With the development of modern high-tech, electromagnetic interference (EMI) and electromagnetic compatibility (EMC) caused by electromagnetic waves are becoming increasingly serious. They not only cause interference and damage to electronic instruments and equipment, affecting their normal operation, seriously restricting the international competitiveness of China's electronic products and equipment, but also pollute the environment and endanger human health; In addition, electromagnetic wave leakage can also endanger national information security and the security of military core secrets. Especially as a new concept weapon, electromagnetic pulse weapons have made substantial breakthroughs, capable of directly striking electronic instruments and equipment, power systems, etc., causing temporary failure or permanent damage to information systems, etc.
Therefore, exploring efficient methods
electromagnetic shielding materialPreventing electromagnetic interference and compatibility issues caused by electromagnetic waves is of great significance for improving the safety and reliability of electronic products and equipment, enhancing international competitiveness, preventing attacks from electromagnetic pulse weapons, and ensuring the safe and smooth operation of information communication systems, network systems, transmission systems, weapon platforms, etc.
1. Electromagnetic shielding principle
Electromagnetic shielding refers to the use of shielding materials to block or attenuate the propagation of electromagnetic energy between the shielded area and the outside world. The principle of electromagnetic shielding is to utilize the reflection, absorption, and guidance of electromagnetic energy flow by the shielding body, which is closely related to the induced charges, currents, and polarization phenomena on the surface and inside the shielding structure. Shielding can be divided into electric field shielding (electrostatic shielding and alternating electric field shielding), magnetic field shielding (low-frequency magnetic field and high-frequency magnetic field shielding), and electromagnetic field shielding (shielding of electromagnetic waves) according to their principles. The electromagnetic shielding commonly referred to refers to the latter, which involves shielding both electric and magnetic fields simultaneously.
2. Electromagnetic shielding material
Currently, the most widely used ones are
Composite electromagnetic shielding coatingIts composition is mainly composed of film-forming resin, conductive filler, diluent, coupling agent and other additives, among which conductive filler is an important component. Commonly used ones include silver powder, copper powder, nickel powder, silver coated copper powder, carbon nanotubes, graphene, nano ATO, etc.
2.1 Carbon nanotubes
Carbon nanotubes have a great aspect ratio and excellent electrical and magnetic properties, demonstrating outstanding performance in conductivity and absorption shielding. Therefore, their research and development as conductive fillers for electromagnetic shielding coatings are increasingly being valued. This places high demands on the purity, production capacity, and cost of carbon nanotubes. The carbon nanotubes produced by Hongwu Nano Factory, including single-walled and multi walled, have a purity of up to 99% The dispersion of carbon nanotubes in the matrix resin and their good affinity with the matrix resin become direct factors affecting the shielding performance. Hongwu Nano also provides well dispersed carbon nanotube dispersion solutions.
2.2 Nanosheet silver powder
The earliest publicly available conductive coating was the patent published by the United States in 1948 for making conductive adhesive from silver and epoxy resin. The electromagnetic shielding paint prepared using ball milled silver powder produced by Hongwu Nano has the characteristics of low resistance, good conductivity, high shielding effectiveness, strong environmental resistance, and easy construction. Widely used in communication, electronics, medical, aerospace, nuclear facilities and other fields, shielding paint is also suitable for surface coating of engineering plastics such as ABS, PC, ABS-PCPS, etc. The performance indicators include wear resistance, high and low temperature resistance, moisture and heat resistance, adhesion, electrical resistivity, electromagnetic compatibility, etc., all of which can meet the standards.
2.3 Copper powder and nickel powder
Copper powder conductive coatingLow cost, easy to coat, good electromagnetic shielding effect, widely used, especially suitable for anti electromagnetic wave interference of electronic products with engineering plastics as the shell. Copper powder conductive coating can be easily sprayed or brushed on various shapes of plastic surfaces, metalizing the plastic surface to form an electromagnetic shielding conductive layer, thereby achieving the purpose of shielding electromagnetic waves in plastics. The morphology and dosage of copper powder have a significant impact on the conductivity of coatings. Copper powder can be spherical, dendritic, flaky, etc. The contact area of flakes is much larger than that of spheres, exhibiting better conductivity. In addition, coating copper powder with inert metal silver powder (silver coated copper powder) is not easy to oxidize, with a general silver content of 5-30% Copper powder conductive coating is used to solve the electromagnetic shielding and conductivity problems of engineering plastics such as ABS, PPO, PS, and wood, and has wide application and promotion value.
In addition, the measurement results of electromagnetic shielding effectiveness of nano nickel powder and electromagnetic shielding coatings mixed with nano nickel powder and micro nickel powder show that although the addition of nano nickel powder reduces electromagnetic shielding effectiveness, it can increase absorption loss. The reason is that it increases the magnetic loss tangent, reduces the damage caused by electromagnetic waves to the environment, equipment, and human health.
2.4 Nano ATO tin antimony oxide
Nano ATO powderAs a unique filler with high transparency and conductivity, it has a wide range of applications in display coating materials, conductive anti-static coatings, transparent thermal insulation coatings, and other fields. Among the coating materials for optoelectronic devices, ATO material has anti-static, anti glare, and anti radiation functions, and was first used as an electromagnetic shielding coating material for displays. Nano ATO coating materials have good light color transparency, good conductivity, mechanical strength, and stability, and their application in display devices is currently one of the main industrial application areas of ATO materials. Electrochromic devices, such as displays or smart windows, are an important aspect of the current application of nano ATO in the display field.
2.5 Graphene
As a new type of carbon material, graphene is more likely to become a new and effective electromagnetic shielding or microwave absorbing material than carbon nanotubes. The main reasons include the following aspects:
① Graphene is a hexagonal planar thin film composed of carbon atoms, a two-dimensional material with only one carbon atom thickness;
② Graphene is the thinnest and hardest nanomaterial in the world;
③ The thermal conductivity is higher than that of carbon nanotubes and diamond, reaching 5300W/m · K;
④ Graphene is currently the material with the lowest electrical resistivity in the world, only 10-6 Ω· cm;
⑤ At room temperature, the electron mobility of graphene is higher than that of carbon nanotubes or silicon crystals, exceeding 15000 cm2/V · s Compared with traditional materials, graphene can break through its original limitations and become an effective new type of absorber, meeting the requirements of "thin, light, wide, and strong" for absorbing materials.
The improvement of electromagnetic shielding and absorbing material performance depends on the content of absorbing agent, the performance of absorbing agent, and good impedance matching of absorbing substrate. Graphene not only has a unique physical structure and excellent mechanical and electromagnetic properties, but also has good microwave absorption performance. By combining it with magnetic nanoparticles, a new type of absorbing material can be obtained, which has both magnetic and electrical losses, and has good application prospects in the fields of electromagnetic shielding and microwave absorption.
Characteristics after curing:
| Items |
Data |
Remark |
| project |
measured value |
Preparation |
| Appearance |
Brown |
|
| appearance |
brown |
|
| Viscosity |
25-35Pa·s |
Brookfield 52Z ,5rpm |
| Viscosity |
| Specific gravity |
1.07 |
Cup |
| proportion |
Pycnometer
GB/T 13354-1992 |
| Cure time |
10-15seconds |
160 ℃ * 15 seconds 180 ℃ * 10 seconds |
| Curing Time |
| Storage |
3months |
-Below 5 ℃ |
| Storage conditions |
3days |
25℃ |
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