Conductive ink composition and method thereof

Abstract

The present disclosure relates to a graphene-based conductive ink composition and a method thereof. The composition demonstrates improved binding to substrates, superior resistance to hydrolysis, and enhanced mechanical strength and electrical conductivity. The present disclosure relates to a conductive ink composition and a method to obtain said conductive ink, wherein the conductive ink comprises: 4 to 25 wt.% of graphene as a first carbon-based conductive material; 0.1 to 10 wt.% of a second carbon-based conductive material; 0.01 to 5 wt.% of a first dispersant comprising styrene-co-acrylate for improving the distribution; 0.01 to 3 wt.% of a second dispersant for preventing the flocculation; 0.1 to 60 wt.% a binder comprising polyimide; 0.1 to 90 wt.% of a solvent.

Description

DESCRIPTION CONDUCTIVE INK COMPOSITION AND METHOD THEREOF TECHNICAL FIELD

[0001] The present disclosure relates to a conductive ink composition that can be used as an ink. The present disclosure relates to a conductive ink composition comprising graphene and a method to produce said composition. Specifically, it pertains to a conductive ink composition exhibiting enhanced binding to substrates, improved resistance to hydrolysis, and superior mechanical strength and electrical conductivity. BACKGROUND

[0002] The use of graphene-based conductive inks is revolutionising the printed electronics industry. Graphene is a unique material that possesses several properties, such as high electrical conductivity, oxidation resistance, flexibility, and durability, making it an excellent alternative for creating printed electronic circuits.

[0003] With conductive graphene inks it is possible to print electronic circuits on any surface, including curves and irregular surfaces, as they have an exceptional level of flexibility, allowing for the creation of devices that are more flexible and adaptable to user needs.

[0004] Document US20160293286A1 discloses a conductive complex to use in electronic devices that employs a conductive nanobody network including a plurality of conductive nanobodies randomly arranged and non-conductive nanobodies covering the network. However, the two layers use several kinds of conductive nanobodies, like silver or copper, and several kinds of non-conductive nanobodies, like semi-crystals. Then, the conductive complex won't have too much flexibility and durability. Furthermore, this conductive complex has a high sheet resistance, with values up to 1000 Ohms / square. The same metal issue is observed in documents CN107025951B and KR20160014409A.

[0005] Document WO2020264110A1 discloses electrically conductive inks using graphene, carbon nanotubes, graphene aerosol gel, and graphene oxide. It also describes the use of a graphene chemically modified or oxidised. The ratio of surfactant used in this solution is 500mg / mL, while the carbon materials quantities are low 10mg / mL.

[0006] Document WO2018195170 discloses energy storage devices and methods of forming thereof, comprising a conductive graphene ink on substrates to form durable, flexible, and facile graphene films and energy storage devices for use with and within a variety of electronics and devices.

[0007] US20160208124 discloses a conductive ink composition for the wireless antenna with adhesion enhancement by carbon flakes that aims to reduce the solid content of the conductor and can be used to print antennas. Carbon flakes (such as graphene nanoplatelets) are added as a conductive “cage” to reduce the use of insulated binder and significantly improve the conductivity of ink under low addition of conductor.

[0008] These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure. GENERAL DESCRIPTION

[0009] The present disclosure relates to a graphene-based conductive ink and a method thereof.

[0010] Surprisingly, the composition of the present disclosure has an improved binding to the substrates / materials, promoting a good resistance to hydrolysis.

[0011] Unexpectedly, the composition of the present disclosure has an improved mechanical strength or electrical conductivity of the composition is enhanced.

[0012] The present disclosure relates to advancements in the field of printable electronics, flexible electronics, sensors, plastronics, in-mould labelling, and grounding applications, with a focus on sustainability properties. The present disclosure introduces a novel conductive ink composition and a method for its formulation,offering numerous potential applications in the fields of electronics, automotive, and aerospace.

[0013] In the electronics industry, the conductive ink composition can be used for the production of printable electronics and flexible electronics. Printable electronics involve the fabrication of electronic devices using printing techniques, enabling cost- effective and scalable manufacturing processes. The conductive ink can be used to print conductive traces, interconnects, and components onto various substrates, such as paper, plastic, or fabric, among others. This allows for the creation of flexible electronic devices like wearable electronics, smart textiles, and bendable displays.

[0014] The automotive industry can benefit from the conductive ink composition in several ways. One potential application is in sensors, where the ink can be used to print conductive traces for various sensor types, such as touch sensors, proximity sensors, or strain sensors. These sensors can be integrated into the vehicle's interior, exterior, or engine components to enhance functionality and safety.

[0015] Another application in the automotive sector is in-mould labelling (IML). IML involves the integration of graphics, labels, or user interfaces directly into moulded plastic parts during the manufacturing process. The conductive ink composition can be used to print conductive traces and patterns for touch-sensitive controls, sensors, switches or backlighting features, enabling seamless integration of electronic functionalities into plastic surfaces.

[0016] In the aerospace industry, the conductive ink composition can contribute to the development of plastronics, a field that combines electronics with plastics. Plastronics enables the integration of electronic components directly into lightweight, durable, and aerodynamic structures. The conductive ink can be used to print conductive traces and connections on plastic substrates, facilitating the incorporation of electronic functionalities into aircraft components, such as wing surfaces, fuselage panels, or interior modules.

[0017] Furthermore, the conductive ink composition's properties make it an attractive choice for grounding applications. Grounding refers to the process of dissipating static electricity to prevent damage to sensitive electronic equipment. The ink can be appliedto create conductive paths or grounding pads on surfaces, providing an effective and eco-friendly conductive ink composition for grounding applications.

[0018] Another advantage of graphene conductive inks is their durability. They are highly resistant to oxidation and have a longer lifespan than conductive metal-based inks, which means that electronic circuits printed with conductive graphene inks last longer, which is especially important in applications that require an extended service life. Furthermore, conductive graphene inks can be non-toxic to organisms, unlike metal-based conductive inks, due to the intrinsically toxic nature of the metals. This might allow the production of safe graphene-based types of inks for medical devices.

[0019] In summary, graphene-based conductive inks are a promising solution for creating printed electronic circuitry, offering several advantages such as consistency, flexibility, and durability, while promoting excellent signal integrity with their stable electrical conductivity. Their use is paving the way for better and faster processing of electronics, allowing the creation of personalised electronic devices and the ability to print circuits in previously inaccessible places. Moreover, there is some expectation for better and / or easier recyclability of electronic parts using this kind of graphene-based electronics.

[0020] The present disclosure can be used in: Flexible displays and touch / membrane pads: to create flexible displays that are thin and lightweight. These displays can be used in wearable devices, e-books, and other applications. RFID tags: to create radio frequency identification (RFID) tags. These tags can be used to track inventory, authenticate products, and more. Sensors: to create sensors that can detect temperature, pressure, humidity, and other environmental factors. These sensors can be used in medical devices, smart homes, smart packaging, e-textiles, and other applications. Solar cells: to create thin-film solar cells that can be integrated into building materials, vehicles, and other structures.Capacitors: to create batteries that are thin and flexible. These batteries can be used in wearable devices, medical implants, and other applications. Printed circuit boards: to create printed circuit boards (PCBs) that are more environmentally friendly and less expensive than traditional PCBs. Printed Antennas: to create antennas that are thin and lightweight. These antennas can be used in mobile devices, wireless networks, and other applications. Positive temperature coefficient printed heaters: to create heaters that are thin and flexible. These heaters can be used in medical devices, automotive applications, and other products.

[0021] Several methods can be used for applying the conductive composition, preferably the graphene-based ink, preferably: Screen printing; Inkjet printing, Flexographic printing; Gravure printing; Spray coating; Dip coating; Roll-to-roll coating; Vacuum deposition; Transfer printing and Lamination.

[0022] An aspect of the present disclosure relates to a conductive ink composition comprising: 4 to 25 wt.% of graphene as a first carbon-based conductive material; 0.05 to 10 wt.% of a second carbon-based conductive material; 0.01 to 5 wt.% of a first dispersant comprising styrene-co-acrylate for improving the composition distribution; 0.01 to 3 wt.% of a second dispersant for preventing composition flocculation; 0.1 to 60 wt.% of a binder comprising polyimide; 0.1 to 90 wt.% of a solvent.

[0023] Preferably, the polyimide is polyetherimide.

[0024] The present disclosure provides a graphene-based conductive ink composition that exhibits: improved binding to substrates, resulting in enhanced adhesion; superior resistance to hydrolysis, thereby extending the durability and lifespan of the printed electronic components; enhanced mechanical strength and electrical conductivity, ensuring reliable performance in various applications.

[0025] In an embodiment, the second dispersing additive comprises a quaternary ammonium salt.

[0026] The presence of the first dispersant, namely styrene-co-acrylate, in a graphene nanoplatelets dispersion facilitates aromatic ring interactions, especially π−π stacking, between aromatic rings of graphene and the aromatic rings present in the dispersant. Stacking is described as an attraction caused by the alignment and overlap of electron clouds between aromatic rings in the vicinity. High shear pressures utilised during the manufacturing process with a mechanical stirrer assist the alignment of the graphene nanoplatelets and the styrene-co-acrylate chains, promoting the dispersion stability of graphene nanoplatelets by encouraging π−π stacking. This eliminates agglomerates and ensures better control over graphene particles' organisation and distribution, improving dispersion, flexibility, flexural strength, adhesion, abrasion resistance, water resistance of the ink and electrical properties.

[0027] The second dispersing agent, comprises quaternary ammonium salt, preferably is quaternary ammonium salt, prevents flocculation and stabilises the system (composition) by creating considerable repulsive forces between particles, so avoiding uncontrolled flocculation and, consequently, sedimentation, thus improving system stability and electrical properties.

[0028] The selection of polyimide as a binder is related to its long-term heat resistance, high strength and rigidity at elevated temperatures, and dimensional stability. It has low water absorption ability and an extremely good dielectric constant. Preferably the polyimide is polyetherimide.

[0029] In an embodiment, the conductivity of the composition is from 400 S / m to 8 000 S / m at 25 °C, preferably from 850 S / m to 5.000S / m at 25 °C. The advantages of described conductive ink are its high conductivity, flexibility, chemical and thermal stability, as well as eco-friendliness and scalability.

[0030] In the state of the art, the conductivity may be measured by many methods. The electrical conductivity can be measured by standard methods, namely by utilizing a four-point probe at 25 °C. Here, the resistivity of the conductive inkcomposition is measured with 4 parallel pins that are lined up, with 2 inner pins connected to a milli-ohmmeter and 2 outer pins connected to a current source.

[0031] In an embodiment, the viscosity of the conductive composition is 100 mPa.s to 50000 mPa.s at 25 °C, preferably from 1000 mPa.s to 20000 mPa.s at 25 °C, more preferably 2000 mPa.s to 14000 mPa.s at 25 °C, more preferably from 3000 mPa.s to 10000 mPa.s at 25°C.

[0032] In the state of the art, the viscosity may be measured by many methods. In the present disclosure the viscosity measurement was carried out as measured on a cone- plate geometry rheometer equipment, a rotation of between 0.3 and 1500 rpm, and a torque between 0.05 and 30 mNm and 100%, at 25 °C or 30 °C.

[0033] The lowest viscosities are read at high shear rate conditions (fixed value 130 s-1), using 10 rpm. The torque read here is 12 mNm.

[0034] On the other hand, the highest viscosities are read at low shear rate conditions (fixed value 20 s-1), using 1.7 rpm. The torque read here is 2.64 mNm. Figure 4 shows the equations for shear stress and shear rate.

[0035] In an embodiment, the graphene is selected from graphene nanoplatelets, few- layer graphene, multi-layer graphene; graphene oxide, and reduced graphene oxide, or combinations thereof.

[0036] In an embodiment, the graphene is graphene nanoplatelets.

[0037] In an embodiment, the amount of graphene as a first carbon-based conductive material is 5 to 20 wt.%, more preferably 10 to 15 wt.%.

[0038] In an embodiment, the amount of the first dispersant is 0.1 to 4 wt.%, preferably 0.4 to 2 wt.%.

[0039] In an embodiment, the amount of binder is 2 to 50 wt.%, preferably 5 to 35 wt. %, more preferably 10 to 25 wt. %.

[0040] In an embodiment, the binder further comprises silicone polymers, carboxymethyl cellulose, methyl-hydroxy-propyl-cellulose, ethyl cellulose, polyesters, polyethers, polycarbonates, polyurethanes, polyimide, polyetherimide, polysiloxane, or mixtures thereof.

[0041] In an embodiment, the binder is polyimide, preferably polyetherimide.

[0042] In an embodiment, the first dispersant is a vinyl-acrylic copolymer or a styrene- acrylic copolymer, preferably a styrene-co-acrylate.

[0043] In an embodiment, the amount of the second dispersant is 0.05 to 2 wt.%., preferably 0.1 to 1.5 wt.%.

[0044] In an embodiment, the second dispersant comprises a quaternary ammonium salt.

[0045] In an embodiment, the second dispersant is an anionic surfactant, derived from lignin, a natural polymer found in wood. Its sulfonate groups provide the anionic charge, which helps in the dispersion of pigments and particles. The dispersant promotes electrostatic and / or steric stabilization to dispersed particles, ensuring effective dispersion and long-term stability in formulations.

[0046] In an embodiment, the second dispersant is quaternary ammonium salt.

[0047] In an embodiment, the ink composition further comprises an odour- neutralising agent for reducing the odour, preferably 0.02 to 0.3 wt.% of odour- neutralising agent, more preferably 0.03 to 0.2 wt.%. The odour reduction is important to reduce the volatile organic compounds (VOCs) or other potentially harmful chemicals. Moreover, odours can have a significant impact on the perception of a product. Unpleasant odours associated with coatings can create a negative impression and diminish the overall aesthetic appeal.

[0048] In an embodiment, the odour-neutralising agent is selected from carbitol, coumarin or musk ketone.

[0049] In an embodiment, the amount of the solvent is 50 to 80 wt. %, more preferably 60 to 75 wt. %.

[0050] In an embodiment, wherein the solvent is selected from water, xylene, kerosene, toluene, dimethyl sulfoxide, butanone, diethylene glycol monoethyl ether acetate, cyrene, tetrahydrofuran, ethanol, terpineol, limonene, isopropyl alcohol, 1- methoxy-2-propanol, glycerol, ethylene glycol, ethylene glycol diacetate, or mixtures thereof.

[0051] In an embodiment, for better results, the solvent is water. The use of water as solvent serves to dissolve or disperse the water-based polyimide resin. It helps in achieving a suitable consistency and viscosity for the coating formulation. It also acts as a dispersion medium for the graphene nanoplatelets. It helps to evenly distribute and suspend the graphene throughout the coating formulation, ensuring a uniform distribution of the filler material. This is important for achieving the desired properties and performance of the coating, such as enhanced mechanical strength or electrical conductivity. Water plays a role in the film formation process of the coating. When the coating is applied onto a substrate, water evaporates, leaving behind the polyrimide resin and graphene to form a solid film. This film provides the desired functional and protective properties to the coated surface. Additionally, water-based formulations can be often preferred for their lower volatile organic compound (VOC) content compared to solvent-based coatings. This makes them more environmentally friendly and safer to handle during the application and curing processes.

[0052] In an embodiment, the solvent is toluene. The use of toluene as solvent serves to dissolve or disperse the solvent-based polyrimide resin, acting as a dispersion medium for the graphene nanoplatelets. With toluene, the desired properties can be achieved, such as enhanced mechanical strength or electrical conductivity.

[0053] In an embodiment, the amount of the second carbon-based conductive material is 0.1 to 4 wt. %, more preferably 0.3 to 2 wt. %.

[0054] In an embodiment, the second carbon-based conductive material is selected from a list consisting of: natural and synthetic graphite, carbon black, carbon nanotubes, carbon fibres, carbon nano onions, graphene oxide, carbon nanospheres, fullerenes, or mixtures thereof.

[0055] In an embodiment, the second carbon-based conductive material does not comprise graphene.

[0056] In an embodiment, the second carbon-based conductive material is carbon black. The second carbon-based conductive material, preferably carbon black will promote a synergistic effect with the graphene nanoplatelets. When combined, they both create a network of conductive pathways throughout the coating, improving the overall electrical conductivity. Carbon black also acts as a strengthening agent, complementing the reinforcing effect of graphene nanoplatelets and resulting in a synergistic improvement in mechanical properties such as tensile strength, impact resistance, and hardness. Moreover, graphene nanoplatelets and carbon black can have different surface properties and tendencies to agglomerate. When used together, they can exhibit improved dispersion stability. The presence of graphene nanoplatelets can help prevent the agglomeration of carbon black particles, leading to a more homogeneous distribution within the coating. This results in improved coating properties, such as a smoother surface finish, better colour consistency, and reduced risk of defects.

[0057] In an embodiment, the composition further comprises an odour-neutralising agent, preferably 0.01 to 0.5 wt.% of an odour-neutralising agent, more preferably 0.02 to 0.3 wt.%, even more preferably 0.03 to 0.2 wt.%.

[0058] In an embodiment, the odour-neutralising agent is selected from a list consisting of: carbitol, coumarin, musk ketone, and mixtures thereof.

[0059] In an embodiment, the composition further comprises an additive, such as stabilizer, cross-linking agent, dye, or combinations thereof.

[0060] It is also disclosed a substrate comprising the conductive ink composition described.

[0061] In an embodiment, the substrate is paper, fabric, plastic, or combinations thereof.

[0062] It is also disclosed a method to obtain the conductive ink composition comprising the following steps: mixing a first dispersant and a second dispersant in a solvent to obtain a solution; adding a second carbon-based conductive material to the solution and maintaining the mixing until the second carbon-based conductive material is homogeneously dispersed in the solution; adding a binder to the solution obtained in the previous step; adding and mixing the first carbon-based conductive material to the solution until obtaining a homogeneous solution.

[0063] In an embodiment, the method further comprises the step of adding an odour- neutralising agent.

[0064] Another aspect of the present disclosure relates to a method for applying the graphene-based conductive ink to a substrate, comprising: preparing the substrate; printing the conductive ink composition according to claims 1-21 onto the substrate; curing the printed ink.

[0065] In an embodiment, the curing process involves thermal curing, UV curing, or other methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of the invention.

[0067] Figure 1: Graphic representation of the results of viscosity data of Table 2 as a function to the shear rate of an embodiment of a graphene-based aqueous ink (Formulation 1 and Formulation 2).

[0068] Figure 2: Graphic representation of the results of viscosity data of Table 3 as a function to the shear rate of an embodiment of a graphene-based aqueous ink (Formulation 3 and Formulation 4).

[0069] Figure 3: Graphic representation of the results of viscosity data of Table 4 as a function to the shear rate of an embodiment of a graphene-based solvent ink (Formulation 1 and Formulation 2).

[0070] Figure 4: Shows the equations for shear stress and shear rate. DETAILED DESCRIPTION

[0071] The present disclosure relates to a graphene-based conductive ink composition and a method thereof. The composition demonstrates improved binding to substrates, superior resistance to hydrolysis, and enhanced mechanical strength and electrical conductivity.

[0072] The present disclosure relates to a conductive ink composition. Namely it relates to a conductive ink composition comprising: 4 to 25 wt.% of graphene as a first carbon-based conductive material; 0.1 to 10 wt.% of a second carbon-based conductive material; 0.01 to 5 wt.% of a first dispersant comprising styrene-co-acrylate for improving the distribution; 0.01 to 3 wt.% of a second dispersing additive; 0.1 to 60 wt.% of a binder comprising polyimide and 0.1 to 90 wt.% of a solvent, preferably 50 to 80 wt.%.

[0073] Conductive graphene-based ink for printed electronics is composed of several elements that are essential to its performance.

[0074] In an embodiment, the binder is the medium in which the particles are arranged and organised in the best possible way according to their morphology. After the ink is dried and cured, it forms a protective film and is mainly responsible for thedrying time, appearance, adhesion of the ink to the substrate, and the mechanical and thermal resistance of the ink composition.

[0075] The solvent allows the fine-tuning of the viscosity in order to facilitate the final application. Preferably, the viscosity of the ink is 100 mPa.s to 50000 mPa.s, preferably 4 000 mPa.s to 20000 mPa.s, more preferably 5 000 mPa.s to 16 500 mPa.s, more preferably 2000 mPa.s to 14000 mPa.s. Viscosity is a measure of a fluid’s resistance to flow. The viscosity of the ink can have a significant impact on any application. Inks with a higher viscosity will flow more slowly and require more pressure to apply, while inks with a lower viscosity will flow more easily and may require less pressure to apply. In the context of printable electronics, the viscosity of the ink can affect the quality and consistency of the printed pattern, circuit, drawing or other format.

[0076] The table below shows the percentage weight of each component of an embodiment of the conductive composition, preferably the graphene-based aqueous ink formulation.

[0077] Table 1 - Percentage weight of each component of a specific graphene-based aqueous ink formulation. Formulation Formulation Formulation Formulation 1 2 3 4 Binder 60 wt. % 30 wt. % 19 wt. % 1 wt. % Graphene 21 wt. % 5 wt. % 10 wt. % 25wt. % Nanoplatelets Carbon Black 10 wt. % 0.3 wt. % 0.4 wt. % 0.15 wt. % Water 2 wt. % 60 wt. % 70 wt. % 73.69 wt. % Styrene-co-acrylate 5 wt. % 1.6 wt. % 0.25 wt. % 0.05 wt. % Quaternary 1.5 wt. % 2.6 wt. % 0.25 wt. % 0.1 wt. % ammonium salt Odour Neutralizer 0.5 wt. % 0.5 wt. % 0.1 wt. % 0.01 wt. %

[0078] Table 2 - Percentage weight of each component for two examples of specific graphene-based solvent ink formulations. Formulation 1 Formulation 2 Binder 14.9 wt. % 20 wt. % Graphene 15 wt. % 10 wt. % Nanoplatelets Carbon Black 0.05 wt. % 4 wt. % Ethylene glycol 0 wt. % 65 wt. % Toluene 70 wt. % 0 wt. % Styrene-co- 0.03 wt. % 0.4 wt. % acrylate Quaternary 0.01 wt. % 0.55 wt. % ammonium salt Odour Neutralizer 0.01 wt. % 0.05 wt. %

[0079] Table 3 - Viscosity as a function to the shear rate - graphene-based aqueous Ink (Formulation 1 and Formulation 2). Viscosity (mPa⋅s) Shear Rate (s-1) Formulation 1 Formulation 2 25°C 30°C 25°C 30°C 20 13526 ± 161 1327 ± 3225 6692 ± 176 668 ± 86 25 11962 ± 129 1150 ± 2787 5823 ± 143 561 ± 64 30 10672 ± 345 1061 ± 2558 5032 ± 131 592 ± 124 35 9854 ± 82 1029 ± 2474 4502 ± 164 527 ± 41 40 8647 ± 92 942 ± 2254 3892 ± 136 465 ± 48 45 8033 ± 242 910 ± 2172 3490 ± 122 415 ± 27 50 7556 ± 64 857 ± 2035 3265 ± 110 423 ± 3855 7118 ± 85 811 ± 1917 3122 ± 115 394 ± 64 60 6677 ± 141 790 ± 1860 2996 ± 110 392 ± 12 65 6323 ± 91 770 ± 1807 2951 ± 102 402 ± 58 70 6184 ± 70 720 ± 1653 2940 ± 103 386 ± 33 75 5986 ± 89 684 ± 1589 2908 ± 101 413 ± 45 80 5704 ± 46 697 ± 1613 2896 ± 104 406 ± 34 85 5434 ± 71 673 ± 1550 2850 ± 102 409 ± 16 90 5441 ± 52 658 ± 1508 2799 ± 101 413 ± 33 95 5282 ± 67 625 ± 1423 2761 ± 95 388 ± 33 100 5081 ± 35 625 ± 1416 2697 ± 93 354 ± 19 105 5008 ± 60 626 ± 1415 2603 ± 95 350 ± 15 110 4952 ± 58 595 ± 1334 2566 ± 88 345 ± 9 115 4746 ± 37 577 ± 1284 2497 ± 86 337 ± 20 120 4635 ± 38 585 ± 1298 2456 ± 89 353 ± 45 125 4642 ± 20 576 ± 1272 2400 ± 87 360 ± 21 130 4532 ± 15 552 ± 1208 2379 ± 83 349 ± 11

[0080] Table 4 - Viscosity as a function to the shear rate - graphene-based aqueous Ink (Formulation 3 and Formulation 4). Viscosity (mPa⋅s) Formulation 3 Formulation 4 Shear Rate (s-1) 25°C 30°C 25°C 30°C 20 2463 ± 50 2340 ± 27 669 ± 10 574 ± 16 25 2296 ± 38 2298 ± 25 621 ± 7 507 ± 6 30 2215 ± 39 2226 ± 56 593 ± 9 497 ± 535 2123 ± 26 2106 ± 21 545 ± 10 475 ± 4 40 2094 ± 95 2056 ± 21 543 ± 13 464 ± 4 45 2019 ± 21 2007 ± 111 513 ± 11 448 ± 6 50 2019 ± 40 2002 ± 33 500 ± 11 446 ± 10 55 1986 ± 13 2002 ± 31 492 ± 4 443 ± 3 60 1960 ± 40 1998 ± 43 487 ± 46 440 ± 7 65 1942 ± 19 1970 ± 9 482 ± 2 439 ± 8 70 1907 ± 51 1959 ± 67 475 ± 4 437 ± 6 75 1898 ± 6 1946 ± 22 471 ± 4 433 ± 15 80 1836 ± 34 1923 ± 27 471 ± 5 431 ± 3 85 1799 ± 13 1849 ± 14 465 ± 4 429 ± 4 90 1762 ± 32 1818 ± 16 464 ± 4 429 ± 25 95 1753 ± 14 1808 ± 55 464 ± 7 427 ± 1 100 1735 ± 38 1776 ± 13 461 ± 1 425 ± 4 105 1653 ± 10 1752 ± 23 455 ± 3 424 ± 3 110 1622 ± 16 1734 ± 26 452 ± 17 419 ± 3 115 1584 ± 19 1706 ± 14 449 ± 2 412 ± 3 120 1552 ± 19 1651 ± 8 436 ± 2 410 ± 0 125 1546 ± 29 1642 ± 21 433 ± 6 409 ± 22 130 1508 ± 12 1629 ± 21 429 ± 9 403 ± 3

[0081] In an embodiment, the above table (Table 3 and Table 4) shows the viscosity data for four formulations of graphene aqueous-based inks when shear rate and temperature are varied, 20 to 130 s-1and 25°C and 30°C, respectively. Formulation 1 and Formulation 2 exhibit the same behaviour: viscosity decreases as temperature rises, due to increased intermolecular forces, reducing resistance to flow and decreasing viscosity. Regarding shear rate, when increasing the shear rate the viscosity decreases until reaching constant value. This behaviour is observed in thixotropicfluids. Regarding Formulation 3 and Formulation 4 viscosity is maintained when temperature rises due to high solvent content. However, when shear rate increases the viscosity decreases slightly. This behaviour is observed in smooth thixotropic fluids.

[0082] Table 5 – Represents the viscosity as a function of shear rate - graphene-based solvent Ink. Viscosity (mPa⋅s) Shear Rate (s-1) Formulation 1 Formulation 2 25°C 30°C 25°C 30°C 20 4826 ± 34 4419 ± 65 6110 ± 182 5259 ± 20 25 4084 ± 52 3962 ± 11 5726 ± 71 4705 ± 36 30 3457 ± 46 3336 ± 41 5213 ± 182 4263 ± 35 35 3156 ± 33 3017 ± 22 5036 ± 201 3918 ± 18 40 2892 ± 26 2778 ± 40 4828 ± 60 3692 ± 51 45 2702 ± 15 2576 ± 21 4586 ± 36 3459 ± 157 50 2477 ± 26 2375 ± 91 4450 ± 203 3350 ± 31 55 2389 ± 63 2226 ± 12 4339 ± 40 3244 ± 110 60 2278 ± 18 2142 ± 25 4216 ± 171 3120 ± 22 65 2146 ± 17 2033 ± 59 4196 ± 78 3065 ± 46 70 2052 ± 21 1965 ± 10 4163 ± 37 3110 ± 98 75 2027 ± 12 1908 ± 17 4091 ± 19 3056 ± 118 80 1962 ± 38 1886 ± 44 4009 ± 128 3006 ± 72 85 1875 ± 15 1799 ± 10 3968 ± 23 2913 ± 110 90 1794 ± 17 1681 ± 5 3860 ± 52 2879 ± 19 95 1726 ± 13 1586 ± 8 3846 ± 75 2826 ± 6 100 1644 ± 17 1552 ± 5 3825 ± 18 2793 ± 20

[0083] The table above (Table 5) shows the viscosity data for two formulations of graphene solvent-based ink when shear rate and temperature are varied, 20 to 100 s-1and 25°C and 30°C, respectively. It is possible to observe that the impact of temperature in viscosity is very high for both formulations. Both formulations exhibit the same behaviour: viscosity decreases as temperature rises. However, the Formulation 2 showed a higher influence of temperature when compared with Formulation 1. Regarding shear rate, when increasing the shear rate the viscosity decreases until reaching constant value. This behaviour is observed in thixotropic fluids.

[0084] In conclusion, the graphene aqueous-based ink and graphene solvent-based ink are thixotropic fluids. In the field of printable electronics, the thixotropic fluids offer advantages such as improved printability, smooth and controlled ink deposition, reduced ink migration, enhanced stability, ease of processing, resulting in high-quality, precise, and reliable printed electronics devices.

[0085] In an embodiment, the flocculation controlling agent (second dispersant) and the dispersant agent are paramount in the incorporation of a high content of carbon- based materials. As previously mentioned, the graphene used in this type of ink is not oxidised or chemically modified (neither functionalized), thus not compromising the electrical characteristics of the material. In the case of inks that contain water in their formulation, interactions between low oxygen-content (<5%) carbon materials and water are not favourable, thus requiring intermediates that promote interactions between them all.

[0086] The following table (Table 6) contains an example of conductivity values measurements of a sample made of an aqueous ink. The composition used is 30 wt. % of binder, 5 wt. % of Graphene Nanoplatelets, 0.3 wt. % of Carbon Black, 60 wt. % of water, 1.6 wt. % of styrene-co-acrylate, 2.6 wt. % of a second dispersing additive and 0.5 wt. % of a odour neutralizer (Formulation 2 of Table 2).

[0087] Table 6 - Conductivity values of the Graphene-based aqueous Ink samples Surface Thickness Resistanc Rsheet Rbulk Replicas Conductivity (μm) e (Ω) (Ω / square) (Ω.m) (S / m) 1 92.4 ± 5.8 1.4 ± 0.1 4.9 ± 0.4 4.5E-04 ± 3.6E-05 2227.1 ± 225.3 2 95.9 ± 8.0 1.3 ± 0.1 4.6 ± 0.3 4.4E-04 ± 3.2E-05 2253.4 ± 249.5 3 76.9 ± 1.7 1.2 ± 0.1 4.2 ± 0.2 3.3E-04 ± 1.4E-05 3067.4 ± 146.8 4 67.0 ± 4.9 1.5 ± 0.1 5.4 ± 0.4 3.6E-04 ± 2.6E-05 2764.0 ± 282.1 5 63.6 ± 3.7 1.5 ± 0.1 5.5 ± 0.2 3.5E-04 ± 1.4E-05 2859.1 ± 201.7 6 59.2 ± 4.0 1.7 ± 0.2 6.1 ± 0.6 3.6E-04 ± 3.5E-05 2759.3 ± 324.1 7 43.4 ± 3.0 2.2 ± 0.2 7.8 ± 0.7 3.4E-04 ± 2.8E-05 2974.8 ± 323.0

[0088] Table 6 presents the conductivity of various replicas with different coatings thickness samples. It is evident that conductivity decreases with increasing coating thickness.

[0089] Coatings with thicknesses below 77 microns achieve their maximum performance level ( >3000 S / m), while above 80 microns, this coating sample reaches a state of conductivity saturation.

[0090] From an economic standpoint, this is advantageous for consumers, as a thinner coating requires less material compared to a thicker one, while still maintaining high- performance levels.

[0091] This coating is well-suited for flexible electronics due to its ability to achieve high performance with a thickness below 80 microns. Finally, a high concentration of graphene is desirable to minimise the number of required printing steps / stages.

[0092] In an embodiment, the odour neutralizer is an additive that does not promote any aroma or allows a more pleasant aroma of the formulation to stand out during and after the final application of the ink.

[0093] In an embodiment, the composition of the graphene-based conductive ink for printed electronics is:4 to 20 wt.% of the graphene nanoplatelets; 0.1 to 10 wt.% of carbon-based conductive material; 0.01 to 5 wt.% of a first dispersant; 0.01 to 3 wt.% of a second dispersing additive; 0.01 to 0.5 wt.% of an additive (odour neutralizer); 0.1 to 30 wt.% of a binder; 0.1 to 90 wt.% of a solvent.

[0094] Preferably the aqueous-based binder can be selected from: cellulosic polymers, polystyrene, acrylic polymers, polyvinyl alcohol, aqueous polyurethane resins, polyimide, polyetherimide or other mixtures.

[0095] Preferably the solvent-based binder can be selected from: silicone polymers, carboxymethyl cellulose, methyl-hydroxy-propyl-cellulose, ethyl cellulose, polyesters, polyethers, polycarbonates, polyurethanes, polyetherimide, polyimide, polysiloxane, polyethyleneimine or other mixtures. Preferably, it is polyimide because of its high strength and rigidity at elevated temperatures, long-term heat resistance, dimensional stability, and dimensional accuracy. Furthermore, it has good resistance to hydrolysis. Preferably is polyetherimide.

[0096] Preferably the solvent of the composition can be selected from: water, xylene, kerosene, toluene, dimethyl sulfoxide, butanone, diethylene glycol monoethyl ether acetate, cyrene, tetrahydrofuran, ethanol, polyacrylic acid, polyvinyl acid, terpineol, limonene, isopropyl alcohol, 1-methoxy-2-propanol, glycerol, polyethylene glycol, ethylene glycol diacetate, or mixtures thereof.

[0097] There are several advantages associated with this type of ink in a wide range of applications in the field of printed electronics, such as: Flexibility (enabling printing on irregular / tortuous substrates); Non-toxicity (ensuring health and safety); Oxidation resistance, resulting in a longer service life; Reduced weight; Easy application;Possibility to regulate the viscosity according to the intended application and process, without impairing the conductive properties; High conductivity (approximately or higher than 3 000 S / m with 40 - 100 microns).

[0098] The method comprises the following steps. Mixing the styrene-co-acrylate and the second dispersing additive in a solvent to prepare a solution; Adding the carbon black (or other carbons) to the solution, and maintain the mixing process until the material is homogeneously dispersed in the solution; Adding the odour neutralizer to the solution; Adding the binder to the previous solution; Finally, adding and mixing the graphene nanoplatelets until obtaining a homogeneous solution.

[0099] The mixing or blending can be made with instruments such as an ultrasonic bath, a rotary mixer, a stirrer, and / or others to obtain a homogeneous mixture.

[0100] In another embodiment, the polymeric binder is dissolved in the solvent by mixing.

[0101] In another embodiment, carbon black (or other carbons) is added to make and promote a dispersion.

[0102] In another embodiment, the graphene nanoplatelets are added to the previous dispersion and blended until a homogenous dispersion is obtained.

[0103] In an embodiment, Figure 1 shows a graphic representation of the viscosity data (Table 3) as a function of the shear rate at different temperatures - Graphene-based aqueous Ink (Formulation 1 and Formulation 2).

[0104] In an embodiment, Figure 2 shows a graphic representation of the viscosity data (Table 4) as a function of the shear rate at different temperatures - Graphene-based aqueous Ink (Formulation 3 and Formulation 4).

[0105] In an embodiment, Figure 3 shows a graphic representation the viscosity data (Table 5) as a function of shear rate at different temperatures - graphene-based solvent Ink.

[0106] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0107] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof. The above-described embodiments are combinable.

[0108] The following claims further set out particular embodiments of the disclosure.

Claims

CLAIMS 1. Conductive ink composition comprising: 4 to 25 wt.% of graphene as a first carbon-based conductive material; 0.05 to 10 wt.% of a second carbon-based conductive material; 0.01 to 5 wt.% of a first dispersant comprising styrene-co-acrylate for improving the composition distribution; 0.01 to 3 wt.% of a second dispersant for preventing the composition flocculation; 0.1 to 60 wt.% of a binder comprising polyimide; 0.1 to 90 wt.% of a solvent.

2. Composition according to the previous claim wherein the conductivity of the composition is from 400 S / m to 8000 S / m at 25 °C, preferably from 850 S / m to 5000 S / m at 25 °C.

3. Composition according to any of the previous claims wherein the viscosity of the conductive composition is from 100 mPa.s to 50000 mPa.s at 25 °C, preferably from 1 000 mPa.s to 20000 mPa.s at 25 °C, more preferably 2000 mPa.s to 14000 mPa.s at 25 °C, more preferably from 3000. mPa.s to 10000 mPa.s at 25 °C.

4. Composition according to any of the previous claims wherein the graphene is selected from graphene nanoplatelets, few-layer graphene, multi-layer graphene; oxide graphene, or combinations thereof.

5. Composition according to any of the previous claims wherein the graphene is graphene nanoplatelets.

6. Composition according to any of the previous claims wherein the amount of graphene as a first carbon-based conductive material is 5 to 20 wt.%; preferably 10 to 15 wt.%.

7. Composition according to any of the previous claims wherein the amount of the first dispersant is 0.1 to 4 wt.%; preferably 0.4 to 2 wt.%.

8. Composition according to any of the previous claims wherein the amount of binder is 2 to 50 wt.%; preferably 5 to 35 wt.%, more preferably 10 to 25 wt.%.

9. Composition according to any of the previous claims wherein the binder further comprises silicone polymers, carboxymethyl cellulose, methyl-hydroxy-propyl- cellulose, ethyl cellulose, polyesters, polyethers, polycarbonates, polyurethanes, polyetherimide, polysiloxane, or mixtures thereof.

10. Composition according to any of the previous claims wherein the binder is polyetherimide.

11. Composition according to any of the previous claims wherein the first dispersant is a vinyl-acrylic copolymer or a styrene-acrylic copolymer, preferably a styrene-co- acrylate.

12. Composition according to any of the previous claims wherein the amount of the second dispersant is 0.05 to 2 wt. %., preferably 0.1 to 1.5 wt. %.

13. Composition according to any of the previous claims wherein the second dispersant comprises a quaternary ammonium salt.

14. Composition according to any of the previous claims wherein the amount of the solvent is 50 to 80 wt. %.

15. Composition according to any of the previous claims wherein the solvent is selected from a list consisting of: water, xylene, kerosene, toluene, dimethyl sulfoxide, butanone, diethylene glycol monoethyl ether acetate, cyrene, tetrahydrofuran, ethanol, terpineol, limonene, isopropyl alcohol, 1-methoxy-2-propanol, glycerol, ethylene glycol, ethylene glycol diacetate, polyethylene glycol or mixtures thereof; preferably water.

16. Composition according to any of the previous claims wherein the amount of the second carbon-based conductive material is 0.1 to 4 wt. %, preferably 0.1 to 2 wt. %.

17. Composition according to any of the previous claims wherein the second carbon- based conductive material is selected from a list consisting of: natural and synthetic graphite, carbon black, carbon nanotubes, carbon fibres, carbon nano onions, graphene oxide, reduced graphene oxide, carbon nanospheres, fullerenes, or mixtures thereof.

18. Composition according to any of the previous claims wherein the second carbon- based conductive material does not comprise graphene.

19. Composition according to any of the previous claims wherein the second carbon- based conductive material is carbon black.

20. Composition according to any of the previous claims further comprises an odour- neutralising agent, preferably 0.01 to 0.5 wt.% of an odour-neutralising agent, more preferably 0.02 to 0.3 wt.%, even more preferably 0.03 to 0.02 wt.%.

21. Composition according to the previous claim wherein the odour-neutralising agent is selected from a list consisting of: carbitol, coumarin, musk ketone, and mixtures thereof.

22. Composition according to any of the previous claims further comprising an additive, such as stabilizer, cross-linking agent, dye, or combinations thereof.

23. Substrate comprising the conductive ink composition according to any of the previous claims 1 to 22; wherein the substrate is paper, fabric, plastic, or combinations thereof.

24. Method to obtain the conductive ink composition according to any of the previous claims 1 to 22 comprising the following steps: mixing a first dispersant and a second dispersant in a solvent to obtain a solution;adding a second carbon-based conductive material to the solution and mix until second carbon-based conductive material is homogeneously dispersed in the solution; adding a binder to the solution obtained in the previous step; adding and mixing the graphene to the solution until obtaining a homogeneous solution.

25. Method according to the previous claim further comprising the step of adding the odour-neutralising agent.

26. Method for applying the graphene-based conductive ink to a substrate, comprising: preparing the substrate; printing the conductive ink composition according to claims 1-22 onto the substrate; curing the printed ink.

27. Method according to the previous claim wherein the curing process involves thermal curing, UV curing.

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