conductive ink

Abstract

The present invention relates to an ink composition for printing highly conductive tracks for electronic applications, in which the conductive particles can be recovered by an environmentally friendly extraction process and reused in additional conductive ink compositions without further processing. Also provided are substrates containing printed current tracks formed from such compositions; substrates containing surface-mount electronic components adhered to the substrate by contact with an adhesive composition formed from such ink compositions; and substrates containing conductive coatings formed from such ink compositions, e.g., for use in induction sealing and / or to provide antibacterial coatings. Methods for forming such printed tracks, coated substrates, and / or methods for adhering surface-mount electronic components to substrates are also provided.

Description

[Technical Field]

[0001] The present invention relates to an ink composition for printing highly conductive tracks for electronic applications, in which the conductive particles can be recovered by an environmentally friendly extraction process and reused in additional conductive ink compositions without further processing. Also provided are substrates including printed tracks formed from such ink compositions; substrates including surface-mount electronic components adhered to the substrate by contact with an adhesive composition formed from such ink compositions; and substrates including conductive coatings formed from such ink compositions, e.g., for use in induction sealing and / or to provide antibacterial coatings. Methods for forming such printed current tracks, coated substrates, and / or methods for adhering surface-mount electronic components to substrates are also provided. [Background technology]

[0002] An increasing number of electronic devices rely on flexible, low-cost printed circuit film technology. The circuitry itself is printed onto the film, using silver, copper, or gold as the conductors. Examples in consumer electronics include wearable devices, RFID antennas, energy harvesting, sensors, and solar panels. Surface-mount components are then attached to the film using conductive adhesives. Consumer demand and the ever-increasing use of short-life, disposable electronics are generating vast amounts of electronic waste (e-waste). Approximately 54 million tons of e-waste were generated in 2019, and this is expected to grow at a rate of 2 million tons per year, with less than 25% of this being recycled.

[0003] Printed electronics offers a means to mitigate the environmental impact of e-waste generation by providing a biodegradable and recyclable solution. It involves applying functional (conductive, dielectric, or semiconductive) materials from digital or physical patterns onto a carrier substrate. Research in this area has already been accomplished by investigating recycled substrates [2][3] and carbon-based printing inks [4][5]. Carbon-based inks have significantly lower conductivity compared to metallic inks such as silver, gold, and copper [6]. These metallic inks can be in the form of either microflakes that form interconnect structures or nanoparticles that are sintered to form solid conductive layers. These highly conductive inks are used for interconnects between components, printed RFID antennas, energy harvesting, sensors, and solar panels. Summary of the Invention [Problem to be solved by the invention]

[0004] However, the extraction of these metals from printed electronics is no different from other e-waste extraction methods, using highly corrosive and toxic chemicals, commonly referred to as piranha solution, to dissolve the waste, including the substrate and ink. For example, current methods for extracting silver from e-waste involve producing a leachate from the waste using cyanide, hydrochloric acid, thiosulfate, or thiourea. This method dissolves both the silver and the substrate, preventing the substrate from being recycled in its own waste stream. Silver is extracted and purified from the leachate using carburization, ion exchange, and solvent extraction, which involves additional toxic chemicals. In addition to the extensive use of toxic chemicals, reusing the recovered silver in printed electronics requires further processing, such as smelting to refine the silver and remove traces of the chemicals used for extraction. Therefore, there is an unmet need for conductive inks that can be easily recycled from printed electronics without the need for toxic recovery methods.

[0005] This paper describes a unique formulation of a highly conductive water-based silver ink and a chemical-free extraction process that enables the recycling of silver from printed electronics. This provides an alternative to the silver conductive inks currently used in electronics, which use toxic chemicals to recover the precious metal. In particular, the printed ink can be easily recovered by magnetic recovery methods, which do not use chemicals in the extraction process. This allows the ink to be recovered from the substrate, allowing the ink to be reused without further processing, reducing energy use and material costs. After the ink is extracted, the substrate can be returned to the original waste stream for recycling. This ink and subsequent recovery method therefore pave the way for the first fully recyclable printed electronics, providing an environmentally sustainable alternative to the silver, copper, and gold conductive inks currently used in the manufacture of printed electronics. This could include consumer electronics, high-performance devices, smart packaging, sensors, point-of-care health, wearable devices, RFID antennas, membrane switches, and circuit boards. [Means for solving the problem]

[0006] The invention, in its various aspects, is as set out in the appended claims.

[0007] According to a first aspect of the present invention there is provided an ink composition for use in printing conductive tracks, for providing a surface coating and / or for use as a conductive adhesive for attaching surface mount components to a substrate, which ink composition has high conductivity for electronic applications and which can be recycled without further processing to recover the conductive particles by an environmentally friendly extraction process for reuse in further conductive ink compositions.

[0008] The ink composition of the present invention comprises (a) one or more coated magnetic particles, (b) one or more binders, and (c) one or more solvents, wherein the particles are coated with one or more conductive metals.

[0009] The magnetic particles are not particularly limited and may themselves comprise any magnetic metal core and / or may be coated with any conductive metal. Suitable magnetic metals include, but are not limited to, iron (Fe), nickel (Ni), and alloys thereof. Similarly, suitable conductive metals include, but are not limited to, silver (Ag), gold (Au), copper (Cu), aluminum (Al), and alloys thereof. However, in preferred embodiments, the magnetic particles comprise iron or an iron alloy and / or the conductive metal is silver or an alloy thereof. Silver-coated iron (AgFe) particles, including silver-coated iron microparticles (AgFeMP) and silver-coated iron nanoparticles (AgFeNP), which are readily available from several commercial sources, are particularly preferred.

[0010] As used herein, the term nanoparticle refers to a particle having a diameter of about 1 to about 1000 nm.

[0011] Similarly, as used herein, the term microparticle refers to particles having a diameter of about 1 to about 500 μm, preferably about 5 to 250 μm.

[0012] The coated magnetic particles are bifunctional. First, because they have a magnetic metal core, the particles are magnetic, providing a property that is exploited in the process of recovering the particles for reuse in conductive ink compositions. Second, because they have a conductive metal coating, the particles impart sufficient conductivity to the ink composition to allow for the printing of conductive lines, shapes, patterns, or circuits onto a substrate. Furthermore, as one skilled in the art will readily appreciate, the overall conductive and magnetic properties of the particles can be fine-tuned by varying the ratio of magnetic core to conductive coating. That is, particles with a higher percentage of magnetic metal core and a lower percentage of coating conductive metal will be more magnetic (and therefore more easily recoverable using a lower-power magnet), but will have a higher resistance when deposited as a conductive track on a substrate.

[0013] A good balance of magnetic and conductive properties, which allows the particles to be used in conductive inks and to be recovered and recycled, is achieved by using coated particles having a weight ratio of magnetic metal in the core to conductive metal in the coating of about 5:95 to about 40:60, or about 10:90 to about 30:70. In a particularly preferred embodiment, the coated particles comprise a magnetic metal, preferably iron, and a conductive metal, preferably silver, in a weight ratio of about 20:80.

[0014] The overall conductivity of the ink, and therefore the conductive composition printed from the ink, also depends on the particle concentration in the ink composition. For example, a preferred ink composition contains about 40 to about 80 wt. % of coated magnetic particles, more preferably about 60 wt. %, based on the total weight of the ink composition, and has about half the conductivity of conventional silver inks, making it a viable alternative for highly conductive inks.

[0015] The particle size of the coated magnetic particles is not particularly limited, and those skilled in the art will select an appropriate particle size as needed. However, in an exemplary embodiment of the present invention, the conductive ink comprises coated magnetic microparticles or nanoparticles, preferably microparticles, and most preferably microparticles having an average particle size of about 10 μm to about 40 μm, more preferably about 25 μm, as measured using a Malvern Morphologi 4 particle size analyzer.

[0016] In the ink compositions of the present invention, the coated magnetic particles are dispersed in one or more binder or resin components. Such binders provide adhesion to the substrate and, depending on the concentration, impart the desired rheological properties to the ink composition. As will be readily understood by those skilled in the art, the type of binder is not particularly limited, but the binder should be soluble in the selected solvent and allow printing of the ink composition onto substrates such as paper, plastic, and / or fabric surfaces.

[0017] However, in preferred embodiments, the binder or resin is a hydrophilic polymer, examples of which include polyvinyl alcohol, polyvinylpyrrolidone, gelatin, cellulose, pectin, polyoxazoline, polyvinylacetamide, partially hydrolyzed polyvinyl acetate / vinyl alcohol, polyacrylic acid, polyacrylamide, polyalkylene oxide, sulfonated or phosphated polyesters and polystyrene, casein, zein, albumin, and derivatives thereof. More preferably, the binder comprises one or more celluloses and / or one or more pectins.

[0018] Preferably, the cellulose is a cellulose ether, and even more preferably, carboxymethylcellulose (i.e., a cellulose derivative in which carboxymethyl [—CH—COOH] or its metal salt [e.g., —CH—COONa] is attached to one or more hydroxyl groups of the glucopyranose monomers that form the cellulose backbone). Particularly preferred cellulose, cellulose ether, and carboxymethylcellulose binders have a molecular weight of about 50,000 to about 150,000 Da.

[0019] Similarly, for ink compositions, there are no particular limitations regarding the solvent used, provided that (a) the binder is sufficiently soluble in the solvent to prepare a composition having the required rheological properties, and (b) the solvent is compatible with the substrate, such as paper, plastic, and / or fabric surfaces. However, in a preferred example, the solvent is water.

[0020] As mentioned above, the binder is provided in an amount sufficient to control the rheological profile of the ink composition. In a preferred example, the ink composition is a shear thinning composition, more preferably having a shear viscosity of 0.1 to 100 s. -1 The shear thinning compositions have a shear thinning viscosity of about 80 to about 2 Pa·s, or about 45 to about 4 Pa·s, in the shear range of about 80 to about 2 Pa·s, or about 45 to about 4 Pa·s, which ensures compatibility with screen printing processes commonly used in printing electronic circuits. Shear viscosity can be measured using a shear rheometer such as a Netzsch Kinexus Pro.

[0021] The ink of the first aspect of the present invention is adapted to be used to print a conductive composition onto a substrate. Such a printed composition may be used to form conductive tracks and / or surface coatings and / or as a conductive adhesive for attaching surface mounted components to the substrate. Thus, according to a second aspect, the present invention provides a substrate having deposited thereon a conductive composition, the composition comprising a cured ink composition according to the first aspect.

[0022] In some embodiments, the conductive composition forms conductive tracks, ie, lines, shapes, patterns, or circuits.

[0023] In another embodiment, the conductive composition is an adhesive composition that directly contacts the substrate and the surface mount component, thereby elastically bonding them together. By using such an ink composition as a conductive surface mount adhesive, both the conductive particles and the adhered surface mount component can be recovered / recycled using the environmentally friendly extraction process of the present invention.

[0024] In a further embodiment, the conductive composition forms a conductive coating on the surface of a substrate, which can be advantageously applied to a thermoplastic substrate for use in induction seals (replacing the aluminum layer traditionally used), such as in tamper-evident packaging and hermetic seals in food packaging.

[0025] Furthermore, when the coating is formed from magnetic particles coated with silver or copper, the coating may have antibacterial effects, due to the well-documented antibacterial activity of such metals. Therefore, such coatings may be particularly suitable for application to medical devices, which are generally disposable products, and the environmentally friendly extraction process of the present invention allows for the recovery / recycling of the conductive / antibacterial particles.

[0026] The ink compositions, such as conductive tracks, adhesives, and coatings, can be deposited on a wide variety of substrate surfaces, including but not limited to paper, plastic, metal, and fabric, although paper is preferred for ease of recycling and recovery of the ink components.

[0027] A conductive composition, such as a conductive track, adhesive, or coating, can be printed onto a substrate by a method representing the third aspect of the present invention, which method comprises (a) printing an ink composition according to the first aspect onto the surface of a substrate, and then (b) curing said ink composition.

[0028] The conductive composition can form conductive tracks, i.e. lines, shapes, patterns or circuits, or conductive coatings, or conductive adhesive compositions for surface mounted components.

[0029] As will be readily understood, when the conductive composition forms such a conductive adhesive, the method further comprises (a) printing the ink composition according to the first aspect onto the surface of a substrate, (a1) placing a surface mount component on the printed ink composition, and then (b) curing the ink composition to elastically bond the substrate and the surface mount component.

[0030] In a preferred method, the ink is deposited on the substrate surface in step (a) by screen printing.

[0031] As will be readily understood, curing of the deposited ink composition in step (b) can occur passively, i.e., at room temperature without heating. However, in a preferred embodiment, curing step (b) includes heating to accelerate the curing process. In a particularly preferred embodiment, the printed substrate is placed in an enclosed environment (e.g., an oven) and heated to a temperature of at least about 50°C, preferably at least about 75°C. To avoid thermal degradation of the substrate and / or ink, and due to environmental considerations, the temperature is preferably about 125°C or less, more preferably about 100°C or less.

[0032] The ink composition of the first aspect is configured not only for printing conductive tracks and coatings and / or as a highly conductive adhesive composition for, for example, electronic applications, but also to enable the recycling and recovery of conductive particles (and surface mounted components fixed using such conductive inks as adhesives) from "used" substrates such as printed electronics by an environmentally friendly extraction process for reuse in further conductive ink compositions without further processing.

[0033] Thus, according to a fourth aspect of the present invention there is provided a method of recycling conductive metal particles for reuse in a conductive ink composition, comprising the steps of: (a) providing a substrate according to the second aspect of the present invention; (b) immersing the substrate in a solvent to dissolve the binder component of the substrate and / or the cured ink composition, thereby forming a collection medium containing the free-coated magnetic particles; (c) separating the conductive metal particles from the collection medium by applying a magnetic force; and (d) optionally drying the recovered metal particles. A method is provided which includes:

[0034] As the skilled reader will readily appreciate, drying step (d) is preferably performed when the recovered conductive metal particles must be stored in dry form for later use. Similarly, such a drying step is preferably performed when the recovered conductive metal particles are combined with one or more binders and one or more solvents to prepare a recycled conductive ink composition, when the solvent used in recovery step (b) is different from the solvent used in the recycled conductive ink composition.

[0035] The method may further comprise an optional washing step after the separating step (c) and, if performed, before the drying step (d).

[0036] In a preferred embodiment, the solvent used in step (b) is water. Additionally or alternatively, heating is preferably performed in step (b) to facilitate the dissolution process. For example, the solvent can be heated to a temperature of about 50°C to about 90°C.

[0037] The recovered coated metal particles have been found to be unchanged by the magnetic recovery process of the present invention and are therefore suitable for reuse in new ink formulations without further processing steps. Thus, the recycling method of the fourth aspect of the present invention may further comprise, after step (c) and, if performed, step (d), combining the recovered conductive metal particles with one or more binders and one or more solvents to prepare an ink composition according to the first aspect of the present invention.

[0038] Throughout this description and the claims, the words "comprise" and "contain," as well as variations of these words, such as "comprising" and "comprises," mean "including but not limited to," and do not exclude other moieties, additives, components, integers, or steps. Throughout this description and the claims, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, it is to be understood that the specification contemplates the plural as well as the singular, unless the context otherwise requires.

[0039] All references cited herein, e.g., patents or patent applications, are hereby incorporated by reference. No reference is admitted to constitute prior art, nor is it admitted that any of the prior art forms part of the common general knowledge in the art.

[0040] Preferred features of each aspect of the invention may be those described in relation to any of the other aspects.

[0041] Other features of the present invention will become apparent from the following examples. Generally speaking, the present invention extends to any novel one or any novel combination of features disclosed in this specification (including the accompanying claims and drawings). Thus, it should be understood that any feature, integer, property, compound, or chemical moiety described in connection with a particular aspect, embodiment, or example of the present invention is also applicable to any other aspect, embodiment, or example described herein, unless inconsistent therewith.

[0042] Moreover, unless stated otherwise, any feature disclosed herein may be replaced by an alternative feature serving the same or a similar purpose.

[0043] The invention will now be described, by way of example only, with reference to the following figures and tables: [Brief explanation of the drawings]

[0044] [Figure 1] FIG. 1 is a diagram of the "blending" method for extracting silver-coated ferrite particles from a water-based ink printed on a paper substrate. [Figure 2] Illustrative illustration of the "mixing" method for extracting silver-coated ferrite particles from aqueous ink printed on a paper substrate. This method could also be used for recovery from plastic substrates. [Figure 3] FIG. 10 shows the recovery efficiency of a sample of silver-coated ferrite particles printed on paper, comparing two different extraction methods. [Figure 4] Particle size distribution of silver-coated ferrite produced using Malvern Morphology 4 (left), example of measured average particle size (center), and example of composite fiber and multiple AgFe particles (right). (a) Raw AgFe particles, (b) AgFe particles recovered by blending, (c) AgFe particles recovered by compounding. DETAILED DESCRIPTION OF THE INVENTION

[0045] Example 1 - Ink Formulation Printing inks typically consist of functional materials dispersed in a resin. This resin provides adhesion to the printed electronic substrate and the necessary rheological properties to support the functional material. A water-based resin system printable on both paper and plastic substrates was used. The resin consisted of 2.5 wt.% sodium carboxymethylcellulose (CMC) with a molecular weight of 90,000 and 2.5 wt.% citrus peel-derived pectin dissolved in deionized (DI) water at 80°C using a magnetic stirrer.

[0046] The conductive material selected for the ink was silver-coated ferrite (AgFe, Hart Materials) with a silver content of 20% and a particle size of 25 μm. This material was chosen for its magnetic and conductive properties and is typically used in EMI shielding and conductive tape. Ferrite is a less dense and less hazardous substrate than nickel. The AgFe was added to the resin at 60% by weight and allowed to wet for 12 hours. The ink was then milled using a simulated ball milling method, after which glass beads were added to the ink, and the pot was rotated for 2 hours.

[0047] The rheology of the resin ink, silver ink, and AgFe ink was measured using a Netzsch Kinexus Pro rheometer. The inks were measured at 0.1 to 100 s -1 The inks exhibited shear thinning behavior with shear viscosities ranging from 45 to 4 Pa·s over a shear range of 1000 to 1500 Pa·s, respectively. The rheological profile of the inks makes them suitable for use in screen printing processes commonly used in printing electronic devices.

[0048] To investigate the suitability of AgFe ink for use in printed electronics, we compared it with Haydale Flexible Silver Conductive Ink, a commercial-grade silver screen printing ink. Both inks were coated onto paper substrates (15 mm x 210 mm) using an RK Control Coater. Samples were dried in an oven at 80 °C, and resistance was measured at a distance of 50 mm using a two-point voltmeter. The average resistance of the AgFe ink was 2.7 ohms, compared with 1.7 ohms for the commercial silver ink. Although the resistance of the AgFe ink was nearly twice that of the silver ink, it is a viable alternative as a highly conductive ink. Additional printed layers or wider conductive tracks could be used to overcome these differences, and ink design could be optimized to improve the performance of printed electronics.

[0049] Example 2 - Recovery Method The use of magnetic fields to capture metal particles passing through filters is commonly used to remove unwanted debris in central heating systems, automobile transmissions, and gas turbines. The recovery of AgFe from prints took advantage of the magnetic properties of the coating provided by ferrite.

[0050] To verify the effectiveness of this method, ten samples of AgFe ink were coated onto paper substrates. The samples were weighed before and after coating to determine the volume of ink deposited on the substrate, allowing the weight of AgFe in the coating to be determined. Two AgFe extraction methods were investigated.

[0051] In the first method (mixing) (Figure 1), the sample was immersed in a beaker of 80°C water and then mixed using a hand blender to create a recovery medium (a). A strong neo-rhodium magnet was placed next to the beaker to pull the AgFe particles out of solution (b). The paper / water solution was poured off while maintaining the magnet's position to keep the AgFe in place (c). This process was repeated to remove the paper contaminating the AgFe. The remaining AgFe sample was decanted into a petri dish using boiling water to rinse the beaker (d). A magnet on the petri dish was used to pull the AgFe out of the water (e). The sample was then dried, and the weight of the recovered AgFe was measured (f).

[0052] In the second method (mixing) (Figure 2), the sample was immersed in a beaker of 80°C water and mixed with a plastic spatula on a magnetic hotplate (a), separating the AgFe ink from the paper substrate while maintaining its structure. A neo-rhodium magnet was used to hold the AgFe in the beaker while pouring off the water / paper solution (b). The remaining AgFe sample was decanted into a Petri dish using boiling water to rinse it from the beaker (c). A magnet placed above the Petri dish was used to lift the AgFe out of the water, allow it to dry, and measure the amount of recovered material (d).

[0053] The efficiency of these two methods was determined by comparing the weight of AgFe recovered from the sample with the weight of AgFe in the dried ink on the substrate (Figure 3). The recovery rate for the first method (blending) (78%) was lower than that for the second method (mixing) (94%). This was due to the additional steps required to remove small traces and fibers of the paper substrate from the AgFe, which resulted from mixing the sample to form the collection medium. The mixing method avoided these steps by maintaining the integrity of the substrate, resulting in a higher recovery rate. We believe this mixing method can also be used to recover AgFe particles from plastic substrates.

[0054] Example 3 - Particle size distribution Using Malvern Morphology 4 (Figure 4), the particle size distribution of raw AgFe was compared with that of recovered AgFe from samples containing at least 1,500 particles. The particle size distribution of the samples showed the highest peak at the same location, indicating that the majority of the particles remained unchanged as a result of the magnetic recovery process. This suggests that these particles can be reused in new inks without further processing. The average particle size of the recovered AgFe samples increased. This is due to an increase in the number of larger particles formed from the combination of silver particles and paper fibers. The samples obtained using the blending method showed a smaller increase in average particle size and fewer large particles compared to the blending method.

[0055] summary Printed electronics offer a way to reduce the environmental impact of consumer electronics such as wearables, RFID antennas, energy harvesting, sensors and solar panels. As with traditional electronics, the problem arises at the "end of life" stage of life cycle assessment: methods for recovering metals such as silver from electronics involve the use of highly corrosive chemicals, making it difficult to recover the printed substrate.

[0056] This paper demonstrates the formulation of a highly conductive silver ink for printed electronics that is easily recyclable with an efficiency of 94%. This was achieved by using silver-coated ferrite (AgFe) particles instead of silver flakes and extracting the particles using the magnetic properties provided by the ferrite core. Two methods were investigated for calculating AgFe recovery and efficiency. Blending paper samples resulted in a recovery efficiency of 78%, while blending yielded a recovery efficiency of 94%. This difference is attributed to the additional washing step required to remove the AgFe particles from the paper fibers, which were dissolved in water during the blending process. This blending process may also be applicable to plastic substrates.

[0057] The particle sizes of the raw AgFe and the recovered AgFe were compared. The increase in the average particle size of the recovered AgFe was due to the measurement of paper fibers. It was revealed that the AgFe recovered by blending had a significant reduction in paper fibers and a small increase in the average particle size. The magnetic extraction process did not change the particles, and the peak of the particle size distribution was at the same position for the raw AgFe and the recovered AgFe. This means that these AgFe can be reused in the production of new inks without further processing steps.

[0058] Therefore, the inks disclosed herein, and the associated recovery methods that can be considered, offer a solution to this e-waste problem. Using a specially formulated silver ink that can be recovered from printed electronics using hot water and a magnet, we demonstrated a recycling efficiency of 94%. Magnetic recovery of the silver does not alter its particle size distribution, allowing it to be reused in new ink formulations without further processing steps. The remaining substrate can also be processed through a unique waste treatment flow, enabling fully recyclable printed electronics.

[0059] References [Table 1]

Claims

1. (a) one or more coated magnetic particles; (b) one or more binders; and (c) one or more solvents An ink composition comprising: An ink composition wherein the particles are coated with one or more conductive metals.

2. 2. The ink composition of claim 1, wherein said magnetic particles comprise a core of a magnetic metal, said magnetic metal optionally being selected from iron, nickel and alloys thereof.

3. 3. The ink composition according to claim 1, wherein the conductive metal is selected from the group consisting of silver, gold, copper, aluminum, and alloys thereof.

4. The ink composition of claim 3 , wherein the magnetic particles comprise iron or an iron alloy and / or the conductive metal is silver or an alloy thereof.

5. 5. The ink composition of claim 2, wherein the weight ratio of the magnetic metal core to the conductive metal is from about 5:95 to about 40:

60.

6. The ink composition of any one of claims 1 to 5, wherein the coated magnetic particles are in an amount of about 40 to about 80% by weight, based on the total weight of the ink composition.

7. The ink composition of any one of claims 1 to 6, wherein the coated magnetic particles have an average particle size of from about 10 µm to about 40 µm.

8. 8. The ink composition of claim 1, wherein the binder comprises or consists of one or more hydrophilic polymers, optionally selected from polyvinyl alcohol, polyvinylpyrrolidone, gelatin, cellulose, pectin, polyoxazoline, polyvinylacetamide, partially hydrolyzed polyvinyl acetate / vinyl alcohol, polyacrylic acid, polyacrylamide, polyalkylene oxide, sulfonated or phosphated polyester or polystyrene, casein, zein, albumin, and derivatives thereof.

9. The ink composition of claim 8 , wherein the binder comprises one or more celluloses and / or one or more pectins.

10. The ink composition according to any one of claims 1 to 9, wherein the solvent is water.

11. The ink composition of any one of claims 1 to 10, wherein the ink composition is a shear thinning composition, optionally having a shear viscosity of from about 80 to about 2 Pa·s.

12. A substrate having deposited thereon a conductive composition, the substrate comprising the ink composition of any one of claims 1 to 11, the composition being cured.

13. The substrate of claim 12 , wherein the conductive composition forms a conductive line, shape, pattern, or circuit.

14. 13. The substrate of claim 12, wherein the conductive composition is an adhesive composition that directly contacts the substrate and the surface mount component, thereby resiliently bonding them together.

15. The substrate of claim 12 , wherein the conductive composition forms a conductive coating on a surface of the substrate.

16. The substrate according to any one of claims 12 to 15, wherein the substrate is paper.

17. 1. A method for printing a conductive composition onto a substrate, comprising: a. printing the ink composition according to any one of claims 1 to 11 onto the surface of a substrate; and then b. Curing the ink composition A method comprising:

18. 20. The method of claim 17, wherein the conductive composition forms a conductive line, shape, pattern, circuit, or coating.

19. The conductive composition forms a conductive adhesive composition, and the method a. printing the ink composition of any one of claims 1 to 11 onto a surface of a substrate; a1. Placing a surface mount component on the printed ink composition; and then b. Curing the ink composition to elastically bond the substrate and the surface-mounted component.

18. The method of claim 17, comprising:

20. (i) in step (a), depositing the ink composition onto the surface of the substrate by screen printing; and / or (ii) The method of any one of claims 17 to 19, wherein the curing step (b) comprises applying heat to accelerate the curing process.

21. 1. A method for recycling conductive particles for reuse in a conductive ink composition, comprising: a. providing a substrate according to any one of claims 12 to 16; b. immersing the substrate in a solvent to dissolve the substrate and / or the binder component of the cured ink composition, thereby forming a collection medium containing the free-coated magnetic particles; c. Separating the conductive metal particles from the collection medium by applying a magnetic force; and d. Optionally, drying the recovered metal particles. A method comprising the steps of:

22. (i) the method further comprises a washing step after the separating step (c) and before the drying step (d), if any; (ii) the solvent is water; and / or 22. The method of claim 21, wherein (iii) the solvent is heated to about 50°C to about 90°C in step (b).

23. 23. The method of claim 21 or claim 22, comprising, after step (c), and if step (d), afterwards, combining the recovered conductive metal particles with one or more binders and one or more solvents to prepare the ink composition of any one of claims 1 to 11.

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