Liquid metal particle based electrically conductive ink resistant to mechanical wear and method of making the same

Abstract

The application belongs to the field of electronic materials, and provides a kind of mechanically wear-resistant liquid metal particle-based conductive ink and its preparation method, the conductive ink includes: liquid metal particles, hot melt polymer particles and polymer solution;The polymer solution includes organic solvent and functional additives, and the liquid metal particles and hot melt polymer particles are dispersed in the polymer solution, and the polymer particles are not dissolved in the polymer solution.The application also provides a preparation method for preparing mechanically wear-resistant flexible stretchable conductor from the conductive ink.The application adds hot melt polymer particles in the ink, since the hot melt polymer is dispersed in the ink rather than directly dissolved in the ink, during the hot pressing process, a local protective network will be formed between the hot melt polymer particles rather than a dense polymer film, which can effectively improve the mechanical wear resistance of the flexible stretchable conductor, and at the same time, the excellent conductivity and stretchability of the flexible stretchable conductor will not be sacrificed.

Description

Technical Field

[0001] This invention belongs to the field of electronic materials, specifically relating to a conductive ink based on liquid metal particles that resists mechanical wear and its preparation method. Background Technology

[0002] Flexible and stretchable electronics technology has enormous application potential in the field of human health, and in recent years, it has made significant progress. The key to flexible and stretchable electronics lies in the fabrication of elastic conductors. Currently, there are generally two methods for fabricating elastic conductors. One method involves designing the structure of the interconnecting wires in electronic devices, making them flexible so that when the electronic device is deformed by external forces, the bent interconnecting wires can counteract the deformation like a spring. The other method uses flexible and stretchable conductive materials as the flexible wires in electronic devices, such as carbon nanomaterials, metal nanomaterials, and liquid metals. Liquid metals are particularly noteworthy for their excellent conductivity, strong deformability, relatively low cost, and biocompatibility. However, liquid metals have a large surface energy, making it difficult to wet the material surface, thus hindering printing and printing. Furthermore, liquid metals are liquid at room temperature, exhibiting extremely poor resistance to mechanical wear; even slight scratches can cause circuits made of liquid metals to fail without encapsulation.

[0003] Existing technical solutions:

[0004] Liquid metal refers to metals with low melting points that are liquid at room temperature. It possesses the electrical conductivity of metals and the deformability of liquids, making it an ideal material for fabricating flexible and stretchable electronics. In flexible and stretchable electronics, liquid metal is often used as a conductor material, acting as a flexible and stretchable conductor to connect various electronic devices, thus giving electronic instruments flexibility and stretchability. Flexible and stretchable conductors can be fabricated by printing liquid metal. Existing methods for printing liquid metal mainly include direct printing, liquid metal injection, and liquid metal particle printing. Direct printing involves directly printing liquid metal onto the surface of a substrate material that can be wetted by the liquid metal using inkjet printing, spraying, handwriting, or other methods. Liquid metal injection involves injecting liquid metal into microchannels to form conductive patterns. This method generally uses microfluidic chip fabrication methods to create channels with different patterns, and then injects liquid metal into the hollow channels using a syringe to form the patterns. Liquid metal particle printing involves converting liquid metal into liquid metal particles, dispersing them in an organic polymer solution to create ink, and then using inkjet printing, spraying, handwriting, or other methods to print the liquid metal onto most substrates. Finally, physical sintering or high-temperature sintering methods are used to make the liquid metal conductive.

[0005] However, because liquid metal is liquid at room temperature and has fluidity, the flexible and stretchable liquid metal conductors prepared by the above methods have poor adhesion to the substrate. They will flow when in contact with other surfaces and are easily rubbed off the substrate during mechanical friction, leading to open-circuit failure. Therefore, although flexible and stretchable liquid metal conductors have excellent conductivity and stretchability, their surface is very fragile, and even slight mechanical friction upon contact with other objects can cause them to fail.

[0006] In liquid metal particle printing, the adhesion performance of liquid metal conductors can be improved to some extent by dissolving a large amount of polymer additives into the liquid metal particle paste. However, dissolving a large amount of polymer additives into the liquid metal paste will seriously affect the conductivity of the liquid metal conductor. This is because after the solvent evaporates, the polymer additives dissolved in the organic solvent will precipitate out and form a dense polymer film on the surface of the liquid metal particles, which will seriously affect the connection between the liquid metal particles, thereby causing a serious decrease in the conductivity of the liquid metal conductor.

[0007] To address these issues, this invention proposes a conductive ink based on liquid metal particles. This ink disperses liquid metal particles and thermoplastic polymer particles. Upon hot pressing, the thermoplastic polymer particles deform, melt, and adhere to the liquid metal surface. On one hand, the thermoplastic polymer adhering to the liquid metal particle surface increases the adhesion between the liquid metal particles and the substrate. On the other hand, the thermoplastic polymer adhering to the liquid metal particle surface forms a polymer network, effectively protecting the liquid metal and significantly improving its resistance to mechanical wear. Since the thermoplastic polymer is dispersed in the ink rather than directly dissolved in it, it does not form a continuous and dense film that would affect the ink's conductivity. Its typical advantages are as follows: the liquid metal conductor printed with this ink possesses both extremely high stretchability and conductivity, excellent adhesion and resistance to mechanical wear, and is easy and quick to print on most substrate materials. Summary of the Invention

[0008] The purpose of this invention is to provide a conductive ink based on liquid metal particles, its preparation method and application, overcoming the technical problems of poor adhesion and poor resistance to mechanical wear of liquid metal conductors in the prior art.

[0009] To achieve the above objectives, a first aspect of the present invention provides a conductive ink based on liquid metal particles that resists mechanical wear, the conductive ink comprising: liquid metal, hot-melt polymer particles, and a polymer solution, wherein the polymer solution comprises an organic solvent and functional additives;

[0010] Furthermore, the mass fractions of each component in the ink are as follows: liquid metal 50%-85%, hot-melt polymer particles 2%-15%, organic solvents 20%-50%, and functional additives 0.2%-2%.

[0011] The liquid metal is selected from one or more of the following: elemental gallium, gallium-indium alloy, gallium-zinc alloy, gallium-tin alloy, gallium-indium-tin alloy, gallium-indium-zinc alloy, bismuth-tin alloy, and bismuth-tin-lead-indium alloy; preferably, the liquid metal is selected from one or more of the following: gallium, gallium-indium alloy, gallium-zinc alloy, and gallium-indium-tin alloy.

[0012] The melting point of the hot-melt polymer material is 50 to 300 degrees Celsius, and it is selected from one or more of the following: styrene-based thermoplastic elastomer particles, ethylene-vinyl acetate copolymer particles, thermoplastic polyurethane particles, polyvinyl alcohol particles, hydrogenated styrene-butadiene block copolymer particles, polycarbonate particles, and polystyrene-based elastic particles.

[0013] The organic solvent is selected from one or more of the following: ethanol, propanol, isopropanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, ethanol acetate, diethyl ethylene glycol, acetone, N,N-dimethylformamide, dipropylene glycol methyl ether acetate, and propylene glycol methyl ether acetate.

[0014] The functional additives, such as surfactants, thickeners, thixotropic agents, and anti-settling agents, are selected from one or more of the following: fluorocarbon surfactants, chitosan, sodium dodecylbenzene sulfonate, hydroxyethyl cellulose, polyvinylpyrrolidone, polyacrylic acid, polylactic acid-glycolic acid copolymer, polycaprolactone, polyoxyethylene, polyacrylamide polyurethane, polyamide rheology modifiers, organobentonite, diatomaceous earth, amide wax thixotropic agents, and fatty acid amine waxes.

[0015] A second aspect of the present invention provides a method for preparing the conductive ink described in the first aspect, the method comprising the following steps:

[0016] (1) Add functional additives such as surfactants, thickeners, thixotropic agents, and antisettling agents to an organic solvent, heat and stir to dissolve them fully into a homogeneous solution, and cool to room temperature for later use; the heating temperature is 40-90℃ and the stirring time is 0.5-24h.

[0017] (2) The liquid metal is added to the above polymer solution, and the liquid metal is pulverized into liquid metal particles by means of ultrasound, cutting, grinding, high-speed mixing, etc., and dispersed in the solution to form a paste-like slurry. The average diameter of the liquid metal particles is selected in the range of 20 nanometers to 20 micrometers.

[0018] (3) The hot-melt polymer particles are refined using instruments such as ultrafine pulverizers, colloid mills, and cell wall breakers to produce particles of 100 nanometers to 50 micrometers.

[0019] (4) Add the hot-melt polymer particles to the slurry and disperse the particles fully in the slurry by stirring, ultrasonication, or high-speed rotational shearing. The conductive ink of the present invention creatively introduces hot-melt polymer particles into the ink. During the subsequent hot pressing process, the hot-melt polymer particles in the ink deform and melt, adhering to the surface of the liquid metal. This increases the adhesion between the liquid metal particles and the substrate, conducts stress between the liquid metal particles and the substrate, and makes the strain sintering process possible. Furthermore, the hot-melt polymer adhering to the surface of the liquid metal particles can form an effective protective network without forming a continuous and dense film that would affect the conductivity of the ink. This can effectively increase the resistance of the liquid metal to mechanical wear.

[0020] A third aspect of the present invention provides a method for preparing a flexible, stretchable liquid metal conductor resistant to mechanical wear, wherein the conductor is drawn using conductive ink according to the first aspect of the present invention, and the preparation method includes the following steps:

[0021] (a) Preparation of conductive ink: Conductive ink is prepared according to the method of the first aspect of the present invention;

[0022] (b) Ink Printing: The desired two-dimensional pattern is printed directly onto an elastic substrate without strain using prepared ink, or the elastic substrate is first subjected to a pre-tension strain of 20%-100%, and then the prepared ink is printed onto the pre-strained substrate. After printing, the substrate is dried at room temperature or in an oven to allow the organic solvents to evaporate. The printing methods include, but are not limited to, hand-drawing, stencil printing, spraying, screen printing, inkjet printing, etc.

[0023] (c) Ink after hot-press printing. After the printed ink dries, it is hot-pressed using equipment such as a hot press, heat transfer machine, and electric iron. The hot-pressing temperature is 80-250 degrees Celsius, and the duration is 10-180 seconds. This invention creatively introduces hot pressing into the ink processing to deform and melt the thermoplastic polymer particles in the ink, allowing them to adhere to the surface of liquid metal. This increases the adhesion between the liquid metal particles and the substrate, conducts stress between the liquid metal particles and the substrate, making strain sintering possible. Furthermore, the thermoplastic polymers adhering to the surface of the liquid metal particles form an effective protective network without forming a continuous and dense film that would affect the ink's electrical properties and stretchability. This effectively increases the resistance of the liquid metal to mechanical wear.

[0024] (d) Strain Sintering. After hot pressing printing, the printed ink is not conductive because the insulating oxide film on the surface of the liquid metal particles is not destroyed, and no conductive path is formed between the particles. To break the insulating oxide film of the liquid metal particles and form a conductive path between them, strain sintering is required on the printed ink, i.e., applying tensile or compressive strain to the elastic substrate with the printed ink. For elastic substrates without strain applied during the printing step, applying 20%-100% tensile strain to the substrate is sufficient to make the printed liquid metal ink on the substrate immediately conductive, thus completing the strain sintering process. After removing the strain, the printed liquid metal ink on the substrate remains conductive. The printed liquid metal ink thus acquires excellent stretchability and can maintain conductivity even under large deformations. For substrates with a pre-tension strain of 20%-100% applied during the printing step, simply removing the applied pre-tension strain, i.e., applying a corresponding compressive strain to the pre-stretched substrate, will make the printed liquid metal ink on the substrate immediately conductive, thus completing the strain sintering process. The printed liquid metal ink has excellent stretchability and can still maintain conductivity under large deformation.

[0025] This invention provides a conductive ink based on liquid metal particles that is resistant to mechanical wear and a method for preparing a flexible, stretchable liquid metal conductor. This invention solves the problems of poor adhesion and poor resistance to mechanical wear of liquid metal conductors, while retaining their high conductivity and high stretchability. This invention provides a stable and reliable solution for wearable devices, human-machine interfaces, flexible and stretchable displays, soft robots, smart skin, electronic tattoos, flexible semiconductors, and electronic devices combined with tissue engineering.

[0026] The conductive ink based on liquid metal particles of the present invention may have, but is not limited to, the following beneficial effects:

[0027] 1. This invention improves the resistance to mechanical wear of liquid metal while maintaining its excellent stretchability. In this invention, thermoplastic polymer particles are added to the ink, rather than being directly dissolved in the ink. This is because if the same mass fraction of thermoplastic polymer is directly dissolved in the ink, after printing, the polymer precipitates from the organic solvent, forming a continuous and dense polymer film on the surface of the liquid metal particles. While this continuous and dense polymer film can increase the resistance to mechanical wear of the liquid metal elastic conductor, it causes the liquid metal elastic conductor to lose its excellent stretchability. Furthermore, it hinders the contact between liquid metal particles, affecting the conductivity of the liquid metal elastic conductor. This invention adds thermoplastic polymer particles to the ink. These particles form a local network after hot pressing, rather than a dense and continuous polymer film. Therefore, while increasing the resistance to mechanical wear of the liquid metal elastic conductor, its excellent conductivity and stretchability are not sacrificed.

[0028] 2. This invention is suitable for printing on most substrates. This invention employs a method of printing liquid metal particles, which, compared to directly printing liquid metal, eliminates the enormous surface energy of the liquid metal. Furthermore, the organic solvents and functional additives in the liquid metal ink of this invention can be adjusted according to the type of printing substrate, making it suitable for printing on most material substrates and thus having a wider range of applications.

[0029] 3. This invention provides a highly efficient sintering method. The strain sintering method of this invention can instantly sinter the liquid metal particles on the substrate by directly applying strain to the substrate printed with liquid metal ink, causing the liquid metal particles to break and form conductive paths between them. Compared with the method of directly touching the liquid metal particles with a pen tip or needle tip, this method is simpler and more efficient, and there is no waste of liquid metal. Attached Figure Description

[0030] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0031] Figure 1 The composition of a conductive ink based on liquid metal particles that resists mechanical wear and the fabrication process of a flexible, stretchable liquid metal conductor are shown.

[0032] Figure 2 The resistivity change rate of a liquid metal flexible stretchable conductor prepared from a conductive ink based on liquid metal particles and resistant to mechanical wear is shown as a function of strain applied to it.

[0033] Figure 3 The diagram illustrates the change in resistance rate of a liquid metal flexible stretchable conductor during 1000 cyclic stretching cycles (with strain varying between 0% and 50%).

[0034] Figure 4 The diagram illustrates the relationship between the rate of change of resistance and the wear test time in the case of the liquid metal flexible stretchable conductor in Example 1 and the liquid metal flexible stretchable conductor (without the addition of hot-melt polymer particles) in Example 5. Detailed Implementation

[0035] The present invention will be further illustrated below with specific embodiments. However, it should be understood that these embodiments are merely for more detailed and specific illustration and should not be construed as limiting the present invention in any way.

[0036] This section provides a general description of the materials and testing methods used in the experiments of this invention. While many of the materials and methods of operation used to achieve the objectives of this invention are well known in the art, the invention is still described in as much detail as possible herein. It will be apparent to those skilled in the art that, unless otherwise stated in the context, the materials and methods of operation used in this invention are well known in the art.

[0037] The reagents and instruments used in the following examples are as follows:

[0038] Reagents:

[0039] Thermoplastic polyurethane granules (TPU Elastollan 1185A) were purchased from BASF; polyvinylpyrrolidone (average molecular weight 1,300,000), organobentonite, polylactic acid (PLA), Tween 20, N-(2-hydroxyethyl)dodecylamide, and chitosan were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; polyurethane elastomer film was purchased from Dongsheng Plastics Factory; fluorocarbon surfactant (FS-30) was purchased from Shanghai Jianbang Industrial Co., Ltd.; liquid gallium indium alloy, ethylene-vinyl acetate copolymer granules, hydroxyethyl cellulose, hexafluoroisopropanol, diethyl ethylene glycol, and pentanol were purchased from Sigma Aldrich. Polydimethylsiloxane prepolymer and its curing agent (Sylgard 184) were purchased from Dow Corning. Ecoflex 0030 silicone was purchased from Smooth-On, Inc. (USA). Waterborne polyurethane (Archsol 8560) was purchased from Wanhua Chemical Group Co., Ltd. The thermoplastic polyurethane (TPU 65A) was purchased from Dongguan Xinxin Plastic Raw Materials Co., Ltd.

[0040] instrument:

[0041] The following equipment was purchased: an oven (DHG-9030A) from Shanghai Pudong Rongfeng Scientific Instruments Co., Ltd.; an ultrasonic cell disruptor (S-450D) from BNEN SINGAPORE Ultrasonic Co., Ltd.; a manual screen printing table (23*30cm) from Guangzhou Junyu Screen Printing Equipment Co., Ltd.; a precision multimeter (8846A) from Fluke Electronic Instruments Co., Ltd.; an RCA tape abrasion tester (ST) from Lugong Precision Instruments Co., Ltd.; a programmable guide rail (FSK40) from Chengdu Fuyu Technology Co., Ltd.; an ultrafine pulverizer (ACW135) from Auari Electric Appliances; a hot press (G311) from Freamc Digital Technology; a high-speed disperser (YKFS-680) from Yakoo Electromechanical Co., Ltd.; and a dynamic mechanical analyzer (DMA Q800).

[0042] Example 1

[0043] This embodiment illustrates a method for preparing a liquid metal elastic conductor.

[0044] Liquid gallium-indium alloy (Ga 75.5%wt, In 24.5%wt), thermoplastic polyurethane particles (3000 mesh), polyvinylpyrrolidone, and organobentonite were added to an ethanol solution, wherein the mass fraction of liquid gallium-indium alloy was 70%, the mass fraction of thermoplastic polyurethane particles was 5%, the mass fraction of polyvinylpyrrolidone was 1%, the mass fraction of organobentonite was 2%, and the mass fraction of ethanol was 22%. This mixture was added to a high-speed disperser and stirred at 5000 rpm for 24 hours, then stirred at 15000 rpm for 30 minutes to obtain a uniform liquid metallic ink. The ink was printed onto a polyurethane elastomer film using screen printing technology. The printed substrate was then placed in a constant temperature drying environment at 80°C for 10 minutes to allow the ink to dry completely. After drying, the ink was treated with a hot press at approximately 150°C for 30 seconds. After hot pressing and cooling, the printed liquid metallic ink on the film was not conductive. After completing the strain sintering process, the printed ink becomes conductive. Applying a 50% tensile strain to the polyurethane film printed with the ink immediately makes the liquid metal on the polyurethane film conductive. It remains conductive after returning to its original length, with a conductivity of 9200 S / cm and a maximum conductive tensile strength of 800%. It loses its conductivity after 560 seconds using an RCA abrasion tester (175g load).

[0045] Example 2

[0046] This embodiment illustrates a method for preparing a liquid metal elastic conductor.

[0047] Liquid gallium-zinc alloy (Ga 95% wt, iZn 5% wt) was added to ethanol and ultrasonically disrupted at 30% amplitude for 30 seconds using an ultrasonic cell disruptor to form liquid metal particles. After standing for 10 minutes, the particles precipitated, and the ethanol solution was removed, leaving the liquid metal particles for later use. Ethylene-vinyl acetate copolymer particles were processed using an ultrafine pulverizer to produce 3000-mesh particles for later use. The liquid metal particles and ethylene-vinyl acetate copolymer particles were added to a diethyl glycol solution, along with hydroxyethyl cellulose and fatty acid amine wax. The mass fractions of the liquid metal particles were 60%, the ethylene-vinyl acetate copolymer particles 10%, the organic solvent 27%, the hydroxyethyl cellulose 1%, the fatty acid amine wax 1%, and the fluorocarbon surfactant 1%. The mixture was stirred for 24 hours to prepare ink. The ink was printed onto a silicone film using stencil printing technology. The printed substrate was then placed in a constant temperature drying oven at 80 degrees Celsius for 10 minutes to allow the ink to dry completely. After the ink dries, an electric iron is used to press the printed ink at approximately 100 degrees Celsius for 30 seconds. After hot pressing and cooling, the printed liquid metal ink on the film is not conductive. Completing the strain sintering process makes the printed ink conductive; that is, applying a 20% tensile strain to the silicone film printed with the ink immediately makes the liquid metal in the silicone film conductive. It remains conductive after returning to its original length, with a conductivity of 8300 S / cm and a maximum conductive tensile strength of 1000%. It loses its conductivity after 580 seconds using an RCA abrasion tester (175g load).

[0048] Example 3

[0049] The ink preparation method in this embodiment is the same as in Example 1. Before printing, a 30% pre-stretch strain is applied to the polyurethane elastomer film, and then the ink is printed onto the pre-stretched polyurethane elastomer film using screen printing technology. After the same drying and hot-pressing process as in Example 1, the liquid metal ink printed on the pre-stretched polyurethane elastomer film is not conductive. By removing the pre-stretch applied to the polyurethane elastomer film, the liquid metal ink printed on the polyurethane elastomer film immediately becomes conductive, with a conductivity of 10100 S / cm and a maximum conductive stretchability of 900%. It loses its conductivity after 620 seconds of testing with an RCA abrasion tester (175g load).

[0050] Example 4

[0051] This embodiment illustrates a method for preparing a liquid metal elastic conductor.

[0052] Liquid gallium-indium alloy (Ga 75.5% wt, In 24.5% wt) and thermoplastic polyurethane particles (3000 mesh) were added to a pentanol solution, wherein the mass fraction of liquid gallium-indium alloy was 75%, the mass fraction of thermoplastic polyurethane particles was 8%, and the mass fraction of pentanol was 17%. The above mixture was treated with a cell disruptor at 30% amplitude for 10 minutes to obtain a uniform liquid metallic ink. The ink was printed onto a polyurethane elastomer film using stencil printing technology. The printed substrate was then placed in a constant temperature drying oven at 80°C for 10 minutes to allow the ink to dry completely. After drying, the ink was treated with a hot press at approximately 150°C for 30 seconds. After hot pressing and cooling, the printed liquid metallic ink on the film was not conductive. After completing the strain sintering process, the printed ink becomes conductive. Applying a 50% tensile strain to the polyurethane film printed with the ink immediately makes the liquid metal on the film conductive. It remains conductive after returning to its original length, with a conductivity of 11000 S / cm and a maximum conductive tensile strength of 900%. It loses its conductivity after 470 seconds using an RCA abrasion tester (175g load).

[0053] Example 5

[0054] This example illustrates that liquid metal flexible stretchable conductors without the addition of thermoplastic polymer particles are not resistant to mechanical wear.

[0055] Liquid gallium-indium alloy (Ga 75.5% wt, In 24.5% wt), polyvinylpyrrolidone, and organobentonite were added to an ethanol solution, wherein the mass fraction of liquid gallium-indium alloy was 70%, the mass fraction of polyvinylpyrrolidone was 1%, the mass fraction of organobentonite was 2%, and the mass fraction of ethanol was 27%. The mixture was then added to a high-speed disperser and stirred at 5000 rpm for 24 hours, followed by stirring at 15000 rpm for 30 minutes to obtain a uniform liquid metal ink. The ink was then screen-printed onto a polyurethane elastomer film. The printed substrate was then placed in a constant temperature drying environment at 80°C for 10 minutes to allow the ink to dry completely. After drying, the printed liquid metal ink on the film was non-conductive. Once the strain sintering process is completed, the printed ink can become conductive. That is, when a 50% tensile strain is applied to the polyurethane film printed with ink, the liquid metal on the polyurethane film can still become conductive immediately. After returning to its original length, it is still conductive with a conductivity of 8000 S / cm and a maximum conductive stretchability of 950%. However, the liquid metal elastic conductor is not resistant to mechanical wear. It loses its conductivity after 2 seconds of testing with an RCA wear tester (175g load).

[0056] Example 6

[0057] This embodiment illustrates that liquid metal elastic conductors prepared by directly dissolving hot-melt polymers in liquid metal ink have poor conductivity and no stretchability.

[0058] Liquid gallium-indium alloy (Ga 75.5%wt, In 24.5%wt) was added to ethanol and ultrasonically disrupted at 30% amplitude for 30 seconds using an ultrasonic cell disruptor to form liquid metal particles. After standing for 10 minutes, the particles precipitated, and the ethanol solution was removed, leaving the liquid metal particles for later use. Polyvinyl alcohol particles were processed using an ultrafine pulverizer to produce 3000-mesh particles for later use. The liquid metal particles and polyvinyl alcohol particles were added to a diethylene glycol diethyl ester solution, along with hydroxyethyl cellulose and fatty acid amine wax. The mass fractions of the liquid metal particles were 60%, polyvinyl alcohol particles 10%, organic solvent 28%, hydroxyethyl cellulose 1%, and fatty acid amine wax 1%. The mixture was stirred for 24 hours to prepare ink. The ink was printed onto a silicone film using stencil printing technology. The printed substrate was then placed in a constant temperature drying oven at 80 degrees Celsius for 10 minutes to allow the ink to dry completely. After the ink dries, it is hot-pressed at 220 degrees Celsius for 30 seconds using a heat transfer machine. After cooling, the printed liquid metal ink on the film is not conductive. Completing the strain sintering process makes the printed ink conductive; that is, applying a 20% tensile strain to the silicone film with the ink immediately makes the liquid metal in the silicone film conductive. It remains conductive after returning to its original length, with a conductivity of 9400 S / cm and a maximum conductive tensile strength of 1000%. It loses its conductivity after 530 seconds using an RCA abrasion tester (175g load).

[0059] Example 7

[0060] This embodiment illustrates that liquid metal elastic conductors prepared by directly dissolving hot-melt polymers in liquid metal ink have poor conductivity and no stretchability.

[0061] The difference between this embodiment and Example 6 is that the diethylene glycol diethyl ester solution is replaced with a hexafluoroisopropanol solution. Polyvinyl alcohol particles are insoluble in diethylene glycol diethyl ester solution but can dissolve in hexafluoroisopropanol solution. The liquid metallic elastic conductor prepared using this method has a conductivity of 20 S / cm and a maximum conductive tensile strength of 15%. It loses its conductivity after 320 seconds of testing with an RCA abrasion tester (175g load).

[0062] Experimental Example 1

[0063] This experimental example illustrates the change in resistance rate with tensile deformation after the pattern printed with the ink of this invention becomes conductive, and explores the maximum strain it can withstand. The inventors used the method of Example 1 to print a 50 mm long and 2 mm wide liquid metal elastic conductor on a polyurethane elastomer film. Then, using a linear guide rail, the liquid metal elastic conductor was stretched from its original length to a deformation of 800%. The resistance change during the stretching process was recorded using a precision multimeter, and the result was converted into a resistance rate, as shown below. Figure 2 The graph shown illustrates the relationship between electrical conductivity and tensile deformation. This graph demonstrates the exceptional tensile properties of conductive patterns.

[0064] Experimental Example 2

[0065] This experimental example illustrates the change in resistance rate of the liquid metal elastic conductor of the present invention during cyclic stretching with the number of stretching cycles at a 50% stretching deformation. The inventors used the method of Example 1 to print a 50 mm long and 2 mm wide liquid metal elastic conductor on the surface of a polyurethane film, and then stretched the liquid metal elastic conductor using a linear guide. Using the linear guide, the liquid metal elastic conductor was stretched from 0% deformation to 50% deformation at a speed of 10 mm / s along its length, and then returned to 0% at the same speed. This cycle was repeated 1000 times. During the stretching process, the resistance change of the liquid metal elastic conductor was measured in real time using an electrochemical workstation, and the resistance change rate could be obtained through calculation. Figure 3 As shown in the figure, this diagram illustrates the excellent fatigue resistance of liquid metal elastic conductors.

[0066] Experimental Example 3

[0067] This test example illustrates the mechanical wear resistance of the liquid metal elastic conductor of the present invention. The inventors printed a 50 mm long and 2 mm wide liquid metal elastic conductor on a polyurethane elastomer film using the method of Example 1. We used an RCA abrasion tester to apply a 175 g load to the paper tape to perform abrasion tests on the liquid metal elastic conductor. Simultaneously, we used an electrochemical workstation to measure the resistance of the liquid metal elastic conductor in real time. When the recorded rate of change of resistance approached infinity, it indicated that the liquid metal elastic conductor had failed due to wear. The liquid metal elastic conductor in Example 1 lost conductivity after 560 seconds of testing with the RCA abrasion tester (175 g load), while in Example 5, it lost conductivity after only 2 seconds of testing with the RCA abrasion tester (175 g load). Figure 4 As shown, the addition of thermoplastic polymer particles can greatly enhance the mechanical wear resistance of liquid metal elastomers.

Claims

1. A conductive ink based on liquid metal particles that resists mechanical wear, characterized in that, It is composed of liquid metal particles, thermoplastic polymer particles, and a polymer solution. The liquid metal particles and thermoplastic polymer particles are dispersed in the polymer solution, while the thermoplastic polymer particles are insoluble in the polymer solution. The thermoplastic polymer particles will deform and melt after hot pressing. The polymer solution includes organic solvents and functional additives. The mass percentages of each component in the ink are as follows: liquid metal particles 50%–85%, hot-melt polymer particles 2%–15%, organic solvents 20%–50%, and functional additives 0.2%–2%, with the sum of the mass percentages of all components in the ink being 100%. The hot-melt polymer particles have a melting point of 50 to 300 degrees Celsius and are selected from one or more of the following: styrene-based thermoplastic elastomer particles, ethylene-vinyl acetate copolymer particles, thermoplastic polyurethane particles, polyvinyl alcohol particles, and polycarbonate particles; the diameter of the hot-melt polymer particles is 100 nanometers to 50 micrometers. The organic solvent is selected from one or more of the following: ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, diethyl ethylene glycol, acetone, N,N-dimethylformamide, dipropylene glycol methyl ether acetate, and propylene glycol methyl ether acetate. The functional additives are selected from one or more of the following: fluorocarbon surfactants, chitosan, sodium dodecylbenzenesulfonate, hydroxyethyl cellulose, polyvinylpyrrolidone, polyacrylic acid, polylactic acid-glycolic acid copolymer, polycaprolactone, polyoxyethylene, polyamide rheology modifiers, organobentonite, diatomaceous earth, amide wax thixotropic agents, and fatty acid amine waxes.

2. The conductive ink according to claim 1, characterized in that, The liquid metal particles are made of one or more of the following materials: elemental gallium, gallium-indium alloy, gallium-zinc alloy, gallium-tin alloy, gallium-indium-tin alloy, gallium-indium-zinc alloy, bismuth-tin alloy, and bismuth-tin-lead-indium alloy; the diameter of the liquid metal particles is 20 nanometers to 20 micrometers.

3. The method for preparing conductive ink according to claim 1 or 2, characterized in that, The method includes the following steps: (1) Add the functional additive to an organic solvent, heat and stir to dissolve it completely into a homogeneous solution, and cool it to room temperature for later use; the heating temperature is 40-90℃, and the stirring time is 0.5-24 h. (2) Add liquid metal to the above solution, and process the liquid metal by ultrasonication, cutting, grinding or high-speed mixing until the liquid metal particles are dispersed in the solution to form a paste-like slurry; the processing time is 1 min to 2 h; (3) The hot-melt polymer particles are refined using an ultrafine pulverizer, colloid mill or cell wall breaker, and the processing time is 0.5 to 4 hours; (4) Add the refined hot-melt polymer particles to the slurry and mix them thoroughly by stirring, ultrasound or high-speed rotation shearing; the processing time is 0.5 to 12 h.

4. A flexible, stretchable liquid metal conductor resistant to mechanical wear, characterized in that, The liquid metal pattern is prepared using the conductive ink according to claim 1 or 2.

5. The method for preparing a liquid metal flexible stretchable conductor according to claim 4, characterized in that, The method includes the following steps: (a) Preparation of conductive ink: preparing conductive ink according to the method of claim 3; (b) Ink printing: Using the ink prepared in step (a), printing on a substrate material without applied strain, or on a substrate material with a pre-exposed tensile strain of 20% to 100%; (c) Hot pressing: After the printed ink has dried, the printed ink is hot pressed using a hot press, heat transfer machine or electric iron. The hot-pressing temperature is 80-250 degrees Celsius, and the hot-pressing duration is 10-180 seconds; (d) Strain sintering: Apply tensile or compressive strain to the elastic substrate printed with ink; for substrates for which no strain was applied in step (b), apply 20%-100% tensile strain to make the liquid metal ink printed on the substrate immediately conductive, thus completing the strain sintering process; for substrates for which 20%-100% pre-tension strain was applied in step (b), remove the applied pre-tension strain to make the liquid metal ink printed on the substrate immediately conductive, thus completing the strain sintering process.

6. The application of the conductive ink according to claim 1 or 2 or the liquid metal flexible stretchable conductor according to claim 4 in the fabrication of electronic devices.

Images