CN106782757B - A kind of printable compliant conductive slurry and its conducting wire and preparation method - Google Patents

Abstract

The invention discloses a printable flexible conductive paste, a conductive circuit and a preparation method thereof. Specifically, the printable flexible conductive paste is made of composite conductive particles and polyorganosiloxane; wherein, the mass percentage of the composite conductive particles is 40%-85%. The composite conductive particles are particles with a diameter not higher than 20 μm, with a non-metal inner core coated with a metal surface layer. The invention uses silver-plated conductive particles to replace traditional pure metal conductive particles or carbon-based conductive fillers, which has high conductivity, low density and low cost characteristics, and is not easy to settle in polyorganosiloxane flexible polymers, and can be prepared with high conductivity Flexible conductive paste, and can be easily produced by traditional printing methods such as screen printing. The invention has the advantages of low cost, simple structure, and easy fabrication, and is suitable for emerging fields such as flexible printed circuits, flexible display screens, flexible wearable electronics, and electronic skins.

Description

A kind of printable flexible conductive paste and its conductive circuit and preparation method

technical field

The invention relates to a printable flexible conductive paste, a conductive circuit and a preparation method thereof.

Background technique

In addition to the conductive function of traditional conductive lines, flexible conductive lines also have mechanical flexibility, which can adapt to various mechanical deformations such as stretching, bending, winding, folding, and twisting. They are used in flexible printed circuits, flexible displays, flexible electronic skins, Emerging fields such as wearable electronics have important application prospects. Printing technology is one of the important methods to realize large-area, fast and efficient production of circuit patterns. The conductive paste and its conductive circuit, which integrates conductivity, flexibility and printability, are the frontier direction in the field of modern electronic material research and have attracted widespread attention.

The main components of the conductive paste are conductive filler and resin matrix. Conductive fillers include metal materials such as gold, silver, copper, and nickel, carbon-based conductive materials such as carbon black, graphite, and carbon nanotubes, and conductive fillers with metal plating on the surface, such as silver plating on copper, metal plating and polymerization on the surface of glass beads. The surface of the microsphere is coated with metal, etc. According to the packing size, it can be divided into spherical, random particles, two-dimensional sheet and one-dimensional linear packing. The different types and shapes of conductive fillers will have an important impact on the percolation threshold, conductivity, viscosity and other properties of the conductive paste. The resin matrix mainly provides mechanical and mechanical properties and bonding properties. Traditional conductive pastes usually use silver micropowder as a filler, but silver is expensive, and the amount usually needs to be more than 75wt% to obtain stable high conductivity. In order to reduce the percolation threshold of conductive fillers in the slurry, reduce the amount of fillers used and reduce costs, the patent CN 103400637 A uses dendritic silver silver with a three-dimensional dendritic metal crystal structure to replace traditional silver micropowder, and compound it with resin to obtain conductive slurry. The diameter of the three-dimensional dendrite metal crystal structure used is 0.5 μm to 50 μm, and the length of the secondary dendrite structure is 5 nm to 5 μm. The electrical performance of the prepared conductive silver paste is equivalent to that of the traditional silver paste, but the filling amount of silver is significantly reduced, which effectively reduces the cost of raw materials. However, the preparation of the three-dimensional dendritic metal silver powder itself used in this patent is difficult, the technical threshold is high, and it is difficult to produce in large quantities to meet the quantitative needs of the industry.

In order to reduce costs and meet the requirements of electrical conductivity as much as possible, the patent CN 101419851 A selects carbon-based conductive materials such as graphite powder, carbon fiber, expanded graphite, carbon black, coke, carbon nanotubes or their combinations as fillers to prepare composite conductive materials. The method uses hot pressing or kneading to form, and the process is relatively complicated. The maximum conductivity of the conductive composite material is 150-200S/cm, which is still low. In order to solve the problem that the conductive filler density is too high and easy to settle and the cost of gold, silver and precious metals is high, precious metals such as gold and silver are deposited on the surface of low-density and cheap materials to form a metal-plated core-shell structure conductive filler, which can reduce the density of the filler. It can also reduce the cost of the filler, and at the same time, it can largely retain the high conductivity characteristics of metals such as gold and silver. Patent CN 105225768 A uses silver-plated glass microspheres and silver-plated glass fibers as conductive fillers, mixes them uniformly with diluted PDMS and solidifies to obtain a flexible conductive film with a sandwich structure. This invention patent uses metal-plated materials as conductive fillers to reduce costs and increase electrical conductivity. However, the flexible conductive film with a sandwich structure cannot be used as conductive paste to make flexible conductive lines by printing.

In order to obtain a flexible conductive paste that can adapt to mechanical deformation, the invention patent CN 105702323 A uses silver nanowires as the conductive material, and hydroxyethyl methacrylate phosphate, polyurethane resin, polyvinyl butyral, solvent, defoaming A flexible conductive silver paste with excellent adhesion and bending resistance is prepared by compounding with agent, curing agent, etc. However, the price of silver nanowires used in this invention is much higher than that of conventional conductive fillers such as silver powder, and the amount used in this system is as high as 30% to 60%, which will significantly increase the cost of the flexible conductive silver paste. At the same time, the use of organic solvents in the flexible conductive silver paste will limit its use on certain substrate materials, such as organic solvents may dissolve or corrode fiber paper-based substrates.

Contents of the invention

In view of this, in order to overcome the above-mentioned defects and problems, the present invention provides a flexible conductive paste with low cost, simple structure, convenient production, solvent-free, printable, wide range of substrate application, and low temperature curing, as well as its printed circuit and preparation method. The invention selects light polymer microspheres as cores, and chemically silvers the surface to prepare low-density conductive fillers with core-shell structure. By simply mixing with PDMS prepolymer and its curing agent, the flexible conductive paste can be prepared, and the paste can be used to print films, circular circuits, etc. Various patterns, and then through the curing process, the flexible conductive circuit can be made.

One aspect of the present invention provides a printable flexible conductive paste, which is characterized in that it is made of composite conductive particles and polyorganosiloxane; Particles not higher than 20 μm;

Preferably, the conductive paste does not contain organic or inorganic solvents;

More preferably, the organic solvent is selected from acetone, methyl ethyl ketone, ethanol, methanol, isopropanol, benzene, toluene, styrene, n-hexane, cyclohexane, dichloromethane, chloroform, ether, ethylene glycol monomethyl One or more of ether, acetonitrile, pyridine, etc.;

The inorganic solvent is selected from one or more of water, liquid ammonia, sulfuric acid, nitric acid and the like.

In a specific embodiment of the present invention, the mass percentage of the composite conductive particles is 40%-85%.

In a specific embodiment of the present invention, the non-metallic core of the composite conductive particle is selected from microspheres formed by glass, ceramics, and inert polymers;

More preferably, the microspheres are selected from polystyrene microspheres (PS), polyacrylic acid microspheres (PAA), polymethyl methacrylate microspheres (PMMA), polyphenolic resin microspheres (PF), poly One or more of vinylbenzene microspheres (PDVB) or its copolymer microspheres, with a particle size of 200nm to 10μm (200nm, 400nm, 600nm, 800nm, 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm);

More preferably, the non-metallic inner core has a density of 0.6-1.5 g/cm ³ (preferably 0.8-1.2 g/cm ³ , more preferably 0.9-1.1 g/cm ³ , 1.0 g/cm ³ );

More preferably, the content of the metal surface layer on the surface of the non-metal inner core accounts for 30%-80% of the mass of the composite conductive particles.

In a specific embodiment of the present invention, the metal in the metal surface layer is selected from one or more of gold, silver, copper, nickel, aluminum, tungsten, iron, titanium, palladium, and platinum;

Preferably, the metal surface layer is plated on the surface of the non-metal inner core by chemical or physical methods;

More preferably, the metal surface is plated with at least one layer of metal; more preferably one or two layers.

In a specific embodiment of the present invention, polyorganosiloxane is made of polyorganosiloxane prepolymer and its curing agent;

Preferably, the mass ratio of the polyorganosiloxane prepolymer to the curing agent is 5:1 to 15:1;

More preferably, the polyorganosiloxane is selected from polydimethylsiloxane, cyclomethicone, aminosiloxane, polymethylphenylsiloxane, polyether polysiloxane copolymer one or more of

More preferably, the polyorganosiloxane prepolymer is selected from polydimethylsiloxane (PDMS);

More preferably, the curing agent is selected from small molecule silanes, preferably small molecule silanes with silanol and siloxy groups.

Another aspect of the present invention provides a printable flexible conductive paste composition, which is characterized in that it includes composite conductive particles, polyorganosiloxane prepolymer and curing agent thereof;

The composite conductive particles are particles with a diameter not higher than 20 μm, with a non-metallic inner core coated with a metal surface layer;

Preferably, the conductive paste does not contain organic or inorganic solvents;

More preferably, the organic solvent is selected from acetone, methyl ethyl ketone, ethanol, methanol, isopropanol, benzene, toluene, styrene, n-hexane, cyclohexane, dichloromethane, chloroform, ether, ethylene glycol monomethyl One or more of ether, acetonitrile, pyridine, etc.;

The inorganic solvent is selected from one or more of water, liquid ammonia, sulfuric acid, nitric acid and the like.

In a specific embodiment of the present invention, the mass percentage of the composite conductive particles in the printable flexible conductive paste composition is 40%-85% (preferably 40%-80%, more preferably 50%-65%).

In a specific embodiment of the present invention, the non-metallic core of the composite conductive particle is selected from microspheres formed by glass, ceramics, and inert polymers;

In a specific embodiment of the present invention, the microspheres are selected from polystyrene microspheres (PS), polyacrylic acid microspheres (PAA), polymethyl methacrylate microspheres (PMMA), polyphenolic resin microspheres (PF ), polydivinylbenzene microspheres (PDVB) or one or more of its copolymer microspheres, the particle size of which is 200nm～10μm;

In a specific embodiment of the present invention, the non-metallic inner core has a density of 0.6-1.5 g/cm ³ (preferably 0.8-1.2 g/cm ³ , more preferably 0.9-1.1 g/cm ³ , more preferably 1.0 g /cm ³ );

In a specific embodiment of the present invention, the content of the metal surface layer on the surface of the non-metal inner core accounts for 30% to 80% of the mass of the composite conductive particles.

In a specific embodiment of the present invention, the metal in the metal surface layer is selected from one or more of gold, silver, copper, nickel, aluminum, tungsten, iron, titanium, palladium, and platinum;

Preferably, the metal surface layer is plated on the surface of the non-metal inner core by chemical or physical methods;

Preferably, at least one layer of said metal surface is plated; more preferably one or two layers.

In a specific embodiment of the present invention, the mass ratio of the polyorganosiloxane prepolymer to the curing agent is 5:1 to 15:1;

More preferably, the polyorganosiloxane prepolymer is selected from polydimethylsiloxane (PDMS);

More preferably, the curing agent is selected from small molecule silanes, preferably small molecule silanes with silanol and siloxy groups.

The particle size of the composite conductive particles used in the present invention is 1-11 μm.

Another aspect of the present invention provides a kind of preparation method of printable flexible conductive paste or its composition, and its preparation step comprises:

(1) Synthesis of composite conductive particles

The non-metal core is used as the substrate, and the metal surface is plated on the surface;

(2) Preparation of mixed slurry of silver-plated conductive particles and polyorganosiloxane

Weighing the polyorganosiloxane prepolymer and its curing agent and the composite conductive particles obtained in step 1);

Optionally, the ingredients obtained in step 2) are mixed by mechanical stirring or high-speed rotary mixing to form uniformity.

Preferably, the step of plating a metallic surface on a non-metallic core is produced by:

i) coarsening

Coarsening with strong acid on the non-metallic core;

ii) Sensitization

Perform sensitization treatment on the non-metal core obtained in step i) in an aqueous solution of stannous chloride; sensitization treatment at room temperature for 30 minutes to 3 hours;

iii) Electroless plating

Prepare a silver ammonia solution, add the sensitized non-metallic inner core obtained in step ii) into the silver ammonia solution, then add a reducing agent, and react completely to obtain composite conductive particles.

Another aspect of the present invention provides a flexible conductive medium, which is obtained by printing the aforementioned conductive paste on a substrate;

Preferably, the printing is selected from screen printing, doctor blade printing, mask printing.

Another aspect of the present invention provides a flexible conductive circuit board, characterized in that the aforementioned flexible conductive medium is printed on the substrate,

Preferably, the substrate is selected from a sheet of rigid material, a sheet of flexible material or a sheet of elastic material;

More preferably, the plate of hard material is selected from silicon wafers, glass plates, metal plates, plastic plates, wood plates;

The flexible and flexible material sheet is selected from plastic film, paper, fabric of natural fiber or synthetic fiber, etc.;

The elastic material plate is selected from silicone rubber film, polyurethane film, ethylene-vinyl acetate copolymer film, polyethylene film, polyvinyl chloride film, polybutadiene film, and styrene-based thermoplastic film.

The substrate of the present invention can be mechanically deformed, specifically including flexible and rigid bending, twisting and stretching.

Another aspect of the present invention provides a method for preparing a flexible conductive circuit board, which includes the following steps:

The printable flexible conductive paste of the present invention is patterned by printing technology, and cured to form a flexible conductive circuit board;

Preferably, the conditions for curing and molding are curing at 20-150° C. for 10 minutes to 24 hours.

In a specific embodiment, the present invention provides a printable flexible conductive paste and its conductive circuit, which include (1) silver-plated conductive particles; (2) PDMS flexible polymer. The mass percentage of the silver-plated conductive particles is 40%-85%.

Preferably, the silver-plated conductive particles are conductive particles with a core-shell structure with polymer microspheres as the core and silver-plated on the surface, and the silver content on the surface accounts for 30% to 80% of the mass of the silver-plated conductive particles.

Preferably, the polymer microspheres are one or more of polystyrene, polymethyl methacrylate, polyacrylic acid, polydivinylbenzene or their copolymers, and the particle size is 200nm-10μm.

Preferably, the PDMS flexible polymer includes a PDMS prepolymer and its curing agent, the mass ratio of the two is 10:1, the curing temperature is from room temperature to 150° C., and the curing time is 24 hours to 10 minutes.

In addition, the present invention also provides a method for preparing a printable flexible conductive paste and a conductive circuit thereof, comprising the following steps:

(1) Synthesis of silver-plated conductive particles

Low density (approx. 1.0 g/cm ³ ) spherical polymer particles are used as the matrix, and silver particles are deposited on the surface by electroless plating to prepare conductive particles with silver-plated surfaces.

(2) Preparation of mixed slurry of silver-plated conductive particles and PDMS flexible polymer

Add silver-plated conductive particles directly into the mixture of PDMS prepolymer and its curing agent, and mix by mechanical stirring or high-speed rotation to form a uniform mixed slurry.

(3) The mixed slurry is patterned by printing technology, and cured to form a flexible conductive circuit.

Print the mixed slurry prepared in step (2) into a set pattern on the substrate by screen printing, scrape printing, mask printing and other printing techniques, and cure at room temperature to 150°C for 24h to 10min to obtain a conductive circuit pattern . The substrate can be hard materials such as silicon chips, glass chips, and metal plates, flexible materials such as plastic films, paper, and fiber fabrics, or high elastic materials such as silicon rubber films and polyurethane films.

The present invention adopts polymer microspheres as the center of the composite conductive particles. On the one hand, only the surface of the particles is coated with metal, which reduces the cost of the conductive particles; on the other hand, the density of the polymer microspheres is lower than that of the metal coating, so that The density of the filler is reduced, and the sedimentation tendency of the filler in PDMS is slowed down; moreover, the filler with a spherical structure is beneficial to reduce the viscosity of the PDMS mixed slurry, thereby increasing the printing effect, and at the same time, due to the uniform dispersion of the composite conductive particles, it is also correspondingly reduced. The amount of composite conductive particles is increased, and the conductive efficiency is increased.

The printable flexible conductive paste provided by the present invention and its conductive circuit and preparation method have the following advantages:

1. The present invention uses polymer microspheres as the core of silver-plated conductive particles. The silver-plated conductive particles produced have the characteristics of low density and are not easy to deposit in PDMS flexible polymer solutions. The conductive paste has uniform structure, stable performance and good conductivity;

2. The present invention uses a spherical polymer as the core of silver-plated conductive particles, and its particle size is easy to control. The preferred size of 200nm to 10μm is moderate, and the viscosity of the prepared slurry is moderate, which can realize the large-area printing of refined flexible conductive circuits. ;

3. The conductive paste of the present invention does not use any solvent, which is beneficial to realize the printing of the conductive paste on substrate materials that are not resistant to organic solvents or have strong hygroscopicity;

4. The printed conductive circuit of the present invention exhibits good stretchability and flexibility, and can withstand large deformations, such as stretching, bending, folding, winding and twisting.

5. The preparation method of the present invention is simple and easy, and the cost is low.

Description of drawings

Figure 1 is a SEM image of silver-plated conductive particles.

Figure 2 is a partial enlarged SEM image of silver-plated conductive particles.

Figure 3 is a cross-sectional SEM of a conductive circuit printed on paper.

Fig. 4 is a cross-sectional SEM image of a conductive circuit printed on a PI film.

Fig. 5 is a demonstration diagram of the conductive performance of the conductive circuit printed on the silicon wafer.

Fig. 6 is a demonstration diagram of the conductive performance of the conductive circuit printed on the PI film in a bent state.

Fig. 7 is a demonstration diagram of the conductive performance of the conductive circuit printed on a conventional A4 paper in a folded state.

Fig. 8 is a demonstration diagram of the conductive performance of the conductive circuit printed on the dust-free cloth in the winding state.

Fig. 9 is a particle size distribution diagram of silver-plated conductive particles.

Fig. 10 is the viscosity test result of the printable flexible conductive paste of the present invention.

Detailed ways

Example 1:

(1) Synthesis of composite conductive particles

Using polystyrene microspheres with an average particle size of about 5.5 μm as the core, the surface is plated with silver by electroless plating process to obtain silver-plated conductive particles (as shown in Figure 1 and Figure 2). The preparation steps of silver-plated conductive particles are as follows: i) coarsening: 1 gram of styrene microsphere powder is added in a beaker, and 20 milliliters of concentration is added into the beaker as 98% concentrated sulfuric acid, and the beaker is placed in an ultrasonic device to ultrasonically make the polymer Styrene powder was uniformly dispersed in concentrated sulfuric acid, then the beaker was transferred to a water bath at 50°C, reacted for 4 hours under magnetic stirring, washed with deionized water, and then prepared into a 200mL 5mg/mL aqueous dispersion; ii) sensitive Chemicalization: Add 200mL of 5mg/mL coarse polystyrene microsphere aqueous dispersion to 200mL of 10mg/mL stannous chloride solution, stir and mix at 30°C for 1h to fully sensitize the polystyrene microspheres, and deionized water After washing, it was made into 200mL 5mg/mL aqueous dispersion; iii) Electroless plating: 200mL 5mg/mL tinned polystyrene microsphere aqueous dispersion was added to freshly prepared 200mL 15mg/mL silver ammonia solution and 200mL 20mg/mL In a mixed solution of potassium sodium tartrate solution in mL, stir and react at 30° C. for 2 h, wash with deionized water, and dry to obtain silver-plated polystyrene conductive particles.

(2) Preparation of mixed slurry of silver-plated conductive particles and PDMS flexible polymer

Add silver-plated polystyrene conductive particles to the mixture of PDMS prepolymer and its curing agent (the mass ratio of conductive particles to PDMS is 3:2), rotate and mix at a high speed at room temperature, and then vacuumize and debubble for 30 minutes to obtain Flexible conductive paste. The above pastes were printed on substrates of different materials such as silicon wafers, polyimide (PI) films, A4 paper, dust-free cloths, etc. by screen printing technology, and heated at 120°C for 30 minutes to cure the printing pastes , that is, a flexible conductive circuit is made.

The internal microstructure of the printed conductive circuit is shown in Figure 3 and Figure 4, and it can be seen that the silver-plated conductive microspheres are uniformly dispersed in the PDMS matrix. It can also be seen from Figure 3 that the printed circuit has high resolution, and the line width and line spacing are about 100 μm respectively. After testing and calculation, the conductivity of the fabricated conductive line is 3.85×10 ⁴ S/m. In order to visually demonstrate the conductivity and flexibility of the printed conductive circuit, the printed circuit is connected to the external circuit and the LED bulb. The material can light up the LED bulb under different mechanical deformations, as shown in Figures 5-8.

Example 2:

(1) Synthesis of composite conductive particles

The polystyrene microsphere with an average particle diameter of about 1 μm is used as the core, and the surface is plated with silver by an electroless plating process to obtain silver-plated conductive particles.

(2) Preparation of mixed slurry of silver-plated conductive particles and PDMS flexible polymer

Add silver-plated polystyrene conductive particles to the mixture of PDMS prepolymer and its curing agent (the mass ratio of conductive particles to PDMS is 7:3), rotate and mix at a high speed at room temperature, and then vacuumize and debubble for 30 minutes to obtain Flexible conductive paste. The above slurry was printed on substrates of different materials such as glass, polyethylene terephthalate (PET) film, A4 paper, etc. by metal mask scraping technology, and heated at 80°C for 4h to print The slurry is cured and formed to form a flexible conductive circuit. After testing and calculation, the conductivity of the fabricated conductive circuit is 4.7×10 ⁴ S/m.

Example 3:

(1) Synthesis of composite conductive particles

The polystyrene microsphere with an average particle diameter of about 1 μm is used as the core, and the surface is plated with silver by an electroless plating process to obtain silver-plated conductive particles.

(2) Preparation of mixed slurry of silver-plated conductive particles and PDMS flexible polymer

Silver-plated polystyrene conductive particles were added to the mixture of PDMS prepolymer and its curing agent (the mass ratio of conductive particles to PDMS was 1:1), mechanically stirred and mixed evenly at room temperature, and then vacuumed to remove air bubbles for 30 minutes to obtain Flexible conductive paste. Print the above paste on substrates of different materials such as glass, stainless steel sheet, plastic, rubber, A4 paper, etc. by screen printing technology, and leave it at room temperature for 24 hours to cure the printing paste to form a flexible conductive circuit. . After testing and calculation, the conductivity of the fabricated conductive line is 9.2×10 ³ S/m.

Embodiment 4 viscosity test

The polystyrene microsphere is used as the core, and the surface is plated with silver through an electroless plating process to obtain silver-plated conductive particles. A laser particle size analyzer (Malvern, Mastersizer 3000) was used to test the particle size and distribution of the silver-coated conductive particles produced. The results are shown in Figure 9, the particle size range is about 1-11 μm, and the average particle size is about 5.7 μm. Mix the silver-plated conductive particles with the PDMS prepolymer and its curing agent uniformly in different proportions to obtain a flexible conductive paste. The viscosity of the conductive paste is tested by a rotational rheometer (MCR302, Anton Paar, Austria). The diameter of the rotating parallel plate is 25 mm, the gap distance between the parallel plate and the test disc is 106 μm, and the shear rate test range is 1 to 100 s ^{- 1} . When no silver-plated conductive particles were added, the viscosity of PDMS was 3.18Pa·s; when the amount of silver-plated conductive particles was 30wt%, the viscosity of the mixed slurry was 3.83Pa·s; with the addition of silver-plated conductive particles gradually increased to 40wt% , 50wt%, 55wt% and 60wt%, the viscosity of the mixed slurry increased to 5.06, 6.41, 8.33 and 9.14Pa·s respectively, and the viscosity of the above slurry did not change significantly with the increase of the shear rate. When the addition of silver-plated fillers was further increased to 65wt%, 70wt% and 75wt%, the initial viscosity of the slurry (when the shear rate was 1s ^-1 ) increased significantly to 35.7, 107 and 1090Pa·s, and the viscosity increased with the shear The increase of velocity decreases gradually to 9.42, 10.03 and 10.69Pa·s (when the shear rate is 100s ^-1 ). From the results of actual printing, when the amount of silver-plated particles added is less than 50wt%, the viscosity of the slurry is too low, which easily causes the lateral diffusion of the printed circuit; when the amount of silver-plated particles added is higher than 65wt%, the viscosity of the paste is too high, It is difficult to obtain fine printed lines by screen printing process, but conductive lines can be printed and produced by mask plate scraping and other methods. When the content of silver-plated particles is 50wt%-65wt%, the viscosity of the paste is relatively moderate, which is suitable for both screen printing and scraping printing, and can easily obtain high-resolution printed conductive lines.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone with ordinary knowledge in the technical field may make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be defined by the patent scope of the claims.

Claims (36)

1. A printable flexible conductive paste is characterized in that it is made of composite conductive particles and polyorganosiloxane; the composite conductive particles are non-metallic inner core surface coated with a metal surface layer with a diameter not higher than 20 μm Particles; the conductive paste does not contain organic or inorganic solvents; The metal in the metal surface layer is selected from one or more of gold, silver, copper, nickel, aluminum, tungsten, iron, titanium, palladium, platinum; The mass percentage of the composite conductive particles in the printable flexible conductive paste is 50wt% to 85wt%; The density of the non-metal inner core is 0.6-1.5 g/cm ³ . 2. The printable flexible conductive paste according to claim 1, the organic solvent is selected from acetone, butanone, ethanol, methyl alcohol, Virahol, benzene, toluene, styrene, normal hexane, hexanaphthene, methylene dichloride , one or more of chloroform, ether, ethylene glycol monomethyl ether, acetonitrile, pyridine; The inorganic solvent is selected from one or more of water, liquid ammonia, sulfuric acid, and nitric acid. 3. The printable flexible conductive paste according to claim 1 or 2, characterized in that the mass percentage of the composite conductive particles in the printable flexible conductive paste is 50wt%-80wt%. 4. A flexible conductive paste composition that can be printed is characterized in that it includes composite conductive particles, polyorganosiloxane prepolymer and curing agent thereof; Particles with a diameter not higher than 20 μm; the conductive paste composition does not contain organic or inorganic solvents; The metal in the metal surface layer is selected from one or more of gold, silver, copper, nickel, aluminum, tungsten, iron, titanium, palladium, platinum; The mass percentage of the composite conductive particles in the printable flexible conductive paste composition is 50wt% to 85wt%; The density of the non-metal inner core is 0.6-1.5 g/cm ³ . 5. The printable flexible conductive paste composition according to claim 4, the organic solvent is selected from acetone, methyl ethyl ketone, ethanol, methyl alcohol, Virahol, benzene, toluene, styrene, normal hexane, cyclohexane, di One or more of methyl chloride, chloroform, ether, ethylene glycol monomethyl ether, acetonitrile, pyridine; The inorganic solvent is selected from one or more of water, liquid ammonia, sulfuric acid, and nitric acid. 6. The printable flexible conductive paste composition according to claim 4 or 5, characterized in that, the mass percentage of the composite conductive particles in the printable flexible conductive paste composition is 50wt%-80wt%. 7. The printable flexible conductive paste according to any one of claims 1-2 or the printable flexible conductive paste composition according to any one of claims 4-5, wherein the non- The metal core is selected from microspheres formed of glass, ceramics, and inert polymers. 8. The printable flexible conductive paste according to any one of claims 1-2 or the printable flexible conductive paste composition according to any one of claims 4-5, wherein the non- The metal core is selected from glass, ceramics, microspheres formed by inert polymers, and the microspheres are selected from polystyrene microspheres (PS), polyacrylic acid microspheres (PAA), polymethylmethacrylate microspheres (PMMA) 1. One or more of polyphenolic resin microspheres (PF), polydivinylbenzene microspheres (PDVB) or copolymer microspheres, the particle diameter of which is 200nm-10μm. 9. The printable flexible conductive paste according to any one of claims 1-2 or the printable flexible conductive paste composition according to any one of claims 4-5, the density of the non-metallic inner core is 0.8 -1.2g/cm ³ . 10. The printable flexible conductive paste or the printable flexible conductive paste composition according to claim 9, the density of the non-metallic inner core is 1.0 g/cm ³ . 11. The printable flexible conductive paste or the printable flexible conductive paste composition according to claim 10, the content of the metal surface layer on the surface of the non-metal inner core accounts for 30%-80% of the mass of the composite conductive particles. 12. The printable flexible conductive paste according to any one of claims 1-2 or the printable flexible conductive paste composition according to any one of claims 4-5, wherein the metal surface layer is chemically Or physically plated on the surface of the non-metal core. 13. The printable flexible conductive paste or printable flexible conductive paste composition according to claim 12, wherein the metal surface layer is plated with at least one layer. 14. The printable flexible conductive paste or printable flexible conductive paste composition according to claim 13, the metal surface layer is plated with 1 or 2 layers. 15. The printable flexible conductive paste according to any one of claims 1-2, wherein the polyorganosiloxane is made of a polyorganosiloxane prepolymer and a curing agent thereof. 16. The printable flexible conductive paste according to claim 15, wherein the mass ratio of the polyorganosiloxane prepolymer to the curing agent is 5:1˜15:1. 17. The printable flexible conductive paste according to claim 15, the polyorganosiloxane is selected from the group consisting of polydimethylsiloxane, cyclomethicone, aminosiloxane, polymethylphenyl One or more of siloxane, polyether polysiloxane copolymer. 18. The printable flexible conductive paste according to claim 15, said polyorganosiloxane prepolymer being selected from polydimethylsiloxane (PDMS). 19. The printable flexible conductive paste according to claim 15, the curing agent is selected from small molecular silanes. 20. The printable flexible conductive paste according to claim 15, the curing agent is a small molecule silane with silanol and siloxy groups. 21. The printable flexible conductive paste composition according to any one of claims 4-5, wherein the polyorganosiloxane is made from a polyorganosiloxane prepolymer and a curing agent thereof. 22. The printable flexible conductive paste composition according to claim 21, wherein the mass ratio of the polyorganosiloxane prepolymer to the curing agent is 5:1˜15:1. 23. The printable flexible conductive paste composition according to claim 21, said organopolysiloxane being selected from the group consisting of polydimethylsiloxane, cyclomethicone, aminosiloxane, polymethicone One or more of phenylsiloxane, polyether polysiloxane copolymer. 24. The printable flexible conductive paste composition according to claim 21, said polyorganosiloxane prepolymer being selected from polydimethylsiloxane (PDMS). 25. The printable flexible conductive paste composition according to claim 21, the curing agent is selected from small molecule silanes. 26. The printable flexible conductive paste composition according to claim 21, the curing agent is a small molecule silane with silanol and siloxy groups. 27. The printable flexible conductive paste according to any one of claims 1-2 or the printable flexible conductive paste composition according to any one of claims 4-5, the composite conductive particles account for the printable flexible The mass percentage of the conductive paste or the printable flexible conductive paste composition is 50wt%-65wt%. 28. Claims 1-3,7-20,27 any one of the printable flexible conductive paste or claim 4-14,21-27 any one of the printable flexible conductive paste composition Preparation method, its preparation step comprises: (1) Synthesis of composite conductive particles The non-metal core is used as the substrate, and the metal surface is plated on the surface; (2) Preparation of mixed slurry of silver-plated conductive particles and polyorganosiloxane Weighing the polyorganosiloxane prepolymer and its curing agent and the composite conductive particles obtained in step 1); The components obtained in step 2) are mechanically stirred or mixed at a high speed to form a homogeneous mixture. 29. The preparation method according to claim 28, the step of plating a metal surface layer on the non-metallic core is made in the following manner: i) Coarsening Coarsening with strong acid on the non-metallic core; ii) Sensitization Perform sensitization treatment on the non-metal core obtained in step i) in an aqueous solution of stannous chloride; sensitization treatment at room temperature for 30 minutes to 3 hours; iii) Electroless plating Prepare a silver ammonia solution, add the sensitized non-metallic inner core obtained in step ii) into the silver ammonia solution, then add a reducing agent, and react completely to obtain composite conductive particles. 30. A flexible conductive medium, which is made of the printable flexible conductive paste according to any one of claims 1-3, 7-20, 27 or the flexible conductive paste described in any one of claims 4-14, 21-27 The printed flexible conductive paste composition is obtained by printing on a substrate. 31. The flexible conductive medium of claim 30, said printing being selected from the group consisting of screen printing, doctor blade printing, mask printing. 32. A flexible conductive circuit board, characterized in that the flexible conductive medium according to any one of claims 30-31 is printed on the substrate. 33. The flexible conductive circuit board according to claim 32, characterized in that, the substrate is selected from a hard material board, a flexible flexible material board or an elastic material board. 34. The flexible conductive circuit board according to claim 33, the hard material plate is selected from a metal plate, a plastic plate, and a wood plate; Sheets of flexible flexible material selected from plastic films, paper, fabrics of natural or synthetic fibers; The elastic material plate is selected from silicone rubber film, polyurethane film, ethylene-vinyl acetate copolymer film, polyethylene film, polyvinyl chloride film, polybutadiene film, and styrene-based thermoplastic film. 35. The preparation method of the flexible conductive circuit board described in any one of claims 32-34, it comprises the following steps: By printing the printable flexible conductive paste composition described in any one of claims 1-3,7-20,27 or any one of claim 4-14,21-27 The technology is patterned and cured to form a flexible conductive circuit board. 36. The preparation method according to claim 35, the condition of curing and molding is curing at 20-150° C. for 10 minutes-24 hours.