “particle-free” ink is one that does not include any particles at a diameter of greater than about 10 nm. In some embodiments, a “particle- free” ink is one that has less than about 1 % particles, preferably less than about 0.1% particles. Silver salts are employed in the inks as a precursor material, which ultimately yields the silver in the conductive silver coatings, lines, or patterns. Any suitable silver precursor may be used. Silver Carboxylates
[0087] The silver carboxylates of the instant conductive ink compositions include silver salts of aliphatic carboxylic acids. In some embodiments, the silver carboxylate includes silver salts of long-chain aliphatic carboxylic acids. In specific embodiments, the silver carboxylate includes silver salts of long chain aliphatic carboxylic acids having 5 to 15 carbon atoms, 8 to 12 carbon-n atoms, or even 9 to 1 1 carbon atoms.
[0088] In preferred embodiments, the silver carboxylate of the instant compositions comprises a particular silver decanoate isomer or mixture of silver decanoate isomers. For example, in some embodiments, at least one decanoic acid isomer used to generate the silver decanoate of the conductive ink composition is a compound of formula (II A): wherein Rf and R2’ is each independently an alkyl group, wherein R3’ is either hydrogen or an alkyl group, and wherein Ri’, R2’, and R3’ together comprise eight total carbon atoms. The silver decanoate formed from the above decanoic acid isomer accordingly has the structure of formula (IIB): wherein the Ri’, R2’, and R3’ groups have the definitions provided above. Such structures will be referred to herein as a-branched silver decanoate isomers.
[0089] In some embodiments, the Rf and R2’ group of the a-branched silver decanoate isomer is each independently methyl or ethyl.
[0090] In specific embodiments, at least one decanoic acid isomer used to generate the silver decanoate of the instant conductive ink composition can, for example, be 2,2- dimethyloctanoic acid, 2,2,3,5-tetramethylhexanoic acid, 2,4-dimethyl-2- isopropylpentanoic acid, 2,5-dimethyl-2-ethylhexanoic acid, 2,2-diethylhexanoic acid, 2- butylhexanoic acid, or any combination of these a-branched decanoic acid isomers. [0091] Corresponding silver carboxylates can be formed from each of these decanoic acid isomers, as described in PCT International Publication No. WO2023/168452 A2, and as would be understood by those of ordinary skill in the art. Specifically, the silver decanoate isomers can accordingly be, for example, an a-branched silver decanoate isomer, such as silver 2, 2-dimethyloctanoate, silver 2,2,3,5-tetramethylhexanoate, silver 2,4-dimethyl-2-isopropylpentanoate, silver 2,5-dimethyl-2-ethylhexanoate, silver 2,2- diethylhexanoate, silver 2-butylhexanoate, or any combination of these compounds.
[0092] The silver carboxylate is preferably not formed from a linear alkanoic acid. For example, the silver carboxylate preferably does not comprise silver n-decanoate.
Adhesion Promoters
[0093] In another aspect are provided conductive ink compositions that further comprise an adhesion promoter to increase adhesion of the ink to the substrate on which it is printed. It is envisioned that any agent that both improves the adhesive properties of the ink and that does not significantly degrade either the fluidic or other physical properties of the ink composition, including stability of the ink composition, or the electrical or other physical properties of conductive structures that are generated using the ink, can be utilized as an adhesion promoter in the instant ink compositions.
[0094] It should be understood that one or more adhesion promoters and one or more acid or non-acid stabilizers can be included in the conductive ink compositions of the instant disclosure, either together, or separately, in any combination.
[0095] The adhesion promoter is preferably chosen in coordination with the choice of substrate on which the ink will be printed.
[0096] In some embodiments, the adhesion promoter is a cyclic azasilane adhesion promoter.
[0097] In more specific embodiments, the adhesion promoter is a compound of formula (I): wherein each Ri is independently hydrogen, Ci-Cs alkyl, or Ci-Cs alkoxy; R2 is hydrogen or an optionally substituted Ci-Cs alkyl or alkylene; and each R3 is independently hydrogen, Ci-Cs alkyl, or Ci-Cs alkoxy.
[0098] In some embodiments, the adhesion promoter is a compound of formula (I), wherein each Ri is independently hydrogen or C1-C3 alkyl, R2 is hydrogen or C1-C3 alkyl, and each R3 is independently hydrogen or C1-C3 alkyl.
[0099] In more specific embodiments, the adhesion promoter is a compound of formula (I), wherein each Ri, R2, and R3 is independently hydrogen or methyl.
[0100] In still more specific embodiments, the adhesion promoter has the structure:
This structure can be alternatively referred to as N-methyl-aza-2,2,4- trimethylsilacyclopentane or 1 ,2,2,4-tetramethyl- 1 ,2-azasilolidine.
[0101] In some embodiments, the adhesion promoter has the structure:
[0102] As mentioned above, the instant conductive ink compositions comprise at least one dissolving agent that is capable of dissolving the disclosed silver carboxylates, preferably fully dissolving the silver carboxylates, to generate a particle-free conductive ink composition. Specifically, the dissolving agent acts as a stabilizer and a solvent but is not intended to act as a reducing agent for the silver carboxylate. In some embodiments, the dissolving agent has a boiling point of about 250 °C or less. In some embodiments, the dissolving agent has a boiling point of about 200 °C or less. In some embodiments, the dissolving agent has a boiling point of about 100 °C or less. In some embodiments, the dissolving agent has a boiling point of about 220 °C or less, about 210 °C or less, about 190 °C or less, about 180 °C or less, about 170 °C or less, about 160 °C or less, about 150 °C or less, of about 140 °C or less, of about 130 °C or less, of about 120 °C or less, of about 1 10 °C or less, of about 90 °C or less, of about 80 °C or less, of about 70 °C or less, of about 60 °C or less, or of about 50 °C or less.
[0103] In some embodiments, the dissolving agent may be selected based on the type of silver carboxylate used to make the ink composition. In some embodiments, the dissolving agent may be selected based on the boiling point/tack time for a specific application. In some embodiments, the dissolving agent may be selected based on the type of substrate the ink composition will be applied to for compatibility and wettability issues. For example, for deposition methods such as inkjet printing or e-jet, greater stability is generally preferred, and thus it may be preferable to use a dissolving agent with a higher boiling point.
[0104] In some embodiments, the dissolving agent comprises an alkane hydrocarbon, a carbamate, an alkene, a cyclic hydrocarbon, an aromatic hydrocarbon, an amine, a polyamine, an amide, an ether, an ester, an alcohol, a thiol, a thioether, a phosphine, or a combination thereof.
[0105] In some embodiments, the dissolving agent comprises an organic solvent. In some embodiments, the dissolving agent comprises one or more linear or branched alkane hydrocarbons of length C5-20. For example, the dissolving agent may comprise a pentane, a hexane, a heptane, an octane, a nonane, a decane, an undecane, a dodecane, a tridecane, a tetradecane, a pentadecane, a hexadecane, an octadecane, a nonadecane, or an icosane. [0106] In some embodiments, the dissolving agent comprises one or more cyclic hydrocarbons of length Cs-io. For example, the dissolving agent may comprise a cyclohexane, a cycloheptane, a cyclooctane, a cyclononane, a cyclodecane, or a decalin. In some embodiments, the dissolving agent comprises an aromatic hydrocarbon. For example, the dissolving agent may comprise benzene, a toluene, a xylene, or a tetralin. In some embodiments, the dissolving agent comprises a xylene.
[0107] In some embodiments, the dissolving agent comprises a linear ether, a branched ether, or a cyclic ether. In some embodiments, the dissolving agent comprises a linear or branched ether. For example, the dissolving agent may comprise dimethyl ether, diethyl ether, dipropyl ether, dibutyl ether, or methyl t-butyl ether. In some embodiments, the dissolving agent comprises one or more cyclic ethers. For example, the dissolving agent can comprise tetrahydrofuran, tetrahydropyran, dihydropyran, or 1 ,4-dioxane. [0108] Tn some embodiments, the dissolving agent comprises an alcohol. In some embodiments, the dissolving agent comprises a primary alcohol, a secondary alcohol, or a tertiary alcohol. In some embodiments, the alcohol comprises a propanol, a butanol, a pentanol, a hexanol, an octanol, or combinations thereof. In some embodiments, the alcohol comprises 1-propanol, 2-propanol, l-methoxy-2-propanol, 1 -butanol, 2-butanol, 1- pentanol, 2-pentanol, 3-pentanol, 1 -hexanol, 2-hexanol, 3-hexanol, 1 -octanol, 2-octanol, 3- octanol, tetrahydrofurfuryl alcohol, cyclopentanol, terpineol, or a combination thereof. [0109] In some embodiments, the dissolving agent comprises a ketone. More specifically, in some embodiments, the dissolving agent comprises actylacetone.
[0110] The dissolving agent used in the instant conductive ink compositions is ideally suitable for use at an industrial scale in mass production. In some embodiments, it can therefore be advantageous for the dissolving agent to be non-toxic and/or to be less damaging to the environment than is the case for many commonly-used organic solvents. In some embodiments, it can be advantageous for the dissolving agent to have a higher flash point than is the case for many commonly-used organic solvents. In some embodiments, it can be advantageous for the dissolving agent to be subject to fewer regulations than is the case for many commonly-used organic solvents. For example, aromatic hydrocarbons such as xylene, toluene, mesitylene, and the like, are highly regulated in most industrial countries. The use of alternatives to these solvents can therefore be advantageous. In addition, conductive inks formulated from aromatic hydrocarbons can have flash points that are lower than 60°C and that are therefore not typically acceptable in mass production environments. Accordingly, in some embodiments, the dissolving agent of the instant conductive ink compositions does not comprise an aromatic hydrocarbon.
[0111] In preferred embodiments, the dissolving agent comprises a terpene, a terpenoid, or a combination thereof. For example, in some embodiments, the dissolving agent comprises a pinene, a limonene, in particular a D-limonene, a terpineol, or a combination thereof. In preferred embodiments, the dissolving agent comprises limonene. In other preferred embodiments, the dissolving agent comprises terpineol. In still other preferred embodiments, the dissolving agent comprises a combination of limonene and terpineol. [0112] Not all terpenes and terpenoids are suitable for use in the conductive ink compositions of the instant disclosure. For example, in some embodiments, the instant dissolving agent does not comprise alpha-terpinene, gamma-terpinene, terpinolene, or terpene-4-ol. Alternatively, or in addition, in some embodiments, it can be advantageous for the dissolving agent to be a purified form of the dissolving agent. For example, in some embodiments, the dissolving agent is a purified terpineol, a purified limonene, or a combination of a purified terpineol and a purified limonene. A purified dissolving agent is understood to be at least 95% pure, at least 97% pure, at least 98% pure, at least 99% pure, or even more pure.
[0113] In some embodiments, an amount of dissolving agent is added so that the silver carboxylate is substantially dissolved or completely dissolved in the dissolving agent. In some embodiments, “substantially dissolved” means the silver carboxylate has a solubility in the dissolving agent at 25 °C of at least about 200 g/L, at least about 300 g/L, at least about 400 g/L, or even higher. In embodiments where the silver carboxylate is substantially dissolved or completely dissolved in the dissolving agent, the conductive ink composition can be considered particle-free.
[0114] In some embodiments, the conductive ink composition comprises two or more dissolving agents. In some embodiments, the volume ratio of two dissolving agents in the conductive ink is about 1 to about 1 of the first dissolving agent to the second dissolving agent. In some embodiments, the volume ratio of two dissolving agents in the conductive ink is about 2 to about 1 of the first dissolving agent to the second dissolving agent. In some embodiments, the volume ratio of two dissolving agents is about 3 to about 1 of the first dissolving agent to the second dissolving agent. In some embodiments, the volume ratio of two dissolving agents is about 4 to about 1 of the first dissolving agent to the second dissolving agent.
[0115] In some embodiments, the flash point of the conductive ink composition can be varied by varying the volume ratio of two or more dissolving agents in the conductive ink. For example, in some embodiments, the flash point of the conductive ink composition is increased by increasing the relative amount of a dissolving agent that has a higher flash point compared to a dissolving agent that has a lower flash point. More specifically, in some embodiments, the flash point of the conductive ink composition is modulated by varying the ratio of a limonene to a terpineol in the conductive ink composition. Even more specifically, the flash point of the conductive ink composition can be decreased by increasing the ratio of a limonene to a terpineol in the conductive ink composition. Acid Stabilizers
[0116] In another aspect are provided conductive ink compositions that further comprise an organic acid to stabilize the ink composition. Although it should be understood that residual organic acids can remain present at low levels in the silver carboxylates of the instant conductive ink compositions (e.g., in the silver decanoate preparations described below), even if no additional organic acid is added to the composition, it can in some cases be advantageous for an acid stabilizer to be added to the conductive ink compositions of the instant disclosure. For example, the presence of an acid stabilizer in the conductive ink compositions can increase the stability of the compositions, particularly during storage at elevated temperatures (e.g., at 30°C or 40°C). Without intending to be bound by theory, it is believed that the presence of an acid stabilizer in these compositions inhibits the formation of metallic silver during storage.
[0117] In some embodiments, the added acid stabilizer is a Ce-12 a-branched alkanoic acid. In preferred embodiments, the added acid stabilizer is one or more of the decanoic acid isomers used to generate the silver decanoate of the instant conductive ink compositions. For example, the added acid stabilizer can be an a-branched decanoic acid isomer. In other preferred embodiments, the added acid stabilizer is 2,2-dimethylhexanoic acid or 2,2-dimethylnonanoic acid.
[0118] The added acid stabilizer is preferably not a linear alkanoic acid. For example, the added acid stabilizer is preferably not n-heptanoic acid, n-octanoic acid, or //-decanoic acid. The added acid stabilizer is also preferably not a secondary alkanoic acid, such as 2- butyl hexanoic acid.
[0119] The added acid stabilizer is preferably included in a conductive ink composition in amounts ranging from 0 to 15% by weight. In some embodiments, the added acid stabilizer is included at about 0.5% by weight, about 1.5% by weight, about 3% by weight, about 5% by weight, about 10% by weight, or even about 15% by weight.
Non- Acid Stabilizers
[0120] In another aspect are provided conductive ink compositions that further comprise a non-acid agent to stabilize the ink composition. The presence of a non-acid stabilizer in the conductive ink formulations can increase the stability of the formulations, particularly during storage at elevated temperatures (e.g., at 30°C or 40°C), for example by inhibiting the formation of metallic silver during storage. The non-acid stabilizer can either be in addition to, or as an alternative to, any of the acid stabilizers described above.
[0121] In some embodiments, the non-acid stabilizer is a P-diketone stabilizer.
[0122] More specifically, the P-diketone is a compound of formula (III): wherein each R4 group is independently a Ci-Ce straight-chain or branched-chain alkyl group, optionally substituted with an aryl group, or is an aryl group, and wherein each R5 group is independently -H, a Ci-Ce straight-chain or branched-chain alkyl group, optionally substituted with an aryl group, or wherein two R5 groups, taken together, form a double bond that is optionally substituted with a Ci-Ce straight-chain or branched-chain alkyl group, optionally further substituted with an aryl group, or is optionally substituted with an aryl group.
[0123] In some embodiments, the R4 and Rs groups in the compound of formula (III) are independently substituted with an alkoxy, hydroxy, thio, amino, halo, cyano, or nitro group.
[0124] In more specific embodiments, each R4 group is independently a C1-C4 straightchain or branched-chain alkyl group, optionally substituted with a phenyl group, or is a phenyl group, and each R5 group is independently -H, a C1-C4 straight-chain or branched- chain alkyl group, optionally substituted with a phenyl group, or two R5 groups, taken together, form a double bond that is optionally substituted with a C1-C4 straight-chain or branched-chain alkyl group, optionally further substituted with a phenyl group, or is optionally substituted with a phenyl group.
[0125] In even more specific embodiments, each R4 group is independently methyl, ethyl, or phenyl, and each Rs group is independently hydrogen, methyl, ethyl, or benzyl, or two Rs groups, taken together, form a double bond that is optionally substituted with a methyl, ethyl, or phenyl group.
[0126] In still more specific embodiments, the P-diketone is one of the following compounds:
[0127] In some embodiments, the conductive ink formulations comprise more than one of any of the above-described non-acid stabilizers.
Particle-Free Conductive Ink Compositions [0128] Provided herein are conductive ink compositions comprising any of the abovedescribed silver carboxylates, in particular a silver decanoate. For example, in some embodiments, the silver decanoate comprises at least one a-branched silver decanoate isomer, as described above. In some embodiments, the at least one a-branched silver decanoate isomer is the silver salt of 2,2-dimethyloctanoic acid, 2, 2,3,5- tetramethylhexanoic acid, 2,4-dimethyl-2-isopropylpentanoic acid, 2,5-dimethyl-2- ethylhexanoic acid, 2,2-diethylhexanoic acid, 2-butylhexanoic acid, or any combination of these a-branched decanoic acid isomers.
[0129] The conductive ink compositions of the instant disclosure further comprise a cyclic azasilane adhesion promoter. More specifically, the cyclic azasilane adhesion promoter is any of the above-described cyclic azasilanes. In some embodiments, the conductive ink compositions may comprise more than one cyclic azasilane adhesion promoters or may further comprise a different adhesion promoter.
[0130] The conductive ink compositions of the instant disclosure still further comprise at least one dissolving agent, wherein the at least one dissolving agent is chosen from any of the above-described dissolving agents. In preferred embodiments, the silver decanoate and the cyclic azasilane adhesion promoter are both soluble in the dissolving agent. Solubility, as known to one of ordinary skill, is the property of a substance, such as a silver carboxylate, in particular a silver decanoate, to dissolve in a solvent, such as a dissolving agent. The conductive ink compositions of the instant disclosure are preferably particle free.
[0131] In some embodiments, the conductive ink compositions further comprise one or more of the above-described acid stabilizers and/or non-acid stabilizers, in any combination.
[0132] In some embodiments, the conductive ink compositions do not comprise a catalyst. In particular, when the silver carboxylate of the composition is a silver decanoate, it may not be necessary to include a catalyst in the composition, let alone a catalyst comprising an amine.
[0133] In some embodiments, an amount from about 0.4 grams to about 1.0 grams of a silver carboxylate, specifically a silver decanoate, is dissolved per gram of the dissolving agent. In some embodiments, about 0.4 grams, about 0.5 grams, about 0.6 grams, about 0.7 grams, about 0.8 grams, about 0.9 grams, or even about 1.0 grams of the silver carboxylate is dissolved per gram of the dissolving agent.
[0134] In some embodiments, the conductive ink composition has a concentration of about 1 to about 50 weight percent silver of the conductive ink composition. In some embodiments, the conductive ink composition has a concentration of about 1 to about 40 weight percent silver of the conductive ink composition. In some embodiments, the conductive ink composition has a concentration of about 1 to about 30 weight percent silver of the conductive ink composition. In some embodiments, the conductive ink composition has a concentration of about 1 to about 20 weight percent silver of the conductive ink composition. In some embodiments, the conductive ink composition has a concentration of about 1 to about 10 weight percent silver of the conductive ink composition. In some embodiments, the conductive ink composition has a concentration of about 5 to about 15 weight percent silver of the conductive ink composition. In some embodiments, the conductive ink composition has a concentration of about 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent), about 5 weight percent, about 6 weight percent, about 7 weight percent, about 8 weight percent, about 9 weight percent, about 10 weight percent), about 11 weight percent), about 12 weight percent, about 13 weight percent, about 14 weight percent, about 15 weight percent, about 16 weight percent), about 17 weight percent), about 18 weight percent, about 19 weight percent, about 20 weight percent, about 21 weight percent, about 22 weight percent), about 23 weight percent, about 24 weight percent, about 25 weight percent, about 26 weight percent, about 27 weight percent, about 28 weight percent), about 29 weight percent, about 30 weight percent, about 31 weight percent, about 32 weight percent, about 33 weight percent, about 34 weight percent), about 35 weight percent, about 36 weight percent, about 37 weight percent, about 38 weight percent, about 39 weight percent, about 40 weight percent, about 41 weight percent, about 42 weight percent, about 43 weight percent, about 44 weight percent, about 45 weight percent, about 46 weight percent, about 47 weight percent, about 48 weight percent, about 49 weight percent, about 50 weight percent, or even higher weight percent silver in the conductive ink composition. [0135] In some embodiments, the conductive ink composition of the disclosure has a desired viscosity. In some embodiments, the desired viscosity is obtained using a micro VISC viscometer. In some embodiments, the conductive ink composition has a viscosity from about 50 centipoise to about 1000 centipoise. In some embodiments, the conductive ink composition has a viscosity from about 5 centipoise to about 50 centipoise. In some embodiments, the conductive ink composition has a viscosity from about 10 centipoise to about 40 centipoise. In some embodiments, the conductive ink composition has a viscosity from about 20 centipoise to about 30 centipoise. In some embodiments, the conductive ink composition has a viscosity from about 18 centipoise to about 20 centipoise. In some embodiments, the conductive ink composition has a viscosity of about 18, about 19, or about 20 centipoise. In some embodiments, the conductive ink composition has a viscosity of at least about 5 centipoise, about 10 centipoise, about 20 centipoise, about 30 centipoise, about 40 centipoise, about 50 centipoise, about 60 centipoise, about 70 centipoise, about 80 centipoise, about 90 centipoise, about 100 centipoise, about 200 centipoise, about 300 centipoise, about 400 centipoise, about 500 centipoise, about 600 centipoise, about 700 centipoise, about 800 centipoise, or about 900 centipoise. In some embodiments, the conductive ink composition has a viscosity of at most about 1000 centipoise, about 900 centipoise, about 800 centipoise, about 700 centipoise, about 600 centipoise, about 500 centipoise, about 400 centipoise, about 300 centipoise, about 200 centipoise, about 100 centipoise, about 90 centipoise, about 80 centipoise, about 70 centipoise, about 60 centipoise, about 50 centipoise, about 40 centipoise, about 30 centipoise, about 20 centipoise, or about 10 centipoise.
[0136] In some embodiments, the viscosity of the conductive ink composition is adjusted based upon the amount of dissolving agent used. In some embodiments, the viscosity of the complex is adjusted based upon the type of dissolving agent used. For example, in embodiments where the dissolving agent comprises limonene and terpineol, an increase in the percentage of terpineol in the conductive ink composition can increase the viscosity of the ink. In some embodiments, the viscosity of silver complex can be tuned from less than 5 centipoise with a large proportion of limonene to 50 centipoise with a large portion of terpineol. Unless otherwise indicated, all viscosity values are for samples at room temperature.
[0137] As has been described above, the conductive ink compositions of the instant disclosure can be used to form conductive structures by heating the compositions at low temperatures. In some embodiments, the ink composition is applied to a suitable substrate prior to heating. In some embodiments, the silver carboxylate is converted to a conductive silver structure at a temperature of about 250 °C or less. In some embodiments, the silver carboxylate is converted to a conductive silver structure at a temperature of about 100 °C or less. In some embodiments, the silver carboxylate is converted to a conductive silver structure at a temperature of about 220 °C, of about 210 °C or less, of about 190 °C or less, of about 180 °C or less, of about 170 °C or less, of about 160 °C or less, of about 150 °C or less, of about 140 °C or less, of about 130 °C or less, of about 120 °C or less, of about 110 °C or less, of about 90 °C or less, of about 80 °C or less, of about 70 °C or less, of about 60 °C or less, or of about 50 °C or less.
[0138] In some embodiments, the electrical conductivity of the conductive structure formed from the conductive ink composition is measured. In some embodiments, the electrical conductivity of the conductive structure is from about 2x10‘6 Ohm-cm to about IxlO-3 Ohm-cm. In some embodiments, the electrical conductivity of the conductive structure is from about 3x1 O’6 Ohm-cm to about 6x1 O’6 Ohm-cm. In some embodiments, the electrical conductivity of the conductive structure is at least about 2x1 O’6 Ohm-cm, about 3xl0-6 Ohm-cm, about 4xl0'6 Ohm -cm, about 5xl0-6 Ohm-cm, about 6xl0-6 Ohm- cm, about 7x106 Ohm-cm, about 8x106 Ohm-cm, or about 9x106 Ohm-cm. In some embodiments, the electrical conductivity of the conductive structure is at most about lx 10'5 Ohm-cm, about 9xl0‘6 Ohm-cm, about 8xl0-6 Ohm-cm, about 7xl0-6 Ohm-cm, about 6xl0-6 Ohm-cm, about 5xl0-6 Ohm-cm, about 4xl0-6 Ohm-cm, or about 3xl0-6 Ohm-cm. [0139] The electrical conductivity of the conductive structure may in some embodiments be expressed in terms of sheet resistance (z.<?., bulk resistivity divided by thickness) in units of ohms per square or mohms per square (also referred to as OPS). For example, in some embodiments, the sheet resistance of the conductive structure is no more than 5 ohms per square, no more than 2 ohms per square, no more than 1 ohm per square, no more than 0.5 ohms per square, or even lower. Preferably, the sheet resistance of the conductive structure is no more than 1 ohm per square (or 1,000 mohm per square).
[0140] The conductive ink compositions of the instant disclosure can be used to form conductive structures having high levels of bulk silver. Specifically, in some embodiments, the conductive structure has a bulk silver content of at least 1%. In more specific embodiments, the conductive structure has a bulk silver content of at least 2%, at least 5%, at least 10%, at least 15%, at least 20%, or even higher.
Methods for Making Conductive Ink Compositions
[0141] According to another aspect, the disclosure provides methods for making a conductive ink composition, in particular a conductive ink composition as described above. These methods comprise the step of dissolving a silver carboxylate, in particular a silver decanoate, and a cyclic azasilane adhesion promoter in at least one dissolving agent to form a conductive ink composition. Suitable silver decanoates, cyclic azasilane adhesion promoters, and dissolving agents are described above.
[0142] In some embodiments, the methods comprise the further step of dissolving a stabilizing agent, including one or more of any of the above-described acid or non-acid stabilizers, in the at least one dissolving agent.
Methods of Forming a Conductive Structure
[0143] In another aspect are disclosed methods of forming a conductive structure. In some embodiments, the methods include the step of applying any of the above-described conductive ink compositions to a substrate and heating the conductive ink composition on the substrate at a decomposition temperature of about 250 °C or less to form the conductive structure. In some embodiments, the methods include the step of heating the conductive ink composition on the substrate at a decomposition temperature of about 100 °C or less to form the conductive structure. In some embodiments, the methods include the step of heating the conductive ink composition on the substrate at a decomposition temperature of about 210 °C or less, of about 200 °C or less, of about 190 °C, of about 180 °C or less, of about 170 °C or less, of about 160 °C, of about 150 °C or less, of about 140 °C or less, of about 130 °C or less, of about 120 °C or less, of about 110 °C or less, of about 90 °C or less, of about 80 °C or less, of about 70 °C or less, of about 60 °C or less, or of about 50 °C or less to form the conductive structure. In some embodiments, the conductive ink composition is heated with a heat source. Examples of heat sources include an IR lamp, oven, or a heated substrate.
Applications of the Conductive Ink Compositions
[0144] The conductive ink compositions of the instant disclosure can be used in various printing applications, including slot die coating, spin coating, roll-to-roll printing, including gravure, flexography, rotary screen printing, screen printing, aerosol jet printing, inkjet printing, airbrushing, Mayer rod coating, flood coating, 3D printing, dispenser, and electrohydrodynamic printing. In particular, the inks can be used in inkjet printing, dip coating, and spray coating.
[0145] Furthermore, patterns can be created using photolithography to create a mask to etch silver from certain areas, thereby creating high-fidelity features. Both positive and negative patterning processes may be used to create the patterns.
[0146] In some embodiments, the silver salt of the silver carboxylate is completely dissolved in at least one dissolving agent. The fully dissolved silver salt is compatible with many nonpolar polymer substrates, glasses, and ceramic substrates where polar complexes do not wet particularly well. In some embodiments, the conductive ink composition comprising the silver complex is applied to a polymer substrate, for example a flexible polymer substrate, such as a polyimide (PI) substrate, for example Kapton. In some embodiments, the conductive ink composition comprising the silver complex is applied to a nonpolar polymer substrate. In some embodiments, the conductive ink composition comprising the silver complex is applied to a glass substrate. In some embodiments, the conductive ink composition comprising the silver complex is applied to a ceramic substrate.
[0147] Furthermore, elastomers and 3D substrates with specifically non-planar topography can be used in conjunction with the conductive structures. In some embodiments, the conductive ink composition comprising the silver complex is applied to an elastomer. In some embodiments, the conductive ink composition comprising the silver complex is applied to a 3D substrate.
[0148] In some embodiments, the conductive ink compositions of the instant disclosure can be applied to an epoxy substrate, such as, for example, an epoxy molding compound (EMC) substrate or the like. In some embodiments, the epoxy substrate has residual mold release on the surface of the substrate.
[0149] In some embodiments, the conductive ink compositions of the instant disclosure can be applied to a silver nanowire (SNW) substrate, a solder resist substrate (also referred to as a solder mask substrate), or any other suitable substrate material.
[0150] In some embodiments, the ink composition of the instant methods has a concentration of about 0.1-50 weight percent metal salt of the ink composition. In some embodiments, the ink composition of the instant methods has a concentration of about 0.1- 40 weight percent metal salt of the ink composition. In some embodiments, the ink composition has a concentration of about 1-30 weight percent metal salt of the ink composition. In some embodiments, the ink composition has a concentration of about 1- 20 weight percent metal salt of the ink composition. In some embodiments, the ink composition has a concentration of about 1-10 weight percent metal salt of the ink composition. In some embodiments, the ink composition has a concentration of about 5- 15 weight percent metal salt of the ink composition. In some embodiments, the ink composition has a concentration of about 0.1 weight percent), about 0.2 weight percent), about 0.3 weight percent>, about 0.4 weight percent>, about 0.5 weight percent>, about 0.6 weight percent>, about 0.7 weight percent, about 0.8 weight percent, about 0.9 weight percent, about 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent), about 5 weight percent), about 6 weight percent, about 7 weight percent, about 8 weight percent, about 9 weight percent, about 10 weight percent, about 11 weight percent), about 12 weight percent, about 13 weight percent, about 14 weight percent, about 15 weight percent, about 16 weight percent, about 17 weight percent), about 18 weight percent, about 19 weight percent, or about 20 weight percent metal of the ink composition. [0151] In some embodiments, the ink composition of the instant methods has a concentration of at least about 0. 1 weight percent, about 0.2 weight percent, about 0.3 weight percent, about 0.4 weight percent, about 0.5 weight percent, about 0.6 weight percent, about 0.7 weight percent, about 0.8 weight percent, about 0.9 weight percent, 1 weight percent, about 2 weight percent, about 3 weight percent, about 4 weight percent), about 5 weight percent), about 6 weight percent, about 7 weight percent, about 8 weight percent, about 9 weight percent, about 10 weight percent, about 11 weight percent), about 12 weight percent, about 1 weight percent, about 14 weight percent, about 15 weight percent, about 16 weight percent, about 17 weight percent), about 18 weight percent, about 19 weight percent, or about 20 weight percent metal salt of the ink composition. In some embodiments, the ink composition has a concentration of at most about 40 weight percent), about 39 weight percent, about 38 weight percent, about 37 weight percent, about 36 weight percent, about 35 weight percent, about 34 weight percent, about 33 weight percent, about 32 weight percent, 31 weight percent, about 30 weight percent, about 29 weight percent, about 28 weight percent, about 27 weight percent), about 26 weight percent, about 25 weight percent, about 24 weight percent, about 23 weight percent, about 22 weight percent, about 21 weight percent), about 20 weight percent, about 19 weight percent, about 18 weight percent, about 17 weight percent, about 16 weight percent, about 15 weight percent, about 14 weight percent, about 13 weight percent, or about 12 weight percent metal salt of the ink composition.
[0152] In some embodiments, the ink composition of the instant methods has a concentration of about 0.1-50 weight percent metal complex of the ink composition. In some embodiments, the ink composition of the instant methods has a concentration of about 0.1-40 weight percent metal complex of the ink composition. In some embodiments, the ink composition has a concentration of about 1-30 weight percent metal complex of the ink composition. In some embodiments, the ink composition has a concentration of about 1 -20 weight percent metal complex of the ink composition. In some embodiments, the ink composition has a concentration of about 1-10 weight percent metal complex of the ink composition. In some embodiments, the ink composition has a concentration of about 5-15 weight percent metal complex of the ink composition. In some embodiments, the ink composition has a concentration of about 0.1 weight percent, about 0.2 weight percent, about 0.3 weight percent, about 0.4 weight percent, about 0.5 weight percent, about 0.6 weight percent, about 0.7 weight percent, about 0.8 weight percent, about 0.9 weight percent), 1 weight percent), about 2 weight percent, about 3 weight percent, about 4 weight percent, about 5 weight percent, about 6 weight percent, about 7 weight percent), about 8 weight percent), about 9 weight percent, about 10 weight percent, about 11 weight percent, about 12 weight percent, about 13 weight percent), about 14 weight percent), about 15 weight percent, about 16 weight percent, about 17 weight percent, about 18 weight percent, about 19 weight percent, or about 20 weight percent metal complex of the ink composition.
Decomposition
[0153] In another aspect, the conductive ink compositions of the disclosure are decomposed on a substrate to form a conductive structure on the substrate. In some embodiments, the conductive ink composition is decomposed by heating the reducible metal complex at a temperature of about 250 °C or less. In some embodiments, the conductive ink composition is decomposed by heating the conductive ink composition at a temperature of about 240 °C or less, about 230 °C or less, about 220 °C or less, about
210 °C or less, about 200 °C or less, about 190 °C or less, about 180 °C or less, about
170 °C or less, about 160 °C or less, about 150 °C or less, about 140 °C or less, about
130 °C or less, about 120 °C or less, about 110 °C or less, about 100 °C or less, about
90 °C or less, about 80 °C or less, or about 70 °C or less. In some embodiments, the conductive ink composition is heated by a heat source. Examples of heat sources include an IR lamp, oven, or a heated substrate.
[0154] In some embodiments, the conductive ink composition is decomposed by exposing the composition to a light source at a wavelength from about 100 nm to about 1500 nm. In some embodiments, the conductive ink composition is decomposed by exposing the composition to a light source such as a Xenon lamp or IR lamp at a wavelength from about 100 nm to about 1000 nm. In some embodiments, the conductive ink composition is decomposed by exposing the composition to a light source at a wavelength from about 100 nm to about 700 nm. In some embodiments, the conductive ink composition is decomposed by exposing the composition to a light source at a wavelength from about 100 nm to about 500 nm. In some embodiments, the conductive ink composition is decomposed by exposing the composition to a light source at a wavelength from about 100 nm to about 300 nm. In some embodiments, the conductive ink composition is decomposed by exposing the composition to a light source at a wavelength of about 100 nm, about 200 nm, about 300 nm, about 400 nm, about 500 nm, about 600 nm, about 700 nm, about 800 nm, about 900 nm, or about 1000 nm.
[0155] In some embodiments, the conductive ink composition is decomposed by a combination of heating the reducible metal complex, for example at any of the abovelisted temperatures, and exposing the composition to a light source, for example at any of the above-listed wavelengths.
[0156] In some embodiments, the electrical conductivity of the conductive structures is measured. In some embodiments, the electrical conductivity of the conductive structures is about IxlO'6 Ohm-cm or greater. In some embodiments, the electrical conductivity of the conductive structures is from about 1x106 Ohm-cm to about 8x104 Ohm-cm. In some embodiments, the electrical conductivity of the conductive structures is from about 3x1 O’6 Ohm-cm to about 6xl0'6 Ohm-cm. In some embodiments, the electrical conductivity of the conductive structures is at least about IxlO'6 Ohm-cm, about 2x1 O’6 Ohm-cm, about 3x1 O’6 Ohm-cm, about 4x1 O’6 Ohm- cm, about 5xl0'6 Ohm-cm, about 6x1 O'6 Ohm-cm, about 7x1 O'6 Ohm-cm, about 8x1 O'6 Ohm-cm, about 9x1 O'6 Ohm-cm, about IxlO'5 Ohm- cm, about 2xl0‘5 Ohm-cm, about 3xl0'5 Ohm-cm, about 4xl0'5 Ohm-cm, about 5xl0'5 Ohm-cm, about 6x10'5 Ohm-cm, about 7x10'5 Ohm-cm, about 8x10'5 Ohm-cm, about 9xl0'5 Ohm-cm, about IxlO'4 Ohm-cm, about 2xl0'4 Ohm-cm, about 3xl0 Ohm-cm, about 4xl0‘4 Ohm-cm, about 5xl0‘4 Ohm-cm, about 6xl0‘4 Ohm-cm, or about 7xl0'4 Ohm-cm. In some embodiments, the electrical conductivity of the conductive structures is at most about 8xl0'4 Ohm-cm, 7xl0'4 Ohm -cm, about 6xl0 Ohm-cm, about 5xl0'4 Ohm- cm, about dxlO"4 Ohm-cm, about 3xl0'4 Ohm-cm, about 2xl0'4 Ohm-cm, or about IxlO'4 Ohm-cm, about 9xl0'5 Ohm-cm, about 8xl0'5 Ohm-cm, about 7xl0'5 Ohm-cm, about 6x1 O'5 Ohm-cm, about 5x10s Ohm-cm, about 4x1 O'5 Ohm-cm, about 3x10s Ohm-cm, about 2x10'5 Ohm-cm, about IxlO'5 Ohm-cm, about 9xl0‘6 Ohm-cm, about 8xl0'6 Ohm-cm, about 7xl0'6 Ohm-cm, about 6xl0'6 Ohm-cm, about 5xl0'6 Ohm-cm, about 4xl0'6 Ohm - cm, about 3xl0'6 Ohm-cm, or about 2xl0'6 Ohm-cm.
[0157] It will be readily apparent to one of ordinary skill in the relevant arts that other suitable modifications and adaptations to the compositions and methods described herein may be made without departing from the scope of the invention or any embodiment thereof. Having now described the present invention in detail, the same will be more clearly understood by reference to the following Examples, which are included herewith for purposes of illustration only and are not intended to be limiting of the invention.
EXAMPLES
Preparation of silver decanoate isomer mixtures
[0158] The decanoic acid used to form the silver carboxylates of the instant improved conductive ink compositions and the acid stabilizer included in these compositions preferably comprises at least one a-branched decanoic acid isomer, as described in detail in PCT International Publication No. WO2023/168452 A2, which is incorporated by reference herein for all purposes. The a-branched decanoic acid isomer, or mixture of a- branched decanoic acid isomers, can be converted to a silver decanoate isomer, or mixture of silver decanoate isomers, for use in the conductive ink compositions of the instant disclosure by reaction with Ag2O, for example, as was also described in detail in PCT International Publication No. WO2023/168452 A2.
Exemplary ink formulations comprising a silver decanoate and an azasilane adhesion promoter
Formulation 1
[0159] In one exemplary ink preparation, a silver decanoate isomer mixture (36 wt %) was dissolved in a mixture of a-terpineol (32 wt %) and limonene (32 wt %). To this mixture was added the decanoic acid isomer mixture as an acid stabilizer (3 wt %) and N- methyl-aza-2,2,4-trimethylsilacyclopentane (0.5 wt %) as an adhesion promoter.
Formulation 2
[0160] This ink preparation is the same as Formulation 1, except that the N-methyl-aza- 2,2,4-trimethylsilacyclopentane adhesion promoter was added to 0.25 wt %.
Formulation 3
[0161] This ink preparation is the same as Formulations 1 and 2, except that the N- methyl-aza-2,2,4-trimethylsilacyclopentane adhesion promoter was added to 0.3 wt %.
Formulation 4
[0162] This ink preparation is the same as Formulations 1, 2, 3, except that the N- methyl-aza-2,2,4-trimethylsilacyclopentane adhesion promoter was added to 0.4 wt %. Formulation 5
[0163] This ink preparation is the same as Formulation 1, except that 2, 2, 6, 6 tetramethyl 3, 5 -heptanedione was added to 1 wt % as a non-acid stabilizer.
Properties of the exemplary ink formulations and their use in forming conductive silver structures
[0164] All of the above-described ink formulations yielded clear, colorless ink compositions comprising approximately 13.5% silver. The formulations could all be printed on suitable substrates using standard inkjet technologies to form conductive silver films at relatively low temperatures. For example, as shown in FIG. 1, Formulation 1 was printed on two different substrates (standard epoxy molding compound (“Reg. EMC”) and “nightmare epoxy” (or “n. epoxy”), which contains residual mold release on the surface) under the indicated conditions, where the platen temperature was 50 °C in all cases, and where the curing conditions and printing passes per drop space (DS) were varied. Where indicated (“Ar- 5 min”), the substrate was pretreated using an argon plasma, where the sample was held in the plasma environment for 5 min at 300 Watt.
[0165] The curing conditions are as indicated in the figure, where “UV-90%” represents a post-printing ultraviolet cure using a system that delivers 8.1 W/cm2 at 405 nm. In some cases, the ink was cured between printed layers, as indicated. For example, “180 C- 10 per 2 layer +20 min final cure” indicates that the sample was cured at 180 °C for 10 minutes after every 2 layers of printing and was given a final cure at 180 °C for 20 minutes.
[0166] After curing, the resulting silver films had the indicated thickness, sheet resistance, and resistivity. The silver films were also subjected to an adhesion test, with the results shown in the right column of the figure, both in the form of images of the cured silver films after the adhesion test and the ASTM classification (0B-5B) for each tested film.
[0167] FIG. 2 shows the results of additional reliability testing of silver films prepared from Formulation 1 on the two substrates, using a pressure cooker test (12 psi) and a high temperature storage (HTS) test in an oven at 125 °C. Formulation 1 passed a 96 hour pressure cooker test and a 700 hour HTS test on a plasma-treated standard EMC substrate when cured at 180 °C for 1 hour.
[0168] FIG. 3 shows the results of testing silver films prepared from Formulation 2 on two different substrates. This formulation included half the concentration of the azasilane adhesion promoter as in Formulation 1. [0169] Silver films prepared from Formulation 1 or Formulation 2 were compared for adhesion and reliability, as shown in FIG. 4.
[0170] FIGs. 5A and 5B show photographic images of an inkjet printer nozzle plate in the process of printing fresh preparations of Formulation 1 (FIG. 5A) or Formulation 2 (FIG. 5B) at day 0. These images demonstrate that these ink compositions enable stable printing with no nozzle clogging and no plate wetting.
[0171] The stability of Formulation 1 over time is demonstrated in FIG. 6, where each vial was stored for the indicated number of days at 40 °C (column A), at 40 °C with water spike (column B), or at 60 °C (column C). The formulation remains stable at 40 °C for at least 20 days and is stable at 60 °C for at least 3 days. The other above-described formulations were likewise stable at 60 °C for at least 3 days.
[0172] All patents, patent publications, and other published references mentioned herein are hereby incorporated by reference in their entireties as if each had been individually and specifically incorporated by reference herein.
[0173] While specific examples have been provided, the above description is illustrative and not restrictive. Any one or more of the features of the previously described embodiments can be combined in any manner with one or more features of any other embodiments in the present invention. Furthermore, many variations of the invention will become apparent to those skilled in the art upon review of the specification. The scope of the invention should, therefore, be determined by reference to the appended claims, along with their full scope of equivalents.