Weather-resistant bio-based conductive coating based on water-based palm wax / shellac and preparation method of weather-resistant bio-based conductive coating

Abstract

The invention relates to the technical field of conductive coatings, and discloses a weather-resistant bio-based conductive coating based on water-based palm wax / shellac and a preparation method thereof, the weather-resistant bio-based conductive coating comprises the following raw materials by mass: 20-30 parts of a natural palm wax nano emulsion, 70-80 parts of a shellac ethanol solution, 1-3 parts of Tween 80, and 30-80 parts of a silver coated copper powder / carbon nanofiber composite material. According to the scheme, the super-hydrophobic barrier is constructed by introducing the water-based palm wax, the moisture absorption rate is reduced, electrochemical corrosion and stress stripping are effectively reduced, and the service life of a base material is prolonged. Meanwhile, lac is added in the scheme, a three-dimensional network structure is formed through crosslinking of the water-based palm wax emulsion and biomass hydroxyl, and the flexibility and moisture resistance of the coating are effectively improved. Specifically, according to the scheme, the water-based palm wax and the shellac are combined and used, so that the weather resistance of the coating is effectively improved, for example, the moisture absorption rate of the coating is reduced to 12% (ASTMD570 standard), and the flexibility of the coating is improved (the elongation at break gt; 50%), the moisture resistance is improved by 3 times (the water vapor permeability lt; 10 g / m < 2 >. Day).

Description

Technical Field

[0001] The present invention relates to the technical field of conductive coatings, and particularly relates to a weather-resistant biobased conductive coating based on waterborne palm wax / shellac and a preparation method thereof. Background Art

[0002] With the sharp increase in the annual output of global electronic products, the total amount of electronic waste has risen sharply, which contains a relatively high proportion of non-degradable petroleum-based plastic components. These materials have a long half-life in the environment and cause continuous harm to the ecosystem through the combined pollution effects of microplastic migration and heavy metal ion leaching. Using biobased degradable polymers to replace traditional electronic materials has become an industry consensus. Materials such as polylactic acid (PLA) and polyhydroxyalkanoates (PHA) have achieved a controllable degradation cycle of 60-90 days under composting conditions through molecular structure design, effectively reducing the carbon footprint of the entire life cycle of electronic products.

[0003] However, the existing biobased conductive materials still have the following defects:

[0004] (1) Poor weather resistance of the coating, shortening the life of the matrix material: The traditional biobased conductive coating has a high density of hydroxyl groups, and the moisture absorption rate increases in an environment with relatively high humidity and forms a water molecule penetration channel. When the silver-based conductive filler contacts the penetrated water, the electrochemical corrosion rate is greatly increased, thereby accelerating the resistance damp heat aging.

[0005] (2) Poor interfacial compatibility between the coating and the matrix: There is a polarity mismatch between the biobased conductive coating and the conductive filler matrix (such as carbon-based materials), resulting in uneven dispersion of the filler and forming a local insulation barrier, which affects the conductive performance.

[0006] (3) Poor resource recyclability: There is a conflict in the degradation rate between the biobased conductive coating and the conductive filler matrix, and the traditional separation technology has low efficiency, resulting in environmental pollution.

[0007] In view of this, developing a biobased conductive coating with good weather resistance and compatibility not only effectively makes up for the deficiencies of the existing technology, but also effectively solves the material performance defects caused by the poor weather resistance and compatibility of the existing biobased conductive coatings, which is of great significance for taking into account the degradability and comprehensive performance of biobased conductive coatings. Summary of the Invention

[0008] The present invention aims to provide a weather-resistant biobased conductive coating based on waterborne palm wax / shellac and a preparation method thereof to solve the technical problem that the existing biobased conductive coating has poor weather resistance and shortens the life of the matrix material.

[0009] To achieve the above object, the present invention adopts the following technical solution: a weather-resistant bio-based conductive coating based on waterborne palm wax / shellac, comprising the following raw materials in parts by mass: 20-30 parts of natural palm wax nanoemulsion, 70-80 parts of shellac ethanol solution, 1-3 parts of Tween 80, and 30-80 parts of silver-coated copper powder / carbon nanofiber composite.

[0010] The principle and advantages of this solution are as follows:

[0011] 1. Improvement of coating weather resistance: In this solution, a superhydrophobic barrier is constructed by introducing waterborne palm wax to reduce the moisture absorption rate, effectively reducing electrochemical corrosion and stress peeling, and prolonging the service life of the matrix material. At the same time, shellac is added in this solution. Through crosslinking of the waterborne palm wax emulsion with biomass hydroxyl groups, a three-dimensional network structure is formed, effectively improving the flexibility and moisture barrier properties of the coating. Specifically, by combining the use of waterborne palm wax and shellac in this solution, the weather resistance of the coating is effectively improved. For example, the moisture absorption rate of the coating is reduced to 12% (ASTM D570 standard), the flexibility of the coating is improved (elongation at break > 50%), and the moisture barrier property is improved by 3 times (water vapor transmission rate < 10g / m 2 ·day).

[0012] 2. Optimization of interfacial compatibility: In this solution, a multi-scale filler compounding technology is adopted, combining carbon nanotubes and silver-coated copper powder. The percolation threshold is reduced by using the topological complementary effect, effectively improving the electrical conductivity. At the same time, the surface of the filler is graft-modified by a silane coupling agent to regulate the interfacial energy and achieve uniform dispersion at the nanoscale. Specifically, the percolation threshold of the multi-scale filler compounding system in this solution is reduced to 6wt%, and the sheet resistance < 50 / sq.

[0013] 3. Improvement of resource recyclability: In this solution, shellac is selected as the main biomass matrix material. Utilizing its high solubility in ethanol, a green separation process is used to achieve efficient recovery of the filler, reducing the separation energy consumption and environmental pollution. Resource recyclability: The recovery rate of silver-coated copper powder > 92% (purity > 99%), the solvent can be recycled more than 5 times (recovery rate > 90%), and the separation energy consumption is reduced by 70%.

[0014] 4. The bio-based conductive coating developed in this solution is applicable to multiple fields such as electronic packaging, electromagnetic shielding, flexible electronic devices, energy storage and conversion systems, etc. Its excellent electrical conductivity, weather resistance and environmental protection characteristics will promote technological innovation and industrial upgrading in related fields. In addition, this coating also meets the requirements of sustainable development and is expected to play an important role in future green manufacturing and circular economy.

[0015] Preferably, as an improvement, the preparation method of the natural palm wax nanoemulsion is as follows: The natural palm wax is crushed to a particle size < 100 μm, deionized water is added in a mass ratio of 1:1 - 3, and then an emulsifier accounting for 3.5 - 5% of the total mass of the system is added. After mixing evenly, it is emulsified at 90 - 95 °C for 2 - 3 h, and then cooled and filtered to obtain the natural palm wax nanoemulsion.

[0016] Beneficial effects: With the above settings in this solution, it is convenient for the natural palm wax to form a uniformly dispersed natural palm wax nanoemulsion in water, thereby improving the weather resistance of the bio-based conductive material. Through long-term experiments, the applicant found that if the particle size of the natural palm wax powder is too large or there is too much water, the emulsifier cannot effectively wrap and disperse the palm wax particles, resulting in enhanced interaction between the palm wax particles, easy aggregation and sedimentation, which destroys the uniform dispersion of the emulsion and reduces the stability of the emulsion. If the temperature is too high, the palm wax will be overly softened or even decomposed, changing the chemical structure and properties of the palm wax. At the same time, it may also cause the emulsifier to fail or reduce its emulsifying performance, resulting in poor uniform dispersion of the emulsion and emulsion breaking. If the temperature is too low, the viscosity of the palm wax is relatively large, and it is difficult for the emulsifier to penetrate and wrap the palm wax particles, resulting in poor emulsification effect. The palm wax particles cannot be evenly dispersed in the water phase and are prone to form large particle aggregates, affecting the uniform dispersion and stability of the emulsion. An overly long emulsification time may cause excessive collision of the already formed nanoemulsion particles, resulting in aggregation and flocculation between the particles, destroying the uniform dispersion of the emulsion and reducing the stability of the emulsion. An overly short emulsification time will cause the emulsifier and the palm wax to not fully interact, and the palm wax particles cannot be completely wrapped by the emulsifier, resulting in unemulsified palm wax particles in the emulsion, affecting the uniform dispersion and stability of the emulsion.

[0017] Preferably, as an improvement, the acid value of the natural palm wax ≤ 5 mg KOH / g, and the particle size of the natural palm wax nanoemulsion < 100 nm.

[0018] Beneficial effects: With the above settings in this solution, it is convenient to improve the uniform dispersion and stability of the natural palm wax nanoemulsion. Specifically, the acid value reflects the content of free fatty acids in the palm wax. A lower acid value means higher purity of the palm wax, with fewer impurities and free fatty acids. Excessive free fatty acids will affect the surface properties and chemical stability of the palm wax, and may cause unnecessary chemical reactions with the emulsifier during the emulsification process, or affect the adsorption and arrangement of the emulsifier on the surface of the palm wax particles. A low acid value can ensure the stable properties of the palm wax during the emulsification process, which is conducive to the emulsifier evenly wrapping the palm wax particles, thereby improving the uniform dispersion and stability of the emulsion. In the emulsion prepared by this solution, the palm wax particles are refined to the nanoscale, enabling them to have better Brownian motion characteristics in the system, being able to be more evenly dispersed in the water phase, and not easily settling under the influence of gravity, thus greatly improving the uniform dispersion and stability of the emulsion.

[0019] Preferably, as an improvement, the preparation method of the shellac ethanol solution is as follows: Add shellac powder to the ethanol solution with a concentration of 95% according to a mass ratio of 1:8 to 12, stir until completely dissolved, filter to remove impurities, and obtain a clear shellac ethanol solution.

[0020] Beneficial effects: With the above settings in this solution, it is convenient for the film-forming continuity of the shellac ethanol solution. The mixing ratio of shellac powder and ethanol and the concentration of ethanol in this solution enable shellac molecules to be deposited and arranged orderly on the surface of the ethanol substrate during the film-forming process, intertwining and arranging closely to form a continuous film structure. Through long-term experiments, the applicant found that if the shellac concentration is too low, there is insufficient film-forming substance and it is difficult to form a complete and continuous film; while too high a shellac concentration may lead to too high a solution viscosity, restricted molecular movement, and is also not conducive to forming a uniform and continuous film. This mass ratio provides a material basis for forming a good continuous film. Too low an ethanol concentration means a relatively high water content in the solution, and water will reduce the solubility of shellac in the solution, making the shellac unable to dissolve completely, and some shellac may exist in the solution in the form of particles. During the film-forming process, these undissolved shellac particles will hinder the film formation, resulting in a rough and uneven film surface, and even film breakage, affecting the film-forming continuity.

[0021] Preferably, as an improvement, the preparation method of the silver-coated copper powder / carbon nanofiber composite material is as follows: Mix silver-coated copper powder and carbon nanofibers according to a mass ratio of 5 to 10:2 to 4, ball mill in a ball mill for 4 to 6 hours, and control the ball mill rotation speed at 300 to 400 rpm to obtain composite conductive fillers with uniform particle sizes.

[0022] Beneficial effects: With the above settings, this solution facilitates the improvement of the interfacial bonding strength of the composite material. Specifically, the silver-coated copper powder has good electrical conductivity and ductility, and the carbon nanofibers have a high specific surface area, high strength, and good electrical conductivity. In this solution, the mixing ratio of the two enables the silver-coated copper powder to better fill the gaps between the carbon nanofibers during the ball milling and crushing process, and the carbon nanofibers can also be evenly dispersed in the silver-coated copper powder, increasing the contact area between the two, which is conducive to the formation of strong physical and chemical bonds between them through mechanical force during the ball milling process, thereby improving the interfacial bonding strength. Through long-term experiments, the applicant found that if the dosage of the silver-coated copper powder is too high or too low, the gaps between the silver-coated copper powder and the carbon nanofibers cannot form effective connections, resulting in a reduction in the bonding points at the interface in the composite material and a decrease in the interfacial bonding strength, and the overall performance of the material will also be affected. If the ball milling time is too long, it may cause excessive fragmentation of the silver-coated copper powder and the carbon nanofibers, generating too much fine powder. These fine powders have a large specific surface area and are prone to adsorbing impurities and moisture in the air, affecting the cleanliness of the interface and being unfavorable for the bonding between the two. If the ball milling speed is too high, the impact force of the grinding balls on the material will be too large, resulting in excessive fragmentation and deformation of the silver-coated copper powder and the carbon nanofibers, and even the carbon nanofiber structure may be damaged, losing its original performance advantages. At the same time, too high a speed will also cause the material to move too violently in the ball milling tank, resulting in the silver-coated copper powder and the carbon nanofibers being quickly thrown up before they have time to be fully mixed and bonded, which is not conducive to the formation of interfacial bonding.

[0023] Preferably, as an improvement, the particle size D90 of the silver-coated copper powder / carbon nanofiber composite material is less than 200 nm.

[0024] Beneficial effects: With the above settings, this solution facilitates the improvement of the electrical conductivity of the bio-based conductive coating. Specifically, a smaller particle size means that the silver-coated copper powder / carbon nanofiber composite material has a larger specific surface area and can be more evenly dispersed in the bio-based conductive coating, forming more conductive paths. Electrons are more likely to be transmitted in these paths, thereby improving the electrical conductivity of the coating and enabling it to better meet the requirements of various conductive applications. Moreover, the particle size of the composite material in this solution can better fill the voids in the natural palm wax nanoemulsion, shellac ethanol solution, etc. when mixed, form a tighter bond with other components, contribute to improving the continuity and denseness of the coating film formation, make the formed coating more uniform and smooth, reduce defects such as pinholes and cracks, and thus improve the overall quality and performance of the coating. And it is not prone to agglomeration or phase separation phenomena, ensuring the stability of the coating during storage and use and being conducive to the long-term maintenance of the coating performance.

[0025] Preferably, as an improvement, this solution also provides a preparation method for a weather-resistant bio-based conductive coating based on aqueous palm wax / shellac, including the following steps:

[0026] Step 1: Mix palm wax emulsion and shellac ethanol solution at a volume ratio of 1:2 - 4 to obtain Solution I.

[0027] Step 2: Add Tween 80 to Solution I and stir evenly to obtain Solution II.

[0028] Step 3: Add silver-coated copper powder / carbon nanofiber composite conductive material to Solution II and mix evenly to obtain a bio-based conductive coating solution.

[0029] Beneficial effects: With the above settings in this solution, during the mixing process, Tween 80 acts as an emulsifier and stabilizer, which can reduce the interfacial tension of each component, improve the stability of the dispersion system, and prevent the sedimentation and agglomeration of fillers.

[0030] Preferably, as an improvement, in Step 3, the stirring speed of the mixing is 300 - 500 rpm, and the stirring time is 20 - 30 min.

[0031] Beneficial effects: With the above settings in this solution, the mixing uniformity of the bio-based conductive coating solution is effectively improved. And during the mixing process, attention should be paid to avoiding the introduction of air bubbles, maintaining the stirring uniformity, and preventing local agglomeration of each component.

[0032] Preferably, as an improvement, this solution also provides an application of a weather-resistant bio-based conductive coating based on waterborne palm wax / shellac, including the application of the above bio-based conductive coating solution as a coating in the fields of integrated electronics, intelligent packaging, anti-static and electromagnetic shielding packaging, and health monitoring devices.

[0033] Beneficial effects: With the above settings in this solution,

[0034] Preferably, as an improvement, during the application process, first stir the above bio-based conductive coating solution evenly, and then use the spraying method or screen printing method to coat it on the surface of the device to form a coating.

[0035] Beneficial effects: With the above settings in this solution, it is convenient to form a coating of the bio-based conductive coating solution on the substrate. Specifically, the spraying method uses a spray gun or a disc atomizer to disperse the coating into uniform droplets by pressure or centrifugal force and apply it to the surface of the object to be coated, which is suitable for large-scale production and the coating thickness is easy to control. The screen printing method uses a screen mask and makes the ink transfer to the substrate through the mesh by the pressure of a squeegee, which is suitable for ultra-fine and high aspect ratio coating with high pattern accuracy.

[0036] Preferably, as an improvement, the thickness of the coating is 10 - 30 μm.

[0037] Beneficial effects: With the above settings, this solution facilitates the full utilization of the conductive properties of the coating. When used on different substrates, the coating thickness can be determined according to actual needs. For example, when used on the surface of disposable electronic products, the coating serves as the conductive layer of a temporary electronic tag, with a thickness of approximately 15 μm. It is biodegradable after use and has stable conductive properties. When used on the surface of smart packaging, the coating can be used for simple sensors on the packaging, with a thickness of approximately 20 μm, enabling reliable signal transmission. In anti-static and electromagnetic shielding packaging, the coating can be used on the inner layer of electronic component packaging, with a thickness of approximately 25 μm, which can prevent electrostatic damage to components and provide electromagnetic shielding protection. In the field of health monitoring devices, the coating can be applied to disposable medical sensors, with a thickness of approximately 10 μm, meeting medical-grade environmental protection and conductive requirements.

[0038] Preferably, as an improvement, this solution also provides a method for recycling conductive fillers in a bio-based conductive coating, which includes ultrasonic dissociation using an ethanol solvent system and then vacuum filtration deposition to obtain the recycled conductive filler carbon nanotube-silver-coated copper powder.

[0039] Beneficial effects: With the above settings, the ethanol solvent system in this solution facilitates the cleaning of the bio-based conductive coating, and ultrasonic treatment facilitates the dissociation of the conductive filler carbon nanotube-silver-coated copper powder from the coating solution. Subsequently, the conductive filler carbon nanotube-silver-coated copper powder can be recovered through vacuum filtration deposition. Specifically, through long-term experiments, the applicant found that ethanol enables the separation rate of the coating from the substrate to exceed 90%, and the recovery rate of shellac is not less than 50%; the conductive material can be recycled through vacuum filtration deposition, with a recovery rate exceeding 50%, effectively improving resource utilization efficiency and reducing costs. Description of the Drawings

[0040] Figure 1 STM image (scale bar is 10 μm) of the coating obtained by spraying the bio-based conductive coating prepared in Example 1 of the present invention.

[0041] Figure 2 STM image (scale bar is 2 μm) of the coating obtained by spraying the bio-based conductive coating prepared in Example 1 of the present invention.

[0042] Figure 3 STM image (scale bar is 1 μm) of the coating obtained by spraying the bio-based conductive coating prepared in Example 1 of the present invention.

[0043] Figure 4 STM image (scale bar is 500 nm) of the coating obtained by spraying the bio-based conductive coating prepared in Example 1 of the present invention.

[0044] Figure 5 STM image (scale bar is 50 μm) of the coating obtained by spraying the bio-based conductive coating prepared in Example 1 of the present invention.

[0045] Figure 6 STM image (scale bar: 10 μm) of the coating obtained by spraying the biobased conductive coating prepared in Example 1 of the present invention.

[0046] Figure 7 STM image (scale bar: 2 μm) of the coating obtained by spraying the biobased conductive coating prepared in Example 1 of the present invention.

[0047] Figure 8 STM image (scale bar: 1 μm) of the coating obtained by spraying the biobased conductive coating prepared in Example 1 of the present invention.

[0048] Figure 9 STM image (scale bar: 500 nm) of the coating obtained by spraying the biobased conductive coating prepared in Example 1 of the present invention.

[0049] Figure 10 Water resistance test diagram of the biobased conductive coating in Example 1 of the present invention (showing that the conductive pattern has water resistance characteristics and the pattern remains unchanged before and after soaking).

[0050] Figure 11 Conductivity test diagram of the biobased conductive coating in Example 1 of the present invention (the printed pattern has good conductive effect; the button battery drives the LED lamp through the conductive pattern).

[0051] Figure 12 Flow chart of the recovery of conductive fillers in the biobased conductive coating in Example 1 of the present invention.

[0052] Figure 13 Actual scene diagram of the recovery of conductive fillers in the biobased conductive coating in Example 1 of the present invention (the printed conductive pattern can be quickly dissolved in ethanol). Detailed implementation manners

[0053] The present invention will be further described in detail below with reference to examples, but the implementation manners of the present invention are not limited thereto. Unless otherwise specified, the technical means used in the following examples and experimental examples are conventional means well known to those skilled in the art, and the materials, reagents, etc. used can be obtained from commercial sources.

[0054] Example 1

[0055] The present solution provides a weather-resistant biobased conductive coating based on aqueous palm wax / shellac, comprising raw materials in the following mass fractions: comprising raw materials in the following mass parts: 20 - 30 parts of natural palm wax nanoemulsion, 70 - 80 parts of shellac ethanol solution, 1 - 3 parts of Tween 80 (i.e., polyoxyethylene sorbitan monooleate), and 30 - 80 parts of silver-coated copper powder / carbon nanofiber composite material.

[0056] Among them, the preparation method of the natural palm wax nanoemulsion is as follows: The natural palm wax (acid value ≤ 5 mg KOH / g, ASTM D1387) is crushed to a particle size < 100 μm, deionized water is added according to a mass ratio of 1:1 - 3 (specifically 1:2 in this example), and then an emulsifier accounting for 3.5 - 5% of the total system mass is added [specifically, any one of Span 80 (sorbitan monooleate), Tween 80 (polyoxyethylene sorbitan monooleate), and lecithin can be selected, and Span 80 is specifically selected in this example]. After mixing evenly, it is emulsified at 90 - 95 °C, a pressure of 150 MPa, and a shear rate of 10 6 s -1 for 2 - 3 h under the conditions, and then cooled and filtered to obtain the natural palm wax nanoemulsion with a particle size < 100 nm.

[0057] The preparation method of the shellac ethanol solution is as follows: The shellac powder is added to the 95% ethanol solution according to a mass ratio of 1:8 - 12 (specifically 1:10 in this example), stirred until completely dissolved, and the impurities are removed by filtration to obtain a clear shellac ethanol solution.

[0058] The preparation method of the silver-coated copper powder / carbon nanofiber composite material is as follows: The silver-coated copper powder and carbon nanofibers are mixed according to a mass ratio of 5 - 10:2 - 4, ball-milled in a ball mill for 4 - 6 h, and the ball-milling speed is controlled at 300 - 400 rpm to obtain a composite conductive filler with uniform size. After detection, the particle size D90 of the prepared silver-coated copper powder / carbon nanofiber composite material < 200 nm.

[0059] This solution also provides a preparation method of a weather-resistant bio-based conductive coating based on aqueous palm wax / shellac, including the following steps:

[0060] Step 1: Mix the palm wax emulsion and the shellac ethanol solution according to a volume ratio of 1:2 - 4 to obtain Solution I;

[0061] Step 2: Add Tween 80 to Solution I and stir evenly to obtain Solution II;

[0062] Step 3: Add the silver-coated copper powder / carbon nanofiber composite conductive material to Solution II, and stir for 20 - 30 min at a stirring speed of 300 - 500 rpm to mix evenly to obtain the bio-based conductive coating solution.

[0063] The STM image of the coating of the bio-based conductive coating prepared by this solution on the substrate is as Figures 1 to 9 shown, where Figures 1 to 4 shows different magnifications in one field of view, Figures 5 to 9The different magnifications in another field of view all show that the components in the coating have good dispersion uniformity and high stability, and only contain three forms: silver-coated copper particles, graphite flakes and one-dimensional carbon nanotubes. The applicant analyzed the advantages of using silver-coated copper particles and graphite flakes in conductive coatings: silver-coated copper has high conductivity (10 -4 Ω·cm level) and economical (silver content 5% to 30%), and can also inhibit copper oxidation; graphite sheets form a continuous conductive network through a layered structure, and the two work together to fill the gaps and reduce interface resistance. In terms of cost, silver-coated copper reduces the amount of silver used, and the low price and light weight of graphite further reduce costs; in terms of application, it is suitable for high-precision electronics and large-area coating scenarios, and its anti-oxidation and chemical stability adapt to complex environments; in terms of process, the complementary morphology improves coating uniformity and adhesion, and is compatible with a variety of coating methods, achieving a comprehensive balance between high performance and low cost.

[0064] In addition, in traditional conductive materials, a single conductive particle has a limited contact area, so a high filling amount is required to form a continuous conductive path. This high filling amount not only increases the material cost, but may also cause the coated film to be too hard after drying and curing, affecting flexibility, while reducing the fluidity of the slurry, causing inconvenience in processing.

[0065] To this end, this solution innovatively introduces a multi-material system, combining granular (silver-coated copper), flake (graphite flakes) and one-dimensional (carbon nanotubes) conductive materials to optimize conductive properties and processing characteristics. Specifically, the granular conductive materials of this solution can provide a basic conductive network, while the flake materials, with their large surface area and two-dimensional expansion capabilities, effectively increase the contact area between adjacent conductive particles, thereby promoting the formation of conductive pathways at a lower filling amount. One-dimensional carbon nanotubes, due to their excellent aspect ratio and conductivity, can build a "bridge" in the system to achieve connections across a large spatial span, further enhancing the continuity and stability of the conductive network.

[0066] In summary, this solution not only significantly reduces the amount of conductive filler used and achieves effective cost control through the synergistic effect of multiple materials, but also greatly improves the rheological properties of the coating slurry. Experimental data show that while the optimized slurry maintains excellent conductive properties, the flexibility of the coated film after drying and curing is significantly improved, avoiding the problem of film cracking or performance degradation caused by the material being too hard. In addition, the fluidity of the slurry has also been significantly improved, making it more suitable for high-precision printing or coating processes, providing the possibility for large-scale production applications. The innovative multi-material system design of this solution has opened up new avenues for the performance optimization and practical application of conductive inks.

[0067] Experimental Example 1: Performance Testing

[0068] The performance of the conductive coating was tested according to the following test methods and reference standards (see Table 1 for details):

[0069] 1. Electrical property testing

[0070] Percolation threshold (6 wt%) and sheet resistance (<50 Ω / sq): The percolation behavior of the conductive filler and the coating resistance were measured by the four-probe method. The formation efficiency of the conductive network was evaluated in accordance with ASTM D4496 standard, and the filler dispersion state and the integrity of the conductive path were verified by scanning electron microscopy (SEM).

[0071] Sheet resistance of the conductive line (<60 Ω / sq): Measured by a micro-ohmmeter (such as Keysight B2900 series) in combination with a four-point probe station. The test conditions refer to IEC 60440 standard, and the microscopic structure of the line was observed by a metallurgical microscope.

[0072] 2. Moisture resistance and moisture absorption rate

[0073] Moisture absorption rate (12% → 1.2%): According to ASTM D570 standard, the samples were placed in a thermostatic and humidity-controlled chamber (25°C / 95% RH) for 48 hours, and then the mass change was measured. The moisture adsorption amount was verified by thermogravimetric analysis (TGA).

[0074] Water vapor transmission rate (50 → 10 g / m 2 ·day): Tested by the cup method for water vapor transmission according to ASTM E96 standard at 38°C / 90% RH. The influence of the crosslinking density of the coating on the barrier performance was analyzed by Fourier transform infrared spectroscopy (FTIR).

[0075] 3. Surface characteristics and mechanical properties

[0076] Contact angle (85° → 145°): Measured by a contact angle measuring instrument (such as Krüss DSA100). The surface hydrophobicity was evaluated according to ASTM D7334 standard, and the modification effect of the surface chemical groups was analyzed by X-ray photoelectron spectroscopy (XPS).

[0077] Elongation at break (20% → 50%): Tensile test was carried out according to ASTM D638 standard. The mechanism of improving the flexibility of the coating was studied by dynamic mechanical analysis (DMA), and the fracture surface morphology change was observed by SEM.

[0078] 4. Corrosion resistance

[0079] Salt spray corrosion rate (30% → 5%): Neutral salt spray test (5% NaCl solution, 35°C) was carried out according to ASTM B117 standard. The anti-corrosion mechanism of the coating was analyzed by electrochemical impedance spectroscopy (EIS), and the composition of the corrosion products was detected by energy dispersive spectrometer (EDS).

[0080] Table 1 Detection reference standards

[0081]

[0082]

[0083] After testing, after the dispersion uniformity of the palm wax nanoemulsion in this solution is improved, the moisture absorption rate drops from 12% of the raw material to 1.2% (ASTM D570 standard), and the water vapor transmission rate drops from 50 g / m 2 ·day to 10 g / m 2 ·day, and the moisture barrier property is improved by 3 times; the contact angle increases from 85° to 145°, and the elongation at break in the bending property test increases from 20% to 50%. Moreover, in the salt spray resistance test of the optimized coating, the salt spray corrosion rate drops from 30% of the raw material to 5%, and the service life is extended by more than 3 times, fully demonstrating the technical advantages of this solution in improving weather resistance.

[0084] In addition, the water resistance of the printed conductive pattern was also tested by water immersion, and the results are as Figure 10 shown. The pattern remains unchanged before and after soaking, indicating that the conductive pattern has water resistance.

[0085] The conductivity of the printed conductive pattern was tested by forming a circuit with a button battery and an LED lamp. The results are as Figure 11 shown. The button battery drives the LED lamp to emit light through the conductive pattern (as shown by the red circle in the figure), indicating that the printed pattern has good conductivity.

[0086] This solution also provides an application of a weather-resistant bio-based conductive coating based on aqueous palm wax / shellac, including the application of the above bio-based conductive coating solution as a coating in the fields of integrated electronics, smart packaging, anti-static and electromagnetic shielding packaging, and health monitoring devices. During the application process, first stir the above bio-based conductive coating solution evenly, and then use the spraying method or screen printing method to coat it on the surface of the device to form a coating.

[0087] According to different substrates, the coating thickness is 10 - 30 μm. When used on the surface of disposable electronic products, the coating serves as a conductive layer for temporary electronic tags, with a coating thickness of about 15 μm, which can be degraded after use and has stable conductivity. When used on the surface of smart packaging, the coating can be used for simple sensors on the packaging, with a thickness of about 20 μm, which can reliably transmit signals. For anti-static and electromagnetic shielding packaging, the coating can be used on the inner layer of electronic component packaging, with a thickness of about 25 μm, which can prevent electrostatic damage to components and provide electromagnetic shielding protection. In the field of health monitoring devices, the coating can be applied to disposable medical sensors, with a thickness of about 10 μm, meeting medical-grade environmental protection and conductivity requirements.

[0088] The sheet resistance of the conductive circuit prepared by using the coating of this solution is lower than 60 Ω / sq, meeting the application requirements of disposable electronics, intelligent packaging, etc.; the adhesion between the conductive film and the substrate is good, and the conductive performance remains stable after 100 bending tests.

[0089] This solution also provides a method for recycling conductive fillers in a bio-based conductive coating. By using an ethanol solvent system combined with ultrasonic dissociation technology, the conductive fillers (carbon nanotube-silver-coated copper powder) in the shellac-based conductive coating are efficiently recycled. The recycling process is as Figure 10 shown, and the actual operation state diagram is as Figures 12 to 13 shown. The printed conductive pattern can be quickly dissolved in ethanol, and the conductive fillers are deposited at the bottom. Then, the conductive materials can be recycled again by vacuum filtration. The shellac dissolved in ethanol and the undissolved biomass materials can be recycled after evaporating the solvent. The recycling results are as follows: the recovery rate of silver-coated copper powder > 92%, the purity > 99%, and the solvent can be recycled more than 5 times with a recovery rate > 90%.

[0090] The above are only embodiments of the present invention. Specific technical solutions and / or common knowledge such as characteristics well known in the art are not described in detail herein. It should be noted that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the implementation effect of the present invention and the practicality of the patent. The protection scope required by this application shall be subject to the content of its claims, and the specific implementation manners and the like described in the specification can be used to interpret the content of the claims.

Claims

1. A weather-resistant bio-based conductive coating based on aqueous palm wax / shellac, characterized in that: It includes raw materials in the following parts by mass: 20 - 30 parts of natural palm wax nano - emulsion, 70 - 80 parts of shellac ethanol solution, 1 - 3 parts of Tween 80, and 30 - 80 parts of silver - coated copper powder / carbon nanofiber composite material.

2. The weather-resistant bio-based conductive coating based on aqueous palm wax / shellac according to claim 1, characterized in that: The preparation method of the natural palm wax nano - emulsion is as follows: The natural palm wax is crushed to a particle size < 100 μm, deionized water is added in a mass ratio of 1:1 - 3, and then an emulsifier accounting for 3.5 - 5% of the total system mass is added. After mixing evenly, it is emulsified at 90 - 95 °C for 2 - 3 h, and then cooled and filtered to obtain the natural palm wax nano - emulsion.

3. The weather-resistant biobased conductive coating based on aqueous palm wax / shellac according to claim 2, wherein: The acid value of the natural palm wax ≤ 5 mg KOH / g, and the particle size of the natural palm wax nano - emulsion < 100 nm.

4. A weather-resistant bio-based conductive coating based on aqueous palm wax / shellac according to claim 1, characterized in that: The preparation method of the shellac ethanol solution is as follows: The shellac powder is added to a 95% ethanol solution in a mass ratio of 1:8 - 12, stirred until completely dissolved, and the impurities are removed by filtration to obtain a clear shellac ethanol solution.

5. A weather-resistant bio-based conductive coating based on aqueous palm wax / shellac according to claim 1, characterized in that: The preparation method of the silver - coated copper powder / carbon nanofiber composite material is as follows: The silver - coated copper powder and carbon nanofiber are mixed in a mass ratio of 5 - 10:2 - 4, and ball - milled in a ball mill for 4 - 6 h, with the ball - milling speed controlled at 300 - 400 rpm to obtain a composite conductive filler with uniform size.

6. The weather-resistant bio-based conductive coating based on aqueous palm wax / shellac according to claim 5, wherein: The particle size D90 of the silver - coated copper powder / carbon nanofiber composite material < 200 nm.

7. The preparation method of a weather-resistant bio-based conductive coating based on aqueous palm wax / shellac according to any one of claims 1 to 5, characterized in that: It includes the following steps: Step 1: Mix the palm wax emulsion and the shellac ethanol solution in a volume ratio of 1:2 - 4 to obtain Solution I; Step 2: Add Tween 80 to Solution I and stir evenly to obtain Solution II; Step 3: Add the silver - coated copper powder / carbon nanofiber composite conductive material to Solution II and mix evenly to obtain the bio - based conductive coating solution.

8. The preparation method of a weather-resistant bio-based conductive coating based on aqueous palm wax / shellac according to claim 7, characterized in that: In Step 3, the stirring speed of the mixing is 300 - 500 rpm, and the stirring time is 20 - 30 min.

9. Application of a weather-resistant bio-based conductive coating based on aqueous palm wax / shellac, characterized in that, It includes the application of the bio - based conductive coating solution described in Claim 7 as a coating in the fields of integrated electronics, intelligent packaging, anti - static and electromagnetic shielding packaging, and health monitoring devices.

10. Use of a weather-resistant bio-based conductive coating based on aqueous palm wax / shellac according to claim 9, characterized in that: The thickness of the coating is 10 - 30 μm.

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