Conductive inks, pastes and conductive polymer composites containing metal particles based on silver nanowires and corresponding methods

Abstract

A concentrated flowable composition having a total metal weight of at least about 45% by weight is used to form a conductive material. The compositions include metal microparticles, such as silver flakes, silver particles, and / or silver nanowires, and for particularly interested embodiments, reducible metal compositions, such as one or more silver salts, are also included. The composition includes an organic precursor forming a polymeric matrix and includes a dissolved polymeric binder, a crosslinkable or polymerizable monomer, oligomer or polymer, or a mixture thereof. The flowable precursor compositions can be used to form electrically conductive structures, such as composites of a solid polymer matrix and at least about 45% by weight of a metal. The composite may have a resistivity of no more than about 5 * 10 <-3 > ohm-cm. Methods of forming the flowable precursor compositions and composites are described.

Description

Conductive inks, pastes, and conductive polymer composites containing metal particles based on silver nanowires, and corresponding methods.

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 540,772, filed September 27, 2023, entitled “Silver Nanowire Based, Electrically Conductive Inks, Pastes and Electrically Conductive Adhesives and Corresponding Methods,” which is incorporated herein by reference. Technical Field

[0003] This invention relates to conductive composite materials comprising polymers and metal microparticles such as silver nanowires. The invention further relates to supplementing the conductivity of the conductive composite with in-situ reduced silver to form a cured composite material. The invention also relates to methods for forming these composites. Background Technology

[0004] Metal-loaded polymers (e.g., cross-linked polymers) have been found to provide useful alternatives to solders and other metal-only electrical connector materials. Conductive structures can be formed by depositing suitable precursor materials, which can be pastes or more fluid inks and may contain, for example, monomers, oligomers, dissolved polymers, solvent mixtures of the aforementioned. Particulate metals, such as silver nanoparticles or silver flakes, can be used as metal fillers. Silver is the most conductive metal, but other metals can also provide sufficient conductivity and thermal conductivity. These materials can be readily applied in a variety of processing environments. Summary of the Invention

[0005] In a first aspect, the present invention relates to a flowable precursor composition (also referred to as a flowable precursor composition) for forming a conductive material, having at least about 45% by weight of total metal and at least about 2% by weight of an organic precursor for forming a polymer matrix relative to the total weight of the composition. This flowable precursor composition can be used to form a conductive material. The composition comprises metal microparticles such as silver flakes and / or silver particles and a reducible metal composition such as one or more silver salts. The metal microparticles may also comprise metal nanowires such as silver nanowires. The composition comprises an organic precursor for forming a polymer matrix. The precursor may comprise a dissolved polymer binder, a crosslinkable or polymerizable monomer (also referred to as a crosslinkable or polymerizable monomer), an oligomer or polymer, or a mixture thereof. For example, the precursor may comprise one or more monomers, such as (meth)acrylate monomers, hydroxyl and / or epoxy-functionalized urethane acrylate monomers, and monomers for forming epoxy resins. The precursor may be thermosetting and / or ultraviolet (UV) curable.

[0006] In another aspect, the present invention relates to a flowable precursor composition for forming a conductive structure, comprising: an organic precursor for a polymer matrix; and metal particles comprising silver nanowires and non-nanowire metal particles, wherein the metal particles comprise from about 5% to about 90% by weight of silver nanowires relative to the total weight of the metal particles. The non-nanowire metal particles may include silver flakes, silver particles, or combinations thereof.

[0007] In another aspect, the present invention relates to a composite conductive material formed from the flowable precursor composition. The composite comprises a solid polymer matrix and at least about 45% by weight of a metal, wherein the metal comprises: a1) features formed from metal particles that are not nanowires and b1) features formed from silver nanowires, metal deposited from a reduced metal composition, or both; or a2) a structure formed from silver nanowires and b2) metal deposited from a reduced metal composition. The composite conductive material may have a density not exceeding about 5 × 10⁻⁶. -3 Resistivity in ohm-cm.

[0008] In another aspect, the present invention relates to a method for forming a precursor composition for forming a conductive composite material. The method comprises: combining a) a polymer matrix precursor comprising a crosslinkable polymer precursor, a polymerizable monomer / oligomer, a dissolved polymer binder, or a combination thereof, with b) a metal component provided in the form of 1) metal microparticles that are not nanowires, 2) silver nanowires, or 3) a reducible metal composition, to form the precursor composition, wherein the precursor composition comprises at least about 45% by weight of total metal in all forms, and wherein if the metal is provided only in the form of silver nanowires and a reducible metal composition, the polymer matrix after curing comprises at least 2% by weight, and in some embodiments 8.5% by weight of the polymer matrix precursor composition.

[0009] In another aspect, the present invention relates to a method for forming a composite material having high conductivity and consisting of organic polymers and metal components. The method comprises: curing a deposited composition to drive the reduction of silver ions to form silver metal, wherein the deposited material is a precursor composition comprising a polymer precursor, silver microparticles, and a dissolved silver composition, and wherein curing comprises applying heat, UV radiation, or both for a sufficient time to reduce the silver ions to silver metal and reduce the resistivity by at least about 25%. Attached Figure Description

[0010] Figure 1 is a graph showing the calculated sheet resistance as a function of sintering time at 250 °C for a composite comprising approximately 19 wt% H-nanowires (HNW), approximately 41 wt% silver flakes (AgFL), approximately 14 wt% silver macroparticles (AgMP), and approximately 7 wt% silver trifluoroacetate (AgTFA) in a UV-cured urethane acrylate polymer matrix.

[0011] Figure 2 is a graph showing the resistivity versus sintering time for the composite shown in Figure 1 and for similar composites containing approximately 13% by weight of AgTFA.

[0012] Figures 3A and 3B are images at 5X magnification of the composite shown in Figure 1 coated on polyterephthalate (PET) and cured, followed by a cross-cut adhesion test.

[0013] Figure 3C is an image at 5X magnification of the composite containing 13% by weight of AgTFA as shown in Figure 2, which was coated and cured on PET and then subjected to a cross-cut adhesion test.

[0014] Figures 4A and 4B are images at 5X magnification of the composite material described in Figure 1, which was coated and cured on glass and then subjected to a cross-cut adhesion test.

[0015] Figure 4C shows an image at 5X magnification of the composite containing 13% by weight of AgTFA as shown in Figure 2, which was coated and cured on glass and then subjected to a cross-cut adhesion test.

[0016] Figure 5 is an image at 5X magnification showing the adhesive side of the tape used in the cross-cut adhesion test of the composite on PET described in Figure 3A.

[0017] Figure 6 is an image at 5X magnification showing the adhesive side of the tape used in the cross-cut adhesion test of the composite on glass described in Figure 4A.

[0018] Figure 7 is a graph showing the resistivity of the composite shown in Figure 1 cured using high-intensity pulsed light (IPL) as a function of curing energy.

[0019] Figure 8A is a cross-sectional image of the composite described in Figure 1 before curing or sintering, at a magnification of 10,000X.

[0020] Figure 8B is a cross-sectional image of the composite described in Figure 8A after it has been cured using IPL at a magnification of 20,000X.

[0021] Figure 8C is a cross-sectional image of the composite described in Figure 8A after sintering at 250°C for 15 minutes, magnified at 10,000X.

[0022] Figures 9A and 9B are images of the cross-section of the composite described in Figure 1 before curing or sintering, at magnifications of 10,000X and 60,000X, respectively.

[0023] Figures 10A and 10B are images of the cross-section of the composite described in Figure 8A after it has been cured using IPL, at magnifications of 350X and 20,000X, respectively.

[0024] Figures 11A and 11B are images of the cross-section of the composite described in Figure 9A after sintering at 250°C for 15 minutes, at magnifications of 3,000X and 10,000X, respectively.

[0025] Figure 12 is a bar graph showing the resistivity of a composite containing approximately 20% by weight HNW, approximately 44% by weight AgFL, approximately 15% by weight AgMP, and approximately 2.5% by weight AgTFA in a UV-cured urethane acrylate polymer matrix.

[0026] Figure 13 is a bar graph showing the resistivity of composites containing various combinations of HNW, AgFL, AgMP and AgTFA in a UV-cured modified acrylate polymer matrix.

[0027] Figure 14 is a bar graph showing the resistivity of composites containing various combinations of about 20 wt% HNW, about 60 wt% to 80 wt% AgFL, about 5 wt% to about 10 wt% AgTFA and about 5 wt% to about 10 wt% silver acetate (AgAc) in a thermosetting epoxy polymer matrix. Detailed Implementation

[0028] Silver nanowires have been found to further improve the conductivity of metal-loaded polymers and resins with high metal loading by achieving extremely low resistivity while maintaining the desired properties imparted by the polymer. The effect of silver nanowires can be disproportionate to their silver content due to the conductive pathways provided by the nanowire morphology. Methods for avoiding the rheological limit to achieve high silver nanowire loading in solvents and loaded polymers have been discovered. Combinations of silver nanowires with other metal shapes can adapt to the material's properties while improving conductivity. Alternatively, the use of reducible metal compounds can provide significant improvements in conductivity based on any base metal particle shape. Reducible metal salts have been found to be beneficial even in composites without silver nanowires, although incorporation with some silver nanowires may be desirable. The resistivity reduction achieved using reduced silver salts is disproportionate to the amount of metal deposited, indicating that some effectively directed metal deposition supports the establishment of conductive pathways through the material. Similarly, silver nanowires can aid in the establishment of conductive pathways based on their length. The polymer matrix can be solidified using curing processes such as polymerization, crosslinking, solvent removal, silver ion reduction, or combinations thereof. Improved conductivity allows for reduced material usage in high-performance applications (e.g., personal electronic devices) while providing good handleability. Extremely low resistivity can be achieved using the composites described herein. The materials can be designed to meet specific application requirements. A wide range of polymer precursors, such as dissolved polymers, monomers, and / or oligomeric resins, can be used. The use of environmentally friendly metals provides a more environmentally friendly alternative to conventional solders for providing electrical connections or other applications such as antistatic agents.

[0029] The properties of the materials described herein will be clear to those skilled in the art. However, uniform terminology may not be used in this art. Although particular care has been taken in explaining alternative terms, it may still be incomplete, and those skilled in the art can make appropriate connections based on the overall discussion presented herein in an appropriate context.

[0030] The treatment described herein involves the formation of a precursor composition that is deposited to form the final conductive structure. Alternatively, the conductive polymer precursor composition may be referred to as an ink, paste, precursor material, conductive adhesive, or resin carrying metal microparticles, but other terms may be used for similar compositions in the art. Precursor compositions share the common characteristic of being depositable, capable of being deposited as coatings, dispensable compositions, printable structures, pastes, etc., and the rheological properties of the composition may vary depending on the deposition method.

[0031] The material is cured after the deposition of the precursor composition. Curing as described herein is broadly used to refer to the conversion of a pourable and coatable flowable precursor composition into a solid conductive material, and unless otherwise stated, it is not intended to imply any particular chemical reaction. Therefore, curing as described herein can refer to solvent removal, polymerization and / or crosslinking of the precursor composition, reduction of the metal composition, various combinations thereof, etc. In some embodiments, the curing process is typically influenced by the processes used to polymerize and / or crosslink the precursor composition. In additional or alternative embodiments, the incorporation of a reducible metal composition can also affect process conditions. Curing may involve solvent evaporation, which may or may not involve heat. Some polymer binders can be used in the precursor composition, wherein the polymer binder is dissolved in a solvent to form the precursor composition, and solvent removal solidifies the polymer binder and the composite conductive structure without necessarily crosslinking the polymer. The polymer binder can also be formed during curing by polymerization without crosslinking, partial crosslinking, or high crosslinking. For crosslinking systems, the initial precursor composition may contain soluble or liquid monomers, oligomers, or polymers as non-volatile solvents. The polymer may be cured by heat (thermal crosslinking), irradiation (e.g., UV-driven crosslinking), or simply by solvent evaporation. The system may also include various photoinitiators or thermal initiators, adhesion promoters, rheology modifiers, reducing agents, and other additives to promote crosslinking. Reduction of metal compounds may be combined with polymer crosslinking or may occur as a result of different treatments.

[0032] The resulting cured material is a solid with metal embedded within a polymer matrix. The composition can be selected to adhere appropriately within the desired structure. The polymer matrix typically provides the desired cohesion with a suitable metal loading, and appropriate processing, to achieve suitable homogeneity. In some embodiments, other organic materials, different from the polymer matrix, may also be deposited, but may then be retained within the final solid structure or removed through subsequent processing. The metal loading can be adjusted to obtain the desired conductivity, possibly in tradeoff with material properties.

[0033] As demonstrated herein, compositions containing a large amount of reducible metal (e.g., silver salts and complexes) can effectively improve the conductivity of the resulting conductive structures. Metallic substances can be reduced by functional groups within the material to form elemental metal deposits throughout the material. Specifically, solvents, solid organic components, and / or dissolved reducing agents can reduce metal ions / complexes. Based on the nucleation of the metal deposition around the metal particles within the composite, the deposited metal can form robust conductive pathways. Similar to the applicant's previous work, the reduction and deposition of elemental metals can significantly improve conductivity by reducing the resistance between metallic nanostructures and microstructures.

[0034] The solvent for the precursor composition can be volatile and / or non-volatile. Specifically, the polymer precursor is typically a liquid (although it may be viscous), which acts as a non-volatile solvent and can be used to disperse metal particles including silver nanowires, and the non-volatile solvent may be the polymer precursor. If the reducible metal compound is soluble in the polymer precursor, the precursor composition may not contain any volatile solvent. Any volatile solvent should be compatible with the polymer precursor, meaning that the polymer precursor is soluble in the volatile solvent. While volatile solvents may be desirable as processing aids for adjusting viscosity, promoting blending, allowing thickening due to evaporation before curing, delaying resin curing until solvent evaporation, or other desired functions, their presence may not be desirable from an environmental and / or health and / or treatment perspective. In some embodiments, viscous, relatively high-boiling-point volatile solvents (e.g., glycol oligomers and their derivatives) may be used so that the removal of the volatile solvent occurs substantially during curing. This solvent can be used not only to adjust the rheological properties of inks or pastes and for subsequent processing, but also as an effective reducing agent for reducing metal ions and complexes. Using solvents with higher boiling temperatures (e.g., above about 125°C) allows the reduction of metal compounds to occur before complete evaporation. However, although not theoretically limited, the presence of solid metal particles reduces the energy barrier for nucleation and reduction, and therefore the heterogeneous nucleation and reduction of reducible metal compounds can occur at lower temperatures (with less energy) compared to isolated or homogeneous systems without solid metal particles. Therefore, even though solvents with lower boiling points can reduce reducible metal compounds, these solvents (e.g., ethanol or isopropanol) may be too volatile for some practical applications, depending on the other components of the precursor composition.

[0035] Although in some embodiments the composite conductive material does not contain a large number of nanowires in the aggregate of metal particles, including silver nanowires can be suitable for providing improved conductivity. Nanowires can also improve other properties, such as flexibility and stretchability. The ability to achieve high silver nanowire loading in a well-dispersed mixture provides the basis for the silver nanowire-based composites described herein. Other silver particles are incorporated prior to crosslinking and / or drying to allow for the desired control over the properties of the loaded resin material. The use of silver nanowires improves conductivity. Conductivity can be further improved by using reducible metal compositions, as the deposition of metal increases the likelihood of the formation of initial metal particles and conductive networks. Existing products, such as conductive adhesives or other metal-loaded conductive resins, are typically based on silver micron or nanoparticles and / or silver flakes to form highly conductive conductive adhesive products. This work represents a significant advancement over the applicant's previous work, revolutionizing several aspects of silver nanowire processing and different works focusing on silver nanoparticles and / or silver flakes. These advances can be viewed as the introduction of large quantities of silver nanowires to improve the conductive pathways through the composite and / or to deposit silver or other metals through the composite via the reduction of metallic substances, where these mechanisms can significantly reduce resistance.

[0036] Numerous works related to silver nanowires have pointed to transparent conductive films, where the morphology of silver nanowires offers significant advantages for forming these structures. The applicant has developed a proprietary melting technique to provide state-of-the-art, high-quality transparent conductive films with low sheet resistance, high transmittance, and extremely low haze. For example, see U.S. Patent No. 10,029,916, entitled "Metal Nanowire Networks and Transparent Conductive Material," and U.S. Patent No. 10,020,807, entitled "Fused Metal Nanostructured Networks, Fusing Solutions With Reducing Agents and Methods for Forming Metal Networks," both of which are incorporated herein by reference. In the case of opaque conductive materials, silver nanowires can be loaded into polymers, such as adhesives, to form conductive fillers. For example, see U.S. Patent Application No. 2024 / 0290516 (hereinafter referred to as '516 application) entitled "Silver Nanowire and Noble-MetalCoated Silver Nanowire Conductive Polymer Composites With Low Loading Percolation Conduction" to Wilcar et al., which is incorporated herein by reference.

[0037] Recently, the applicant has expanded this work to provide a room-temperature processing of proprietary melting processes for metallic loads ranging from highly transparent to translucent and to near opaque. This work is described in U.S. Patent Application No. 2023 / 0416552 (hereinafter referred to as '552 application) entitled "Formation of Electrically Conductive Layers at Room Temperature Using Silver Nanoparticle Processing and Inks for Forming the Layers" and U.S. Patent Application No. 2024 / 0257991 entitled "Formation of Electrically Conductive Layers at Near Ambient Temperature Using Silver Nanoparticle Processing and Inks for Forming the Layers," both of which are incorporated herein by reference.

[0038] In the case of opaque conductive structures formed from silver nanoparticles, the work of Professor Magdassi and colleagues has involved the chemical melting of silver nanoparticles in relatively thick (micrometer-thickness) structures to form small but opaque conductive traces. This work is described, for example, in U.S. Patent Application No. 2012 / 0168684, entitled "Process for Sintering Nanoparticles at Low Temperature," granted to Magdassi et al., which is incorporated herein by reference. Magdassi found that the resistivity obtained was significantly dependent on the substrate material. Furthermore, Magdassi's samples were formed without a polymer or resin matrix, although polymer dispersants are mentioned in the context, but there is insufficient detail to explain this aspect of Magdassi's work. The lack of a polymer matrix implies that the process characteristics would be expected to be different, and the melting mechanism used by Magdassi appears inconsistent with the use of a large polymer matrix.

[0039] The use of silver nanosheets to form conductive pastes for low-temperature processing has been described. These results are described in U.S. Patent No. 11,084,950, entitled "Fast Conductivity Polymer Silver," to Graddy, Jr. et al., which is incorporated herein by reference. The '950 patent describes a material having a resin component. The exemplary conductive material in the '950 patent has 82.5% by weight silver flakes. The '950 patent reports the resistivity values ​​for a sample with a volume of 1 cubic centimeter, but does not appear to provide resistivity values ​​or provides insufficient information to allow for the extraction of resistivity values. The material in the '950 patent can essentially be considered a control material relative to the materials described herein having a silver nanowire component and / or having a metal salt component.

[0040] Conductive pastes containing silver flakes have been described as having the ability to achieve low resistivity. For example, see U.S. Patent Application No. 2015 / 0262728, entitled "Electrically Conductive Paste Composition and Method of Forming an Electrical Circuit on a Polymer Substrate," issued to Ogiwara et al., which is incorporated herein by reference. This reference teaches the use of 87% to 95% silver flakes and treatment at 120°C for up to half an hour. These materials have a higher silver loading than those in the '950 patent, but involve heating to cure the material.

[0041] Previous work involving loading silver nanowires into resins involved relatively low nanowire loadings (aimed at reaching the percolation limit to achieve some useful conductivity), but the resistivity was significantly higher than that of the aforementioned high-loaded materials. The applicant has discovered that the use of noble metal-coated silver nanowires in specific composites has successfully reduced the resistivity at extremely low loadings, thereby enabling a corresponding improvement in achievable conductivity. See the '516 application cited above. However, the resistivity is significantly higher than that described herein.

[0042] An example of using highly loaded thermally sintered silver nanowires to form highly conductive materials can be found in Zhang et al.'s "Electrically Conductive Adhesives with Sintered Silver Nanowires" (2009 International Conference on Electronic Packaging Technology & High Density Packaging (ICEPT-HDP) 978-1-4244-4659-9 / 09 (2009)), which is incorporated herein by reference. Before the materials are doped to form a composite, the nanowires are not well dispersed. Low resistivity values ​​can be achieved. Another procedure involving the directional incorporation of silver nanowires into polymer resins is described in Wang et al.'s "A Comprehensive Study of Silver Nanowires Filled Electrically Conductive Adhesives" (J Mater Sci: Mater electronic, DOI 10.1007 / s10854-015-3446-9 (July 2015)), which is incorporated herein by reference. These empirical studies may demonstrate the feasibility of low resistivity-loaded polymer composites, but the processing methods may not be commercially viable.

[0043] The current progress is based on the applicant's discovery of a technique for forming well-dispersed aggregates with high nanowire loading in a chosen solvent, and also on the applicant's earlier work on improving the resistivity of transparent conductive materials by reducing reducible metal compositions. This high-loading work is described in U.S. Patent Application No. 18 / 634,300 (hereinafter referred to as '300 Application) entitled "High Loadings of Silver Nanowires: Dispersions and Conductive Pastes; And Corresponding Methods," co-filed with Wilcal et al., which is incorporated herein by reference. The ability to form high concentrations of well-dispersed nanowires in a chosen solvent provides significant processing flexibility for the design of conductive adhesives, pastes, inks, and commonly used conductive loaded polymers (collectively, ECAs). Using well-dispersed silver nanowires, homogeneous blends can be formulated into inks for depositing ECAs using suitable deposition methods. '300 Application also describes the rheology dependence of silver nanowire morphology. Thin, long nanowires are particularly suitable for transparent conductive films, but because viscosity increases rapidly with concentration, these long, thin nanowires have a limiting morphology for loading. Therefore, using shorter, thicker silver nanowires allows for achieving higher loading while maintaining reasonable viscosity.

[0044] Under high loads, even shorter and thicker silver nanowires (low aspect ratio) can result in materials that are unprocessable under high loads, with concentrations potentially lower than those required for a particular application. Additionally, silver nanowires can be more expensive than other silver forms. However, high concentrations of silver nanowires can be incorporated into the process at appropriate concentrations, and the solvent can be removed at various processing stages if necessary. In this work, silver nanowires are combined with other silver microparticles suitable for forming ECAs, particularly silver particles and / or silver flakes, but components containing other metals may also be used. Nanowires may be included in an amount from about 1% to about 95% by weight relative to the total metal (e.g., silver). The metal as part of the total solidified solids is typically from about 45% to about 98%. In another embodiment, all metal microparticles may be nanowires (i.e., 100%), but due to contaminants from other metal forms, this embodiment effectively covers 95% to 100% by weight of nanowires as part of the metal microparticles in the precursor composition. Those skilled in the art will recognize that additional ranges within these defined ratios are conceivable and that such additional ranges are within the scope of this disclosure. Regarding other metal microparticles, relative amounts, shapes, and sizes can be selected to provide desired properties and costs. High-load ECAs can be cured into materials with low resistivity values. It has been found that including silver nanowires reduces resistivity compared to similar ECAs without silver nanowires. Although specific resistivity values ​​reported in the art appear to depend on specific polymer matrices, substrates, processing, and possibly other parameters, direct comparisons with similar systems provide confidence in the beneficial effects of including silver nanowires.

[0045] The applicant has developed a proprietary melting technique for improving the conductivity of transparent conductive films without degrading their optical properties. Patents related to this melting technique are cited above. For embodiments of particular interest, the melting technique is based on a reducible metal compound (e.g., a silver composition) that can be reduced to form a network of molten metal nanostructures, thereby producing a highly desirable structure for a transparent conductive film with reduced or eliminated junction resistance while maintaining high flexibility and stability. This melting process for transparent conductive films is understood as a thermodynamically driven curing and / or reduction process, in which silver is deposited towards the junction to reduce the total free energy. As described herein, reducible silver compositions can also be advantageous for enhancing conductivity in materials with high metal loading and low resistivity. Similarly, although not theoretically limited, silver compositions are expected to be reduced at recesses and in low chemical potential regions between nano and micro structures, as these locations are thermodynamically favorable. Additional reducing metals are used to better connect nano and micro structures (e.g., nanowires, sheets, and micro and nanoparticles), resulting in better electrical connectivity throughout the structure and lower total resistivity for the total metal content. The ability to reduce the metal content required for the target resistivity provides an improved range of achievable material properties.

[0046] In this paper, it has been found that incorporating and reducing reducible metal compositions, particularly silver compositions, can reduce resistivity without significantly affecting material handleability. Even with high metal loading in the composition, additional filling with in-situ reduced metals can be significantly beneficial. Current observations suggest that the reduction in resistivity may reach its maximum with increasing amounts of reducible silver composition, but this can also be a strong function of the overall composition, including the choice and ratio of fillers and the chemical properties of the reducible metal composition, in addition to final curing and processing. The beneficial effects of the reduced metal composition can be observed regardless of the presence of silver nanowires, which can be the sole metal particles while still benefiting from the use of the reducible metal composition.

[0047] Surprising properties were observed with high-load dispersions of silver nanowires. See the '300 application cited above. First, there is a strong rheological dependence on the shape and size of the silver nanowires. Thinner and longer silver nanowires can exhibit paste-like, non-Newtonian behavior at relatively low weight percentage concentrations; however, even with surprisingly low solid volume percentages, these materials do not exhibit a homogeneous, separated material. Using shorter and thicker nanowires creates conditions for forming materials with higher silver nanowire concentrations. In this prior work described in the '300 application, the amount of organic polymeric dispersant relative to the weight of the nanowires can be less than about 20% by weight and can be significantly lower. Polyvinyl pyrrolidone (PVP) is typically used during nanowire synthesis, and further processing of the nanowires often incorporates PVP or related polymers (e.g., copolymers) into subsequent processes. PVP bound to the nanowires provides dispersing power, and excess PVP can be copurified with the nanowires. Excess PVP not bound to the nanowire surface can be removed by additional purification. In this context of complex formation, the polymeric dispersant (e.g., PVP) for the silver nanowires can act as a dissolved binder that forms a solid upon removal of the solvent. Thus, the polymeric dispersant for the nanowires can be the sole or primary organic component of the resulting conductive composite composition.

[0048] Silver nanowires are typically single-crystal structures, exhibiting extremely high conductivity along their length, as well as high metal loading and / or nano-adhesives. TM (NanoGlue) TM The use of silver nanowires has been employed to reduce junction resistance. This work extends the application of nanowires in composite materials by introducing other shapes of silver structures to replace a significant portion of the silver nanowires and / or supplement them, thereby achieving high metal loading levels with lower silver nanowire loading. Other suitable metal particle shapes include, for example, silver particles (generally spherical), silver flakes, other microparticle shapes, or various mixtures thereof. The relative proportion of silver nanowires to other metal particles can be selected based on considerations of curing material performance, cost, processing, the properties of ECA precursor inks, or other factors.

[0049] Composition - Precursor and Cured Conductive Material

[0050] Regarding the composition, precursor compositions and conductive product materials may be considered. In the absence of volatile solvents, the total weight of the metal and organic components may not change significantly. During curing, any reducible metal composition can be reduced to the elemental metal, and the polymer precursor (monomers, oligomers, dissolved polymer binders, i.e., resin systems) can crosslink into a monolithic material. Solvent removal can also solidify the previously dissolved binder polymer from the precursor composition. Although the crosslinking process may generate small amounts of volatile byproduct compounds, this effect is generally insignificant to any significant change in the metal-to-organic ratio. In relevant embodiments, the crosslinked polymer, crosslinked physically or chemically, can be considered a cohesive single unitary mass. When a large amount of reducible metal composition is present, the reduced loaded metal during curing can form a monolithic mass entangled with the crosslinked polymer as a cohesive composite structure. As a result of these processes, the significant difference between the precursor material and the cured material can be due to the individual components of the precursor composition losing their respective properties to varying degrees. While the crosslinking density of polymers or the entanglement of adhesive polymers (where appropriate) is generally understood, a comprehensive assessment of this can be difficult, but details may vary under high metal loadings. In some embodiments, uncrosslinked organic matter can also be removed by further processing, such as dissolving the organic material after reducing the reducible metal composition. Generally, all or most organic components can be removed, for example, by using higher temperatures or ablation.

[0051] Precursor compositions typically comprise both metallic and organic components. As described herein, if the total metal mass (e.g., silver microparticles) in the precursor composition is part of the precursor composition, this total metal mass can be an upper limit ranging from an upper limit of no more than about 98% by weight, in another embodiment no more than 95% by weight, in one embodiment no more than about 92% by weight, in additional embodiments no more than about 90% by weight, and in some embodiments no more than about 85% by weight, to a lower limit of at least about 50% by weight, in some embodiments about 55% by weight, in other embodiments about 57.5% by weight, in additional embodiments about 60% by weight, and in some embodiments about 65% by weight. Therefore, the ranges are described based on either of these upper or lower limits (e.g., about 55% by weight to about 98% by weight). The total metal mass may comprise metal microparticles and, if desired, reducible metal ions provided in the form of a reducible metal composition. The range of reducible metal compositions is provided below. In some embodiments, the metal microparticles comprise about 1% to about 95% by weight of silver nanowires as part of the metal microparticles, in other embodiments about 5% to about 90% by weight, in some embodiments about 10% to about 90% by weight, and in other embodiments about 20% to about 85% by weight. In additional embodiments, all the metal microparticles may be silver nanowires (95% to 100% by weight), and there are also other ranges based on any selected lower limit and any selected upper limit values ​​of these ranges. In additional embodiments, the composite is primarily formed of non-nanowire microparticles, wherein the silver nanowires complement the material and further contribute to conductivity. For these embodiments, the metal microparticles may comprise about 1% to about 45% by weight of silver nanowires, in other embodiments about 2% to about 40% by weight, in some embodiments about 3.5% to about 35% by weight, and in additional embodiments about 5% to about 30% by weight of silver nanowires. The contribution of reducible silver salts is given below. Those skilled in the art will recognize that additional ranges of total metal mass and silver nanowire portions of metal particles within the aforementioned defined range are conceivable and that such additional ranges are within the scope of this disclosure.

[0052] The precursor composition generally comprises from about 2% by weight to about 80% by weight of an organic component (including any volatile solvent) and a polymer matrix precursor (e.g., monomers, oligomers, dissolved binder polymers, and / or crosslinkable resins). In some embodiments, the precursor composition may comprise from a lower limit (any lower limit within the range) of about 2% by weight, in other embodiments about 5% by weight, in additional embodiments about 7% by weight, in some embodiments about 8.5% by weight, in other embodiments about 10% by weight and in other embodiments about 15% by weight to an upper limit of about 80% by weight, in other embodiments about 70% by weight, in additional embodiments about 60% by weight and in some embodiments about 50% by weight, and there is also a range extending from any specified lower limit to any specified upper limit. The organic component of the precursor composition can be considered to include both non-volatile and volatile components. Some polymeric components may be volatile prior to polymerization or crosslinking, but these components can be considered non-volatile if they are boiled at sufficiently high temperatures under process conditions to transform them into a non-volatile polymeric composition before they become significantly volatile. During curing, volatile components are generally expected to evaporate, but some amounts may remain bound to the material. Although precursor compositions may contain small amounts of volatile solvents (e.g., residual solvents from processing), in some embodiments, maintaining additional volatile solvents in the precursor composition as process aids may be desirable. Generally, polymeric precursors can act as non-volatile solvents. Thus, in some embodiments, the precursor composition may contain no more than about 40% by weight of volatile solvent, in some embodiments about 1% to about 35% by weight, in still others about 3% to about 30% by weight, and in additional embodiments about 5% to about 25% by weight, and any range including either of these upper or lower limits also exists. Correspondingly, the precursor composition may comprise from about 2% to about 55% by weight of a non-volatile organic component, in some embodiments from about 4% to about 50% by weight, in some embodiments from about 5% to about 45% by weight, and in additional embodiments from about 7% to about 40% by weight, and there are also ranges involving any combination of upper and lower limits of these ranges. The precursor composition may typically comprise up to about 10% by weight (as needed) of process aids, in some embodiments from about 0.05% to about 8% by weight, and in other embodiments from about 0.1% to about 5% by weight, such as crosslinking agents, viscosity modifiers, plasticizers, curing agents (copolymer components), surfactants, etc. The remainder of the precursor composition typically comprises a metallic component. The metallic component may comprise silver nanowires, other metal particles, and, if desired, a reducible metal composition.In particular, for embodiments containing reducible metal salts, the solvent, precursor resin, or resulting polymer matrix typically has hydroxyl groups or other functional groups suitable for reducing the metal substance. Furthermore, a reducing agent may be intentionally added to reduce the reducible metal composition. For example, suitable reducing agents may include ammonium or other salts that can oxidize anions (e.g., sulfites, bisulfites, thiosulfates, phosphites, hydrogenphosphites, oxalates, tartrates, etc.), formic acid, N,N-dimethylformamide, alcohols, phenolic compounds (e.g., phenol, aminophenol, metol, hydroquinone, gallol, catechol, 4-amino-3-hydroxy-1-naphthalenesulfonic acid, etc.); polyols, including sugar alcohols; sugars, such as monosaccharides and disaccharides; hydroxylamine and its derivatives; aldehydes; hydroxycarbonyl compounds, such as hydroxy ketones, such as benzoin, furazolidone, hydroxyacetone; acylhydrazide derivatives, such as phthalylhydrazide, adipate dihydrazide, phenidone, etc.; reduced aromatic compounds, such as 1-methyl-1,4-cyclohexadiene, dihydrodiazine, etc.; and various combinations of the foregoing. The amount of reducing agent can be selected based on the molar amount of the metal salt to be reduced (according to equivalence).

[0053] Regarding the relative amounts of materials in the cured composition, the total weight changes due to the loss of any volatile components, and the relative amount can then be calculated relative to any combination produced by the curing process (as described above, such as the total amount of metals, the total amount of organic matter, and any individually identifiable constituents). Those skilled in the art will recognize that additional ranges of organic matter concentrations within the aforementioned defined ranges are conceivable and that such additional ranges are within the scope of this disclosure.

[0054] After volatile removal and curing, the total non-volatile organic compound (NOC) content of the product conductive solid material typically does not exceed about 55% by weight, including products from the polymer precursor and any residual process aids. Generally, the product conductive solid material may contain about 3% by weight to about 50% by weight of organic matter, in some embodiments about 5% by weight to about 45% by weight, in other embodiments about 7% by weight to about 40% by weight, and in additional embodiments about 8% by weight to about 35% by weight, and also within ranges based on any specified lower and upper limits. Although this weight percentage is relatively small compared to the metal component, the organic content can be relatively large in volume percentage due to the higher density of the metal component. Generally, the ECA composition has a volume percentage of organic components not exceeding about 85% by volume, in some embodiments about 10% by volume to about 80% by volume, in other embodiments about 15% by volume to about 77.5% by volume, and in additional embodiments about 20% by volume to about 75% by volume, and also within ranges based on any specified lower and upper limits. Even with a significant volume fraction of organic matter, good electrical conductivity can be achieved. Those skilled in the art will recognize that additional ranges of organic components within the aforementioned defined range are conceivable, and these additional ranges are within the scope of this disclosure.

[0055] To provide the required contribution to conductivity, suitable nanowires typically have an average aspect ratio of at least about 10, but in some embodiments, the use of silver nanowires with an aspect ratio of at least about 50 may be suitable. In still other embodiments, the silver nanowires may have an aspect ratio of about 20 to about 3000, in some embodiments about 30 to about 1500, in still other embodiments about 50 to about 1000, and in additional embodiments about 60 to about 500, or any other range based on any specified lower limit and any specified upper limit. The average diameter of the silver nanowires typically ranges from about 15 nanometers to about 250 nanometers, in some embodiments about 20 nanometers to about 200 nanometers, in some embodiments about 25 nanometers to about 150 nanometers, and in additional embodiments about 30 nanometers to about 100 nanometers, and also ranges based on any lower limit and any upper limit value. The average length of the silver nanowires can be from about 1 micrometer to about 1000 micrometers, in some embodiments from about 2 micrometers to about 800 micrometers, in some embodiments from about 3 micrometers to about 700 micrometers, and in additional embodiments from about 4 micrometers to about 500 micrometers, and there are also any ranges based on any specified lower limit range and any specified upper limit range. Those skilled in the art will recognize that additional ranges of aspect ratio, average diameter, or average length within the specific ranges described above are conceivable and said additional ranges are within the scope of this disclosure. The synthesis of thin, high aspect ratio silver nanowires with high uniformity is described in U.S. Patent No. 10,714,230 to Hu et al. entitled Thin and Uniform Silver Nanowires, Methods of Synthesis and Transparent Conductive Films Formed From the Nanowires, which is incorporated herein by reference. The formation of thicker and shorter (low aspect ratio) silver nanowires is described in '300 application. To obtain particularly robust metal nanowires resistant to environmental corrosion, silver nanowires can be formed into thin coatings with noble metals. The applicants have developed scalable synthetic methods, as described in U.S. Patent No. 9,530,534B2 to Hu et al., entitled "Transparent Conductive Films," which is incorporated herein by reference. These noble metal-coated silver nanowires are used similarly to silver nanowires to form transparent conductive coatings. As described herein, for forming high metal-loaded ECAs, the performance of noble metal-coated silver nanowires should be comparable to that of silver nanowires.The noble metal coating should be relevant to any silver nanowire size, and silver nanowires coated with noble metal are considered silver nanowires in this document.

[0056] For suitable implementations, other metal particles (e.g., silver particles) besides silver nanowires can have any reasonable shape, but specific particles are commercially available for use in loaded polymers, adhesives, or resins. Specifically, generally spherical metal sheets and particles are readily available for commercial-scale production at a reasonable cost. Generally spherical silver nanoparticles are commercially available, with a size in the nanometer range, an average particle size not exceeding about 200 nanometers, and an average particle size ranging from about 10 nanometers to 200 to 300 nanometers. Generally spherical particles in the micrometer range are also commercially available, with an average particle size from about 1 micrometer to about 100 micrometers. An average particle size of about 100 nanometers to about 10 micrometers achieves a reasonable balance between performance and cost. Suitable suppliers of silver particles (micrometer-sized particles or nanoparticles) include Heraeus, Inframat Advanced Materials, Ames Goldsmith, Sigma Aldrich, SS Nano, Cerion Nanomaterials, SkySpring Nanomaterials, and Nanocomposix. Silver flakes can have micrometer-scale lengths (or equivalent diameters) and small thicknesses, for example, an average diameter of about 1 to about 20 micrometers, and an average thickness of about 100 nanometers to about 2 micrometers. A representative example of the synthesis of silver nanosheets can be found in, for example, U.S. Patent Application No. 2016 / 0114390, entitled "Flake-Like Silver Powder, Conductive Paste, and Method for Producing Flake-Like Silver Powder," issued to Hori et al., which is incorporated herein by reference. Silver sheets are commercially available from, for example, Tanaka, Ferro, Reade, and Inferman Advanced Materials. In principle, any suitable conductive microparticles and their admixtures can be used, such as silver-plated particles, copper microparticles, nickel microparticles, etc.

[0057] Generally, the relative amount of silver flakes to silver nanoparticles or other silver microparticle shapes can be selected as needed from 1% by weight to 99% by weight and any range within that range. This selection can be based on cost, precursor composition properties and delivery capability, target curing material properties, and / or other selected parameters. For example, thinner deposits may be more advantageous than silver nanoparticles compared to silver flakes. The relative amount of silver nanowires to other silver microparticle shapes can be similarly affected. As mentioned above, some embodiments may not contain any silver nanowires. However, in embodiments of particular interest, the precursor includes silver nanowires. The range of total metal content in the precursor composition has been given above; the range of silver nanowires as part of the total metal content and the range of contributions of reducible metal ions relative to the total metal content are presented below. For any value within these ranges, non-nanowire silver microparticles comprise the remainder of the metal composition, and the values ​​and ranges of non-nanowire silver microparticles as part of the total metal and the total precursor composition vary accordingly.

[0058] Regarding the relevant implementation schemes, any soluble and reducible metal composition (e.g., a soluble silver composition) can, in principle, be incorporated into the ECA. The applicant has found that silver fluoride is particularly readily reduced in composite systems. This is already useful for the formation of transparent conductive films that can be processed at room temperature. See the '552 application cited above. In these systems with high metal loading and low solvent content, silver fluoride may react too quickly, but potential process modifications can be made if necessary to stabilize these metal compositions in the precursor composition. Furthermore, other chemicals and complexes can be selected to modify the reactivity of silver fluoride. Exemplary reducible metal compositions described herein include silver acetate, silver trifluoroacetate, and silver heptafluorobutyrate. For example, suitable reducible silver compositions include silver acetate (Ag(O2CCH3)), silver trifluoroacetate (Ag(O2CCF3)), silver heptafluorobutyrate (Ag(O2CC3F7)), silver lactate (Ag(O2CCH(OH)CH3)), silver hexafluoroantimonate (AgSbF6), silver fluoride (AgF), silver tetrafluoroborate (AgBF4), silver nitrate (AgNO3), silver perchlorate (AgClO4), silver hexafluorophosphate (AgPF6), or various mixtures of the foregoing, which are generally soluble in the solvent of interest. The choice of the specific silver salt may affect the process conditions. Although silver provides highly conductive deposits through the material, other soluble compositions, such as copper compositions, platinum compositions, gold compositions, and other metals, may also be used as needed. The desired effects of soluble silver compositions are even useful for ECAs without any nanowires.

[0059] As described above, silver ions can be considered part of the metallic component of the composite. The accompanying anions can form volatile or non-volatile components during curing, and correspondingly may or may not evaporate. Generally, the precursor composition may contain silver salts or other reducible metal salts, wherein the weight ratio of metal / silver from the reducible metal ions to silver particles (e.g., silver nanowires) is typically: no more than about 50% by weight of silver nanowires relative to the total metal weight, in some embodiments about 0.5% to about 40% by weight, in other embodiments about 0.75% to about 30% by weight, and in still other embodiments about 1.0% to about 25% by weight. The total weight of the salt depends on the weight of the anion relative to the metal cation. Similarly, the weight percentage of metal ions relative to the total precursor composition or cured material is derived directly from the fraction of total metal and reduced metal ions in the composition or material, and can be readily assessed accordingly. The metal salt should be soluble in a solvent or in the precursor mixture, and for large silver nanowire loads, the concentration of silver or other metal salts can be relatively high. Those skilled in the art will recognize that additional ranges of component concentrations and relative weights within the aforementioned defined ranges are conceivable and that such additional ranges are within the scope of this disclosure. As seen in the examples, the resistivity decreases significantly when used in conjunction with commercial metal pastes of soluble metal composition. Therefore, the use of reducible metal compositions, even independently of silver nanowires, can represent a significant advancement.

[0060] Precursors for the final composite polymer, which may be referred to as resins, monomers, oligomers, adhesives, adhesive resins, polymeric adhesives, or other suitable terms, may be crosslinked or polymerized during processing (typically during curing). In some embodiments, the precursor is essentially a dissolved adhesive polymer that is physically crosslinked into a solid upon removal of the solvent. The crosslinking mechanism is generally not limited with respect to the relevant embodiments. For example, crosslinking can be radiation-driven using ultraviolet light, thermally driven using suitable heating, spontaneous crosslinking upon removal of the solvent, chemical crosslinking, crosslinking upon exposure to moisture, or any other reasonable mechanism. The term polymer precursor as used herein broadly refers to resins, adhesives, etc., before curing, such that the polymer precursor is flowable and handleable, and may be viscous; however, the terms resin or adhesive may have specific meanings in narrow applications. Silver nanowire synthesis typically involves carrying polyvinylpyrrolidone (PVP) with the silver nanowires. Although the amount of PVP can be reduced with further purification, conventional purification can produce PVP of about 1% to about 25% by weight relative to the weight of the silver nanowires, and the PVP carried by the silver nanowires can be considered a component of the total organic composition. Unless otherwise stated, references to polymeric components are naturally interpreted broadly. Numerous commercial adhesives, resins, or other curable polymeric precursors are suitable and effective as adhesives, which are broadly defined as polymers suitable for bonding two surfaces together. Generally, suitable resins include, for example, acrylates, epoxy resins, silicones, such as polydimethylsiloxanes (although they have an inorganic backbone, they are also considered organic), urethanes, polyvinyl acetals, polyvinyl acrylates, various copolymers of the foregoing, various mixtures of the foregoing, etc. Generally, many crosslinkable resins contain functional groups that can reduce metal ions, or the crosslinking of the polymer will form suitable functional groups. Non-crosslinkable polymers can act as adhesives, wherein the treatment involves dissolving the adhesive polymer and then removing the solvent to solidify the polymer. Due to the high metal loading in the composite material, the reducing agent can direct, or may not direct, all or most of the reduction to specific low-energy sites in the metallic structure to achieve the observed improvement in conductivity. However, nucleation for deposition can occur near the metal particles and contribute to the formation of conductive blocks.

[0061] In contrast to the solid organic compositions mentioned above, the term "solvent" used here refers to a liquid composition at room temperature. The process of dispersing silver nanowires may involve initial dispersion in a low-boiling-point solvent, followed by a transition to a higher-boiling-point solvent if necessary, although the dispersion can be maintained in a low-boiling-point solvent. This indicates that solvent transfer is a transfer to a higher-boiling-point solvent, but this relationship may not be particularly restrictive for the transfer solvent, as the initial solvent can be handled under cold or pressurized conditions. For the initial solvent, it should be suitable for forming a diluted, stable silver nanowire dispersion, with water and low molecular weight alcohols being particularly suitable for forming good dispersions at low concentrations. If good solvent transfer is involved in forming a more concentrated dispersion, the transfer solvent should generally be highly soluble or miscible in both the initial dispersion solvent and solvents in which PVP is soluble, to avoid PVP phase separation. For example, suitable volatile solvents for dispersions include water, alcohols, glycols, amides, glycol ethers, sufficiently polar aprotic solvents (e.g., dimethyl sulfoxide), some additional polar solvents, and various mixtures of the aforementioned. For example, specific volatile solvents include water, methanol, ethanol, isopropanol, cyclohexanol, ethylene glycol (EG), propylene glycol, dimethyl sulfoxide, ethyl lactate, triethylene glycol (TEG), butyl cellosolve, butyl carbitol (BC), dimethylacetamide, dimethylformamide, acetonitrile, and various mixtures thereof. In some embodiments, as described above, the use of non-volatile solvents may be desirable. Generally, the solvent comprises the remainder of the precursor composition except for the metal component, metal salt anion, polymer component (unless some or all of the solvent is a polymer component), and any additives.

[0062] Although the solvent refers to a liquid composition, it can be a direct precursor for potential further processing. For example, the solvent can be a monomer, oligomer, or polymer that can be polymerized and / or crosslinked during further processing, such as heating, irradiation, blending with additional reactants, drying, oxidation, various combinations of the foregoing, or other suitable methods. For example, suitable monomers or oligomers include: acrylics, such as hydroxyethyl methacrylate and hydroxyethyl acrylamide; diols or polyols as precursors to polyurethanes, such as tetraethylene glycol and 1,3-propanediol; epoxy resin precursors, such as DGEBA (bisphenol A diglycidyl ether), Celloxide 2021P (Daicel USA, Inc.) or YX8000D (Mitsubishi Chemical Group); radiation-curable liquid adhesives, such as optical adhesive NOA 85 (Norland Products, Inc.), and various combinations thereof, which can be cured by various thermal, radiative, or chemical means. The polymer precursor solvent may or may not be volatile. The polymer precursor solvent may be blended with the volatile solvents mentioned above, and is generally inert under the relevant process conditions.

[0063] In some embodiments, the precursor composition may further include additives, such as process aids. Generally, other processing aids, such as surfactants, thickeners, antioxidants, etc., may or may not be used in various precursor compositions. Generally, the amount of additives, as needed, does not exceed about 5% by weight of the non-volatile component, and in some embodiments is about 0.01% by weight to about 2% by weight. Additives can be selected by composition or amount to not significantly interfere with conductivity.

[0064] As described above, curing refers to the process of converting a precursor composition into a solid and conductive composite material. The precursor composition is flowable in the sense of being depositable, while the cured material is solid and non-flowable. As mentioned above, curing may include solvent removal or any other process that facilitates the conversion of the precursor into a solid material, said solvent removal typically carried out by evaporation, polymerization, crosslinking reduction of the metal composition, or various combinations thereof.

[0065] The properties of cured materials are typically highly dependent on the amount and composition of the polymer matrix. For example, the elastic modulus of a cured composite can be significantly influenced by these parameters. The composition is usually determined by the precursor composition, although a precise curing process can influence the final composition to some extent. While the reduction of the metal composition during curing can alter the internal morphology relative to the initial particle properties, the total metal is particularly significant, especially that remaining from the precursor. In any case, the metal is usually distributed substantially uniformly throughout the composite. The relative amount of metal in the cured composite depends on the total organic components in the cured composite. The total organic contribution of the composite typically includes the non-volatile components of the precursor minus any volatile product composition resulting from the polymerization or crosslinking reaction. Quantitatively, a certain amount of the composite can be heated to a sufficiently high temperature to thermally remove all organic material, leaving only the metal, with the weight loss corresponding to the organic contribution. This assessment can be performed in a calorimeter, or more simply using a balance and oven.

[0066] Regarding the composition of the cured composite material, the total metal mass can range from an upper limit of about 98% by weight, in some embodiments about 95% by weight, in some embodiments about 92% by weight, in additional embodiments about 90% by weight, and in some embodiments about 85% by weight, to a lower limit of at least about 45% by weight, in some embodiments about 50% by weight, in additional embodiments about 55% by weight, in other embodiments about 60% by weight, and in some embodiments about 65% by weight, and there is also a range based on any mentioned upper limit to any mentioned lower limit. Depending on the treatment and the reducible metal composition that may be present in the precursor, the source of the metal may not be quantitatively identified after curing, although this is clear from the precursor composition. Generally, a reasonable analysis of the composite should be able to qualitatively assess the source of the metal used to form the cured composite material. The organic component of the composite typically includes the remaining mass of the composite, although some inorganic byproducts may remain from the reducible metal composition and / or additives. Without knowledge of the precursor composition, it may not be easy to quantify any inorganic byproducts, which may be incorporated into the metal weight, typically less than about 5% by weight of the metal. Any byproducts that are thermally removed along with the organic matter can be considered part of the organic matter weight, and any byproducts that are not thermally removed along with the organic matter can be considered part of the metal weight. For the cured composite composition, the organic component can be an upper limit of about 50% by weight, in some embodiments about 45% by weight, in some embodiments about 42.5% by weight, in additional embodiments about 40% by weight, and in some embodiments about 35% by weight, to a lower limit of about 2% by weight, in some embodiments about 5% by weight, in additional embodiments about 8% by weight, in other embodiments about 10% by weight, and in some embodiments about 15% by weight, and there is also a range based on any mentioned upper limit to any mentioned lower limit.

[0067] Methods for processing and forming dispersions

[0068] Advances in the processing of silver nanowire dispersions have paved the way for the formation of previously unthinkable materials exhibiting surprising properties comparable to novel compositions. For relevant embodiments, the processing procedure is influenced by the presence of nanowires, requiring a suitable manner to incorporate the nanowires into the composite material. To form a well-uniform material, the silver nanowires can be sufficiently dispersed before incorporating with other components of the precursor composition. The applicant has successfully dispersed silver nanowires directly into resins as non-volatile solvents, see the above-cited '300 application. However, dispersing the silver nanowires in a high-boiling-point solvent as a stable stock solution can be ideal, and this method is illustrated herein. The solvent used for the nanowire dispersion can be selected to be compatible with the solubility of the polymer precursor. The polymer precursor may or may not be diluted with a volatile solvent, and both cases are illustrated herein. Low-boiling-point volatile solvents are not necessarily used unless required as a specific processing aid. In additional or alternative embodiments, some of the solvent can typically be removed by evaporation under reduced pressure to remove some or all of the volatile solvent to produce the polymer precursor product. The '300 application teaches a suitable solvent transfer procedure for forming concentrated silver nanowire dispersions in a wide range of solvents. In summary, silver nanowires are generally well dispersed in a more diluted dispersion, typically not exceeding about 10% by weight of solids in low-boiling solvents such as ethanol, which is particularly beneficial for forming good nanowire dispersions. The desired solvent can then be blended with the diluted dispersion in the desired amount, and the low-boiling solvent can be removed by evaporation, vacuum, and / or heating. In an example, a 40% by weight solution of silver nanowires is formed in a solvent blend of butyl carbitol (diethylene glycol butyl ether) and triethylene glycol, wherein the original ethanol solvent is removed by rotary evaporation. If desired and the low-boiling solvent is suitable for the polymer resin, the diluted solution can be used directly, wherein the low-boiling solvent is then removed after blending or during curing.

[0069] The incorporation of a reducible silver composition enables process improvements while providing the ability to reduce metal ions to form in-situ deposited metals, potentially resulting in a significant reduction in the resistivity of the formed metal composite. The remaining components can be similarly prepared for blending all components together, and this process can depend on the nature of the components. Ultimately, a well-mixed composition is typically formed, and the mixing process can depend on the concentration and rheological properties of the composition. Various commercial mixing equipment are suitable for this purpose, although in the presence of silver nanowires, any shearing should not be excessive and ultrasonic treatment should be avoided to prevent nanowire breakage (if this is not desirable).

[0070] Before incorporating a polymer precursor into a precursor solution, the polymer precursor can be dissolved in a solvent, although liquid polymer precursors can be directly incorporated. Ultrasonic treatment, grinding, and vortexing can be used to promote the dissolution of the polymer precursor. The amount of solvent typically depends on the properties of the polymer precursor and the solvent, which can be determined by those skilled in the art using any additional information that may be available from the supplier. Similarly, reduceable silver compositions (typically silver salts) can be dissolved to form a stock solution before being incorporated with other components. The appropriate concentration also depends on the silver salt and the solvent.

[0071] In some embodiments, at one stage of the process, a resin, or a resin having the desired amount of solvent, may be prepared and combined with metal microparticles without silver nanowires. The combination may then be ultrasonically treated and / or mixed using a mechanical mixer to blend the resin and metal microparticles. Once the combination is sufficiently mixed, a silver nanowire dispersion is added to the combination, and then the composite precursor material is mixed and / or ultrasonically treated to form an ECA precursor material with paste-like properties that is immediately ready for coating. If a reducible metal composition is added, this may be added together with, before, or after the silver nanowires to be incorporated into the composite material. Generally, the exemplary processing sequence is variable, at least for some formulations. For example, the resin may first be mixed with silver nanowires and then with other microparticles, or the silver nanowires may be mixed with other material microparticles and then with the resin. Those skilled in the art can use the teachings herein to select a suitable process sequence for a particular formulation.

[0072] As described above, various mechanisms can be applied to crosslink the polymer in the composite or to remove the solvent. For example, if heat treatment is performed, the reduction of the reducible metal composition can be carried out simultaneously with crosslinking. Curing conditions can be adjusted taking into account polymer curing and any metal reduction; this can indicate slightly different conditions, such as radiation for polymer curing and heat for silver reduction. The order in which curing conditions are applied or potentially applied simultaneously can be selected empirically by those skilled in the art, and such selection is generally not expected to have a significant impact on the product. The reduction of the reducible metal composition can also be fine-tuned based on the selected chemical properties and may be further refined by including other reducing agents (which can also be selected based on their reactivity). Thermal curing can be carried out by heating to at least about 75°C, and the upper cutoff temperature can be determined by the thermal stability of the polymer, but typically the heating temperature does not exceed about 400°C. Heating can be carried out for about 2 minutes to about 6 hours. A wide range of suitable polymer matrix materials and solvents are possible, and corresponding processing conditions can also be suitable. The presence of a solvent controls the material temperature based on the solvent's boiling point until the solvent evaporates; therefore, thicker deposits may involve longer curing times to remove the solvent. In some embodiments, the curing temperature may be from about 80°C to about 300°C, in others about 90°C to about 250°C, in still others about 95°C to about 225°C, and in other still others about 100°C to about 200°C. Silver reduction in the composite materials described herein typically involves longer curing times compared to those used in transparent thin conductive systems. In some embodiments, the thermal curing time may be from about 3 minutes to about 5 hours, in others about 5 minutes to about 4 hours, in still others about 7.5 minutes to about 3 hours, and in other still others about 9 minutes to about 2.5 hours. Those skilled in the art will recognize that additional ranges within the aforementioned specific time and temperature ranges are conceivable and are within the scope of this disclosure. Furthermore, laser treatment to remove organic matter or even higher temperatures (e.g., in an oven, etc.) can help further improve the conductivity of the conductive components and, if necessary, remove all organic matter.

[0073] In additional or alternative embodiments, when a suitable UV-curable resin is used, curing can be performed using UV radiation, and, for example, in the presence of ammonia, UV radiation can effectively reduce the reducible metal composition. Since metals are reflective, UV radiation penetration of metal-loaded materials can be problematic. This constraint provides a practical constraint on UV curing thicker composite deposits with a reasonable radiation dose over a suitable time. The actual thickness of the UV-cured material may depend on the degree of metal loading and the possibility of supplementing curing with heat. In some cases, additional heat may be applied before, during, or after UV curing to remove solvents or other volatiles and further improve the final electrical or thermal conductivity of the conductive component. The dose of radiation delivered is expressed as the energy received per unit area during the irradiation time, typically expressed in joules per square centimeter (J / cm²). 2 Suitable light sources can be mercury lamps or UV light-emitting diode (LED) lamps. Irradiation with UV light also induces heating, allowing for simultaneous thermal curing. Commercial UV curing systems for polymer curing are available from various suppliers. Pulsed light can be used to provide the required light, and the intensity of the radiation can further drive metal sintering, removal of volatile components, and curing of organic components. Infrared pulsed light can primarily initiate curing through the resulting thermal effect. Pulsed light systems are available from companies such as Xenon Corporation (Massachusetts, USA), offering a range of wavelength options.

[0074] Depending on the desired composition, precursor compositions can possess a range of properties, from printable inks to pastes. While solvent volume typically provides a generally adjustable parameter, the composition can be similarly adjusted to modify the properties of the precursor composition. The amount of metal can be selected to a significant degree according to the target resistivity, and the amount of metal can also constrain the practical range of precursor properties and corresponding deposition options. However, appropriate composition tuning provides a remarkably broad range of precursor properties. Although the precursor composition itself can possess reasonable conductivity, applications are typically targeted at cured forms with suitable application stability.

[0075] Prior to curing, the precursor composition can be deposited at a suitable location where curing aims to provide the desired conductivity. Deposition can include: blanket coating and patterning, such as using laser ablation, photolithography, or other suitable patterning methods; or selective printing, such as screen printing, gravure printing, gravure offset printing, nanoimprint printing, etc.; or jet delivery to directly form the desired conductive structure. Coating methods can include, for example, slot coating, spraying, extrusion, etc. Generally, commercial printing or coating equipment is suitable for delivering the precursor composition. More viscous precursors can be delivered using syringes, extruders, etc. The configuration of the deposited material is often highly application-dependent. For example, the deposit can be a dotted structure for electrically connecting adjacent components, such as solder balls. In some embodiments, ECA strips can be used to electrically connect structures further apart, such as to replace metal traces. There are no particular limitations on the specific configuration. Curing conditions can be affected by auxiliary materials, which may limit the process temperature. To facilitate a longer process time, the process temperature can be reduced, and the rheological properties of the ECA precursor can be adjusted to provide suitable deposition for a specific application.

[0076] Coating / Material Properties

[0077] Conductive coatings or deposits are typically opaque materials and can be formed as non-transparent structures. Non-transparent layers (e.g., translucent or opaque layers) are often formed with a high metal loading to impart low sheet resistance. For these coatings, haze and other optical properties are usually not a particular concern and may be meaningless. These highly conductive structures can be used to form metal traces, busbars, electromagnetic shielding, etc. Since conductivity is generally an important characterizing property of composite materials, the amount of silver nanowires can be adjusted based on cost and target mechanical properties. This is because a higher proportion of silver nanowires can reduce the metal loading, while increasing the mechanical influence on the polymer matrix and increasing cost, and vice versa.

[0078] The resistance of a thin coating can be expressed as sheet resistance (Rs), which is reported in ohms per square (Ω / □ or ohms / sq) to distinguish sheet resistance from volume resistance based on parameters associated with the measurement process. Sheet resistance along a surface is typically measured using a four-point probe or another suitable method. If the thickness of the structure is known or measurable, the resistivity (ρ) can be evaluated as ρ = R sThe resistance is expressed as R = ρL / A, where t is the average thickness, L is the length, and A is the area of ​​the conductive component perpendicular to the conduction direction. Resistance can be reduced by creating conditions to decrease L or increase A in busbar arrangements or similar conductive component configurations. Resistivity is an intrinsic parameter independent of size and measured in ohms per unit length. Although the measured sheet resistance depends on the properties and dimensions of the corresponding structure, assuming the material is homogeneous, resistivity is an intrinsic property of the material and independent of the structure. The resistivity of bulk silver has been reported to be 1.59 × 10⁻⁶. -6 Ohm-cm is the lower limit of resistivity for silver-based conductors. High-load silver materials can achieve resistivity of no more than approximately 5 × 10⁻⁶. -3 Ohm-cm, in some implementations not exceeding approximately 5 × 10⁻⁶. -4 Ohm-cm, and in some other implementations not exceeding about 1 × 10⁻⁶. -4 Ohm-cm and in other embodiments approximately 5 × 10⁻⁶ -5 To approximately 5 × 10 -6 The resistivity is measured in ohm-cm, and there exists any range of resistivity using either a defined lower limit or any defined upper limit. In some embodiments, reduction of the reduceable metal composition (e.g., silver salt) has been found to effectively reduce the observed resistivity by at least about 25%, in other embodiments by at least about 50%, in some embodiments by at least about 75%, and in still other embodiments by about 80% from the open circuit value to a measurable value. Those skilled in the art will recognize that additional resistivity ranges and resistivity variations within the aforementioned defined ranges are conceivable and are within the scope of this disclosure.

[0079] For testing, a paste-like loading precursor composition is applied to a glass slide between 60-micrometer-thick spacers. The spacers are then removed, and the slide with the paste coating is cured, for example, in a well-ventilated oven at a selected temperature for a selected time. For UV-curable polymers, the prepared slide can be exposed to an appropriate dose of UV light according to the polymer specifications. After curing, the dimensions of the cured ECA specimen can be measured, for example, using a micrometer. Furthermore, the sheet resistance and resistivity can be measured. The resistivity value can be calculated using the measured dimensions and the measured sheet resistance or resistivity.

[0080] Example

[0081] Material

[0082] The following materials were used in Examples 1 to 10:

[0083]

[0084] H-nanowires HNW

[0085] Silver nanowires, termed H-nanowires (HNW), were synthesized in a closed reactor system. The synthesis involved preparing a heated reaction solution of ethylene glycol (EG), polyvinylpyrrolidone (PVP K30 from BASF), and NH4Cl, followed by the addition of AgNO3 and continuous stirring at approximately 160°C for several hours. After synthesis, the silver nanowires were purified by acetone precipitation and redispersed in water or other solvents. The purified silver nanowire dispersion was removed, dried, and characterized by transmission electron microscopy, as described by Hu et al. in U.S. Patent No. 10,714,230.

[0086] H-nanowires (referred to as H-5) with an average diameter of approximately 60 nanometers and an average length of approximately 5 micrometers were prepared. In some embodiments, H-nanowires with an average length of less than 5 micrometers were prepared by ultrasonically processing the H-5 nanowires to reduce the average length to approximately 2 micrometers and 1 micrometer (referred to as H-2 and H-1, respectively). Unless otherwise stated, H-5 nanowires are used in the embodiments.

[0087] Preparation of HNW complex

[0088] The following procedure was used to prepare a composite of 40% by weight HNW in epoxy resin.

[0089] 1. Preparation of HNW stock solution

[0090] The required amount of HNW ethanol solution was placed in a 24 / 40 ground glass Erlenmeyer flask. A solvent mixture of butyl carbitol (BC) and triethylene glycol (TEG) in a weight ratio of 5:1 was added to the flask to provide an HNW / solvent mixture with a silver-to-solvent weight ratio of 4:6. The HNW / solvent mixture was mixed by hand for approximately one minute. The ethanol was removed using a rotary evaporator with a water bath temperature set to 35°C. The resulting HNW dispersion concentrate was further dried at 35°C to 40°C under a vacuum of approximately 60 mmHg for 4 to 8 hours to obtain an ethanol-free 40% by weight HNW dispersion.

[0091] 2. Preparation of silver microparticles / epoxy resin

[0092] The epoxy resin mixture containing the curing agent and hardener was placed in a 20 ml glass vial. A solvent mixture of BC and TEG at a weight ratio of 5:1 was added to the vial, and the mixture was vortexed with the epoxy resin mixture for 1 to 3 minutes. Then, the required amounts of silver flakes (AgFL) and silver microparticles (AgMP) were added to the vial. The mixture was then mixed for 10 minutes using a Thinky Mixer (Thinky USA) running at 1000 rpm, followed by ultrasonic treatment at 40 kHz using a Branson 8800 ultrasonic bath (Branson Ultrasonics Corp.).

[0093] 3. Preparation of composites and coatings

[0094] The HNW stock solution was added to the silver microparticles / epoxy resin, and the resulting mixture was vortexed for 1 minute, followed by mixing using a new base mixer running at 1000 rpm for 10 minutes. The resulting paste was then applied to a microscope slide using 60-micron strip spacers. The coating spacers were then removed, and the applied paste was cured in a well-ventilated box oven at 150°C for 30 minutes. The test coupons were then cooled to room temperature inside a fume hood, and their curing and uniformity were checked.

[0095] The HNW composites used in the examples were prepared in a manner similar to that described above. In some examples, silver curing was performed using high-intensity pulsed light (IPL) provided by a system from CINEX.

[0096] Test program

[0097] The length, width, and actual thickness of the cured uniform coating were measured using a micrometer test piece, and the average thickness was taken as the thickness. The resistance (R) at both ends of the coating length was measured using a Fluke 1507 multimeter (Fluke Corp.), and for subohm resistance values, an EXTECH 380460 milliohm meter (Extech Instruments Co.) was used.

[0098] Example 1 - A complex of urethane acrylate resins containing only HNW

[0099] HNW composites were prepared in different resin systems and cured by UV application (18 joules / cm²) followed by heating at 120°C for 30 minutes. The resistance of each composite was measured and the volume resistivity and 25-micrometer sheet resistance were calculated. The results are shown in Table 1.

[0100] Table 1

[0101]

[0102] HNW composites with EMI-24 crosslinking agent in PB3600 were prepared and cured by applying heat at 120°C for 30 minutes, followed by heat at 150°C for 5 minutes. The resistivity of each composite was measured and the sheet resistance Rs at 25 micrometers was calculated. The results are shown in Table 2.

[0103] Table 2

[0104]

[0105] Example 2 - Complex of HNW, silver microparticles and AgTFA in urethane-acrylate

[0106] As shown in Table 3, a complex of HNW, silver microparticles and silver salt was prepared.

[0107] Table 3

[0108]

[0109] The composite coatings were prepared and cured as described in Table 4, with UV curing at 10 joules / cm² followed by additional heat treatment. The resistance of each coating after each heat treatment was measured and used to calculate the resistivity and sheet resistance Rs. The results are shown in Table 4.

[0110] Table 4

[0111]

[0112] Figure 1 is a graph showing the relationship between the sheet resistance Rs and the curing time at 250°C. The sheet resistance decreases significantly until about 4 minutes later and then plateaus.

[0113] Composites S-1 and S-2 were coated and cured at 250°C for selected times ranging from 1 to 15 minutes. The resistivity of each coating was measured, and the results are shown in Table 5. Figure 2 is a graph showing the relationship between the resistivity of the coating and the curing time. The resistivity of the paste before curing was within 10... -3The range of ohms to centimeters.

[0114] Table 5

[0115]

[0116] Coatings of S-1 and S-2 were prepared on 125 μm PET and 1 mm glass, respectively, and cured using IPL. Cross-cut adhesion was tested, and the adhesion was visually assessed. Figures 3A to 3C show 5x optical micrographs of S-1 (two samples) and S-2 coated on 125 μm PET, respectively. All three samples were rated ASTM 5B (ASTM 3359). Figures 4A to 4C show 5x micrographs of S-1 (two samples) and S-2 coated on 1 mm glass, respectively. All three samples were rated 5B.

[0117] Figures 5 and 6 show images of S-1 coated on 125-micron PET and 1-millimeter glass, obtained at 5X. In each figure, debris from the composite is visible on the surfaces where the dicing lines intersect and is related to the dicing process. For either coating, no debris is present on the surfaces between the dicing lines, indicating that the composite adheres well to the substrate.

[0118] Composites comprising HNW and varying amounts of silver microparticles were prepared as shown in Table 6. The composites were coated onto glass slides and UV-cured at 10 joules / cm², followed by treatment at 100°C for 2 minutes. The resistivity of each coating was measured, and the results are also included in Table 6.

[0119] Table 6

[0120]

[0121] As shown in Table 7, the effect of individual silver sheets (without HNW) was evaluated by preparing composites using V80300 as the resin. Composites S-10 and S-11 are liquid-coated, and S-12 is paste-coated. The resistance and resistivity of each coating were measured and are shown in Table 8.

[0122] Table 7

[0123]

[0124] Table 8

[0125]

[0126] OL = Open line

[0127] Example 3 - Curing of urethane-acrylate composites by pulsed radiation

[0128] A coating of composite S-1 was prepared and cured using IPL. The energy per 300 counts varied between 300 joules and 700 joules.

[0129] Table 9

[0130]

[0131] Figure 7 shows the resistivity of composite S-1 as a function of curing energy. When the curing energy is increased from 300 joules to 700 joules after 300 pulses, the resistivity decreases significantly.

[0132] Figures 8A to 8C show cross-sectional images of S-1 at 10,000X before baking, at 20,000X after IPL, and at 10,000X after curing at 250°C for 15 minutes, respectively. Compared to the IPL-cured sample where the HNW morphology was modified due to the localized heating process and was not completely melted, the HNW in the cured sample was completely melted. The sample before baking exhibited a size of 1.8 × 10⁻⁶. -2 The resistivity in ohm-cm. The sample after IPL exhibits 1.2 × 10⁻⁶. -4 The resistivity in ohm-cm is 1.6 × 10⁻⁶. -5 Resistivity in ohms per centimeter.

[0133] Figures 9A and 9B show cross-sectional images of S-1 before baking at 10,000X (Figure 9A) and 60,000X (Figure 9B). HNW is not uniformly dispersed. Conductivity can be improved by enhancing the dispersion and uniformity of HNW in the bulk composite.

[0134] Figures 10A and 10B show cross-sectional images of S-1 after IPL (600 joules / 300 counts) at 350X (Figure 10A) and 20,000X (Figure 10B).

[0135] Figures 11A and 11B show cross-sectional images of S-1 after curing at 250°C for 15 minutes at 3000X (Figure 11A) and 10,000X (Figure 11B).

[0136] Example 4 - HNW in HEMA:G4335 resin at a ratio of 7:3

[0137] This embodiment relates to a composition of a blend with an alternative curable polymer. The precursor solution contains HEMA and G4335 as resins in a weight ratio of 7:3. The composition is in the form of: 2.25 g AgFL, 0.75 g AgMP, 1.0 g AgNW (HNW), 1.0 g resin, and 0.1 g silver acetate (2.5% of total Ag). The UV dose is 1.8 joules / cm². This composite is referred to as S-13.

[0138] Table 10

[0139]

[0140] The data show that 130℃ yields better results compared to 150℃. Good hardness and adhesion were observed. Figure 12 is a bar graph showing the resistivity of different compositions.

[0141] Example 5 - HNW and silver microparticles in epoxy resin composite

[0142] As shown in Table 11, the composite was prepared using an epoxy resin system.

[0143] Table 11

[0144]

[0145] As shown in Table 12, a reducible silver composition (dissolved in PG / TEG) and a reducing agent additive (introduced by addition to the reducible silver composition solution) were added to the composite. Coatings were prepared using different curing temperatures and times, and the resistivity was measured. The results are shown in Table 12.

[0146] Table 12

[0147]

[0148] 1. FA = formic acid; 2. Am = ammonia 2M from EtOH; 3. DMF = N,N-dimethylformamide.

[0149] The results showed that S-14 was the better system. AgTFA, together with thermosetting ECA formulated with different resins, provided the best resistivity. S-16 did not appear to be a high-efficiency system, but the effectiveness of the Ag composition was still demonstrated. Adding a reducing agent did not enhance the effectiveness of the Ag composition.

[0150] Example 6 - Effect of HNW length in epoxy resin composite

[0151] As shown in Table 13, the composite was prepared using an epoxy resin system. The resin mixture contained 150 mg Epolid PB 3600 + 120 mg Denacol EX-612 + 20 mg EMI-24. 5 mg PVP was also added to the composite at 12 days as a control. AgTFA was used with 5% silver in the total Ag. Both PVP and AgTFA were added in dry powder form and mixed into the resin to dissolve. The AgNP used was 100 nanoparticles from SkySpring Nanomaterials. The results are shown in Table 14.

[0152] Table 13

[0153]

[0154] Table 14

[0155]

[0156] Silver salts significantly reduce resistivity. While there are some variations in the length of the silver nanowires, the trend is not clear. Specifically, with the presence of silver salts, 2-micrometer-long silver nanowires exhibit the lowest resistivity, while without silver salts, 5-micrometer-long silver nanowires have the lowest resistivity.

[0157] Example 7 - Effects of HNW of different lengths and process aids in epoxy resin formulations

[0158] This embodiment explores the results of using silver nanowires of different lengths with process aids. Specifically, a diluent (BC) was added as a process aid. The AgNP and resin mixture were the same as described in the previous embodiments.

[0159] The composite compositions and results are shown in Table 15.

[0160] Table 15

[0161]

[0162] Example 8 - Commercial Ointment Formulation

[0163] This embodiment explores the use of reducible silver compositions combined with various conductive microparticles.

[0164] ACI Materials Commercial Conductive Paste

[0165] S-29: First Commercial Conductive Paste - Reported composition components: 65% to 85% silver + 1% to 10% dimethyl glutarate

[0166] S-30: Second Commercial Conductive Paste - The reported composition consists of 40% to 55% graphite + 10% to 20% carbon black + 5% to 10% 2,2-dimethyl-1,3-dioxolane-4-ylmethanol

[0167] S-31: Third Commercial Conductive Paste - Reported Composition Components 50% to 70% Silver

[0168] As shown in the results table, conductive paste was applied to 125-micron PET and heated. The sheet resistance was measured using a Suragus non-contact resistance meter. The data are summarized in Table 16.

[0169] Table 16

[0170]

[0171] A rectangular coating was applied to a glass slide using 30-micron spacers, and the resistivity across the length was measured and the volume resistivity was calculated. The results are presented in Table 17. Paste S-29 appears to have a higher resistivity on glass compared to PET.

[0172] Table 17

[0173]

[0174] With the aid of a small amount of solvent, a reducible silver composition was added to a silver-based conductive paste. Only EtOH was found to be compatible with paste S-31 (see Table 18). The S-31 / AgTFA / EtOH composite was coated onto a microscope slide with 30-micrometer spacers, and the resistance was measured after heating at 120°C for different times; the results are shown in Table 19. Compared to the original S-31, AgTFA did indeed improve conductivity by more than 10 times, although the curing time was longer.

[0175] Table 18

[0176]

[0177] Table 19

[0178]

[0179] Example 9 - Effect of AgTFA and UV-curable adhesive on resistivity

[0180] AgFL, AgMP, and, if necessary, AgTFA with EtOH were mixed in a flask using a vortex mixer, followed by ultrasonic treatment at 40 kHz for 1 hour. The HNW dispersion in EtOH was added to the mixture, and the flask was gently agitated to mix the silver composition. The monomer resin (V80300) was then slowly added to the flask with gentle agitation, and the mixture was further vortexed for 3 minutes. Subsequently, ethanol was removed using rotary evaporation with heating from a 40°C water bath.

[0181] The resulting ECA paste was then applied onto a microscope slide using a doctor blade technique with 60-micron strip spacers. After application, the ECA specimens were UV cured (3.8 joules / cm²) and then heated in a well-ventilated oven at 120°C for 30 minutes, followed by a second heating at 150°C for 30 minutes.

[0182] The composition and results are shown in Table 20. The resin was 20% by weight of V80300. The thickness was approximately 40 ± 0.5 micrometers. Figure 13 shows a bar graph illustrating the functional relationship between resistivity and the composition.

[0183] Table 20

[0184]

[0185] Example 10 - Thermocurable epoxy resin formulations containing and without reducible silver compositions

[0186] The epoxy resin system EPON 815C uses 2-ethyl-4-methylimidazolium as a curing agent.

[0187] The compositions shown in Table 21 were prepared and cured at 150°C for 30 minutes. The results are shown in Table 22. Figure 14 shows a bar graph illustrating the functional relationship between resistivity and the composition.

[0188] Table 21

[0189]

[0190] Table 22

[0191]

[0192] The above embodiments are intended to be illustrative and not restrictive. Additional embodiments are within the scope of the claims of this invention. Furthermore, although the invention has been described with reference to specific embodiments, those skilled in the art will recognize that changes in form and detail may be made without departing from the spirit and scope of the invention. Any incorporation made above by reference is limited such that any non-incorporation violates the subject matter of the express disclosure herein. With regard to the use of components, elements, ingredients, or other divisions herein to describe specific structures, compositions, and / or processes, it should be understood that the disclosure herein covers the specific embodiments, embodiments including the specific components, elements, ingredients, other divisions, or combinations thereof, and embodiments substantially composed of specific components, ingredients, or other divisions, or combinations thereof, which may include other features that do not alter the fundamental nature of the subject matter, as suggested in the discussion, unless specifically stated otherwise. The term "about" as used herein refers to the anticipated uncertainty of a relevant value as would be understood by one of ordinary skill in the art in the particular context.

Claims

1. A flowable precursor composition for forming a conductive material, the flowable precursor composition comprising: at least about 2.0% by weight of an organic precursor for forming a polymer matrix; metal microparticles comprising silver flakes and / or silver particles; and a reducible metal composition, wherein the total metal weight is at least about 45% by weight relative to the total weight of the composition.

2. The fluid precursor composition according to claim 1, wherein the reducible metal composition is a reducible silver composition.

3. The flowable precursor composition according to claim 2, wherein the reducible silver composition comprises silver acetate (Ag(O2CCH3)), silver trifluoroacetate (Ag(O2CCF3)), silver heptafluorobutyrate (Ag(O2CC3F7)), silver lactate (Ag(O2CCH(OH)CH3)), silver hexafluoroantimonate (AgSbF6), silver fluoride (AgF), silver tetrafluoroborate (AgBF4), silver nitrate (AgNO3), silver perchlorate (AgClO4), silver hexafluorophosphate (AgPF6), or various mixtures thereof.

4. The flowable precursor composition according to claim 2, wherein the reducible metal composition comprises one or more of silver acetate, silver trifluoroacetate, silver heptafluorobutyrate, silver lactate, silver tetrafluoroborate (AgBF4), silver hexafluorophosphate, or silver hexafluoroantimonate.

5. The flowable precursor composition according to any one of claims 2-4, wherein the precursor composition comprises silver ions in an amount of about 0.5% to about 40% by weight relative to the total metal weight.

6. The flowable precursor composition according to any one of claims 1-5, wherein the metal microparticles further comprise silver nanowires.

7. The flowable precursor composition according to any one of claims 1-6, wherein the precursor comprises a (meth)acrylate monomer.

8. The flowable precursor composition according to any one of claims 1-6, wherein the precursor comprises an aliphatic urethane acrylate monomer and an aliphatic (meth)acrylate monomer.

9. The flowable precursor composition according to any one of claims 1-6, wherein the precursor comprises a fluorinated aliphatic (meth)acrylate monomer.

10. The flowable precursor composition of claim 8, wherein the aliphatic urethane acrylate monomer comprises a monomer having one or more terminal hydrocarbon groups, a monomer having one or more terminal epoxy groups, or a combination thereof.

11. The flowable precursor composition of claim 8, wherein the aliphatic urethane acrylate monomer comprises a monomer having one or more terminal hydrocarbon groups, and the aliphatic (meth)acrylate monomer comprises a monomer having one or more hydroxyl groups.

12. The flowable precursor composition according to any one of claims 1-6, wherein the precursor comprises an epoxidized polybutadiene monomer having one or more terminal hydrocarbon groups.

13. The flowable precursor composition of claim 12, wherein the precursor further comprises an aliphatic ether containing one or more epoxy groups.

14. The flowable precursor composition according to any one of claims 1-6, wherein the precursor comprises an anhydride and a monomer containing one or more terminal epoxy groups.

15. The flowable precursor composition of claim 14, wherein the monomer containing one or more terminal epoxy groups is derived from bisphenol A.

16. The flowable precursor composition of claim 14, wherein the monomer containing one or more terminal epoxy groups is derived from hydrogenated bisphenol A.

17. The flowable precursor composition according to any one of claims 1-16, wherein the silver flakes have an average particle size of about 1 micrometer to 20 micrometers.

18. The flowable precursor composition according to any one of claims 1-17, wherein the composition comprises about 30% to about 50% by weight of the silver flakes relative to the total weight of the composition.

19. The flowable precursor composition according to any one of claims 1-18, wherein the composition comprises about 30% to about 50% by weight of the silver flakes and about 5% to about 20% by weight of the silver particles, relative to the total weight of the composition.

20. The flowable precursor composition of claim 19, wherein the silver particles have an average particle size of less than about 5 micrometers.

21. The flowable precursor composition of claim 19, wherein the silver particles have an average particle size of less than about 200 nanometers.

22. The flowable precursor composition according to any one of claims 1-21, wherein the composition comprises about 5% to about 80% silver nanowires and at least about 8.5% organic precursors relative to the total weight of the composition.

23. The fluid precursor composition of claim 22, wherein the silver nanowires have an average length of less than about 10 micrometers and an aspect ratio of at least about 10.

24. The flowable precursor composition according to any one of claims 1-23, wherein the composition comprises about 5% to about 50% by weight of a precursor and at least about 40% by weight of metal particles relative to the total weight of the composition.

25. The flowable precursor composition according to any one of claims 1-24, wherein the flowable precursor composition comprises at least about 5% by weight of a volatile solvent relative to the total weight of the composition.

26. The flowable precursor composition of claim 25, wherein the solvent comprises water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or mixtures thereof.

27. The flowable precursor composition according to any one of claims 1-26, wherein the precursor is thermosetting.

28. The flowable precursor composition according to any one of claims 1-27, wherein the precursor is UV-curable.

29. A fluid precursor composition for forming a conductive structure, the fluid precursor composition comprising: an organic precursor for a polymer matrix; and metal microparticles comprising silver nanowires and non-nanowire metal microparticles, wherein the metal microparticles comprise about 5% to about 90% by weight of silver nanowires relative to the total weight of the metal microparticles.

30. The flowable precursor composition of claim 29, wherein the non-nanowire metal microparticles comprise silver flakes, silver particles, or blends thereof.

31. The flowable precursor composition according to claim 29 or claim 30, wherein the metal particles comprise about 20% to about 85% by weight of silver nanowires relative to the total weight of the metal particles.

32. The flowable precursor composition according to claim 29 or claim 30, wherein the metal particles comprise about 2% to about 45% silver nanowires relative to the total weight of the metal particles.

33. The flowable precursor composition according to any one of claims 29-32, wherein the composition has a total metal weight of about 50% to about 95% by weight relative to the total weight of the composition.

34. The flowable precursor composition according to any one of claims 29-32, wherein the composition has a total metal weight of about 60% to about 85% by weight relative to the total weight of the composition.

35. The flowable precursor composition according to any one of claims 29-34, wherein the silver nanowires have an average diameter of about 30 nm to about 100 nm and an average length of about 1 micrometer to about 100 micrometers.

36. The flowable precursor composition according to any one of claims 29-35, wherein the flowable precursor composition further comprises a reducible metal composition.

37. The flowable precursor composition according to claim 36, wherein the reducible metal composition comprises silver acetate (Ag(O2CCH3)), silver trifluoroacetate (Ag(O2CCF3)), silver heptafluorobutyrate (Ag(O2CC3F7)), silver lactate (Ag(O2CCH(OH)CH3)), silver hexafluoroantimonate (AgSbF6), silver fluoride (AgF), silver tetrafluoroborate (AgBF4), silver nitrate (AgNO3), silver perchlorate (AgClO4), silver hexafluorophosphate (AgPF6), or various mixtures thereof.

38. The flowable precursor composition of claim 36, wherein the reducible metal composition comprises one or more of silver acetate, silver trifluoroacetate, silver heptafluorobutyrate, silver lactate, silver tetrafluoroborate (AgBF4), silver hexafluorophosphate, or silver hexafluoroantimonate.

39. The flowable precursor composition according to any one of claims 29-38, wherein the composition comprises silver ions in an amount of about 0.5% to about 40% by weight relative to the total metal weight of the composition.

40. The flowable precursor composition according to any one of claims 29-39, wherein the flowable precursor composition comprises about 5% to about 55% by weight of the precursor.

41. The flowable precursor composition according to any one of claims 29-40, wherein the flowable precursor composition comprises at least about 5% by weight of a volatile solvent.

42. The flowable precursor composition of claim 41, wherein the solvent comprises water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or mixtures thereof.

43. The flowable precursor composition according to any one of claims 29-42, wherein the organic precursor comprises a dissolved polymer binder, a crosslinkable or polymeric monomer, an oligomer or polymer, or a mixture thereof.

44. The flowable precursor composition according to any one of claims 29-42, wherein the precursor comprises a (meth)acrylate monomer.

45. The flowable precursor composition according to any one of claims 29-42, wherein the precursor comprises a monomer having a hydroxyl functional group, a monomer having an epoxy functional group, a monomer having an isocyanate functional group, or various mixtures thereof.

46. ​​The flowable precursor composition according to any one of claims 29-42, wherein the precursor comprises fluorinated aliphatic (meth)acrylate monomers, aliphatic urethane acrylate monomers and aliphatic (meth)acrylate monomers, aliphatic urethane acrylate monomers having one or more terminal hydroxyl groups, aliphatic urethane acrylate monomers having one or more terminal epoxy groups, or mixtures thereof.

47. The flowable precursor composition according to any one of claims 29-42, wherein the precursor comprises: an aliphatic ether containing one or more epoxy groups; an acid anhydride and a monomer containing one or more terminal epoxy groups; an acid anhydride and a monomer containing bisphenol A and one or more terminal epoxy groups; an acid anhydride and a monomer containing hydrogenated bisphenol A and one or more terminal epoxy groups; or a mixture thereof.

48. The flowable precursor composition according to any one of claims 29-47, wherein the precursor is thermosetting.

49. The flowable precursor composition according to any one of claims 29-48, wherein the precursor is UV-curable.

50. A composite conductive material comprising a solid polymer matrix and at least about 45% by weight of a metal, wherein the metal comprises: a1) a feature formed of non-nanowire metal particles, and b1) a feature formed of silver nanowires, a metal deposited from a reduced metal composition, or both; or a2) a structure formed of silver nanowires, and b2) a metal deposited from a reduced metal composition.

51. The composite conductive material of claim 50, wherein the solid polymer matrix comprises a chemically cross-linked polymer.

52. The composite conductive material of claim 50, wherein the solid polymer matrix comprises a physically cross-linked polymer binder.

53. The composite conductive material of claim 50, wherein the solid polymer matrix comprises a combination of physically cross-linked polymers and chemically cross-linked polymers.

54. The composite conductive material according to any one of claims 50-53, wherein the solid polymer matrix comprises acrylate polymers, urethane polymers, epoxy polymers, silicone polymers, or blends thereof.

55. The composite conductive material according to any one of claims 50-54, wherein the composite conductive material has about 50% to about 95% by weight of metal.

56. The composite conductive material according to any one of claims 50-54, wherein the composite conductive material has about 55% by weight to about 90% by weight of metal.

57. The composite conductive material according to any one of claims 50-56, wherein the composite conductive material comprises metallic features formed of silver nanowires.

58. The composite conductive material according to any one of claims 50-57, wherein the composite conductive material comprises metallic features formed by reduced silver ions and does not comprise features formed by non-nanowire metal particles.

59. The composite conductive material according to any one of claims 50-57, wherein the composite conductive material comprises metallic features formed by reduced silver ions and features formed by non-nanowire metal particles.

60. The composite conductive material according to any one of claims 50-57, wherein the composite conductive material comprises features formed by non-nanowire metal particles and does not comprise metallic features formed by reduced silver ions.

61. The composite conductive material according to any one of claims 50-56, wherein the composite conductive material comprises features formed by non-nanowire metal particles, metallic features formed by reduced silver ions, and does not comprise metallic features formed by silver nanowires.

62. The composite conductive material according to any one of claims 50-61, wherein the composite conductive material comprises an adhesive polymer.

63. The composite conductive material according to any one of claims 50-57 and 59-62, wherein the non-nanowire metal particles comprise silver flakes.

64. The composite conductive material according to any one of claims 50-57 and 59-62, wherein the non-nanowire metal particles comprise silver particles.

65. The composite conductive material according to any one of claims 50-64, wherein the composite conductive material has a density of not more than about 5 × 10⁻⁶. -3 Resistivity in ohms per centimeter.

66. The composite conductive material according to any one of claims 50-64, wherein the composite conductive material has a density of about 1 × 10⁻⁶. -4 Ohms-cm to approximately 5×10 -6 Resistivity in ohms per centimeter.

67. A method for forming a precursor composition for forming a conductive composite material, the method comprising: The precursor composition is formed by combining a) a polymer matrix precursor comprising a crosslinked polymer precursor, a polymeric monomer / oligomer, a dissolved polymer binder, or a combination thereof, with b) a metal component provided in the form of two or more of 1) non-nanowire metal microparticles, 2) silver nanowires, or 3) a reducible metal composition, wherein the precursor composition comprises at least about 45% by weight of total metal in all forms, and wherein if the metal is provided only in the form of silver nanowires and a reducible metal composition, the polymer matrix comprises at least 2% by weight of the polymer matrix composition after curing.

68. The method of claim 67, wherein the silver nanowires are dispersed in a dispersant prior to the merging.

69. The method of claim 67 or claim 68, wherein the reducible metal composition is dissolved in a solvent prior to merging.

70. The method according to any one of claims 67-69, wherein the merging comprises mixing in a mechanical mixer to form a homogeneous precursor composition.

71. The method of claim 70, wherein the homogeneous precursor composition is fluid.

72. The method of claim 70 or claim 71, wherein the homogeneous precursor composition can be deposited by extrusion, spraying, dispensing, printing or slot coating.

73. The method according to any one of claims 67-72, wherein the precursor composition comprises about 5% to about 55% by weight of a polymer matrix precursor.

74. The method according to any one of claims 67-73, wherein the incorporation further comprises incorporating about 5% by weight to about 45% by weight of a volatile solvent.

75. The method of claim 74, wherein the solvent comprises water, alcohol, glycol, amide, glycol ether, polar aprotic solvent, or a mixture thereof.

76. The method according to any one of claims 67-75, wherein the metal component comprises about 20% to about 80% by weight of silver nanowires.

77. The method according to any one of claims 67-76, wherein the non-silver nanowire metal particles comprise silver flakes.

78. The method according to any one of claims 67-77, wherein the non-silver nanowire metal particles comprise silver particles.

79. The method according to any one of claims 67-78, wherein the metal component comprises about 0.5% by weight to about 40% by weight of silver ions relative to the total weight of metal dissolved in the solvent prior to merging.

80. The method according to any one of claims 67-79, wherein the precursor of the polymer matrix precursor comprises a (meth)acrylate monomer.

81. The method according to any one of claims 67-79, wherein the precursor of the polymer matrix precursor comprises hydroxyl functional groups, epoxy functional groups, urethane precursors, epoxy groups, vinyl groups, organosilicones, or various mixtures thereof.

82. The method according to any one of claims 67-79, wherein the precursor of the polymer matrix precursor comprises fluorinated aliphatic (meth)acrylate monomers, aliphatic urethane acrylate monomers, or mixtures thereof.

83. The method according to any one of claims 67-79, wherein the precursor of the polymer matrix precursor comprises: an aliphatic ether containing two or more terminal epoxy groups; an acid anhydride and an aliphatic monomer containing two or more terminal epoxy groups; an aliphatic monomer derived from hydrogenated bisphenol A containing two or more terminal epoxy groups; a hydrogenated bisphenol A monomer containing two or more terminal epoxy groups; or a mixture thereof.

84. The method according to any one of claims 67-83, wherein the precursor of the polymer matrix precursor is thermosetting.

85. The method according to any one of claims 67-84, wherein the precursor of the polymer matrix precursor is UV-curable.

86. A method for forming a deposit of a precursor of a conductive composite, the method comprising depositing the precursor composition formed by the method according to any one of claims 67-85.

87. The method of claim 86, wherein the cured conductive composite comprises at least about 8.5% by weight of a polymer matrix.

88. A method for forming a composite material having high electrical conductivity and containing an organic polymer and a metallic component, the method comprising: The deposited composition is cured to drive the reduction of silver ions to form silver metal, wherein the deposited material is a precursor composition comprising a polymer precursor, silver microparticles and a dissolved silver composition, and wherein curing includes applying heat, UV radiation or both for a sufficient time to reduce silver ions to silver metal and reduce resistivity by at least about 25%.

89. The method of claim 88, wherein curing comprises heating.

90. The method of claim 89, wherein heating is performed in an oven at a temperature of about 90°C to about 250°C for 5 minutes to 4 hours.

91. The method according to any one of claims 88-90, wherein heat crosslinks the organic polymer.

92. The method according to any one of claims 88-91, wherein curing comprises UV radiation.

93. The method according to any one of claims 88-92, wherein curing comprises irradiation with a pulsed light source.

94. The method according to any one of claims 88-93, wherein the silver ions are associated with a reducible metal composition comprising silver acetate (Ag(O2CCH3)), silver trifluoroacetate (Ag(O2CCF3)), silver heptafluorobutyrate (Ag(O2CC3F7)), silver lactate (Ag(O2CCH(OH)CH3)), silver hexafluoroantimonate (AgSbF6), silver fluoride (AgF), silver tetrafluoroborate (AgBF4), silver nitrate (AgNO3), silver perchlorate (AgClO4), silver hexafluorophosphate (AgPF6), or various mixtures thereof.

95. The method according to any one of claims 88-94, wherein the deposition composition further comprises a solvent, which is removed during curing.

96. The method according to any one of claims 88-95, wherein the deposition composition further comprises a reducing agent to promote the reduction of silver ions during curing.

97. The method according to any one of claims 88-96, wherein the silver ions are associated with a reducible metal composition comprising one or more of silver acetate, silver trifluoroacetate, silver heptafluorobutyrate, silver tetrafluoroborate (AgBF4), silver lactate, silver hexafluorophosphate, or silver hexafluoroantimonate.

98. The method according to any one of claims 88-97, wherein the deposition composition comprises silver ions in an amount of about 0.5% to about 40% by weight relative to the total metal weight.

99. The method according to any one of claims 88-98, wherein the deposition composition comprises about 5% to about 55% by weight of a polymer precursor.

100. The method according to any one of claims 88-99, wherein the deposition composition comprises at least about 5% by weight of a volatile solvent.

101. The method according to any one of claims 88-100, wherein the deposition composition comprises a precursor for a polymer matrix, the precursor for the polymer matrix comprising a dissolved polymer binder, a crosslinkable or polymeric monomer, an oligomer or polymer or a mixture thereof.

102. The method of claim 101, wherein the precursor for the polymer matrix comprises a (meth)acrylate monomer.

103. The method of claim 101, wherein the precursor for the polymer matrix comprises hydroxyl functional groups, epoxy functional groups, urethane precursors, epoxy groups, vinyl groups, organosilicones, or mixtures thereof.

104. The method of claim 101, wherein the precursor for the polymer matrix comprises: a fluorinated aliphatic (meth)acrylate monomer, an aliphatic urethane acrylate monomer containing one or more terminal hydroxyl groups, one or more terminal epoxy groups, or blends thereof, or mixtures thereof.

105. The method of claim 101, wherein the precursor for the polymer matrix comprises: an aliphatic ether containing two or more terminal epoxy groups; an acid anhydride and an aliphatic monomer containing two or more terminal epoxy groups; an aliphatic monomer derived from hydrogenated bisphenol A containing two or more terminal epoxy groups; a hydrogenated bisphenol A monomer containing two or more terminal epoxy groups; or a mixture thereof.

106. The method according to any one of claims 88-105, further comprising forming the precursor by means of the following steps: combining a) a polymer matrix precursor comprising a crosslinked polymer precursor, a polymeric monomer / oligomer, a dissolved polymer binder, or a combination thereof, with b) a metal component provided in the form of two or more of 1) non-nanowire metal microparticles, 2) silver nanowires, or 3) a reducible metal composition to form the precursor composition, wherein the precursor composition comprises at least about 45% by weight of total metal in all forms, and wherein if the metal is provided only in the form of silver nanowires and a reducible metal composition, the polymer matrix after curing comprises at least 8.5% by weight of the polymer matrix precursor composition.

107. The method of claim 106, wherein the mixing comprises mixing in a mechanical mixer to form a homogeneous precursor composition, and wherein the homogeneous precursor composition is fluid.

108. The method according to any one of claims 88-107, wherein the resistivity is reduced by at least about 50%.

109. The method according to any one of claims 88-108, wherein the resistivity of the cured composite composition does not exceed about 1 × 10⁻⁶. -4 Ohms-centimeters.

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