Conductive silver paste for electronic skin and preparation method and application thereof

Abstract

The application discloses an electronic skin-oriented conductive silver paste and a preparation method and application thereof, and relates to the technical field of flexible printed electronic materials.The raw materials of the electronic skin-oriented conductive silver paste include flaky silver powder, silver nanoparticles, thermoplastic polyurethane elastomer, acrylic elastomer, PEDOT:PSS microgel dispersion, (3-glycidylpropoxy)trimethoxysilane, polydiallyldimethylammonium chloride, hexanedial modified dopamine copolymer, (3-aminopropyl)triethoxysilane, methacryloyloxypropyltrimethoxysilane, cellulose acetate, modified polyurea thixotropic agent, hydrogenated castor oil, ethylene glycol ether acetate, dibasic acid ester, leveling agent and water.The electronic skin-oriented conductive silver paste has the advantages of good electrical performance, good mechanical-electrical stability, good anti-electromigration and sweat corrosion resistance, and can still maintain dendrite-free and low drift under long-term coupling of sweat and bias, and is suitable for electronic skin.

Description

Technical Field

[0001] This invention relates to the field of flexible printed electronic materials technology, and in particular to a conductive silver paste for electronic skin, its preparation method and application. Background Technology

[0002] As a core component of wearable electronics technology, electronic skin needs to be directly attached to the surface of human skin or integrated into flexible clothing to monitor physiological signals, sense external stimuli, or achieve human-computer interaction. This requires that its conductive pattern not only has excellent conductivity, but also maintains stable performance under mechanical deformation, complex sweat environments, and long-term use conditions. Specifically, the conductive materials for electronic skin should meet the following comprehensive requirements: (1) have a low intrinsic volume resistivity (usually required to be ≤1×10⁻⁶). -4 (1) Ω·cm), to ensure low-loss signal transmission; (2) Under repeated tensile deformation caused by human activity (e.g., 20-40% uniaxial strain), the resistance change rate (ΔR / R0) needs to be controlled at a low level (≤20%), that is, it has good tensile stability; (3) The slurry should have suitable rheological properties (e.g. at 25℃, shear rate 1 s). -1 The viscosity is approximately 20.0±1.0 Pa·s and the thixotropic index is approximately 3.0±1.0, which meets the requirements of high-precision screen printing process for pattern resolution and edge clarity; (4) The curing temperature should not be too high (e.g., 130 ℃, 30 minutes) to adapt to the processing window of common heat-sensitive flexible substrates such as TPU, PET, and PU; (5) In real sweat environments containing NaCl, lactic acid, urea, etc., even if there is a DC bias electric field, it is necessary to resist electrochemical migration and corrosion for a long time to avoid circuit failure due to the growth of silver dendrites.

[0003] Currently, commercially available conductive silver pastes mostly employ a single resin bonding system and conventional coupling strategies. These silver pastes have significant shortcomings when facing the harsh application environments of electronic skin: Firstly, in sweaty environments, traditional silver paste systems struggle to effectively block chloride ions (Cl). - Penetration by corrosive ions and Ag + The migration and dissolution of silver dendrites cannot fundamentally suppress their formation and growth, leading to short circuits or performance drift in circuits under bias voltage. Secondly, a single adhesive resin system often struggles to achieve excellent and stable adhesion on various skin-feeding substrates such as TPU, PET, and PU. Furthermore, under repeated stretching and deformation, interfacial failures easily occur between the conductive silver paste and the polymer matrix, resulting in decreased electrical stability. In addition, achieving high density (low porosity) of the conductive network while effectively suppressing ion migration and ensuring the edge quality of the printed pattern at relatively low curing temperatures (e.g., 130 °C) remains a key challenge that current technologies have not yet adequately addressed.

[0004] Therefore, developing a conductive silver paste that can balance low resistance, high tensile stability, excellent printability, low-temperature curing properties, and superior resistance to sweat corrosion and electromigration is of great significance for promoting the practical application of high-performance electronic skin and is also an urgent need for technological research and development in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a conductive silver paste for electronic skin, its preparation method, and its application, in order to solve the problems existing in the prior art. The conductive silver paste for electronic skin of this invention is a conductive silver paste composition that maintains low resistance, low drift, and dendrite-free properties under typical stretching (20-40%) and sweat electrical biasing environments of electronic skin, and exhibits excellent adhesion to substrates such as TPU, PET, and PU.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] One of the technical solutions of this invention is a conductive silver paste for electronic skin, comprising the following components by mass: 60-75 parts of flake silver powder, 0.5-5 parts of silver nanoparticles, 4-10 parts of thermoplastic polyurethane elastomer, 1-5 parts of acrylic elastomer, 0.3-2 parts of PEDOT:PSS microgel dispersion, 0.1-1 parts of (3-glycidylpropoxy)trimethoxysilane (GPTMS), and 0. 1-1 part, adipaldehyde-modified dopamine copolymer 0.1-1 part, (3-aminopropyl)triethoxysilane (APTES) 0.1-1 part, methacryloyloxypropyltrimethoxysilane (KH-570) 0.05-0.5 part, cellulose ester 0.3-1.5 part, modified polyurea thixotropic agent 0.1-1 part, hydrogenated castor oil 0.05-0.5 part, ethylene glycol ethyl ether acetate 8-25 parts, diester ester 2-10 parts, leveling agent 0-1 part, and water 0.1-1 part.

[0008] The key mechanism of action achieved by the raw material system of this invention is as follows:

[0009] (1) PEDOT:PSS, PDADMAC, and GPTMS work together to construct a composite shielding mesophase: the polyanionic PSS in the PEDOT:PSS microgel dispersion - The PDADMAC cationic segments undergo multi-electrolyte complexation to form electrically neutral or slightly positively charged multi-electrolyte complexes. These complexes are then immobilized on the surface of flake-shaped silver powder and silver nanoparticles by GPTMS cross-linking, forming a dense, localized coating layer. This localized coating layer, acting as a shielding mesophase, effectively blocks Na+ from the sweat environment. + Cl -The penetration of lactate ions and other ions inhibits the dissociation and migration of silver ions, thereby curbing dendrite growth and electrical resistance drift at the source. Simultaneously, the PEDOT backbone in PEDOT:PSS possesses a certain degree of conductivity, providing dynamic micro-conductive bridging when the conductive network undergoes slight slippage under stretching, thus helping to maintain the continuity of the pathway.

[0010] (2) Synergistic cooperation between flake silver powder and silver nanoparticles: the flake silver powder is oriented in the shear field to form a conductive framework, while the silver nanoparticles fill the gaps and combine with the flake silver powder to form a high-conductivity network with low porosity.

[0011] (3) Rheological regulation of the ternary thixotropic system of cellulose ester / modified polyurea thixotropic agent / hydrogenated castor oil: Cellulose ester, modified polyurea thixotropic agent and hydrogenated castor oil constitute a ternary synergistic thixotropic system. This system endows the slurry with unique fast and slow time-scale recovery thixotropic properties, which makes it easy to handle when the viscosity is reduced under printing shear, and can quickly recover high viscosity after printing, thereby ensuring that the printed pattern has clear edges and does not collapse.

[0012] (4) Synergistic toughening and adhesion mechanism of thermoplastic polyurethane elastomer (TPU) with acrylic elastomer and interfacial active components (adipaldehyde-modified dopamine copolymer, APTES, KH-570, etc.): As a thermoplastic elastomer rich in soft segments, thermoplastic polyurethane elastomer provides high elongation and excellent resilience for the cured film, and can bear the main deformation and achieve stress release during repeated stretching; acrylic elastomer contains polar ester groups and has a glass transition temperature close to room temperature, which can interact with TPU, PET, PU and other skin-adhesive substrates as well as the sheet silver powder and silver nanoparticles in the conductive network through polar and van der Waals interactions, providing initial adhesion force and interfacial energy dissipation channels. The dopamine fragments in the adipaldehyde-modified dopamine copolymer can form coordination and hydrogen bonds with the silver surface through catechol groups. Simultaneously, its molecular chains entangle and hydrogen bonds with TPU and acrylic elastomers, effectively introducing "molecular nails" and a flexible bridging layer between the inorganic filler and the organic resin. After hydrolysis and condensation of APTES and KH-570, an inorganic-organic transition layer with Si-O-Ag / Si-OC bonds is formed on the silver surface. This layer interacts chemically and physically with the polar groups in TPU and acrylic elastomers, while also improving the wettability and adhesion of the conductive layer to flexible substrates such as TPU, PET, and PU. Through the combined action of the continuous elastic phase provided by TPU, the interfacial adhesion provided by the acrylic elastomer, and the multi-point chemical bridging provided by the dopamine copolymer and silane coupling agent, a conductive layer with a dual-binder phase and multi-scale interfacial locking structure is constructed. This allows the conductive silver paste of this invention to maintain low resistance drift and good mechanical stability under 20-40% tensile strain and multiple cycling conditions.

[0013] (5) Synergistic dispersion and interface optimization mechanism of organic carrier and additives: Ethylene glycol ethyl ether acetate and diester, as mixed solvents, provide good solubility and suitable volatility gradient, which is conducive to the uniform dispersion of flake silver powder and silver nanoparticles and the stability of cured film quality. Leveling agent helps to form a smooth film surface. Components such as adipaldehyde-modified dopamine copolymer further enhance the adhesion and interfacial compatibility of the system. Through precise synergy, the components successfully achieved the comprehensive performance goals of low resistance, high tensile stability, resistance to sweat corrosion and dendrite growth under the low temperature curing conditions of 130 ℃ × 30 min (i.e., curing at 130 ℃ for 30 min).

[0014] In summary, this invention utilizes a dense shielding mesophase formed by PEDOT:PSS-PDADMAC-GPTMS composites to construct an efficient ion migration barrier on the surface of flake silver powder and silver nanoparticles. This is achieved through a synergistic effect of high aspect ratio flake silver powder orientation and low-temperature fusion with silver nanoparticles to form a low-porosity, high-conductivity network. Furthermore, the invention leverages the dual binder phases of thermoplastic polyurethane and acrylic elastomer to achieve toughness and broad-spectrum adhesion. Finally, the invention employs a ternary thixotropic system of cellulose ester / modified polyurea thixotropic agent / hydrogenated castor oil to precisely control the printing rheology. Thus, under a low-temperature curing condition of 130 ℃, this invention successfully achieves stable conductivity with low resistance, high tensile stability, excellent printing accuracy, and long-term resistance to dendrite formation and corrosion in sweat environments.

[0015] The conductive silver paste provided by this invention is suitable for long-term sweat circulation and bias conditions. Within a curing window of 130℃ × 30 min, it achieves the following comprehensive properties: volume resistivity (ρ... v ≤1×10 -4 The resistance change rate (ΔR / R0) is ≤20% at tensile strain of 20-40% Ω·cm, and no dendrites are generated after 168h in artificial sweat (0.9wt% NaCl, lactic acid, urea system, 40℃, bias electric field 20-50V / mm), showing excellent electrochemical stability and mechanical tolerance.

[0016] Furthermore, the thickness of the flake silver powder is 0.1-0.3 μm, and the aspect ratio is ≥15 (i.e., high aspect ratio flake silver powder).

[0017] Furthermore, the D of the silver nanoparticles 50 The wavelength is 30-70 nm.

[0018] Furthermore, the thermoplastic polyurethane elastomer (TPU) is a polyether-type TPU with a number-average molecular weight of 8.0 × 10⁻⁶. 4 -2.0×10 5 g·mol -1 Preferably 1.0×10 5 -1.6×105 g·mol -1 Its hardness (Shore A hardness) is 80-95.

[0019] Furthermore, the acrylic elastomer is a copolymer of butyl acrylate (BA), methyl methacrylate (MMA), and hydroxyethyl methacrylate (HEMA).

[0020] Optionally, the content of hydroxyethyl methacrylate (HEMA) component in the acrylic elastomer is 1-5 wt%.

[0021] Optionally, the weight-average molecular weight (M) of the acrylic elastomer w ) is 1×10 5 -8×10 5 g·mol -1 .

[0022] Furthermore, the cellulose ester comprises CAB-551-0.2.

[0023] Furthermore, the diester includes DBE-9 (a mixture of dimethyl glutarate and dimethyl succinate).

[0024] Furthermore, the modified polyurea thixotropic agent includes one or more of aliphatic polyurea thixotropic agents, aromatic polyurea thixotropic agents, and polyurea-polyurethane copolymer thixotropic agents.

[0025] Furthermore, the leveling agent includes one or more of alkyl phosphate leveling agents, aryl phosphate leveling agents, phosphate ester polyether leveling agents, and phosphate ester modified acrylic resin leveling agents.

[0026] Further, the preparation steps of the PEDOT:PSS microgel dispersion include: mixing PEDOT:PSS aqueous dispersion with acetone, stirring, centrifuging to obtain precipitate 1; mixing precipitate 1 with isopropanol, stirring, centrifuging, and drying to obtain precipitate 2; mixing precipitate 2 with dimethyl sulfoxide, sonicating in an ice-water bath for 5-10 min, stirring for 1-2 h, and then allowing it to stand to remove bubbles to obtain the PEDOT:PSS microgel dispersion.

[0027] This invention utilizes a solvent replacement process for PEDOT:PSS via "acetone pre-precipitation + dimethyl sulfoxide redispermation": First, acetone is used as a non-solvent to precipitate PEDOT:PSS from the aqueous phase, removing most of the water and some free PSS from the system. -This process essentially completes the initial displacement from the aqueous phase to the organic phase. Subsequently, it is redispersed in dimethyl sulfoxide, allowing PEDOT:PSS to transition from an aqueous environment to a high-boiling-point, highly polar solvent environment. Following this solvent displacement and rearrangement treatment, phase separation and configurational recombination occur within PEDOT:PSS, forming a continuous PEDOT-enriched phase. The PSS phase is relatively reduced, the interfacial contact resistance decreases, and the carrier mobility within the PEDOT phase increases, making interphase connectivity easier. This significantly improves overall conductivity while maintaining flexibility.

[0028] Furthermore, the volume ratio of the PEDOT:PSS aqueous dispersion to the acetone is 1:10-12.

[0029] Furthermore, the solid content of PEDOT:PSS in the PEDOT:PSS microgel dispersion is 0.5-1 wt%.

[0030] Furthermore, the solid content of the PEDOT:PSS aqueous dispersion is 1-1.5 wt%.

[0031] Furthermore, before mixing the PEDOT:PSS aqueous dispersion with acetone, the step of filtering the PEDOT:PSS aqueous dispersion is also included.

[0032] Furthermore, the ratio of precipitate 1 to isopropanol is 1 g: 10-20 mL, preferably 1 g: 12-15 mL.

[0033] Furthermore, the settling and defoaming process is carried out at room temperature for 0.5-1 h.

[0034] Furthermore, the step of filtering is included before the settling and defoaming process.

[0035] Further, the preparation steps of the adipaldehyde-modified dopamine copolymer include: mixing an aqueous solution of dopamine hydrochloride with an aqueous solution of adipaldehyde, adjusting the pH of the mixture to 8-9 with sodium bicarbonate buffer, and then reacting at 20-35 °C for 2-12 h to obtain the adipaldehyde-modified dopamine copolymer.

[0036] Furthermore, the concentration of the dopamine hydrochloride solution is 5-50 mg / mL, and the concentration of the adipic aldehyde aqueous solution is 5-15 mg / mL.

[0037] Furthermore, the molar ratio of dopamine hydrochloride in the dopamine hydrochloride aqueous solution to adipic aldehyde in the adipic aldehyde aqueous solution is 2-4:1.

[0038] The second technical solution of the present invention: a method for preparing the above-mentioned conductive silver paste for electronic skin, comprising the following steps:

[0039] S1: Dissolve polydiallyldimethylammonium chloride in water, mix the resulting aqueous solution of polydiallyldimethylammonium chloride with PEDOT:PSS microgel dispersion, stir for 30-60 min, adjust the pH to 6-7 and add (3-glycidylpropoxy)trimethoxysilane, heat the reaction for 0.5-2 h to obtain mixture 1;

[0040] S2: Mix ethylene glycol ethyl ether acetate, diester, thermoplastic polyurethane elastomer, acrylic elastomer, adipaldehyde-modified dopamine copolymer, (3-aminopropyl)triethoxysilane, methacryloyloxypropyltrimethoxysilane, cellulose ester, modified polyurea thixotropic agent, and hydrogenated castor oil to obtain mixture 2.

[0041] S3: Add flake silver powder and silver nanoparticles to the mixture 2, and shear at medium-low speed for 20-40 min to obtain mixture 3;

[0042] S4: Add mixture 1 to mixture 3, stir for 20-30 minutes, then add leveling agent and grind until D is reached. 90 After vacuum degassing and filtration, the conductive silver paste for electronic skin is obtained.

[0043] Further, the mixing of ethylene glycol ethyl ether acetate, diester, thermoplastic polyurethane elastomer, acrylic elastomer, adipaldehyde-modified dopamine copolymer, (3-aminopropyl)triethoxysilane, methacryloyloxypropyltrimethoxysilane, cellulose ester, modified polyurea thixotropic agent, and hydrogenated castor oil comprises: mixing ethylene glycol ethyl ether acetate and diester to obtain a mixed solvent; adding thermoplastic polyurethane elastomer, acrylic elastomer, cellulose ester, modified polyurea thixotropic agent, hydrogenated castor oil, (3-aminopropyl)triethoxysilane, and methacryloyloxypropyltrimethoxysilane to the mixed solvent and stirring for 15-30 min; then adding adipaldehyde-modified dopamine copolymer and continuing to stir for 5-10 min to obtain mixture 2.

[0044] In step S1, firstly, the polyanionic PSS in the PEDOT:PSS microgel dispersion... -In an aqueous phase, the quaternary ammonium cation segments of PDADMAC electrostatically associate to form electrically neutral or slightly positively charged multi-electrolyte complexes. Upon adjusting the pH to 6-7 and adding GPTMS, the methoxy groups of GPTMS undergo stepwise hydrolysis to generate silanol intermediates. Under heating conditions, the epoxy groups of these intermediates undergo ring-opening addition reactions with the hydroxyl and amino groups on the PEDOT:PSS / PDADMAC segments, causing the multi-electrolyte complexes to crosslink with each other and with other hydroxyl-containing components in the aqueous phase via Si-OC / CN bonds. This provides a pre-crosslinked structural basis for the subsequent construction of a dense shielding intermediate phase on the surface of silver powder and silver nanoparticles.

[0045] Optionally, the temperature of the heating reaction is 40-90 ℃, preferably 50-70 ℃.

[0046] Optionally, the rotational speed of the medium-low speed shearing is 500-1500 rpm.

[0047] Alternatively, the grinding is performed using a three-roll mill or a bead mill.

[0048] Furthermore, the filtration specifically involves using a 300-mesh filter.

[0049] The third technical solution of the present invention: the application of the above-mentioned conductive silver paste for electronic skin in the preparation of electronic skin.

[0050] Furthermore, the application includes: printing the conductive silver paste for electronic skin onto the surface of a substrate and curing it to obtain the electronic skin.

[0051] Furthermore, the curing process specifically involves curing at 120-140 ℃ for 10-40 min, preferably at 130 ℃ for 30 min, or first curing at 110 ℃ for 10 min, and then curing at 130 ℃ for 20 min.

[0052] During the curing stage, the mixed solvent gradually evaporates, and the thermoplastic polyurethane elastomer and acrylic elastomer melt and flow to form a film. Under the action of GPTMS, the PEDOT:PSS / PDADMAC multi-electrolyte composite further undergoes epoxy ring-opening and silanol condensation reactions, firmly anchoring the composite shell to the surface of the flake silver powder and silver nanoparticles. At the same time, the catechol groups of the adipaldehyde-modified dopamine copolymer form coordination bonds and hydrogen bonds with the silver surface and the resin matrix. APTES and KH-570 hydrolyze and condense to play a coupling and thickening role between silver (flake silver powder and silver nanoparticles), TPU, and acrylic phase, so that the conductive filler is co-encapsulated by the dense resin phase and the shielding intermediate phase, ultimately constructing a continuous and stable conductive network and a conductive coating that is firmly bonded to the substrate.

[0053] In addition, the two-stage curing process of 110 ℃×10 min+130 ℃×20 min can optimize the volatilization gradient, resulting in a denser coating and a more stable conductive network.

[0054] Furthermore, after curing, the thickness of the coating formed by the conductive silver paste facing the electronic skin is 12-16 μm.

[0055] Furthermore, the substrate includes a pure TPU (thermoplastic polyurethane elastomer) film without surface treatment (such as silicone coating), a pure PU (polyurethane) film without surface treatment, a pure PET (polyethylene terephthalate) film without surface treatment, a pure PDMS (polydimethylsiloxane) film without surface treatment, or a silicone-coated film.

[0056] Optionally, the silicone-coated film includes a silicone-coated TPU release film, PU release film, PET release film, or PDMS release film.

[0057] Optionally, the substrate may be treated with corona or plasma before printing to increase its surface energy.

[0058] The conductive silver paste for electronic skin of the present invention has the advantages of good electrical properties, good mechanical-electrical stability, and good resistance to electromigration and sweat corrosion. It can still maintain dendrite-free and low drift under long-term coupling of sweat and bias voltage. It can be densified with low resistance at 130 ℃ for 30 min. It is printable and suitable for roll-to-roll large-area manufacturing. It can be used not only for conductive interconnects in electronic skin, but also for skin-attached electrodes and flexible sensors.

[0059] The present invention discloses the following technical effects:

[0060] The conductive silver paste for electronic skin of the present invention has the following main advantages compared with existing conductive silver pastes:

[0061] (1) Excellent electrical properties and printability: By synergistically constructing a low-porosity, high-conductivity network through high aspect ratio flake silver powder and nano-silver particles, and by precisely controlling the rheology of the ternary thixotropic system of cellulose ester / modified polyurea thixotropic agent / hydrogenated castor oil, the volume resistivity of this silver paste is ≤1×10 after low-temperature curing at 130℃. -4 Ω·cm, and features 25℃, 1 s -1 An ideal printing viscosity of 20±1 Pa·s and a thixotropic index of 3.0±1.0 ensure clear pattern edges without collapse.

[0062] (2) Outstanding mechanical-electrical stability: The dual binder phase composed of thermoplastic polyurethane elastomer and acrylic elastomer provides excellent toughness and resilience. At the same time, the PEDOT conductive phase plays a micro-bridging role under strain, so that the resistivity change rate (ΔR / R0) of the silver paste is stable below 20% under tensile strain of 20-40%, and can withstand 1000 cycles of 20% strain with minimal resistance drift.

[0063] (3) Excellent resistance to electromigration and sweat corrosion: Based on the dense shielding intermediate phase constructed on the silver interface by PEDOT:PSS-PDADMAC-GPTMS, it can effectively block the penetration of corrosive media such as chloride ions and lactate ions and inhibit the migration of silver ions. After 168 hours of testing in a sweat environment at 40℃ and 20-50 V / mm bias, the silver paste still showed no dendrite bridging phenomenon.

[0064] (4) Wide range of substrate adhesion: Combining the synergistic effect of silane coupling agent and dual binder phase system, this silver paste exhibits strong adhesion to a variety of skin-penetrating substrates such as TPU, PET, and PU, with an adhesion grade of 5B. Detailed Implementation

[0065] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0066] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0067] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0068] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0069] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0070] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0071] In the following embodiments and comparative examples of the present invention, room temperature refers specifically to 20-25 °C.

[0072] In the following embodiments and comparative examples of the present invention, the term "parts" specifically refers to "parts by mass".

[0073] Unless otherwise specified, all raw materials used in the following embodiments and comparative examples of this invention are commercially available products. Specifically, the thickness of the flake silver powder is 0.1-0.3 μm, and the aspect ratio is ≥15; the D of the silver nanoparticles... 50 The number average molecular weight is 50 nm; the thermoplastic polyurethane elastomer (TPU) is Estane® 58300 polyether-type TPU supplied by Lubrizol, with a number average molecular weight of 1.2 × 10⁻⁶. 5 g·mol -1 The hardness (Shore A hardness) is 82; the acrylic elastomer is a copolymer of BA, MMA and HEMA (of which the content of HEMA component is 5 wt% and the content of MMA component is 40 wt%), and the weight average molecular weight is 2.0 × 10⁻⁶. 5 g / mol; CAS number of (3-glycidylpropoxy)trimethoxysilane (GPTMS) is 2530-83-8; CAS number of (3-aminopropyl)triethoxysilane (APTES) is 919-30-2; CAS number of methacryloyloxypropyltrimethoxysilane (KH-570) is 2530-85-0; CAS number of polydiallyldimethylammonium chloride (PDADMAC) is 26062-79-3; cellulose ester is CAB-551-0.2; modified polyurea thixotropic agent is brand T-720 (it is a polyurea thixotropic agent mainly composed of polyisocyanate and polyether diamine prepolymer, with a solid content of 20 wt%); diester is DBE-9; leveling agent is polyether modified polysiloxane leveling agent, commercial brand name is L-88, with a solid content of 50 wt%.

[0074] The preparation steps of the PEDOT:PSS microgel dispersion used in the following embodiments and comparative examples of this invention are as follows:

[0075] (1) Pretreatment: PEDOT:PSS aqueous dispersion (solid content of 1.2 wt%) was filtered through a 0.45 µm filter membrane to remove large particles and dust particles.

[0076] (2) Induced precipitation: Under stirring at 400 rpm, the filtered PEDOT:PSS aqueous dispersion was slowly added dropwise to anhydrous acetone (the volume ratio of PEDOT:PSS aqueous dispersion to anhydrous acetone was 1:11). Stirring was maintained at 400 rpm for 15 min, and blue-black flocs appeared. Then, the mixture was centrifuged at 4000 rpm for 5 min to obtain precipitate 1.

[0077] (3) Transition wash: Resuspend precipitate 1 in anhydrous isopropanone (the ratio of precipitate 1 to anhydrous isopropanone is 1 g: 10 mL), and centrifuge at 4000 rpm for 5 min after mixing. This helps to disperse the precipitate more quickly in dimethyl sulfoxide.

[0078] (4) Drying: Vacuum at 40 ℃ for 45 min to remove the residual solvent but not completely dry it into a film (to prevent it from being difficult to redisperse), and obtain precipitate 2.

[0079] (5) Redispersing with dimethyl sulfoxide: Add anhydrous dimethyl sulfoxide to precipitate 2 according to the target solid content (0.8 wt%), sonicate in an ice water bath (0 ℃) for 8 min, and then stir magnetically for 90 min to obtain a uniform blue dispersion.

[0080] (6) Filtration and stabilization: Filter through a 0.45 µm filter membrane and let stand at room temperature for 60 min to remove bubbles, to obtain PEDOT:PSS microgel dispersion (stored in a sealed container at 4 ℃).

[0081] The preparation steps of the adipaldehyde-modified dopamine copolymer used in the following embodiments and comparative examples of the present invention are as follows:

[0082] (1) Dissolve dopamine hydrochloride in deionized water to obtain an aqueous solution of dopamine hydrochloride with a concentration of 20 mg / mL; dissolve adipicaldehyde in deionized water to obtain an aqueous solution of adipicaldehyde with a concentration of 10 mg / mL;

[0083] (2) Add hexamethylene dialdehyde solution dropwise to the dopamine hydrochloride aqueous solution under stirring at 25 °C so that the molar ratio of dopamine hydrochloride in the dopamine hydrochloride aqueous solution to hexamethylene dialdehyde in the hexamethylene dialdehyde aqueous solution is 3:1, and adjust the pH of the mixture to 8.5 with sodium bicarbonate buffer solution;

[0084] (3) The pH-adjusted mixture was stirred at 25 °C for 6 h to obtain an aqueous solution of adipaldehyde-modified dopamine copolymer. After dialysis to remove salt and drying, adipaldehyde-modified dopamine copolymer with a number-average molecular weight of 2000 g·mol⁻¹ was obtained. -1 .

[0085] Example 1

[0086] A conductive silver paste for electronic skin comprises the following raw materials: 68 parts flake silver powder, 2 parts silver nanoparticles, 6 parts thermoplastic polyurethane elastomer, 2.5 parts acrylic elastomer, 0.8 parts PEDOT:PSS microgel dispersion, 0.3 parts GPTMS, 0.2 parts PDADMAC, 0.3 parts adipaldehyde-modified dopamine copolymer, 0.3 parts APTES, 0.2 parts KH-570, 0.8 parts cellulose ester, 0.3 parts modified polyurea thixotropic agent, 0.2 parts hydrogenated castor oil, 14 parts ethylene glycol ethyl ether acetate, 4.6 parts diester, 0.5 parts leveling agent, and 0.5 parts water.

[0087] The preparation steps of the conductive silver paste for electronic skin are as follows:

[0088] S1: Dissolve PDADMAC in water, mix the resulting PDADMAC aqueous solution with PEDOT:PSS microgel dispersion, stir for 45 min, adjust the pH to 6.5 and add GPTMS, heat at 50 ℃ for 1 h to obtain mixture 1;

[0089] S2: Ethylene glycol ethyl ether acetate and diester are mixed to obtain a mixed solvent; thermoplastic polyurethane elastomer, acrylic elastomer, cellulose ester, modified polyurea thixotropic agent, hydrogenated castor oil, APTES and KH-570 are added to the above mixed solvent, and the mixture is stirred at high speed for 20 min (4500 rpm); then adipaldehyde modified dopamine copolymer is added, and the mixture is stirred at high speed (4500 rpm) for 5 min to obtain mixture 2;

[0090] S3: Add flake silver powder and silver nanoparticles to mixture 2, and shear at medium-low speed for 30 min (rotation speed of 1000 rpm) to obtain mixture 3;

[0091] S4: Add mixture 1 to mixture 3, stir for 25 min (900 rpm), then add leveling agent and grind until D is achieved. 90 After the particle size is less than 12 μm, vacuum degassing and filtration through a 300-mesh filter are performed to obtain the finished conductive silver paste.

[0092] Example 2

[0093] A conductive silver paste for electronic skin comprises the following raw materials: 68 parts of flake silver powder, 2 parts of silver nanoparticles, 6 parts of thermoplastic polyurethane elastomer, 2.8 parts of acrylic elastomer, 0.8 parts of PEDOT:PSS microgel dispersion, 0.3 parts of GPTMS, 0.2 parts of PDADMAC, 0.3 parts of adipaldehyde-modified dopamine copolymer, 0.35 parts of APTES, 0.25 parts of KH-570, 0.8 parts of cellulose ester, 0.3 parts of modified polyurea thixotropic agent, 0.2 parts of hydrogenated castor oil, 13.7 parts of ethylene glycol ethyl ether acetate, 4.6 parts of diester acid ester, 0.5 parts of leveling agent, and 0.5 parts of water.

[0094] The preparation steps for the conductive silver paste for electronic skin are the same as in Example 1.

[0095] Example 3

[0096] A conductive silver paste for electronic skin comprises the following raw materials: 68 parts flake silver powder, 2 parts silver nanoparticles, 6 parts thermoplastic polyurethane elastomer, 2.5 parts acrylic elastomer, 0.8 parts PEDOT:PSS microgel dispersion, 0.3 parts GPTMS, 0.2 parts PDADMAC, 0.3 parts adipaldehyde-modified dopamine copolymer, 0.3 parts APTES, 0.2 parts KH-570, 1 part cellulose ester, 0.25 parts modified polyurea thixotropic agent, 0.2 parts hydrogenated castor oil, 13.7 parts ethylene glycol ethyl ether acetate, 4.6 parts diester, 0.6 parts leveling agent, and 0.5 parts water.

[0097] The preparation steps for the conductive silver paste for electronic skin are the same as in Example 1.

[0098] Example 4

[0099] A conductive silver paste for electronic skin comprises the following raw materials: 68 parts flake silver powder, 2 parts silver nanoparticles, 6 parts thermoplastic polyurethane elastomer, 2.5 parts acrylic elastomer, 0.8 parts PEDOT:PSS microgel dispersion, 0.3 parts GPTMS, 0.2 parts PDADMAC, 0.3 parts adipaldehyde-modified dopamine copolymer, 0.3 parts APTES, 0.2 parts KH-570, 0.8 parts cellulose ester, 0.3 parts modified polyurea thixotropic agent, 0.2 parts hydrogenated castor oil, 13.2 parts ethylene glycol ethyl ether acetate, 5.2 parts diester, 0.5 parts leveling agent, and 0.5 parts water.

[0100] The preparation steps for the conductive silver paste for electronic skin are the same as in Example 1.

[0101] Example 5

[0102] A conductive silver paste for electronic skin comprises the following raw materials: 68 parts of flake silver powder, 2 parts of silver nanoparticles, 6.5 parts of thermoplastic polyurethane elastomer, 2.8 parts of acrylic elastomer, 0.8 parts of PEDOT:PSS microgel dispersion, 0.3 parts of GPTMS, 0.2 parts of PDADMAC, 0.3 parts of adipaldehyde-modified dopamine copolymer, 0.3 parts of APTES, 0.2 parts of KH-570, 0.8 parts of cellulose ester, 0.3 parts of modified polyurea thixotropic agent, 0.2 parts of hydrogenated castor oil, 13.2 parts of ethylene glycol ethyl ether acetate, 4.6 parts of diester acid ester, 0.5 parts of leveling agent, and 0.5 parts of water.

[0103] The preparation steps for the conductive silver paste for electronic skin are the same as in Example 1.

[0104] Example 6

[0105] A conductive silver paste for electronic skin comprises the following raw materials: 68 parts flake silver powder, 2 parts silver nanoparticles, 6 parts thermoplastic polyurethane elastomer, 2.5 parts acrylic elastomer, 0.8 parts PEDOT:PSS microgel dispersion, 0.35 parts GPTMS, 0.25 parts PDADMAC, 0.35 parts adipaldehyde-modified dopamine copolymer, 0.3 parts APTES, 0.2 parts KH-570, 0.8 parts cellulose ester, 0.3 parts modified polyurea thixotropic agent, 0.2 parts hydrogenated castor oil, 13.6 parts ethylene glycol ethyl ether acetate, 4.6 parts diester, 0.5 parts leveling agent, and 0.5 parts water.

[0106] The preparation steps for the conductive silver paste for electronic skin are the same as in Example 1.

[0107] Comparative Example 1

[0108] Same as Example 1, except that the use of GPTMS is omitted.

[0109] Comparative Example 2

[0110] Same as Example 1, except that GPTMS and other quality are replaced with APTES, that is, GPTMS and other quality in step S1 are replaced with APTES, while APTES in step S2 remains unchanged.

[0111] Comparative Example 3

[0112] Same as Example 1, except that GPTMS and other quality are replaced with KH-570, that is, GPTMS and other quality in step S1 are replaced with KH-570, while KH-570 in step S2 remains unchanged.

[0113] Comparative Example 4

[0114] Same as Example 1, except that the modified polyurea thixotropic agent is replaced by hydrogenated castor oil.

[0115] Comparative Example 5

[0116] Same as Example 1, except that hydrogenated castor oil and other similar substances are replaced with modified polyurea thixotropic agent.

[0117] Comparative Example 6

[0118] Same as Example 1, except that the KH-570 equivalent mass is replaced with GPTMS, that is, the GPTMS in step S1 remains unchanged, while the KH-570 equivalent mass in step S1 is replaced with GPTMS.

[0119] Test Example 1

[0120] Viscosity and thixotropic properties testing:

[0121] This test case aims to systematically characterize the steady-state shear viscosity, thixotropic index (TI), and recovery behavior after shearing of conductive silver paste through rotational rheological testing, in order to evaluate its storage stability, printability, and film quality.

[0122] (1) Test conditions:

[0123] Instruments and Environment: A rotational rheometer was used for testing, and the test temperature was strictly controlled at 25.0±0.1 ℃.

[0124] Measurement fixture: The cone-plate geometry system (40 mm diameter, 2° cone angle, 50 µm intercept, and 50 µm test gap) is preferred. If significant slippage occurs during testing, the parallel plate geometry system (25 mm diameter, 500 µm test gap) should be used for subsequent tests.

[0125] Sample preparation: After loading the silver paste sample into the measuring fixture, it needs to be degassed and the edges trimmed to remove excess sample, ensuring the accuracy of the test area.

[0126] (2) Testing Procedure:

[0127] Sample pretreatment: To ensure that the samples have a consistent initial state before each test, a constant shear rate (10 s⁻¹) is applied first. -1 Pre-shear the sample for 60 seconds. Then, allow the sample to stand under zero-shear conditions for 120 seconds.

[0128] Steady-state shear test: Shear rate (γ) scan was performed using a logarithmic step mode, ranging from γ = 0.5 to 50 s. -1 Ten data points are collected every ten times the range, and the balancing (measurement) time for each shear rate point is 5 seconds.

[0129] Key parameter recording: Record the curve of apparent viscosity (η) as a function of shear rate (γ). Extract the following characteristic parameters from it: η@1 s -1 (Silver paste at a shear rate of 1 s) -1 Apparent viscosity at low shear conditions: η represents the viscosity under low shear conditions and is related to the storage stability and anti-settling ability of the slurry; η@50 s -1 (Silver paste at a shear rate of 50 s) -1 Apparent viscosity at steady-state shear rate: This represents the viscosity at high shear rates during application (such as screen printing), characterizing the flowability of the material. Thixotropic index calculation: Based on steady-state shear test data, the thixotropic index (TI) is calculated as follows: TI = η@0.5 s -1 / η@50 s -1 This ratio directly reflects the ability of the paste to decrease viscosity under shear force and recover viscosity after the shear force is removed. A higher TI value usually means better thixotropy, which helps the printed pattern to remain intact without sagging.

[0130] Three-step thixotropic recovery test: This test simulates the structural damage and recovery process of the grout before and after construction. The specific steps are: 1) Low shear stage: at 0.5 s -1 1) Maintain a shear rate of 120 seconds to simulate storage. 2) High shear phase: Rapidly increase the shear rate to 50 s. -1 And hold for 60 seconds to simulate the shearing process during printing. 3) Recovery phase: Immediately reduce the shear rate back to 0.5 s. -1 The viscosity was monitored for 300 seconds as it recovered over time. 4) Data output: Record the viscosity recovery rate at 60 seconds, 120 seconds, and 180 seconds. By fitting the recovery curve, the time required for the viscosity to recover to half of the final equilibrium value can be calculated, i.e., the recovery half-life (t). 1 / 2 ).

[0131] (3) Data reporting and quality control: Three samples were tested in each group, and the average value of the results was taken, as shown in Table 1.

[0132] Table 1. Viscosity and thixotropic property test results

[0133]

[0134] Test Example 2

[0135] Flexible electronic materials were prepared by printing the silver pastes used in the various embodiments and comparative examples, and the volume resistivity, tensile electrical properties, adhesion and sweat electromigration properties of the prepared flexible electronic materials were tested.

[0136] The specific conditions for printing are as follows:

[0137] 300 mesh screen, 65° squeegee angle; pre-dry at 40 ℃ for 5 min after printing, then cure at 130 ℃ for 30 min; substrate is silicone-coated TPU release film (100 μm thick, 20 dyn / cm surface tension), silicone-coated PET release film (125 μm thick, 21 dyn / cm surface tension), or silicone-coated PU release film (100 μm thick, 20 dyn / cm surface tension); coating thickness is 12-16 μm.

[0138] The specific test conditions for each performance aspect are as follows:

[0139] (1) Volume resistivity (ρ) v ): Cut 10 mm × 80 mm strip samples. The dry film thickness t was measured using a spiral thickness gauge. The resistance R (Ω) at both ends of the strip sample was measured using the end-face method with a four-wire DC system. (The last part, ρ, appears to be a typo and can be omitted.) v =R·(W·t) / L Calculate the volume conductivity (in Ω·cm) (where W=10 mm, which is the width of the strip sample; L=80 mm, which is the length of the strip sample; t is the dry film thickness, in cm). Test three samples in each group and take the average value of the results, as shown in Table 2.

[0140] (2) Tensile electrical properties: Gauge length L0 = 50 mm (i.e., the initial effective length after specimen clamping and before tensile testing). The strain was applied to the tensile test table at a speed of 50 mm / min to the set strain (20% or 40%), held for 60 s each time, and the resistance R was collected in real time using a digital source meter. t (1 Hz), with ΔR / R0 = (R t -R0) / R0×100% (R0 is the steady-state resistance after 0% strain and resting for 5 min, R t Calculate the rate of change of resistance (ΔR / R0) when the strain is 20% or 40% in a single cycle (resistance at strain t). The cyclic conditions are: 20% strain, triangular wave, 0.5 Hz, 1000 cycles, and record ΔR / R0 at the end of the cycle. Three samples are tested in each group, and the average value of the results is taken, as shown in Table 3.

[0141] (3) Adhesion (refer to Method B in ASTM D3359): Make 6×6 intersecting grids with a spacing of 1 mm on the coating (cut to the substrate but do not damage the substrate), and clean off the dust; take 3 M 600 tape (25 mm wide), cut a section about 75 mm long, and press it evenly with a rubber roller 5 times. After 60 seconds, peel it off at 180° and 300 mm / min; rate it according to 0B-5B and take photos for archiving; test three samples in each group, and take the average value of the results, as shown in Table 4.

[0142] (4) Sweat electromigration: Artificial sweat (0.9 wt% NaCl + 5 g / L lactic acid + 1 g / L urea) was used at a constant temperature of 40 ℃. 10 mm × 80 mm strip samples were cut and placed in the constant temperature chamber. A 1.0 mm gap was formed between the two electrodes (two metal electrodes pressed onto the same printed silver strip), and 50 μL of artificial sweat was added to cover the gap (a thin film was applied to prevent evaporation, and the liquid was replenished as needed). A DC field strength of E = 20 V / mm was applied, and the resistance drift ΔR / R0 was recorded continuously for 168 h (sampling at 1 Hz, averaged hourly). After the test, dendrites were examined using a scanning electron microscope (SEM), and the dendrite detection rate was statistically analyzed. Three samples were tested in each group, and the average results were taken, as shown in Table 5.

[0143] Table 2. Volume resistivity test results

[0144]

[0145] Table 3 Tensile electrical property test results

[0146]

[0147] Table 4 Adhesion Test Results

[0148]

[0149] Table 5 Results of sweat electromigration performance test

[0150]

[0151] As shown in Tables 1-5, the silver pastes prepared in Examples 1-6 have better performance than those in Comparative Examples 1-6.

[0152] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. An electrically conductive silver paste for e-skin, characterized by, The raw materials include the following components in mass fraction: flaky silver powder 60-75 parts, silver nanoparticles 0.5-5 parts, thermoplastic polyurethane elastomer 4-10 parts, acrylic elastomer 1-5 parts, PEDOT:PSS microgel dispersion 0.3-2 parts, (3-glycidylpropoxy)trimethoxysilane 0.1-1 part, polydiallyldimethylammonium chloride 0.1-1 part, hexanedial modified dopamine copolymer 0.1-1 part, (3-aminopropyl)triethoxysilane 0.1-1 part, methacryloyloxypropyltrimethoxysilane 0.05-0.5 part, cellulose ester 0.3-1.5 part, modified polyurea thixotropic agent 0.1-1 part, hydrogenated castor oil 0.05-0.5 part, ethylene glycol ethyl ether acetate 8-25 parts, dibasic acid ester 2-10 parts, leveling agent 0-1 part, and water 0.1-1 part, wherein the mass fraction of the leveling agent is not 0.

2. The e-skin oriented conductive silver paste of claim 1, wherein, The flaky silver powder has a thickness of 0.1-0.3 μm and an aspect ratio of ≥15.

3. The e-skin oriented conductive silver paste of claim 1, wherein, The silver nanoparticles have a D50 of 30-70 nm. 50 30-70 nm.

4. The e-skin oriented conductive silver paste of claim 1, wherein, The dibasic acid ester includes DBE-9.

5. The e-skin oriented conductive silver paste of claim 1, wherein, The preparation steps of the PEDOT:PSS microgel dispersion include: mixing PEDOT:PSS aqueous dispersion with acetone, stirring, centrifuging to obtain precipitate 1; mixing the precipitate 1 with isopropyl alcohol, stirring, centrifuging, drying to obtain precipitate 2; mixing the precipitate 2 with dimethyl sulfoxide, ultrasonicating in an ice water bath for 5-10 min, then stirring for 1-2 h, and then standing to remove bubbles to obtain the PEDOT:PSS microgel dispersion.

6. The e-skin oriented conductive silver paste of claim 5, wherein, The volume ratio of the PEDOT:PSS aqueous dispersion to the acetone is 1:10-12. And / or, the solid content of PEDOT:PSS in the PEDOT:PSS microgel dispersion is 0.3-1.5 wt%.

7. The e-skin oriented conductive silver paste of claim 1, wherein, The preparation steps of the hexanedial modified dopamine copolymer include: mixing dopamine hydrochloride aqueous solution with hexanedial aqueous solution, and adjusting the pH of the mixed solution to 8-9 with sodium bicarbonate buffer, and then reacting at 20-35 ℃ for 2-12 h to obtain the hexanedial modified dopamine copolymer.

8. A method of preparing the e-skin oriented conductive silver paste according to any one of claims 1-7, characterized by, The steps include: Dissolving polydiallyldimethylammonium chloride in water, mixing the obtained polydiallyldimethylammonium chloride aqueous solution with the PEDOT:PSS microgel dispersion, adjusting the pH value to 6-7 and adding (3-glycidylpropoxy)trimethoxysilane after stirring for 30-60 min, and heating for 0.5-2 h to obtain mixture 1; Mixing ethylene glycol ethyl ether acetate, dibasic acid ester, thermoplastic polyurethane elastomer, acrylic elastomer, hexanedial modified dopamine copolymer, (3-aminopropyl)triethoxysilane, methacryloyloxypropyltrimethoxysilane, cellulose ester, modified polyurea thixotropic agent, and hydrogenated castor oil to obtain mixture 2; Adding flaky silver powder and silver nanoparticles to the mixture 2, and shearing at low speed for 20-40 min to obtain mixture 3; To the mixture 3, the mixture 1 was added, stirred for 20-30 min, then a leveling agent was added, ground to D 90 <12 μm After vacuum degassing, filtration, the conductive silver paste facing the electronic skin was obtained.

9. The method of claim 8, wherein the conductive silver paste for an e-skin is prepared by mixing silver powder, glass frit, and an organic vehicle, and then performing a drying process and a sintering process. The mixing of the ethylene glycol ether acetate, dibasic acid ester, thermoplastic polyurethane elastomer, acrylic elastomer, adipic aldehyde modified dopamine copolymer, (3-aminopropyl) triethoxysilane, methacryloyloxypropyl trimethoxysilane, cellulose ester, modified polyurea thixotropic agent, hydrogenated castor oil mixture comprises: mixing ethylene glycol ether acetate and dibasic acid ester to obtain a mixed solvent; adding thermoplastic polyurethane elastomer, acrylic elastomer, cellulose ester, modified polyurea thixotropic agent, hydrogenated castor oil, (3-aminopropyl) triethoxysilane and methacryloyloxypropyl trimethoxysilane in the mixed solvent, stirring for 15-30 min; then adding adipic aldehyde modified dopamine copolymer, continuing to stir for 5-10 min to obtain the mixture 2.

10. Use of the electronic skin-oriented conductive silver paste according to any one of claims 1-7 in the preparation of an electronic skin.

Images