Aqueous conductive adhesive composition, its method of preparation and uses thereof

Abstract

The present disclosure relates to an aqueous conductive adhesive composition, its method of preparation and uses thereof. It is disclosed an aqueous conductive adhesive composition for electrical component comprising: 40-95 % (w / w) of a water-dispersible polymer matrix; 5-60 % (w / w) of a conductive agent; wherein the water-dispersible polymer matrix is selected from a list consisting of polyethylene, polypropylene, polystyrene, co-polymer of methyl methacrylate-styrene, copolymer of acrylonitrile-styrene, acrylate, polyvinyl butyral, poly vinyl formal, polyimide, polyamide, polyester, polyvinyl chloride, fluororesin, urea resin, melamine resin, phenol formalin resin, phenol resin, xylene resin, epoxy resin, polyisocyanate resin, phenoxy resin, silicon resin, thermoplastic polyester-amide, polyurethane resin, and combinations thereof; wherein the conductive agent is selected from a list consisting of: polyaniline, polypyrrole, poly(3,4- ethylenedioxythiophene), silver nanoparticles, copper nanoparticles, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, black carbon, and combinations thereof; wherein the viscosity of the aqueous conductive adhesive composition ranges from 30 Pa.s to 90 Pa.s at 20 °C, measured at shear rate 1 s-1 using cone-plate rheometer; wherein the composition is curable or dryable to form a conductive film at temperatures below 150°C; and wherein the composition comprises a conductivity of at least 1000 S / cm, measured by a four-point probe at 25°C.

Description

D E S C R I P T I O NAQUEOUS CONDUCTIVE ADHESIVE COMPOSITION, ITS METHOD OF PREPARATION AND USES THEREOFTECHNICAL FIELD

[0001] The present disclosure relates to an aqueous conductive adhesive composition, its method of preparation and uses thereof.

[0002] In particular, the present disclosure relates to an aqueous conductive adhesive composition suitable for printing on flexible substrates such as textiles, paper or plastics, the composition being patternable and electrically conductive adhesive, and configured to impart conductivity to flexible substrates and to electrically connect electronic components.BACKGROUND

[0003] In the realm of modern electronics, the need for reliable and efficient electrical connections has never been greater. With the continuous push towards miniaturization and increased functionality of electronic devices, traditional methods of bonding and interconnecting components are becoming less effective. Soldering, for instance, although widely used, poses significant challenges, particularly in applications where heat sensitivity, flexibility, and environmental resistance are critical. These challenges have driven the demand for alternative solutions, particularly in the form of conductive adhesives that can provide both mechanical bonding and electrical conductivity without the need for high-temperature processes.

[0004] Current conductive adhesives often lack the necessary characteristics for seamless integration with flexible substrates like textiles, paper, or plastics. In some cases, like the one described in the document CN104487534B, the current conductive adhesives may be rigid, brittle, or incompatible with printing processes.

[0005] Flexible adhesives are commonly preferred over brittle, stiff ones due to their ability to expand and contract, allowing them to bond materials with differentcoefficients of thermal expansion or elastic moduli. These adhesives exhibit high resistance to thermal cycling and crack propagation, as they distribute stress uniformly, eliminating localized stress concentrations. They are frequently used in applications involving plastics, elastomers, and textiles, where environmental service conditions are not extreme, and the adhesive's physical properties match those of the substrates. This makes them ideal for applications in textiles, aerospace, furniture, and packaging.

[0006] Despite their widespread use, high-tech flexible adhesives are continually being developed. One notable advancement is electrically conductive flexible adhesives, which typically consist of a polymer resin filled with conductive agents. The polymer resin forms cohesive joints with the substrate and provides the necessary stretchability, while the conductive agent ensures electrical conductivity. Various polymers, such as polyurethane, polysilicone, polybutadiene, and fluorinated rubber, have been employed as stretchable matrices. Polyamide resin is commonly used due to its high-temperature resistance.

[0007] The conductive path in these adhesives can be achieved using metal powders, such as Ag, Sn, Cu, Bi, Zn, In, Pb, as described in document US 2012 / 0228560, or nanosized fillers, such as nanowires, nanoparticles, graphene, and carbon nanotubes, as described in document US 2020 / 0235245A1. Additionally, conductive polymers, which combine the mechanical features of traditional polymers with the electrical properties of metals, can also be used. Polyaniline (PANI), polypyrrole (PPy), and poly(3,4- ethylenedioxythiophene) (PEDOT) are some of the most attractive conductive polymers for these applications, as described in document US5720892A.

[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 an aqueous conductive adhesive composition for electrical component, its method of preparation and uses thereof.

[0010] This description describes a water-based, flexible and resistant conductive adhesive composition for electrical component. In particular, the adhesive comprises a mixture of a thermoplastic resin and a conductive agent. The chemical composition of the copolymers present in the adhesive provides viscosity, flexibility and transfer temperature suitable for printing in flexible substrates such as textiles, paper or plastics. This technology provides an easily patterned, conductive adhesive that imparts conductivity to flexible substrates and connects electronic components. The adhesive resists chemical variations, such as pH, silicones, resins, detergents and inorganic salts, and mechanical changes while maintaining conductivity.

[0011] Conductive adhesives have emerged as a promising alternative to soldering, especially in applications where traditional methods may damage sensitive components or where thermal management is a concern. However, the existing formulations of conductive adhesives often suffer from trade-offs between conductivity, adhesive strength, and environmental stability. Many of the commercially available conductive adhesives exhibit lower electrical conductivity compared to solder, and their mechanical properties can degrade over time, particularly when exposed to harsh environmental conditions such as humidity, temperature extremes, and chemical exposure.

[0012] The development of an improved conductive adhesive that addresses these shortcomings is crucial for the advancement of electronics manufacturing. Specifically, there is a need for a conductive adhesive that not only offers high electrical conductivity but also maintains strong adhesive properties and stability over a wide range of operating conditions. Such an adhesive is of particularly value in the assembly of printed circuit boards (PCBs), the attachment of surface-mount devices (SMDs), and the fabrication of flexible electronics, where traditional bonding methods are inadequate.

[0013] Moreover, the increasing adoption of wearable devices, automotive electronics, and aerospace applications further underscores the necessity for a versatile conductive adhesive. These applications often require materials that can withstand mechanical stress, temperature fluctuations, and long-term exposure to environmental factors, all while maintaining reliable electrical performance. Thepresent technology seeks to fill this gap by providing a conductive adhesive composition that balances these critical properties, offering a solution that is both technologically and commercially viable for a wide range of electronic applications. This technology aims to produce a robust conductive adhesive that is compatible with flexible substrates such as textiles, paper, and plastic, thereby facilitating the incorporation of electronic devices into these substrates and providing reliable electronic joints.

[0014] This adhesive is ideal for imparting conductivity to flexible substrates, enabling the connection of electronic components, and manufacturing electronic elements, making it a valuable advancement in the field of electronic adhesives

[0015] Furthermore, the technology provides the use of a polymer matrix at least selected from the group consisting of polyethylene, polypropylene, polystyrene, copolymer of methyl methacrylate-styrene, copolymer of acrylonitrile-styrene, acrylate, polyvinyl butyral, poly vinyl formal, polyimide, polyamide, polyester, polyvinyl chloride, a fluororesin, urea resin, a melamine resin, a phenol formalin resin, a phenol resin, a Xylene resin, an epoxy resin, a polyisocyanate resin, a phenoxy resin, a silicon resin, and their combinations.

[0016] Further, the polymer matrix may preferably include a thermoplastic polyesteramide or polyurethane resin.

[0017] The present technology according to another aspect provides a method for manufacturing a conductive flexible adhesive, by mixing the polymer resin with the conductive agent in water, without the need of organic solvents.

[0018] Furthermore, the technology provides the use of intrinsically conducting agents at least selected from the group consisting, but not limited the polyaniline (PANI), polypyrrole (PPy), poly(3,4- ethylenedioxythiophene) (PEDOT) as one of the polythiophene (PTh) derivatives, silver nanoparticles, copper nanoparticles, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, and black carbon.

[0019] The present technology can be applied by printing methods into flexible substrates as paper, textile, or plastic, without restrictions on form or roughness, allowing high conductivity layer, with thermal, chemical and mechanical resistance.

[0020] The technology described in the present disclosure enables the formation of conductive films on surfaces of flexible substrates for use in electrodes, electronic circuits, antennas, sensors, and connectors. The conductive films are capable of providing electrical current, transmitting electrical signals, or functioning as transducers. Strong adhesion to flexible substrates, together with chemical stability, and mechanical and thermal resistance, makes the technology suitable for applications exposed to harsh environmental or industrial conditions.

[0021] The solution of the present disclosure provides an easily patterned aqueous conductive adhesive that imparts electrical conductivity to flexible substrates and electrically connects electronic components.

[0022] This disclosure further provides a method for applying a conductive flexible adhesive, comprising the steps of formulating the conductive adhesive composition; applying the adhesive composition to a substrate; and curing or drying the adhesive composition to produce a solidified conductive film bonded to the substrate.

[0023] Other objects and advantages of the present disclosure will become apparent from the following detailed description as from its use in electronic components such as antennas and sensors.

[0024] An aspect of the disclosure comprises an aqueous conductive adhesive composition for electrical components, comprising: 40-95 % (w / w) of a water- dispersible polymer matrix; and 5-60 % (w / w) of a conductive agent; wherein the water-dispersible polymer matrix is selected from polyethylene, polypropylene, polystyrene, co-polymer of methyl methacrylate-styrene, copolymer of acrylonitrilestyrene, acrylate, polyvinyl butyral, poly vinyl formal, polyimide, polyamide, polyester, polyvinyl chloride, fluororesin, urea resin, melamine resin, phenol formalin resin, phenol resin, xylene resin, epoxy resin, polyisocyanate resin, phenoxy resin, silicon resin, thermoplastic polyester-amide, polyurethane resin, and combinations thereof; wherein the conductive agent is selected from polyaniline, polypyrrole, poly(3,4- ethylenedioxythiophene), silver nanoparticles, copper nanoparticles, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, black carbon, and combinations thereof; wherein the viscosity of the aqueous conductive adhesive composition ranges from 30 Pa.s to 90 Pa.s at 20°C, measured at a shear rate 1 s1using cone-plate rheometer; wherein the composition is curable or dryable to form a conductive film at temperatures below 150°C; and wherein the composition comprises a conductivity of at least greater than 1000 S / cm measured by four-point probe at 25°C.

[0025] In an embodiment, the conductivity of the aqueous conductive adhesive composition is greater than 30000 S / cm, preferably greater than 500000 S / cm.

[0026] In an embodiment, the electrical resistance of the aqueous conductive adhesive composition is from 0.1 to 500 ohm, preferably from 0.1 to 20 ohm.

[0027] In an embodiment, the polymer matrix of the aqueous conductive adhesive composition ranges from 20 to 80 %(w / w), more preferably from 40 to 60 %(w / w).

[0028] In an embodiment, the conductive agent of the aqueous conductive adhesive composition ranges from 5-60 %(w / w), more preferably from 30 to 40 %(w / w).

[0029] In an embodiment, the water-dispersible polymer matrix of the aqueous conductive adhesive composition comprises a polyamide resin; preferably a polyamide resin prepared by ring opening polymerization reaction between at least one primary diamine and at least one lactone.

[0030] In an embodiment, the primary diamine of the aqueous conductive adhesive composition is selected from a list consisting of: ethylene diamine, diethylene triamine, butane diamine, hexane diamine, and their combinations.

[0031] In an embodiment, the lactone of the aqueous conductive adhesive composition is selected from a list consisting of: Y-butyrolactone, 8-valerolactone, S- caprolactone, pentadeca lactone, glycolide, lactides, and their combinations.

[0032] In an embodiment, the weight ratio between lactone and diamine on the aqueous conductive adhesive composition ranges from 0.1-10%(w / w), preferably from 2-3 %(w / w).

[0033] In an embodiment, the aqueous conductive adhesive composition further comprises additives selected from a list consisting of defoamers, pH adjusters, and rheology modifiers, in particular additives selected from a list consisting of: alcohols, ammonium salts, carbon dioxide, silicon dioxide, dimethyl sulfoxide, sodium salts (e.g.sodium iodide, sodium chloride), hydrogen peroxide, sodium dodecylbenzenesulfonate, polyaromatic hydrocarbons, polyvinyl alcohol, polymethyl methacrylate, and combinations thereof.

[0034] In an embodiment, the conductive agent of the aqueous conductive adhesive composition comprises an average particle size of less than 100 nm; preferably from 60 to 90 nm; more preferably from 70 to 80 nm.

[0035] In an embodiment, the pH of the aqueous conductive adhesive composition ranges from 1 to 11, preferably from 5 to 9, more preferably from 6 to 8.

[0036] In an embodiment, the aqueous conductive adhesive composition further comprises an additional solvent used as a dispersant.

[0037] In an embodiment, the additional solvent of the aqueous conductive adhesive composition is selected from a list consisting of alcohol, ketone, ester, and their combinations.

[0038] It is also disclosed a conductive flexible adhesive film comprising the aqueous conductive adhesive composition described herein.

[0039] It is also disclosed an article comprising the aqueous conductive adhesive composition, wherein the article is a sensor, electronic component, or flexible circuit, wherein the adhesive composition facilitates electrical conductivity and maintains adhesion on a flexible substrate under varying environmental conditions.

[0040] It is also disclosed the use of the described conductive flexible adhesive film on electrodes, electronic circuits, antennas, sensors and connectors.

[0041] It is also disclosed a method for applying the described aqueous conductive adhesive composition to a substrate, comprising the steps of: applying the aqueous conductive adhesive composition to a substrate; aligning an electronic component with the substrate; and curing or drying the adhesive composition to bond the electronic component to the substrate.

[0042] In an embodiment, the method further comprises initiating a cooling process or drying process prior to bonding the electronic component to the substrate.

[0043] In an embodiment, the cooling process in the method for applying the described aqueous conductive adhesive composition into a substrate is done through air drying.

[0044] In an embodiment, the aqueous conductive adhesive composition is applied by screen printing, stencil printing, dispensing, or spraying onto the surface of the electronic component or substrate.

[0045] In an embodiment, the method for applying the described aqueous conductive adhesive composition by screen printing is applied in a layer with a thickness ranging from 10 micrometers to 100 micrometers.

[0046] In an embodiment, the method for applying the described aqueous conductive adhesive composition into a substrate further comprises the step of pre-treating the surfaces of the electronic component and / or substrate with a primer or surface activator to enhance adhesion.

[0047] In an embodiment of the method for applying the described aqueous conductive adhesive composition into a substrate, the bonded electronic components are subjected to a post-curing process involving heat treatment or UV exposure to enhance the mechanical strength and electrical conductivity of the adhesive bond.

[0048] In an embodiment, the substrate used in the method for applying the described aqueous conductive adhesive composition into a substrate is selected from the group consisting of textile, paper, plastic, composite, and their combinations.BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of invention.

[0050] Figure 1: Photographic representation of an embodiment of a scanning electron micrograph (SEM) of a textile substrate (top views) the conductive adhesive film on a textile substrate (bottom left) and the cross section of the textile (identified as dielectric) with a top and bottom conductive adhesive layer (identified as patch / ground plane) (bottom right).

[0051] Figure 2: Graphic representation of the relation to electric conductivity of textile substrates, without any type of coating (bare textile), with non-conductive adhesive layer and with conductive adhesive layer

[0052] Figure 3: Graphic representation of electrical resistance (Q) of the printed conductive adhesive before and after exposing it to various chemical environments including detergent, dyeing material, stabilizer, ionic salt and base.

[0053] Figure 4: Graphic representation of a plot showing the characteristic performance of operating antennas built with the conductive adhesive as the patch and ground plane in two different textiles, a polyamide (P-antenna) and wool (B- antenna).

[0054] Figure 5: Graphic representation of the aqueous conductive adhesive composition used as active component in a temperature and humidity sensor. Upper figure: variation of electrical current with different temperatures. Bottom-left figure: variation of electrical current with relative humidity. Bottom-right image: magnification of the left image within the 10-30% relative humidity range.DETAILED DESCRIPTION

[0055] The present disclosure relates to an aqueous conductive adhesive composition, its method of preparation and uses thereof.

[0056] The present disclosure discloses conductive adhesives, in particular conductive adhesives based on a polymeric matrix, such as polysilicone, polyurethane, polybutadiene, fluorinated rubber, polyamide resins, polyol, commonly used in the chemical or textile industry, with at least one conductive filler, such as metallic nanoparticles, conductive polymers, graphene, black carbon, in water that can be transferred to flexible substrates as textile, paper, plastic through printed process.

[0057] The aqueous conductive adhesive composition disclosed herein provides an easily patternable conductive adhesive that imparts electrical conductivity to flexible substrates and enables the electrical connection of electronic components, the composition being suitable for printing on flexible substrates such as textiles, paper and plastics.

[0058] Under the prior art knowledge, conductive adhesives, such as silver pastes, are used to form electrodes, circuits or electronic components. Additionally, these conductive pastes serve as adhesives for bonding components together.

[0059] Applying a layer of adhesive to textile, paper, or plastic substrates imparts conductive properties while preserving their mechanical and elastic characteristics. This conductivity remains stable even under adverse conditions. The integration of flexible substrates with conductive adhesive enables the creation of conductive textile, paper, or plastic materials that seamlessly fit into conventional uses, as well as industrial, biomedical, energy, and communication applications.

[0060] Under this disclosure, it is always used water as a solvent, replacing the conventional organic solvents typically used in the formulation of polymeric adhesives.

[0061] The technology now disclosed imposes no limitations on the roughness or shape of the substrate, ensuring high conductivity.

[0062] The conductive films applied to flexible substrates, as described in this disclosure, exhibit resistance to high temperatures, mechanical pressure, and chemical agents. This enhanced durability in harsh environments broadens the range of potential applications for these materials.

[0063] Applications of this disclosure include technical textile or paper substrates integrated with electronic devices, such as environmental or medical sensors, communication antennas, security devices, thermoelectric or triboelectric energy devices, electrodes, and circuits, actuators, user interfaces, and complex circuits in applications: aerospace, packaging, sensor-based monitoring, acquisition of vital signs, monitoring of physical activity in sports, home and living, safety systems for soldiers or firefighters, among others.

[0064] The current disclosure aims to replace conventional metallic conductors, facilitating the integration of electronic devices into flexible substrates that can withstand harsh conditions.

[0065] Normally, a conductive flexible adhesive is composed by a polymer resin and conductive fillers. While the conductive fillers must provide the electrical conductivity, the polymer resin must to form cohesive joints with the textile or other flexiblesubstrate and must have the capability to stretch. An ideal polymeric matrix should exhibit a long shelf life, fast cure, relatively high glass transition temperature (Tg), low moisture pickup and good adhesion.

[0066] Despite the advancements described in the state of the art, none have succeeded in creating a substrate coated with a flexible, conductive material that withstands environmental and mechanical stress while maintaining its properties. Additionally, the processes used are compatible with flexible substrates.

[0067] In an embodiment, the textile substrates used are made from materials such as polyester, polypropylene, polylactate, polyamide, cotton, wool, aramid, viscose, rayon, modal, and lyocell, all commonly used in the textile industry. These substrates are coated with a water-based conductive adhesive through a printing process. This coating imparts conductivity to the substrates while preserving their mechanical and elastic properties, and ensures resistance to mechanical, thermal, and chemical attacks. This innovation enables the creation of conductive textiles that can be fully integrated into standard textile applications, as well as into textiles incorporating electronic devices such as environmental or medical sensors, communication antennas, security devices, thermoelectric or triboelectric energy devices, electrodes, circuits, actuators, user interfaces, and other complex circuits.

[0068] In an embodiment, the substrate is a paper substrate such as coated paper, adhesive paper, cardboard, recycled paper, transfer paper, photographic paper, and graphic paper. These substrates are coated with a water-based conductive adhesive formulation through a printing process. This coating imparts conductivity to the substrates while preserving their mechanical and elastic properties, and ensures resistance to mechanical, thermal, and chemical attacks. This innovation enables the creation of conductive paper that can be fully integrated into standard paper applications, as well as into paper incorporating electronic devices such as environmental or medical sensors, communication antennas, security devices, thermoelectric or triboelectric energy devices, electrodes, circuits, actuators, user interfaces, and other complex circuits.

[0069] In an embodiment, the substrate is in plastic, such as polyethylene terephthalate, polyamide, polyester, polyethylene, polypropylene, acrylonitrilebutadiene styrene, polyoxymethylene, polycarbonate, thermoplastic polyurethane, and thermoplastic elastomers. These commonly used plastics are coated with a waterbased conductive adhesive through a printing process. The coating imparts conductivity to the substrates while preserving their mechanical and elastic properties, and ensures resistance to mechanical, thermal, and chemical attacks. This innovation enables the creation of conductive plastics that can be fully integrated into standard plastic applications, as well as plastics incorporating electronic devices such as environmental or medical sensors, communication antennas, security devices, thermoelectric or triboelectric energy devices, electrodes, circuits, actuators, user interfaces, and other complex circuits.

[0070] The present technology allows the strong polymeric adhesion to the substrate by thermocoupling, allowing an efficient bonding of the conductive fillers to the substrate, creating a stable and robust conductive film that resist to exposure to chemical agents as pH variation (1-14), ionic salts (sodium sulphate, sodium hydroxide, sodium chloride, sodium carbonate, calcium carbonate), dyes (indigo, azo, anthraquinone, triphenyl methane, stilbene, thiazol, triphenodioxazine derivatives, aromatic carboxylic ester), stabilizers (proteins conjugated to horseradish peroxidase and alkaline phosphatase), polymers (polyfluorinated, polysilicones, polyurethane, polyisocyanate), reductants (hydrosulfite, thiourea dioxide, bisulphite), oxidants (hydrogen peroxide, methanesulfinic acid, bacterial amylase), waterproofing (perfluorooctanesulfonic acid, perfluorooctanoic acid, C6-fluorocarbon resin, polysiloxane, polydimethyl siloxane), detergents (ethanolamine, chlorine hypochlorite, sodium hypochlorite, sodium carbonate, limonene, alcohol ethoxylates, alkylphenol ethoxylates, alkyl polyglucosides and amine oxides, ethoxylated isotridecanol, perchloroethylene, ammonium hydrogen sulfite), base (dihydroxy ethylene urea, sodium hydroxide, ammonia), acid (citric acid, acetic acid, formic acid, methanesulfonic acid).

[0071] The present technology allows the strong polymeric adhesion to the substrate by thermocoupling, allowing an efficient bonding of the conductive fillers to the substrate, creating a stable and robust conductive film that presents high impactresistance to exposure to stressors as high temperature variation, pressure, force, humidity, tensile stress, impact resistance, including delamination suppression.

[0072] In an embodiment, the present disclosure concerns a conductive adhesive whose polymeric matrix is selected from a list consisting of: polyurethane, polysilicone, polybutadiene, fluorinated rubber, polyamide resins, poliol, polyester and their combinations.

[0073] In an embodiment, the conductive adhesive polymer matrix uses polyamide resins prepared by ring opening polymerization (ROP) reaction between at least one primary diamine, with at least two amine groups, with at least one lactone, followed by transesterification reaction of the diamine diol produced with dicarboxylic acid diesters and low molecular weight diols.

[0074] In an embodiment, suitable diamines are ethylene diamine, diethylene triamine, butane diamine and hexane diamine. In turn, the lactone preferably has to have 4, 5 or 6 carbon atoms, therefore Y-butyrolactone, 8-valerolactone, S- caprolactone, pentadeca lactone, glycolide and lactides can be used.

[0075] In one embodiment, suitable conditions to the ROP reaction, requires a molar lactone / diamine ratio of at least 2, preferably in a ratio of 2.0 to 2.5 mol of lactone per mol of diamine. The reaction temperature is preferably maintained at a lower temperature than the melting point of the pure amide diol, preferably lower than 30 °C, to achieve a product comprising a high fraction of the desired amine diol. The reaction is preferably carried out under a nitrogen blanket. The reaction can be carried out using a solvent, however, further solvent removal is required, therefore it is preferable to carry out without using a solvent. Next, the reaction mixture is cooled down to ambient temperature during several hours, preferably for more than 6 hours to allow any remaining diamine to react.

[0076] In one embodiment, the ROP reaction requires a lactone / diamine molar ratio of at least 2, preferably between 2.0 and 2.5. The reaction temperature should be below 30 °C to produce a high fraction of the desired amine diol and is best conducted under a nitrogen blanket. The resulting diamine diol reacts with a low molecular weight dicarboxylic acid diester (less than 258 g / mol) and a low molecular weight diol (lessthan 2000 g / mol). Preferred dicarboxylic acid diesters have 1 to 3 carbon atoms in the alkyl groups and 2 to 8 carbon atoms in the dicarboxylate moieties. Examples include dimethyl adipate, dimethyl oxalate, dimethyl malonate, and dimethyl glutarate, with succinate, glutarate, or adipate being preferred. Suitable diols include monoethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, and 1,7- heptanediol, with 8-octanediol being preferred. The reaction is carried out in a stirred, heated reactor with a reflux column, under an inert gas blanket. The solid amide diol is mixed with the dicarboxylic acid diesters and slowly heated to about 140°C until dissolved. This temperature is maintained for 1.5 to 3 hours. Then, a low molecular weight diol is added in excess, the mixture is homogenized, and a catalyst (such as tetrabutoxy titanium (IV), zinc acetate, or magnesium acetate) is introduced. In the final stage, the reaction is conducted under reduced pressure to remove volatile diols, increase the molecular weight, and convert the pre-polymer into a full polyester amide polymer with a molecular weight higher than 4000 g / mol.

[0077] A conductive additive such as metals, nano-sized fillers, conductive polymers or their mixtures is incorporated into the polymer matrix. To achieve high electrical conductivity, the conductive agent concentration must be at least equal to or higher than the critical concentration predicted by percolation theory. The electrical conductive path produced using metal powders, such Ag, Sn, Cu, Bi, Zn, In, Pb among others, or nano-sized fillers, such as nanowires, nanoparticles, graphene and carbon nanotubes (CNTs), is achieved through the contact of filler particles with each other. When the metals or nano-sized filled adhesives are subjected to repeated cycling conditions, thermal or shear motion, the adhesives deforms to accommodate the shear strain produced.

[0078] In one embodiment, conductive polymers as polypirrole, polythiophene, polyethylenedioxythiophene, polyanilines, polypyrenes, polyfluorenes, polycarbazoles, polyacetilenes, polystyrene sulfonate), poly(p-phenylene sulfide) or their combination were incorporated into the polymer matrix to formulate conductive adhesives.

[0079] In one embodiment, polyethylenedioxythiophene with polystyrene sulfonate) was mixed with the polymer resin.

[0080] The mixture of adhesive and conductive agent was achieved by methods, such as high-speed steering mixing or ultra-sonic mixing, among others. Different mixing time, RPMs or impulse frequency, among others can be used.

[0081] In one embodiment, if the conductive adhesive is obtained by ultrasonication or steering mixing, this is done in an aqueous medium, with an additional solvent used as a dispersant which can be an alcohol, ketone, ester or the like. The concentration of the solution can vary between 10 to 60% (m / v) solid content.

[0082] The application of the conductive adhesive was achieved by direct techniques like screen printing (flat screen printing and the rotary screen printing methods), stencil printing, block printing, roller printing and digital textile printing (also referred as direct-to-garment printing) and indirect process as sublimation transfer printing, heat transfer printing, among others. Alternatively, screen printing transfer (SPT) combines flat screen printing with heat transfer printing, allowing the quality associated to screen printing with the large quantities provide by the transfer printing. In SPT several layers of ink that make up the image are printing on a release paper (transfer, polyester) that favours the release of the image in the pressing process. A final layer of adhesive compatible with the textile substrate is also applied to the last layer of paint by screen printing and then cured. The images produced by this process are subsequently transferred to the substrate in a heated press, then the final activation of the previously printed adhesive takes place.

[0083] In one embodiment, the conductive adhesive applied to the substrate may comprise a resistance preferably between 0.1-500 ohm, more preferably between 0.1- 20 ohm.

[0084] In one embodiment, the conductive adhesive applied to the substrate may comprise a conductivity of at least greater than 1000 Siemens per centimeter (S / cm), preferably greater than 30000 S / cm, more preferably greater than 5000000 S / cm.

[0085] The present disclosure also concerns electronic devices for electrodes, electronic circuits, antennas, sensors, connectors or others, which comprise the conductive adhesive now disclosed.

[0086] In one embodiment, the conductive adhesive layer may further be covered with a protective layer of an elastomer or may comprise in its composition a polymer such as polymethylmethacrylate, polyimide or polydimethylsiloxane.

[0087] In one embodiment, the water composition in the conductive adhesive solution may contain at least 30% (V / V) water, at least 50% (V / V) water, or at least 70% (V / V) water, water, and these variations in concentrations depending on the solutions have a direct effect on the electrical resistance of the conductive adhesive and its interaction with the flexible substrate.

[0088] In one embodiment, the appropriate concentration depends on the application and / or the substrate, that is, it depends on the application method, the final function of the adhesive on the substrate and the type of substrate.

[0089] In one embodiment, additives may be added to improve the dispersion of the conductive element and the polymer matrix to improve homogeneity, in particular additives selected from the following list: alcohols, ammonium salts, carbon dioxide, silicon dioxide, dimethyl sulfoxide, sodium salts (e.g. sodium iodide, sodium chloride), hydrogen peroxide, sodium dodecylbenzenesulfonate, polyaromatic hydrocarbons, polyvinyl alcohol, or polymethyl methacrylate.

[0090] In one embodiment, the conductive adhesive coating may cover the entire flexible substrate or only partially cover it. It can, for example, cover the substrate in a patterned way. The pattern will be appropriate to the function of the intended electronic component.

[0091] In one embodiment, the percentage of flexible substrate coated with conductive adhesive can vary from less than 1% to 100%.

[0092] In one embodiment, one or more optional layers can be deposited on top of the conductive adhesive layer, such as an anti-scratch protective layer and / or an impermeable layer.

[0093] In one embodiment, one or more layers may be deposited on the surface of the substrate opposite the surface comprising the conductive adhesive layer, in particular an anti-scratch protective layer and / or an impermeable layer may be formed.

[0094] In one embodiment, the anti-scratch and waterproof layers can be combined and added together in a single deposition.

[0095] In an embodiment, following the deposition of the conductive adhesive, the flexible substrate can be used in an electrical circuit, with a current source that applies voltage, instigating the circulation of electrical current. The electrical circuit may include other electronic components.

[0096] In an embodiment, the pH of the aqueous conductive adhesive composition ranges from 3 to 11, preferably from 5 to 9, more preferably from 6 to 8, to ensure stability and compatibility with electronic components.

[0097] In an embodiment, the aqueous conductive adhesive composition demonstrates resistance to pH exposure across a range of 1 to 14 and maintains stability under exposure to various chemical agents, ensuring consistent properties in harsh chemical environments and compatibility with electronic components.

[0098] Here are some examples that illustrate the application of this disclosure.

[0099] In one embodiment, the preparation of the conductive adhesive can be carried out as follows: The polymer matrix can be prepared using amine diol monomer prepared by reacting 11.6 L ethylene diamine with 38.5 L of E-caprolactone under a nitrogen atmosphere in a stainless reactor equipped with an agitator. The exothermic condensation reaction between the e-caprolactone and the ethylene diamine occurs which causes the temperature to rise gradually to 80 °C. A white deposit forms and the reactor contents solidify, at which the stirring is stopped. The reactor contents are then cooled to 20 °C and are then allowed to rest for 15 hours. The reactor contents are then heated to 140 °C at which temperature the solidified reactor contents melt. Afterwards, 22.5 kg of dimethyl isophthalate and 22.5 kg of dimethyl terephthalate is added to the reactor and the reaction is carried out during 3 hours under nitrogen atmosphere. Afterwards, 6.15 kg of 1,6-hexanodiol and 0.51 kg of 1,4-butanodiol are added to the reactor and the temperature is gradually raised to 180 °C. Achieved this temperature, the reaction is carried out during 3 hours under nitrogen atmosphere and vacuum (initially 450 mbar and then stepwise to 20 mbar). Hence, the formed methanol which is removed as a vapor by the nitrogen purge from the reactor system.After cooled, the adhesive resin is the removed from the reactor and mixed with poly(3,4- ethylenedioxythiophene) using a mass ratio from 0.2 to 0.6 %wt.

[0100] 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 compact rheometer equipment using a 50 mm cone plate and a measurement gap pf 0.1 mm containing the coating paste up to its maximum capacity, with the shear rate of Is1at 20 °C

[0101] In one embodiment, the conductive adhesive was prepared by ultrasonication of water-based polyol with silver nanoparticles in particular 1 of water, 3 of polyol, in particular 1 g of silver nanoparticles was added to a solution of 100 ml of water / polyol and subjected to ultrasonication, in particular for 30 minutes at room temperature.

[0102] Along this description, it is considered that "room temperature" should be regarded as a temperature between 15-30 °C, preferably between 18-25 °C, more preferably between 20-22 °C.

[0103] In one embodiment, the conductive adhesive was prepares using a water-based polyurethane with poly(3,4- ethylenedioxythiophene) and few-layer graphene (FLG) powder, which were mechanically mixed using a high-speed homogenizer during 30 minutes, in particular 1 of FLG, 1 of poly(3,4- ethylenedioxythiophene), 2 of polyurethane, in particular 1 g of FLG and poly(3,4- ethylenedioxythiophene) was added to 100 ml of water and subjected to ultrasound for 30 minutes to exfoliate the stacked graphene layers resulting in to the uniform suspensions. The resulting mixture was combined with polyurethane at a 50% ratio and stirred for 1 hour.

[0104] In one embodiment, the conductive adhesive was applied on the substrate surface, a polyamide textile, by screen printing transfer (SPT). The conductive adhesive is firstly applied onto transfer sheets of polyester, two to four layers and then cured within the ranges 90-120 °C for 1-5 min between any layer application. After final curing, the transfers are applied to the textile substrates by hot pressing, at 90 °C, 0.6MPa and 4 s. The conductive adhesive adheres to the textile by hot melting and the transfer sheet is remove by delamination.

[0105] In one embodiment, the conductive adhesive was printed onto the flexible substrate, a transfer paper. To enhance the conductivity of the printed layers, they are printed 2 to 3 times on to the substrate, and cured at room temperature for 10 minutes between any layer application. A final curing of 24h at room temperature allowed the bonding of the adhesive to the paper substrate.

[0106] In one embodiment, the conductive adhesive is spread onto release paper using the blading method, with one to four layers applied, followed by curing in the furnace at temperatures ranging from 70 °C to 100 °C for approximately 1 to 4 minutes. Subsequently, they are transferred onto the fabric using a heat press transfer machine.

[0107] In one embodiment, conductivity measurements were carried out. Layer / film resistance and conductivity measurements were measured using a tungsten probe system and a Keithley 237 measuring unit at room temperature. The resistance of the layer / film presented values in the range of 0.1-10 ohm, and the conductivity of the layer / film presented values in the range of 10000-3000000 S / cm.

[0108] In one embodiment, samples of conductive adhesive on textile substrates were tested to evaluate chemical resistance. The test samples, with known conductivity, were immersed in solutions of the chemical agents tested for at least 10 minutes. After immersion, they were washed with water, to remove chemical residues in the sample, and dried in an oven at 60 °C. The conductivity of the samples was determined again and compared with the initial value.

[0109] In one embodiment, samples of conductive adhesive on textile substrates were tested to evaluate resistance to stressors. The test samples, with known conductivity, were exposed to aggressive agents, temperature, pressure, force, torque, tension, for at least 10 minutes. After exposure, the conductivity of the samples was determined again and compared with the initial value. The combination of several aggressive agents was also analyzed. In particular, exposure to 10 minutes oftemperature, followed by 10 minutes of pressure, followed by tension, followed by exposure to temperature again, among other combinations.

[0110] In one embodiment, the conductive adhesive can be applied with a standardized design suitable for operating as a radio frequency antenna, as illustrated in figure 4.

[0111] In one embodiment, the conductive adhesive can be applied as a temperature sensor, with linear resistance characteristics and good stability and accuracy, as illustrated in figure 5 (upper figure).

[0112] In one embodiment, the conductive adhesive can be applied as a humidity sensor, with linear resistance characteristics and good stability and accuracy, as illustrated in figure 5 (bottom figures).

[0113] Table 1 - comparative data on applying the conductive adhesive using different production methods applied to different substrates

[0114] Table 2 - comparative data on a synthetic textile substrate with conductive adhesive on exposure to different chemicals

[0115] Table 3 - comparative data on a synthetic textile substrate with conductive adhesive under exposure to stressors

[0116] The data set out in the tables of this document demonstrate the obtaining of a conductive adhesive described in the present disclosure, applied to various flexible substrates.

[0117] In the state of the art, the electrical resistance may be measured by many methods. In the present disclosure, the electrical resistance was measured using a digital multimeter and a four-point probe resistivity measurement.

[0118] In the state of the art, the flexibility of a conductive film can be measured by many standard methods. In the present disclosure, the flexibility and durability measurement was carried out by measuring the electrical performance and visible structural changes after 1000 bending cycles. Bending cycles were conducted using a bending device programmed with a controller. The device was configured to perform repetitive folding and unfolding movements in a loop, adapted to the sample dimensions. Electrical measurements were recorded using a Semiconductor Device Analyzer over 1000 cycles.

[0119] The data presented in the tables of this document demonstrate that exposure to various chemical agents and stressors do not alter the conductivity of the substrate coated with the conductive adhesive now disclosed, demonstrating its robustness.

[0120] 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.

[0121] 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.

[0122] The following dependent claims further set out particular embodiments of the disclosure.

Claims

C L A I M S1. An aqueous conductive adhesive composition for electrical components comprising:40-95 % (w / w) of a water-dispersible polymer matrix;5-60 % (w / w) of a conductive agent; wherein the water-dispersible polymer matrix is selected from a list consisting of polyethylene, polypropylene, polystyrene, co-polymer of methyl methacrylatestyrene, copolymer of acrylonitrile-styrene, acrylate, polyvinyl butyral, poly vinyl formal, polyimide, polyamide, polyester, polyvinyl chloride, fluororesin, urea resin, melamine resin, phenol formalin resin, phenol resin, xylene resin, epoxy resin, polyisocyanate resin, phenoxy resin, silicon resin, thermoplastic polyester-amide, polyurethane resin, and combinations thereof; wherein the conductive agent is selected from a list consisting of: polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), silver nanoparticles, copper nanoparticles, graphene, graphene oxide, reduced graphene oxide, carbon nanotubes, black carbon, and combinations thereof; wherein the viscosity of the aqueous conductive adhesive composition ranges from 30 Pa.s to 90 Pa.s at 20 °C, measured at shear rate 1 s1using cone-plate rheometer; wherein the composition is curable or dryable to form a conductive film at temperatures below 150°C; and wherein the composition comprises a conductivity of at least 1000 S / cm, measured by a four-point probe at 25°C.

2. The aqueous conductive adhesive composition according to the previous claim, wherein the conductivity is greater than 30000 S / cm, preferably greater than 500000 S / cm.

3. The aqueous conductive adhesive composition according to any of the previous claims, comprising an electrical resistance from 0.1 to 500Q, preferably from 0.1 to4. The aqueous conductive adhesive composition according to any of the previous claims, wherein the polymer matrix ranges from 20-80 %(w / w), more preferably from 40-60 %(w / w).

5. The aqueous conductive adhesive composition according to any of the previous claims wherein the conductive agent ranges from 5-60 %(w / w), more preferably from 30-40 %(w / w).

6. The aqueous conductive adhesive composition according to any of the previous claims, wherein the water-dispersible polymer matrix comprises a polyamide resin; preferably a polyamide resin prepared by ring opening polymerization reaction between at least one primary diamine and at least one lactone.

7. The aqueous conductive adhesive composition according to the previous claim, wherein the primary diamine is selected from a list consisting of: ethylene diamine, diethylene triamine, butane diamine, hexane diamine, and their combinations.

8. The aqueous conductive adhesive composition according to the previous claim 6, wherein the lactone is selected from a list consisting of: Y-butyrolactone, 8- valerolactone, S-caprolactone, pentadeca lactone, glycolide, lactides, and their combinations.

9. The aqueous conductive adhesive composition according to any of the previous claims 6 to 8, wherein the weight ratio between lactone and diamine ranges from 0.1-10%(w / w), preferably from 2-3 %(w / w).

10. The aqueous conductive adhesive composition according to any of the previous claims, further comprising additives selected from a list consisting of defoamers, pH adjusters, and rheology modifiers, in particular additives selected from a list consisting of: alcohols, ammonium salts, carbon dioxide, silicon dioxide, dimethyl sulfoxide, sodium salts (e.g. sodium iodide, sodium chloride), hydrogen peroxide, sodium dodecylbenzenesulfonate, polyaromatic hydrocarbons, polyvinyl alcohol, polymethyl methacrylate, and their combinations.

11. The aqueous conductive adhesive composition according to any of the previous claims, wherein the conductive agent comprises an average particle size of less than 100 nm; preferably from 60 to 90 nm; more preferably from 70 to 80 nm.

12. The aqueous conductive adhesive composition according to any of the previous claims, wherein the pH ranges from 1 to 11, preferably from 5 to 9, more preferably from 6 to 8.

13. The aqueous conductive adhesive composition according to any of the previous claims, further comprising an additional solvent used as a dispersant.

14. The aqueous conductive adhesive composition according to the previous claim, wherein the additional solvent is selected from a list consisting of alcohol, ketone, ester, and their combinations.

15. A conductive flexible adhesive film comprising the aqueous conductive adhesive composition described in the claims 1 to 14.

16. An article comprising a substrate coated with the aqueous conductive adhesive composition according to any of the previous claims 1-14; preferably wherein the article is a sensor, electronic component, or flexible circuit.

17. Use of conductive flexible adhesive film described in the previous claim on electrodes, electronic circuits, antennas, sensors and connectors.

18. A method for applying an aqueous conductive adhesive composition as described in any of the claims 1 to 14 to a substrate, comprising the steps of: applying the aqueous conductive adhesive composition to a substrate; aligning an electronic component with the substrate; and curing or drying the adhesive composition to bond the electronic component to the substrate.

19. The method according to the previous claim, wherein the cooling process is done through air drying.

20. The method according to any of the previous claims 18 to 19, wherein the aqueous conductive adhesive composition is applied by screen printing, stencil printing, dispensing, or spraying onto the surface of the electronic component or substrate.

21. The method according to any of the previous claims 18 to 20, wherein the aqueous conductive adhesive composition is applied in a layer with a thickness ranging from 10 micrometers to 100 micrometers.

22. The method according to any of the previous claims 18 to 21, further comprising the step of pre-treating the surfaces of the electronic component and / or substrate with a primer or surface activator to enhance adhesion.

23. The method according to any of the previous claims 18 to 22, wherein the bonded electronic components are subjected to a post-curing process involving heat treatment or UV exposure to enhance the mechanical strength and electrical conductivity of the adhesive bond.

24. The method according to any of the previous claims 18 to 23, wherein the substrate is selected from the group consisting of textile, paper, plastic, composite, and their combinations.

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