Printed radio-frequency identification tag structure and its method of manufacturing

Abstract

The present disclosure relates to a printed radio-frequency identification tag structure and its method of manufacturing. It is disclosed a printed radio-frequency identification tag structure for high efficiency and impedance matching comprising a printed antenna formed on the substrate using an aqueous conductive adhesive layer; wherein the aqueous conductive adhesive layer comprises a composition of: 0-95% (w / w) of a water-dispersible polymer matrix and 5- 60% (w / w) of a conductive agent; wherein the printed antenna comprises a conductivity ranging from 1000 to 600000 S / cm, measured at 23°C using a four-point probe; and wherein the printed antenna is configured to retain at least 85% of its initial electrical conductivity after exposure to temperatures from −20°C to 200°C, acidic and alkaline environments, and mechanical deformation with flexible substrates.

Description

D E S C R I P T I O NPRINTED RADIO-FREQUENCY IDENTIFICATION TAG STRUCTURE AND ITS METHOD OF MANUFACTURINGTECHNICAL FIELD

[0001] The present disclosure relates to a printed radio-frequency identification tag structure and its method of manufacturing.

[0002] In particular, the present disclosure relates to a printed radio-frequency identification (RFID) tag structure incorporating an aqueous conductive adhesive layer, the tag structure being compatible with flexible substrates such as textiles, paper, and plastic, and being configured to maintain electrical and mechanical integrity under exposure to chemical agents, mechanical deformation, and temperature variations, thereby enabling reliable communication, identification, or labelling applications.BACKGROUND

[0003] The development of flexible electronics has revolutionized numerous industries, particularly in the fields of wearable technology, medical devices, and the Internet of Things (loT). These innovations rely heavily on the ability to integrate electronic components into substrates that can bend, stretch, and conform to various shapes and surfaces. Antennas, as critical components in wireless communication systems, must also evolve to meet the demands of these flexible electronic devices. Traditional antennas, typically constructed from rigid materials, are not suitable for such applications due to their lack of flexibility and adaptability.

[0004] The introduction of printed electronics has provided a promising solution to the challenges associated with creating antennas for flexible substrates. Using additive manufacturing techniques, such as inkjet printing or screen printing, antennas can be directly printed onto flexible substrates. This method allows for the creation of lightweight, low-cost, and customizable antenna structures that can be easily integrated into flexible devices. However, despite these advancements, several technical challenges remain in ensuring that printed antennas on flexible substratesperform reliably under various mechanical stresses, such as bending, stretching, and twisting.

[0005] One of the primary challenges is the selection of suitable conductive materials that can maintain their electrical properties while being flexible enough to adhere to non-rigid substrates. Materials such as silver nanoparticles, carbon nanotubes, and conductive polymers have shown promise in this regard, but there are still issues related to adhesion, durability, and conductivity that need to be addressed. Additionally, the antenna design must be optimized to ensure that it provides the necessary performance characteristics, such as impedance matching and efficient radiation, even when subjected to mechanical deformation.

[0006] Another significant challenge lies in the manufacturing process itself. The printing of antennas onto flexible substrates requires precise control over the deposition of conductive materials to ensure consistent performance. Factors such as the ink's viscosity, the printing speed, and the curing process must be carefully managed to achieve the desired results. Furthermore, protecting the printed antennas from environmental factors, such as moisture, dust, and mechanical wear, is crucial to extending the lifespan and reliability of the antenna in real-world applications.

[0007] Current antennas often lack the necessary characteristics for seamless integration with flexible substrates like textiles, paper, or plastics— they may be rigid, brittle, or incompatible with printing processes, like is mentioned in document EP3623146A1. They also lack mechanical, temperature and chemical robustness and use non-sustainable deposition methods or solvents, like is mentioned in documents US10198677B2 and US9444134B2.

[0008] Flexible adhesives are commonly preferred over brittle, stiff ones due to their ability to expand and contract, allowing them to bond materials with different coefficients 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 enables to print a robust merchandise tag, patch, label, inlay or thelike comprises a substrate and an RFID device including a slot-loop hybrid antenna, disposed on a flexible substrate. This may be used for inventory, security, compliance and tracking.

[0009] Despite their widespread use, high-tech flexible adhesives are continually being developed.

[0010] These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.GENERAL DESCRIPTION

[0011] The present disclosure relates to a printed radio-frequency identification tag structure and its method of manufacturing.

[0012] The present disclosure describes a conductive and resistant printed radiofrequency identification tag structure compatible with flexible substrates and their production methods, capable of withstanding exposure to chemical elements, temperature variations, and mechanical stress. Existing printed radio-frequency identification tag structure are inadequate for flexible substrates, as they are often rigid or brittle, lack appropriate adhesive force, and are incompatible with flexible substrate manufacturing. 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 communication, identification, or labelling.

[0013] It is then disclosed a resistant printed radio-frequency identification tag structure, compatible with flexible substrates and their production methods, capable of withstand exposure to chemical elements, temperature and mechanical stress. Current radio-frequency identification tag structures are not adequate for flexible substrates, which are rigid or brittle, lack an appropriate adhesive force or are not compatible with flexible substrates manufacturing. The present disclosure describes how to produce a robust printed radio-frequency identification tag structure compatible with flexible substrates as textiles, paper and plastic, facilitating theincorporation of electronic devices into these substrates and provide electromagnetic responsive devices.

[0014] The subject matter disclosed and claimed herein, in one possible embodiment, comprises a printed radio-frequency identification tag structure that is formed as part of a printed fabric label or communication device. Generally, a conductive adhesive is attached on a fabric material via a releasable adhesive, direct printing, doctor blade or screen printing. The conductive adhesive may be patterned via a cutter such as a laser, by a mask or direct printing to define the pattern of the radio-frequency identification tag structure. The conductive sheet, can be stripped away through the use of the releasable adhesive or using thermal transfer, and a chip or a strap having a chip or integrated circuit mounted thereon is then attached with a thin layer of conductive adhesive. A small square of hot melt can be used as a top layer of fabric is added and secured via an adhesive that is applied with transfer tape. Alternatively, the top layer of fabric may be applied directly over the strap and antenna. In addition, the top layer of the material may be secured by other suitable means such as sewing, or using a fastening system, e.g., mechanical or hook and loop type features.

[0015] The present technology according to an aspect provides a printed radiofrequency identification tag structure for high efficiency and impedance matching comprising: a flexible substrate; a conductive sheet material deposited on said substrate using an aqueous conductive adhesive layer; wherein the aqueous conductive adhesive layer comprises: 0-95% (w / w) of a water-dispersible polymer matrix and 5-60% (w / w) of a conductive agent; wherein the conductivity of the aqueous conductive adhesive layer ranges from 1000 to 600000 S / cm, measured at 23°C using a four-point probe, and retains at least 85% of initial conductivity after exposure to temperatures from -20°C to 200°C and acidic / a I ka li ne environments.

[0016] 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, aXylene resin, an epoxy resin, a polyisocyanate resin, a phenoxy resin, and a silicon resin.

[0017] Further, the polymer matrix may preferably include a thermoplastic polyesteramide or polyurethane resin.

[0018] The present technology according to another aspect provides a method for production of a printed radio-frequency identification tag structure, by mixing the polymer matrix with the conductive agent in water, without the need of organic solvents.

[0019] 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.

[0020] Furthermore, the conductive flexible adhesive may preferably include about 5- 60 wt % of the conductive agent.

[0021] 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.

[0022] The present disclosure allows creating a conductive film on the surface of flexible substrates for electrodes, electronic circuits, antennas, sensors, connectors. These films can provide electrical current, transmit electrical signals or act as transducers. The strong adhesion to the textile surface and its chemical inertness, and mechanical and thermal resistance, make the technology safe and resilient for use in applications with greater exposure to harsh elements, either environmental or industrial conditions.

[0023] In another aspect, a durable merchandise tag, patch, label, inlay, or similar item comprises a substrate and an RFID device that includes a printed radio-frequency identification tag structure. This antenna features a large-area conductor sheet or foil with an elongated slot, which is entirely within the interior of the conductive sheet except for an open end or branch. A wireless communication device electronicallycouples the opposing sides of the slot at a first location near the open end, while the slot has a closed end at a second location. The sidewalls of the slot determine an average slot width, and the large-area conductor sheet extends substantially uninterrupted from the slot sidewalls and the closed end to the peripheral edge of the conductive material, for a distance greater than the average width of the slot.

[0024] In a further aspect, a durable merchandise tag, patch, label, inlay, or similar item comprises a substrate and an RFID device featuring a slot-loop hybrid radiofrequency identification tag structure. This radio-frequency identification tag structure consists of a large-area conductor sheet or foil with an elongated slot that is entirely within the interior of the conductive sheet, except for an open end or branch. A wireless communication device electronically couples the opposing sides of the slot at a first location along the length of the slot, between the open end and a closed end, referred to as a second location. The sidewalls of the slot define an average slot width, and the large-area conductor sheet extends substantially uninterrupted from the slot sidewalls and the closed end to the peripheral edge of the conductive material for a distance greater than the average width of the slot.

[0025] In an additional aspect, a robust merchandise tag, patch, label, inlay or the like comprises a substrate and an RFID device including a slot-loop hybrid antenna having a large area conductor sheet or foil and an elongated slot fully interior of the conductive sheet except for an open end or branch of the slot. A wireless communication device electronically couples opposing sides of the slot at a first location, a closed end of the slot being at a second location. The first location and the second location generally coincide with each other. The sidewalls of the slot define an average slot width, and the large-area conductor sheet extends substantially uninterrupted from the slot sidewalls and the slot closed end to the conductive material peripheral edge for a distance greater than the average width of the slot.

[0026] In a yet still further embodiment, a method of making a radio-frequency identification (RFID) tag structure for a PFL label is disclosed. The method includes the following steps: Initially providing a first material, each having a top face and a bottom face, an RFID chip, and a conductive adhesive layer laminated to the top face of the first material. The conductive sheet is either cut to form an antenna pattern and aremovable portion or is patterned by a mask or direct printing. The removable portion of the conductive sheet is stripped away to define an antenna with at least one opening. A strap is attached across the at least one opening and the adhesive is cured to bond the strap to the conductive foil and the conductive material to the top face of the first material. An adhesive is applied via transfer tape over the top of the antenna, and a second material is bonded to the first material using the transfer tape adhesive.

[0027] The technology also provides a method for applying a robust printed flexible printed radio-frequency identification tag structure comprising the steps of conductive adhesive formulation of the invention; applying the adhesive formulation to a substrate; cooling the adhesive formulation to produce a solidified adhesive bonded to the substrate; patterning the antenna and device design.

[0028] Other objects and advantages will become apparent with reference to the following detailed description as well its use in electronic components as radiofrequency identification tag structures and sensors.

[0029] In summary, while the concept of printed radio-frequency identification (RFID) tag structures for flexible electronics presents significant potential, their implementation requires careful selection of materials, structural design, and manufacturing processes in order to address durability, reliability, and process compatibility challenges. The disclosed technology addresses these challenges by providing a printed radio-frequency identification tag structure compatible with flexible substrates and capable of reliable operation across a range of demanding applications.

[0030] The disclosed technology addresses these challenges by providing a one-part water-based conductive adhesive comprising a conductive agent as an active element. The chemical composition of the polymer matrix within the adhesive is selected to provide suitable viscosity, flexibility, and transfer temperature for printing conductive structures on flexible substrates, while maintaining resistance to chemical agents, temperature variation, and mechanical stress.

[0031] In addition to improved durability, the printed radio-frequency identification(RFID) tag structure disclosed herein is configured to maintain radio-frequencyperformance when applied to flexible substrates. In particular, the aqueous conductive adhesive formed using the aqueous conductive adhesive composition allows the printed antenna to remain impedance-matched with an associated integrated circuit and to operate within expected efficiency levels, thereby preserving signal transmission and read functionality under conditions involving chemical exposure, mechanical deformation, and temperature variation.

[0032] The solution of the present disclosure enables the reliable integration of electronic devices in printed radio-frequency identification tag structures formed on flexible substrates such as textiles, paper, and plastic, through the use of an aqueous conductive adhesive layer that maintains adhesion and electrical performance under chemical exposure, mechanical deformation associated with flexible substrates, and temperature variations, and capable of reliable operation across a range of demanding applications.

[0033] An aspect of the disclosure comprises a printed radio-frequency identification tag structure comprising: a flexible substrate, a conductive sheet material deposited on said substrate using an aqueous conductive adhesive layer; wherein the aqueous conductive adhesive layer comprises: 0-95% (w / w) of a water-dispersible polymer matrix and 5-60% (w / w) of a conductive agent; wherein the conductivity of the aqueous conductive adhesive layer ranges from 1000 to 600000 S / cm, measured at 23°C using a four-point probe, and is configured to maintain at least 85% of initial electrical conductivity after exposure to temperature variations between -20°C and 200°C, chemical environments including acidic / alkaline conditions, and mechanical deformation associated with flexible substrates.

[0034] Another aspect of the disclosure comprises a printed radio-frequency identification tag structure comprising: a flexible substrate, a printed antenna formed on the substrate using an aqueous conductive adhesive layer; wherein the aqueous conductive adhesive layer comprises a composition of: 0-95% (w / w) of a water- dispersible polymer matrix and 5-60% (w / w) of a conductive agent; wherein the printed antenna comprises a conductivity ranging from 1000 to 600000 S / cm, measured at 23°C using a four-point probe; and wherein the printed antenna is configured to retain at least 85% of its initial electrical conductivity after exposure totemperatures from -20°C to 200°C, acidic and alkaline environments, and mechanical deformation with flexible substrates.

[0035] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification (RFID) tag structure retains electrical continuity after repeated mechanical deformation including bending, stretching, and / or abrasion.

[0036] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification (RFID) tag structure retains electrical performance after exposure to chemical agents including detergents, solvents, acidic environments, alkaline environments, or combinations thereof.

[0037] In an embodiment, the printed radio-frequency identification (RFID) tag structure is washable and retains functionality after repeated washing cycles.

[0038] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification (RFID) tag structure retains electrical conductivity after thermal cycling between -20 °C and 200 °C.

[0039] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification tag structure partially covers the substrate, preferably with a patterned configuration.

[0040] In an embodiment, the printed radio-frequency identification tag structure further comprises an anti-scratch protective layer and / or an impermeable layer on the surface of the substrate opposite the surface comprising the conductive adhesive layer.

[0041] In an embodiment, the flexible substrate of the printed radio-frequency identification tag structure is selected from a list consisting of polyester, polypropylene, polylactate, polyamide, cotton, wool, aramid, viscose, rayon, modal, lyocell polyimide, polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), woven or non-woven materials, coated paper, adhesive paper, cardboard, recycled paper, transfer paper, photographic paper, graphic paper, card stock, polyethylene, acrylonitrile butadiene styrene, polyoxymethylene, polycarbonate, thermoplastic elastomers, polyethylene-based materials and their combinations.

[0042] In an embodiment, the conductive sheet material of the printed radiofrequency identification tag structure is selected from a list consisting of silver nanoparticles, carbon nanotubes, graphene, conductive polymers, and their combinations.

[0043] In an embodiment, the polymer matrix of the printed radio-frequency identification tag structure 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 their combinations.

[0044] In an embodiment, the conductive agent of the printed radio-frequency identification tag structure is selected from a list consisting of: polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), silver nanoparticles, copper nanoparticles, graphene, graphene oxide, carbon nanotubes, black carbon, and their combinations.

[0045] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification tag structure further comprises additives selected from a list consisting of defoamers, pH adjusters, and rheology modifiers.

[0046] In an embodiment, the conductive agent of the aqueous conductive adhesive layer used in the printed radio-frequency identification tag structure comprises an average particle size of less than 10 pm, preferably from 60 nm to 4 pm, more preferably from 70 nm to 140 nm.

[0047] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification tag structure further comprises an additional solvent used as a dispersant.

[0048] In an embodiment, the additional solvent of the printed radio-frequency identification tag structure is selected from a list consisting of alcohol, ketone, ester, and their combinations.

[0049] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification tag structure further comprises additives, 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.

[0050] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification tag structure comprises a resistance preferably from 0.1 to500 ohm, more preferably from 0.1 to20 ohm.

[0051] In an embodiment, the aqueous conductive adhesive layer of the printed radiofrequency identification tag structure comprises a conductivity of at least greater than 30000 S / cm, more preferably greater than 500000 S / cm.

[0052] It is also disclosed a printed fabric label comprising the printed radio-frequency identification tag structure described along this description.

[0053] It is also disclosed a communication device comprising the printed radiofrequency identification tag structure described along this description.

[0054] It is also disclosed the use of printed radio-frequency identification tag structure described along this description on electrodes, electronic circuits, antennas, sensors and connectors.

[0055] It is also disclosed a method for production of a printed radio-frequency identification tag structure as described along this description, comprising the following steps: laminating the conductive adhesive layer to the top face of the first material substrate, patterning the aqueous conductive adhesive layer to form a radiofrequency identification tag structure pattern, attaching a strap across the opening of the radio-frequency identification tag structure, curing the adhesive to bond the strap to the conductive sheet material to the top face of the first material substrate, applying an adhesive layer over the top of the radio-frequency identification tag structure using transfer tape, and bonding a second material to the first material using the transfer tape adhesive.

[0056] In an embodiment, the curing process is carried out by air drying.

[0057] In an embodiment, the aqueous conductive adhesive layer is used in the method through the application by screen printing, stencil printing, dispensing, or spraying onto the surface of the electronic component or substrate.

[0058] In an embodiment, the conductive adhesive layer of the method comprises a thickness ranging from 10 pm to 100 pm.BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The following figures provide preferred embodiments for illustrating the disclosure and should not be seen as limiting the scope of invention.

[0060] Figure 1: Photographic representation of an embodiment of a scanning electron micrograph (SEM) of a textile substrate, top views, the conductive aqueous conductive adhesive layer 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).

[0061] 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

[0062] Figure 3: Top image: Photographic representation of an embodiment of a printed radio-frequency identification (RFID) tag structure applied to various textiles with distinct antenna patterns. Bottom image: Photographic representation of an embodiment highlighting an embedded chip integrated within the printed RFID tag.

[0063] Figure 4: 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.

[0064] Figure 5: Graphic representation of a plot with 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).DETAILED DESCRIPTION

[0065] The present disclosure relates to a printed radio-frequency identification tag structure and its method of manufacturing.

[0066] The present disclosure describes a printed radio-frequency identification tag structure that is formed as part of a printed label, such as a printed fabric label. This label can be constructed from any material known in the art, including woven or nonwoven materials, paper, card stock, polyethylene-based materials, and virgin or recycled materials. Generally, a conductive adhesive, is laminated to a first material substrate layer (e.g., paper or woven fabric). The adhesive can be patterned by direct printing, using a mask or cut, and the matrix is stripped away manually or by machine to define the antenna pattern. A strap or other microprocessor contact extensions, such as interposers or carriers, are then attached with the conductive adhesive.

[0067] The printed radio-frequency identification (RFID) tag structure disclosed herein enables the integration of electronic devices within printed tag structures formed on flexible substrates such as textiles, paper, and plastic through the use of an aqueous conductive adhesive layer.

[0068] In an embodiment, the conductive adhesives used can be conductive adhesives based on a polymeric matrix as polysilicone, polyurethane, polybutadiene, fluorinated rubber, polyamide resins, polyol, commonly used in the chemical or textile industry, with at least one conductive filler as metallic nanoparticles, conductive polymers, graphene, black carbon, in water that can be transferred to flexible substrates as textile, paper, plastic through printed process.

[0069] In an embodiment, 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.

[0070] In an embodiment, 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 ofconductive textile, paper, or plastic materials that seamlessly fit into conventional uses, as well as industrial, biomedical, energy, and communication applications.

[0071] This technology utilizes water as a solvent, replacing the conventional organic solvents typically used in the formulation of polymeric adhesives.

[0072] This technology imposes no limitations on the roughness or shape of the substrate, ensuring high conductivity.

[0073] 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.

[0074] 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.

[0075] The current disclosure aims to replace conventional metallic conductors, facilitating the integration of electronic devices into flexible substrates that can withstand harsh conditions.

[0076] 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 form cohesive joints with the textile or other flexible substrate 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.

[0077] 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.

[0078] In an embodiment, the substrates can be 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.

[0079] In an embodiment, the substrates can be made from coated paper, adhesive paper, cardboard, recycled paper, transfer paper, photographic paper, and graphic paper. 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 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.

[0080] In an embodiment, the substrates can be made from polyethylene terephthalate, polyamide, polyester, polyethylene, polypropylene, acrylonitrile butadiene 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.

[0081] 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, from 1 to 14, ionic salts, such as sodium sulphate, sodium hydroxide, sodium chloride, sodium carbonate, calcium carbonate, dyes, such as indigo, azo, anthraquinone, triphenyl methane, stilbene, thiazol, triphenodioxazine derivatives, aromatic carboxylic ester, stabilizers, such as proteins conjugated to horseradish peroxidase and alkaline phosphatase, polymers, such as polyfluorinated, polysilicones, polyurethane, polyisocyanate, reductants, such as hydrosulfite, thiourea dioxide, bisulphite, oxidants, such as hydrogen peroxide, methanesulfinic acid, bacterial amylase, waterproofing, such as perfluorooctanesulfonic acid, perfluorooctanoic acid, C6-fluorocarbon resin, polysiloxane, polydimethyl siloxane, detergents, such as ethanolamine, chlorine hypochlorite, sodium hypochlorite, sodium carbonate, limonene, alcohol ethoxylates, alkylphenol ethoxylates, alkyl polyglucosides and amine oxides, ethoxylated isotridecanol, perchloroethylene, ammonium hydrogen sulfite, base, such as dihydroxy ethylene urea, sodium hydroxide, ammonia, acid, such as citric acid, acetic acid, formic acid and methanesulfonic acid.

[0082] 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 impact resistance to exposure to stressors as high temperature variation, pressure, force, humidity, tensile stress, shear stress, impact resistance, including delamination suppression.

[0083] 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.

[0084] In an embodiment, the conductive adhesive polymer matrix uses polyamide resins prepared by ring opening polymerization (ROP) reaction between at least oneprimary 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.

[0085] 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.

[0086] In an 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 oC), 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.

[0087] In an 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 (less than 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 molecularweight 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.

[0088] In an embodiment, 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 as 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.

[0089] In an 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.

[0090] In an embodiment, polyethylenedioxythiophene with polystyrene sulfonate) was mixed with the polymer matrix.

[0091] In an embodiment, the mixture of adhesive and conductive agent is 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.

[0092] In an 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% (w / v) solid content.

[0093] 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 favors 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 by a hot press, then the final activation of the previously printed adhesive takes place.

[0094] In an 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.

[0095] In an 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.

[0096] The present disclosure also concerns electronic devices for electrodes, electronic circuits, antennas, sensors, connectors or others, which comprise the conductive adhesive now disclosed.

[0097] In an 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.

[0098] In an 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, 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.

[0099] In an 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.

[0100] In an 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.

[0101] In an 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.

[0102] In an embodiment, the percentage of flexible substrate coated with conductive adhesive can vary from less than 1% to 100%.

[0103] In an 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.

[0104] In an 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.

[0105] In an embodiment, the anti-scratch and waterproof layers can be combined and added together in a single deposition.

[0106] 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.

[0107] In an 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 anitrogen 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.

[0108] In an 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.

[0109] In an embodiment, the conductive adhesive was prepared using a waterbased 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.

[0110] In an 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 finalcuring, the transfers are applied to the textile substrates by hot pressing, at 90°C, 0.6 MPa and 4 s. The conductive adhesive adheres to the textile by hot melting and the transfer sheet is remove by delamination.

[0111] In an embodiment, the conductive adhesive was printed onto the flexible substrate, a transfer paper, by Dr. Blade. 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.

[0112] In an 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.

[0113] In an embodiment, conductivity measurements were carried out. Layer / film resistance was 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.

[0114] In an 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.

[0115] In an 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, 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 of temperature, followed by 10minutes of pressure, followed by tension, followed by exposure to temperature again, among other combinations.

[0116] In an embodiment, the aqueous conductive adhesive layer used in the printed radio-frequency identification tag structure further comprises additives selected from a list consisting of defoamers, pH adjusters, and rheology modifiers to enhance the application properties of the adhesive.

[0117] In an embodiment, the aqueous conductive adhesive layer 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, as illustrated in figure 4 and can be observed in the results of table 2.

[0118] In an embodiment, the conductive adhesive can be applied with a standardized design suitable for operating as a radio frequency antenna, as illustrated in figure 3.

[0119] Table 1 - comparative data on applying the conductive adhesive using different production methods applied to different substrates.

[0120] Table 2 - comparative data on a synthetic textile substrate with conductive adhesive on exposure to different chemicals

[0121] Table 3 - comparative data on a synthetic textile substrate with conductive adhesive under exposure to stressors.

[0122] 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.

[0123] 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.

[0124] 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.

[0125] 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.

[0126] The following dependent claims further set out particular embodiments of the disclosure.

Claims

C L A I M S1. A printed radio-frequency identification tag structure comprising: a flexible substrate, a printed antenna formed on the substrate using an aqueous conductive adhesive layer; wherein the aqueous conductive adhesive layer comprises a composition of: 0- 95% (w / w) of a water-dispersible polymer matrix and 5-60% (w / w) of a conductive agent; wherein the printed antenna comprises a conductivity ranging from 1000 to 600000 S / cm, measured at 23°C using a four-point probe; and wherein the printed antenna is configured to retain at least 85% of its initial electrical conductivity after exposure to temperatures from -20°C to 200°C, acidic and alkaline environments, and mechanical deformation with flexible substrates.

2. The printed radio-frequency identification tag structure according to the previous claim, wherein the aqueous conductive adhesive layer partially covers the substrate, preferably with a patterned configuration.

3. The printed radio-frequency identification tag structure according to any of the previous claims, further comprising an anti-scratch protective layer and / or an impermeable layer on the surface of the substrate opposite the surface comprising the conductive adhesive layer.

4. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the flexible substrate is selected from a list consisting of polyester, polypropylene, polylactate, polyamide, cotton, wool, aramid, viscose, rayon, modal, lyocell polyimide, polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), woven or non-woven materials, coated paper, adhesive paper, cardboard, recycled paper, transfer paper, photographic paper, graphic paper, card stock, polyethylene, acrylonitrile butadiene styrene,polyoxymethylene, polycarbonate, thermoplastic elastomers, polyethylene-based materials and their combinations.

5. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the conductive sheet material is selected from a list consisting of silver nanoparticles, carbon nanotubes, graphene, conductive polymers, and their combinations.

6. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the 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 their combinations.

7. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the conductive agent is selected from a list consisting of: polyaniline, polypyrrole, poly(3,4-ethylenedioxythiophene), silver nanoparticles, copper nanoparticles, graphene, graphene oxide, carbon nanotubes, black carbon, and their combinations.

8. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the composition of the aqueous conductive adhesive layer further comprises additives selected from a list consisting of defoamers, pH adjusters, and rheology modifiers.

9. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the composition of conductive agent of the aqueous conductive adhesive layer comprises an average particle size of less than 10 pm, preferably from 60 nm to 4 pm, more preferably from 70 nm to 140 nm.

10. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the composition of the aqueous conductive adhesive layer further comprises an additional solvent used as a dispersant.

11. The printed radio-frequency identification tag structure according to the previous claim, wherein the additional solvent is selected from a list consisting of alcohol, ketone, ester, and their combinations.

12. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the aqueous conductive adhesive composition further comprises additives, 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.

13. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the aqueous conductive adhesive composition comprises an electrical resistance from 0.1 to 500 ohm, preferably from 0.1 to 20 ohm.

14. The printed radio-frequency identification tag structure according to any of the previous claims, wherein the aqueous conductive adhesive composition comprises a conductivity greater than 30000 S / cm, preferably greater than 500000 S / cm.

15. A printed fabric label comprising the printed radio-frequency identification tag structure described in any of the claims 1 to 14.

16. A communication device comprising the printed radio-frequency identification tag structure described in any of the claims 1 to 14.

17. Use of printed radio-frequency identification tag structure described in any of the previous claims 1 to 14 on electrodes, electronic circuits, antennas, sensors and connectors.

18. A method for production of a printed radio-frequency identification tag structure as described in any of the claims 1 to 14, comprising the following steps: laminating the conductive adhesive layer to the top face of the first material substrate, patterning the aqueous conductive adhesive to form a radio-frequency identification tag structure pattern, attaching a strap across the opening of the radio-frequency identification tag structure, curing the adhesive to bond the strap to the conductive sheet material to the top face of the first material substrate, applying an adhesive layer over the top of the radio-frequency identification tag structure using transfer tape, and bonding a second material to the first material using the transfer tape adhesive.

19. The method according to the previous claim, wherein the curing process is carried out by 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 conductive adhesive layer comprises a thickness ranging from 10 pm to 100 pm.

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