Silver-based electromagnetic shielding coating layer and preparation method thereof

Abstract

The invention discloses a silver-based electromagnetic shielding coating layer and a preparation method thereof, and belongs to the technical field of electromagnetic shielding materials. The coating layer comprises the following components in parts by mass: 30-50 parts of composite modified polystyrene silver-loaded microspheres, 80-150 parts of epoxy resin, 15-40 parts of a polyether amine epoxy curing agent, 0.5-2 parts of a defoaming agent and 0.5-2 parts of a flatting agent, and the coating layer is obtained by mixing all the components, coating the insulating carrier with the mixture and curing. The composite modified polystyrene silver-loaded microspheres are prepared by modifying sulfhydrylated polystyrene microspheres with trimethylpropane monoallyl ester, modifying with histidine, quaternizing, loading with phosphotungstic heteropoly acid and carrying out reduction loading with silver ions. The phosphotungstic heteropoly acid anchors silver ions to form a uniform and compact silver layer, and the silver-loaded microspheres form a three-dimensional conductive network to ensure the shielding effectiveness; the organic modified layer and the epoxy resin matrix form strong interface combination to avoid agglomeration and sedimentation; the oxidation resistance is improved through a multi-barrier structure, the quaternary ammonium salt has the antibacterial property, and high conductivity, excellent oxidation resistance, good matrix compatibility and shielding stability are achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic shielding materials, and in particular relates to a silver-based electromagnetic shielding coating layer and a preparation method thereof. Background Art

[0002] With the rapid development of informatization and intelligentization, electronic devices have been deeply integrated into all areas of production and life. From smartphones and laptops used in daily life to automated control devices in industrial scenarios, to precision diagnostic instruments in the medical field and core electronic systems in aerospace, the density and high frequency of electronic devices have become a significant trend. However, electronic devices inevitably generate electromagnetic radiation during operation, which may interfere with other surrounding devices, such as causing communication signal disturbances and reduced instrument measurement accuracy. At the same time, excessive electromagnetic radiation can also pose a threat to human health. For example, long-term exposure may affect the nervous system and endocrine system. Therefore, the importance of electromagnetic shielding technology, as a core means of blocking the propagation of electromagnetic waves and ensuring the normal operation of equipment and human health, is becoming increasingly prominent.

[0003] The core principle of electromagnetic shielding is to reduce the penetration of electromagnetic waves through the reflection, absorption or attenuation of electromagnetic waves by the material. The conductivity of the material is the key factor in determining the reflection and attenuation ability. The stronger the conductivity, the more significant the reflection effect on electromagnetic waves, and the higher the shielding effectiveness. Among various metal materials, silver is the theoretically optimal core material for electromagnetic shielding due to its extremely low resistivity. However, silver-based shielding materials still face two major outstanding problems in practical applications: First, the cost of silver is relatively high. Although coating technology can alleviate this problem by reducing the amount used, the economic efficiency of the material itself still needs to be optimized; second, the chemical properties of silver are relatively active. It easily reacts with oxygen and sulfides in the air environment, causing the surface to darken and the conductivity to decrease, which in turn significantly reduces the shielding effectiveness and affects the appearance stability of the material.

[0004] Existing silver-based coating technologies mostly use pure silver or simple silver alloy systems. Although they can achieve a certain shielding effect in the short term, it is difficult to balance long-term shielding stability, material compatibility, and economy. Pure silver coatings are easily oxidized and fail in humid or sulfur-containing environments; when the interfacial bonding between silver particles and the organic matrix is ​​weak, they are prone to agglomeration or sedimentation, resulting in a break in the conductive network; although some modification schemes can improve oxidation resistance, they will sacrifice the conductivity of silver and reduce shielding effectiveness. Therefore, developing a silver-based electromagnetic shielding coating layer that can retain the high conductivity of silver to ensure shielding effectiveness, improve oxidation resistance and matrix compatibility through structural design, and control costs at the same time has become an important research direction in this field. Summary of the Invention

[0005] In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a silver-based electromagnetic shielding coating layer with high conductivity, excellent oxidation resistance, good matrix compatibility and shielding stability, and a preparation method thereof. The coating layer uses composite modified silver-loaded polymer microspheres as conductive fillers and combines with an epoxy resin curing system to effectively solve the problems of traditional silver-based coatings that are easily oxidized and fail, have weak interface bonding strength, and unstable shielding effectiveness.

[0006] In order to achieve the above-mentioned purpose, the following technical solution is adopted: the present invention provides a silver-based electromagnetic shielding coating layer, comprising the following components in parts by mass: 30-50 parts of composite modified polystyrene silver-loaded microspheres, 80-150 parts of epoxy resin, 15-40 parts of polyetheramine epoxy curing agent, 0.5-2 parts of defoaming agent, and 0.5-2 parts of leveling agent.

[0007] Furthermore, the composite modified polystyrene silver-loaded microspheres are prepared by the following steps:

[0008] (1) Dispersing thiolated polystyrene microspheres in toluene, adding trimethylolpropane monoallyl ester and boron trifluoride ether complex, and stirring and reacting at 70-80°C for 8-16 hours; after the reaction is completed, cooling to room temperature, filtering and separating the microspheres, washing with toluene and ethanol in sequence, and vacuum drying at 80-100°C for 12-18 hours to obtain trimethylolpropane monoallyl ester modified polystyrene microspheres;

[0009] (2) dispersing trimethylolpropane monoallyl ester modified polystyrene microspheres in N,N-dimethylformamide, adding N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stirring and reacting at room temperature for 24-48 hours. After the reaction is completed, filtering and separating the microspheres, washing with ethanol and deionized water in sequence, and vacuum drying at 80-100°C for 8-12 hours to obtain histidine modified polystyrene microspheres;

[0010] (3) dispersing the histidine-modified polystyrene microspheres in anhydrous ethanol, adding dodecyl chloride, and reflux reacting at 60-70° C. for 12-24 hours. After the reaction is completed, cooling to room temperature, filtering and separating the microspheres, washing with ethanol, and vacuum drying at 80-100° C. for 12 hours to obtain quaternary ammonium-modified polystyrene microspheres;

[0011] (4) dispersing the quaternized modified polystyrene microspheres in deionized water, adding 0.1-0.5 mol / L tungstophosphoric acid solution, and ultrasonically treating at an ultrasonic power of 200-400 W for 30-60 min. After the ultrasonic treatment, standing for 12 h, filtering and separating the microspheres, washing with deionized water, and vacuum drying at 80-100 ° C for 12-18 h to obtain tungstophosphoric acid-loaded polystyrene microspheres;

[0012] (5) The phosphotungstic heteropoly acid-loaded polystyrene microspheres were dispersed in deionized water, 0.1-0.5 mol / L silver nitrate solution was added, and the mixture was stirred at room temperature for 30-60 min. Then, 0.1-0.5 mol / L glucose solution was slowly added dropwise as a reducing agent. After the addition was completed, the mixture was stirred and reacted for 2-4 h. After the reaction was completed, the microspheres were separated by filtration, washed with ethanol, and vacuum dried at 60-80 ° C for 24-36 h to obtain silver-loaded polymer conductive microspheres.

[0013] Furthermore, in the step (1), the mass ratio of the thiolated polystyrene microspheres, trimethylolpropane monoallyl ester, boron trifluoride ether complex, and toluene is 1:0.2-0.5:0.01-0.03:10-20.

[0014] Furthermore, in the step (2), the mass ratio of trimethylolpropane monoallyl ester modified polystyrene microspheres, N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to N,N-dimethylformamide is 1:0.1-0.3:0.1-0.2:0.05-0.1:10-20.

[0015] Furthermore, in step (3), the mass ratio of histidine-modified polystyrene microspheres, dodecyl chloride, and anhydrous ethanol is 1:0.2-0.5:10-20.

[0016] Furthermore, in step (4), the mass ratio of the quaternized modified polystyrene microspheres to the phosphotungstic heteropoly acid solution is 1:5-10.

[0017] Furthermore, in the step (5), the mass ratio of the phosphotungstic heteropoly acid-loaded polystyrene microspheres, the silver nitrate solution, and the glucose solution is 1:5:5.5-8.

[0018] Furthermore, the epoxy resin is epoxy resin E-44 with an epoxy value of 0.41-0.47; and the polyetheramine epoxy curing agent is one of BASF EC311, BASF EC301 and Huntsman T-403.

[0019] Furthermore, the defoaming agent is one of BYK-057, BYK-066N, BYK-067 and EFKA-2022; the leveling agent is one of BYK-354, BYK-358N, EFKA-3772 and EFKA-3777.

[0020] Furthermore, the preparation method of the silver-based electromagnetic shielding coating layer includes: mixing the components of the silver-based electromagnetic shielding coating layer and coating the mixture on an insulating carrier at room temperature, and obtaining the silver-based electromagnetic shielding coating layer after curing, the curing temperature is 100°C, and the curing time is 10 hours.

[0021] The beneficial effects of the present invention are:

[0022] The present invention constructs a highly uniform and dense silver-loaded layer on the surface of polystyrene microspheres through a multi-step modification process. Because phosphotungstic heteropolyacid carries a high-density negative charge on its surface, it can effectively adsorb silver ions in solution through strong electrostatic attraction. In an acidic environment, the negative charge of the heteropolyacid anions is further enhanced, resulting in a stronger adsorption capacity. The oxygen atoms on the surface of the heteropolyacid can act as a Lewis base to form coordination bonds with the silver ions, achieving rivet anchoring of the silver ions, thereby ensuring the uniform distribution of the silver ions on the surface of the microspheres. The silver layer formed by subsequent reduction is dense and continuous, greatly improving the electrical conductivity of the microspheres themselves. A large number of highly conductive silver-loaded microspheres are evenly dispersed in the epoxy resin matrix to form a three-dimensional conductive network. When electromagnetic waves encounter this network, most of the energy is reflected, and part is absorbed and converted into heat energy, thereby achieving the purpose of efficient shielding.

[0023] The organically modified layer on the surface of the polystyrene microspheres prepared by the present invention forms a physical and chemical barrier, preventing oxygen, water vapor and sulfide from directly contacting the silver layer. The cured epoxy resin matrix also forms a dense barrier, providing physical protection and environmental isolation for the silver-loaded microspheres. The quaternary ammonium salt structure on the surface of the microspheres carries a positive charge, achieving a contact sterilization effect.

[0024] The hydrophobic long alkyl chains grafted with dodecyl chloride on the surface of the polystyrene microspheres can be effectively inserted into the molecular chain network of the epoxy resin, forming physical entanglement and hydrophobic interactions, forming a connection between the microspheres and the resin matrix, improving the inorganic-organic interface compatibility, significantly enhancing the interfacial bonding force, and effectively preventing the sedimentation and agglomeration of high-density silver-loaded microspheres during the coating and curing process, ensuring their uniform dispersion in the matrix, and helping to form a continuous conductive network. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0026] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods and materials similar or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only and are not intended to limit the scope of this application.

[0027] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and the experimental materials used in the following examples, unless otherwise specified, are all purchased from commercial channels.

[0028] Example 1: A silver-based electromagnetic shielding coating layer and a preparation method thereof, wherein the silver-based electromagnetic shielding coating layer comprises the following components in parts by mass: 30 parts of composite modified polystyrene silver-loaded microspheres, 80 parts of epoxy resin, 15 parts of polyetheramine epoxy curing agent, 0.5 parts of defoaming agent, and 0.5 parts of leveling agent.

[0029] The composite modified polystyrene silver-loaded microspheres are prepared by the following steps:

[0030] (1) Dispersing thiolated polystyrene microspheres in toluene, adding trimethylolpropane monoallyl ester and boron trifluoride ether complex, and stirring at 70°C for 8 hours; after the reaction, cooling to room temperature, filtering and separating the microspheres, washing with toluene and ethanol in sequence, and vacuum drying at 80°C for 12 hours to obtain trimethylolpropane monoallyl ester modified polystyrene microspheres;

[0031] (2) Dispersing trimethylolpropane monoallyl ester modified polystyrene microspheres in N,N-dimethylformamide, adding N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stirring and reacting at room temperature for 24 hours. After the reaction is completed, filtering and separating the microspheres, washing with ethanol and deionized water in sequence, and drying in vacuo at 80°C for 8 hours to obtain histidine modified polystyrene microspheres;

[0032] (3) Dispersing histidine-modified polystyrene microspheres in anhydrous ethanol, adding dodecyl chloride, and reflux reaction at 60°C for 12 hours. After the reaction is completed, cooling to room temperature, filtering and separating the microspheres, washing with ethanol, and vacuum drying at 80°C for 12 hours to obtain quaternary ammonium-modified polystyrene microspheres;

[0033] (4) The quaternized ammonium modified polystyrene microspheres were dispersed in deionized water, 0.1 mol / L tungstophosphoric acid solution was added, and ultrasonic treatment was performed at an ultrasonic power of 200 W for 30 min. After the ultrasonic treatment, the microspheres were allowed to stand for 12 h, filtered and separated, washed with deionized water, and vacuum dried at 80 ° C for 12 h to obtain tungstophosphoric acid-loaded polystyrene microspheres;

[0034] (5) The polystyrene microspheres loaded with tungstophosphoric acid were dispersed in deionized water, 0.1 mol / L silver nitrate solution was added, and the mixture was stirred at room temperature for 30 min. Then, 0.1 mol / L glucose solution was slowly added dropwise as a reducing agent. After the addition was completed, the mixture was stirred and reacted for 2 h. After the reaction was completed, the microspheres were separated by filtration, washed with ethanol, and vacuum dried at 60 °C for 24 h to obtain silver-loaded polymer conductive microspheres.

[0035] In the step (1), the mass ratio of the mercaptolated polystyrene microspheres, trimethylolpropane monoallyl ester, boron trifluoride ether complex, and toluene is 1:0.2:0.01:10.

[0036] In the step (2), the mass ratio of trimethylolpropane monoallyl ester modified polystyrene microspheres, N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and N,N-dimethylformamide is 1:0.1:0.1:0.05:10.

[0037] In the step (3), the mass ratio of histidine-modified polystyrene microspheres, dodecyl chloride, and anhydrous ethanol is 1:0.2:10.

[0038] In the step (4), the mass ratio of the quaternized modified polystyrene microspheres to the phosphotungstic heteropoly acid solution is 1:5.

[0039] In the step (5), the mass ratio of the phosphotungstic heteropolyacid-loaded polystyrene microspheres, the silver nitrate solution, and the glucose solution is 1:5:5.5.

[0040] The epoxy resin is epoxy resin E-44 with an epoxy value of 0.41; the polyetheramine epoxy curing agent is BASF EC311.

[0041] The defoaming agent is BYK-057; the leveling agent is BYK-354.

[0042] The preparation method of the silver-based electromagnetic shielding coating layer includes: mixing the components of the silver-based electromagnetic shielding coating layer and coating the mixture on an insulating carrier at room temperature, and curing the mixture to obtain the silver-based electromagnetic shielding coating layer. The curing temperature is 100°C and the curing time is 10 hours.

[0043] Example 2: A silver-based electromagnetic shielding coating layer and a preparation method thereof, wherein the silver-based electromagnetic shielding coating layer comprises the following components in parts by mass: 50 parts of composite modified polystyrene silver-loaded microspheres, 150 parts of epoxy resin, 40 parts of polyetheramine epoxy curing agent, 2 parts of defoaming agent, and 2 parts of leveling agent.

[0044] The composite modified polystyrene silver-loaded microspheres are prepared by the following steps:

[0045] (1) Dispersing thiolated polystyrene microspheres in toluene, adding trimethylolpropane monoallyl ester and boron trifluoride ether complex, and stirring at 80°C for 16 hours; after the reaction is completed, cooling to room temperature, filtering and separating the microspheres, washing with toluene and ethanol in sequence, and vacuum drying at 100°C for 18 hours to obtain trimethylolpropane monoallyl ester modified polystyrene microspheres;

[0046] (2) Trimethylolpropane monoallyl ester modified polystyrene microspheres were dispersed in N,N-dimethylformamide, and N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide were added. The reaction was stirred at room temperature for 48 hours. After the reaction was completed, the microspheres were separated by filtration, washed with ethanol and deionized water in sequence, and dried in vacuum at 100°C for 12 hours to obtain histidine-modified polystyrene microspheres.

[0047] (3) The histidine-modified polystyrene microspheres were dispersed in anhydrous ethanol, and dodecyl chloride was added. The reaction was refluxed at 70°C for 24 hours. After the reaction was completed, the microspheres were cooled to room temperature, filtered and separated, washed with ethanol, and vacuum-dried at 100°C for 12 hours to obtain quaternary ammonium-modified polystyrene microspheres.

[0048] (4) The quaternized ammonium modified polystyrene microspheres were dispersed in deionized water, 0.5 mol / L tungstophosphoric acid solution was added, and ultrasonic treatment was performed at an ultrasonic power of 400 W for 60 min. After the ultrasonic treatment, the mixture was allowed to stand for 12 h, and the microspheres were separated by filtration, washed with deionized water, and vacuum dried at 100 ° C for 18 h to obtain tungstophosphoric acid-loaded polystyrene microspheres;

[0049] (5) Phosphotungstic heteropolyacid-loaded polystyrene microspheres were dispersed in deionized water, 0.5 mol / L silver nitrate solution was added, and the mixture was stirred at room temperature for 60 min. Then, 0.5 mol / L glucose solution was slowly added dropwise as a reducing agent. After the addition was completed, the mixture was stirred and reacted for 4 h. After the reaction was completed, the microspheres were separated by filtration, washed with ethanol, and vacuum dried at 80 °C for 36 h to obtain silver-loaded polymer conductive microspheres.

[0050] In the step (1), the mass ratio of the thiolated polystyrene microspheres, trimethylolpropane monoallyl ester, boron trifluoride ether complex, and toluene is 1:0.5:0.03:20.

[0051] In the step (2), the mass ratio of trimethylolpropane monoallyl ester modified polystyrene microspheres, N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and N,N-dimethylformamide is 1:0.3:0.2:0.1:20.

[0052] In the step (3), the mass ratio of histidine-modified polystyrene microspheres, dodecyl chloride, and anhydrous ethanol is 1:0.5:20.

[0053] In the step (4), the mass ratio of the quaternized modified polystyrene microspheres to the phosphotungstic heteropoly acid solution is 1:10.

[0054] In the step (5), the mass ratio of the phosphotungstic heteropolyacid-loaded polystyrene microspheres, the silver nitrate solution, and the glucose solution is 1:5:8.

[0055] The epoxy resin is epoxy resin E-44 with an epoxy value of 0.47; the polyetheramine epoxy curing agent is BASF EC301.

[0056] The defoaming agent is BYK-066N; the leveling agent is BYK-358N.

[0057] The preparation method of the silver-based electromagnetic shielding coating layer includes: mixing the components of the silver-based electromagnetic shielding coating layer and coating the mixture on an insulating carrier at room temperature, and curing the mixture to obtain the silver-based electromagnetic shielding coating layer. The curing temperature is 100°C and the curing time is 10 hours.

[0058] Example 3: A silver-based electromagnetic shielding coating layer and a preparation method thereof, wherein the silver-based electromagnetic shielding coating layer comprises the following components in parts by mass: 40 parts of composite modified polystyrene silver-loaded microspheres, 115 parts of epoxy resin, 27.5 parts of polyetheramine epoxy curing agent, 1.25 parts of defoaming agent, and 1.25 parts of leveling agent.

[0059] The composite modified polystyrene silver-loaded microspheres are prepared by the following steps:

[0060] (1) Dispersing thiolated polystyrene microspheres in toluene, adding trimethylolpropane monoallyl ester and boron trifluoride ether complex, and stirring at 75°C for 12 hours; after the reaction, cooling to room temperature, filtering and separating the microspheres, washing with toluene and ethanol in sequence, and vacuum drying at 90°C for 15 hours to obtain trimethylolpropane monoallyl ester modified polystyrene microspheres;

[0061] (2) Dispersing trimethylolpropane monoallyl ester modified polystyrene microspheres in N,N-dimethylformamide, adding N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stirring and reacting at room temperature for 36 hours. After the reaction is completed, the microspheres are separated by filtration, washed with ethanol and deionized water in sequence, and dried in vacuum at 90°C for 10 hours to obtain histidine modified polystyrene microspheres;

[0062] (3) Dispersing histidine-modified polystyrene microspheres in anhydrous ethanol, adding dodecyl chloride, and reflux reaction at 65°C for 18 hours. After the reaction is completed, cooling to room temperature, filtering and separating the microspheres, washing with ethanol, and vacuum drying at 90°C for 12 hours to obtain quaternary ammonium-modified polystyrene microspheres;

[0063] (4) The quaternized ammonium modified polystyrene microspheres were dispersed in deionized water, 0.3 mol / L tungstophosphoric acid solution was added, and ultrasonic treatment was performed at an ultrasonic power of 300 W for 45 min. After the ultrasonic treatment, the microspheres were allowed to stand for 12 h, filtered and separated, washed with deionized water, and vacuum dried at 90 ° C for 15 h to obtain tungstophosphoric acid-loaded polystyrene microspheres;

[0064] (5) Phosphotungstic heteropolyacid-loaded polystyrene microspheres were dispersed in deionized water, 0.3 mol / L silver nitrate solution was added, and the mixture was stirred at room temperature for 45 min. Then, 0.3 mol / L glucose solution was slowly added dropwise as a reducing agent. After the addition was completed, the mixture was stirred and reacted for 3 h. After the reaction was completed, the microspheres were separated by filtration, washed with ethanol, and vacuum dried at 70 °C for 30 h to obtain silver-loaded polymer conductive microspheres.

[0065] In the step (1), the mass ratio of the mercaptolated polystyrene microspheres, trimethylolpropane monoallyl ester, boron trifluoride ether complex, and toluene is 1:0.35:0.02:15.

[0066] In the step (2), the mass ratio of trimethylolpropane monoallyl ester modified polystyrene microspheres, N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, and N,N-dimethylformamide is 1:0.2:0.15:0.075:15.

[0067] In the step (3), the mass ratio of histidine-modified polystyrene microspheres, dodecyl chloride, and anhydrous ethanol is 1:0.35:15.

[0068] In the step (4), the mass ratio of the quaternized modified polystyrene microspheres to the phosphotungstic heteropoly acid solution is 1:7.5.

[0069] In the step (5), the mass ratio of the phosphotungstic heteropolyacid-loaded polystyrene microspheres, the silver nitrate solution, and the glucose solution is 1:5:6.75.

[0070] The epoxy resin is epoxy resin E-44 with an epoxy value of 0.44; the polyetheramine epoxy curing agent is Huntsman T-403.

[0071] The defoaming agent is BYK-067; the leveling agent is EFKA-3772.

[0072] Example 4: A silver-based electromagnetic shielding coating layer and a preparation method thereof, wherein the defoaming agent is EFKA-2022, the leveling agent is EFKA-3777, and the rest are the same as in Example 3.

[0073] Comparative Example 1: In this comparative example, step (4) loading of phosphotungstic heteropolyacid is omitted, and step (5) loading of silver is directly performed, that is, quaternized ammonium modified polystyrene microspheres are dispersed in deionized water, silver nitrate solution is added and stirred, and glucose is added dropwise for reduction. The rest is the same as in Example 3.

[0074] Comparative Example 2: In this comparative example, the quaternization modification of step (3) is omitted, and step (4) loading of phosphotungstic heteropoly acid is directly performed, and the histidine-modified microspheres are directly loaded with phosphotungstic heteropoly acid. The rest is the same as Example 3.

[0075] Comparative Example 3: In this comparative example, the composite modified polystyrene silver-loaded microspheres are replaced with pure silver powder of equal mass, and the rest are the same as in Example 3.

[0076] Result Analysis

[0077] The silver-based electromagnetic shielding coatings prepared in Examples 1-4 and Comparative Examples 1-3 were tested for electromagnetic shielding performance, and the test results are shown in Table 1. The specific steps were as follows: the coating samples were cut into 30 mm diameter discs; these discs were placed in a coaxial fixture, and both ends were connected to a vector network analyzer over a scanning frequency range of 30 MHz to 1.5 GHz. The transmission coefficient was measured, and the electromagnetic shielding effectiveness (SE) was calculated.

[0078] The silver-based electromagnetic shielding coatings prepared in Examples 1-4 and Comparative Examples 1-3 were tested for their thermal shock resistance. The test results are shown in Table 1. The specific steps were as follows: the samples were maintained at a constant temperature of 25°C / 50% RH for 24 hours; the following thermal and thermal shock settings were applied: high temperature section: 85°C for 30 minutes; low temperature section: -40°C for 30 minutes, with a switching time of ≤5 minutes (temperature ramp rate >10°C / min); the number of cycles was 100 (a total of 100 hours); and post-treatment: the samples were removed and returned to room temperature (25°C), the SE was retested as described above, the attenuation rate was calculated, and the sample appearance was observed.

[0079] The silver-based electromagnetic shielding coatings prepared in Examples 1-4 and Comparative Examples 1-3 were tested for salt spray resistance. The test results are shown in Table 1. The specific steps were as follows: the edges of the coating sample (100×100 mm) were sealed with wax and immersed in a 5% by mass NaCl salt solution; the chamber temperature was 35±2°C, the spray pressure was 70 kPa, and the duration was 96 hours; the sample was removed, rinsed with deionized water, and dried at 50°C for 2 hours; SE was re-measured as described above, the attenuation rate was calculated, and the sample appearance was observed.

[0080] The test results in Table 1 show that the electromagnetic shielding coating layer prepared by the present invention has extremely strong electromagnetic wave shielding capabilities in the frequency range of 30MHz-1.5GHz, meeting the shielding requirements of high-performance electronic equipment. After 100 cycles of thermal shock, the SE attenuation rate of each embodiment was less than 5.6%, and the appearance did not change significantly, indicating that the coating layer has good thermomechanical stability and can effectively resist interface failure and conductive network destruction caused by drastic temperature changes. After exposure to a 5% NaCl salt spray environment for 96 hours, the SE attenuation rate of each embodiment was less than 9.0%, and the appearance did not change significantly, which also shows that the coating layer has excellent corrosion resistance. Its structure effectively isolates the corrosive medium from the corrosion of the silver layer, preventing the decrease in conductivity caused by oxidation, sulfidation or pitting. In summary, the composite modified polystyrene silver-loaded microspheres prepared by the present invention, combined with the epoxy resin system, have high compatibility and interfacial bonding between the microspheres and the resin matrix. The resulting silver-based electromagnetic shielding coating layer has high conductivity, excellent anti-oxidation, anti-sulfurization, corrosion resistance and long-term shielding effectiveness stability.

[0081] Table 1 Test results of electromagnetic shielding performance, thermal shock resistance and salt spray resistance of silver-based electromagnetic shielding coating layer

[0082]

[0083]

[0084] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

[0085] The present invention and its embodiments are described above. Such description is not restrictive. The embodiment shown in the embodiment is only one embodiment of the present invention, and actual application is not limited thereto. In short, if a person skilled in the art is inspired by the above, and does not deviate from the purpose of the invention, without creatively designing methods and embodiments similar to the technical solution, they shall fall within the scope of protection of the present invention.

Claims

1. A silver-based electromagnetic shielding coating layer, characterized in that: The invention comprises the following components in parts by mass: 30-50 parts of composite modified polystyrene silver-loaded microspheres, 80-150 parts of epoxy resin, 15-40 parts of polyetheramine epoxy curing agent, 0.5-2 parts of defoaming agent and 0.5-2 parts of leveling agent.

2. The silver-based electromagnetic shielding coating layer according to claim 1, characterized in that: The composite modified polystyrene silver-loaded microspheres are prepared by the following steps: (1) Dispersing thiolated polystyrene microspheres in toluene, adding trimethylolpropane monoallyl ester and boron trifluoride ether complex, and stirring and reacting at 70-80°C for 8-16 hours; after the reaction is completed, cooling to room temperature, filtering and separating the microspheres, washing with toluene and ethanol in sequence, and vacuum drying at 80-100°C for 12-18 hours to obtain trimethylolpropane monoallyl ester modified polystyrene microspheres; (2) dispersing trimethylolpropane monoallyl ester modified polystyrene microspheres in N,N-dimethylformamide, adding N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, stirring and reacting at room temperature for 24-48 hours. After the reaction is completed, filtering and separating the microspheres, washing with ethanol and deionized water in sequence, and vacuum drying at 80-100°C for 8-12 hours to obtain histidine modified polystyrene microspheres; (3) dispersing the histidine-modified polystyrene microspheres in anhydrous ethanol, adding dodecyl chloride, and reflux reacting at 60-70° C. for 12-24 hours. After the reaction is completed, cooling to room temperature, filtering and separating the microspheres, washing with ethanol, and vacuum drying at 80-100° C. for 12 hours to obtain quaternary ammonium-modified polystyrene microspheres; (4) dispersing the quaternized modified polystyrene microspheres in deionized water, adding 0.1-0.5 mol / L tungstophosphoric acid solution, and ultrasonically treating at an ultrasonic power of 200-400 W for 30-60 min. After the ultrasonic treatment, standing for 12 h, filtering and separating the microspheres, washing with deionized water, and vacuum drying at 80-100 ° C for 12-18 h to obtain tungstophosphoric acid-loaded polystyrene microspheres; (5) The phosphotungstic heteropoly acid-loaded polystyrene microspheres were dispersed in deionized water, 0.1-0.5 mol / L silver nitrate solution was added, and the mixture was stirred at room temperature for 30-60 min. Then, 0.1-0.5 mol / L glucose solution was slowly added dropwise as a reducing agent. After the addition was completed, the mixture was stirred and reacted for 2-4 h. After the reaction was completed, the microspheres were separated by filtration, washed with ethanol, and vacuum dried at 60-80 ° C for 24-36 h to obtain silver-loaded polymer conductive microspheres.

3. The silver-based electromagnetic shielding coating layer according to claim 2, characterized in that: In the step (1), the mass ratio of the mercaptolated polystyrene microspheres, trimethylolpropane monoallyl ester, boron trifluoride ether complex, and toluene is 1:0.2-0.5:0.01-0.03:10-20.

4. The silver-based electromagnetic shielding coating layer according to claim 3, characterized in that: In the step (2), the mass ratio of trimethylolpropane monoallyl ester modified polystyrene microspheres, N-formyl-L-histidine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide to N,N-dimethylformamide is 1:0.1-0.3:0.1-0.2:0.05-0.1:10-20.

5. The silver-based electromagnetic shielding coating layer according to claim 4, characterized in that: In the step (3), the mass ratio of histidine-modified polystyrene microspheres, dodecyl chloride, and anhydrous ethanol is 1:0.2-0.5:10-20.

6. The silver-based electromagnetic shielding coating layer according to claim 5, characterized in that: In the step (4), the mass ratio of the quaternized modified polystyrene microspheres to the phosphotungstic heteropoly acid solution is 1:5-10.

7. The silver-based electromagnetic shielding coating layer according to claim 6, characterized in that: In the step (5), the mass ratio of the phosphotungstic heteropoly acid-loaded polystyrene microspheres, the silver nitrate solution, and the glucose solution is 1:5:5.5-8.

8. The silver-based electromagnetic shielding coating layer according to claim 7, characterized in that: The epoxy resin is epoxy resin E-44 with an epoxy value of 0.41-0.47; the polyetheramine epoxy curing agent is one of BASF EC311, BASF EC301 and Huntsman T-403.

9. The silver-based electromagnetic shielding coating layer according to claim 8, characterized in that: The defoaming agent is one of BYK-057, BYK-066N, BYK-067 and EFKA-2022; the leveling agent is one of BYK-354, BYK-358N, EFKA-3772 and EFKA-3777.

10. A method for preparing the silver-based electromagnetic shielding coating layer according to any one of claims 1 to 9, characterized in that: include: The components of the silver-based electromagnetic shielding coating layer are mixed and coated on an insulating carrier at room temperature, and then cured to obtain the silver-based electromagnetic shielding coating layer. The curing temperature is 100° C. and the curing time is 10 hours.

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